Too windy to fly today, but temperature is down to 70 and low humidity.

I bench ran a couple of ounces of 16% nitro 20% oil (50-50) just to make certain the break-in was complete. My Hangar 9 tach showed a peak RPM of a hair over 25,000. I dialed the needle back and ran the tank out at 24,600, +/- 150 RPM. Cylinder was not even close to smoking hot.

Setup was unmodified stock. APC 5-3. Kudos to Rockin' Rusty for all his work on these when he was still around.

Dave Mo...

What ship are you planning to use the Big Mig in, Dave?

-Chris

I've got a Pinto waiting to be finished off.

Dave Mo...

Tee heee...I got a Pinto waiting to be started!

Mr. Dave, I'll be watching. It is good to see Rusty's name...he is missed on CEF.

Jim

Whatever you do, watch how much weight you build into the tail end. Also maybe push the engine forward a bit. I put all the parts into their proper locations this eve and did a quick balance check with the CG as shown in the plan. She pointed almost straight up.

Not sure what to think here. I kick myself now in looking at the design as it should have been obvious when I was building it.

Dave Mo...

A follow-up to my note above. Lead weight of .4 oz in the front end brings the ship into close balance. So there you have it.

Dave Mo...

Well, I'd like to say that this project has worked out but I can't so far. Been out with it four times and still no dice. It'd make a great hangar Queen, but I'm not giving up yet.

First I had to learn how to start an inverted engine. I'm getting better after multiple floods. Then I got a great run but only because (in spite of) a loose engine. Now I can't find that needle setting if my life depended on it. I get a nice 20K on the tach, launch and it dies out without catching air. After a few such attempts, I likely opened the needle a few clicks too much and it blasted raw fuel out the exhaust. It's trying my patience, but my sensitivity to excess sun and heat on a baseball diamond doesn't help. The saga will be continue.


Dave Mo...

Mr. Dave,

I know holding the plane is, well, inconvenient. Have you tried holding it and starting the engine with the plane upside-down? Then flip back upright to tune and launch.

I ran a Scientific P-40 with an AP .061 and a Jan Haluzko NVA/venturi. The plane was built around a traditional wedge tank and I ran the plane on muffler pressure. I should be up front...all I ever expected was Roundie-Roundie with wing-overs.

I need to review your build...
How did you rig the tank? Muffler pressure or Uni-flow? This plane was designed around the Tee Dee or Medallion if I remember right. The Norvel .061 is a slightly heavier engine, so I'm surprised you needed a bit of extra nose weight. If this is the case, then I may build mine around a Norvel .074.

Oh yeah, Jim. The ship turned out very tail heavy, thus the added weight. In addition, I lengthened the front end by 1/4" to accommodate the tank and shift the Norvel engine forward. The tank is standard vented with muffler pressure.

I'm starting to become leery of the Norvel .061 for this full fuse plane. Unless I missed something, the only people who've run these do so on bladder and plank models. Hoping somebody can correct me if I'm wrong. At any rate, I'll keep at it and let you know. I do have an .051 Tee Dee in the inventory if some drastic change needs to be made.

Dave Mo...

Are you sure your Norvel is the Big Mig version?  Or could it be the AME version?  About the only way you can get a "happy" run with the AME version is to run on pressure.

The Big Mig has 5 relatively small intake ports.  The AME has 3 relatively HUGE intake ports compared to the Big Mig.

Keith

Keith

I just checked and found the Norvel has five nice little ports. I still have high hopes for this ship as I did get a semi-decent run and I'm still convinced the problem is operator malfunction. A starting and running session under controlled circumstances is in order (not at the hot, dusty field). So might try that in my basement for a short run today.

Dave Mo...

I have run several of these engines (Big Mig's) since the Tucson 1/2A Scale contests around 2010.  I know the instructions say to use 15% nitro for break in.  Then the instructions say to use 25% nitro for flight operations.  For me, that helps, but they are happier with 35% nitro.  Problem is that plug life is reduced.

Keith

MUFFLER PRESSURE WORKS VERY GOOD ON THE NORVELS

Keith

I think you're really on to something here. I'd been running 15% nitro (20%) oil. I just mixed up a batch of 25N-20O. What a huge difference starting it in the basement just now. At least with further flight tests I can perhaps look forward to better starting and needling. Will consider higher nitro as needed. At least the glow heads and plugs are still available.

Many thanks.

Dave Mo...

Thanks, Bob!

D...

Mr. Dave,
If you start running low on OEM glow plugs KamTechnik makes interchangeable heads that take Nelson or Turbo plugs. He does great parts! NFI...
https://kamtechnik.com/product-category/norvel-aftermarket/

Nice link, Jim. Looks like good product and very fair prices!

Thanks.

D...

The dilemma continues. After boosting the nitro to 25%, it starts very well. But I get runs of only 3-4 seconds, regardless of needle settings. A few large bubbles appear in the fuel line and then she shuts down, even on a full tank. Looks like a cowl teardown is in order unless you gents think fuel line bubbles originate elsewhere.

Much obliged.

Dave Mo...

I'd take some time with a syringe and hose just to map.out the lines to check they are doing what you think inside the tank.

What happens when you plumb the muffler to the other vent tube instead?

Good suggestion, Jim. Per the building plans, the tank has only one vent. And I've tried using it with and without muffler pressure.

In the back of my mind lies a concern about the tank I built (an extra quarter inch of length to accommodate the Norvel). It could be the Norvel doesn't like that extra length, or maybe the tank sprang a leak after installation. Will check as you suggest. Thanks.

Dave Mo...

Have you tried  balloon tank?

Mark

I've not given that a shot as this is a full fuselage model. If I stay with the Norvel engine, that'd be worth a try. I'm also considering a mill with better fuel draw, e.g., Medallion.

Thanks.

D Moe...

I have trouble believing that another 1/4" added length to the tank would be the cause. There is a bigger issue somewhere. If you haven't already, I would suggest plumbing an external tank at the same height and running the engine. (I assume the tank is built in and has no access?) If the engine will start and run SMOOTHLY thru a full tank with a "same height" external tank, then it is time to do the remote diagnostics on the built-in tank. All the usual stuff and nothing left out just because it is a PITA....

--Pressure test with the syringe and some "no foolin' pressure?"  If the tank was not thoroughly soaked, flushed and rinsed with lacquer thinner after soldering things, the flux may have plugged a pinhole (or three) but once it has had fuel in it for a while you are back to leaks. I still wouldn't expect the drastic symptoms you describe even with pinholes on pressure. But, if you double-check this (triple?) then guys can stop asking about it and you can get after the more likely problem(s).

--Did you pull the fuel line at the NVA and see if the fuel flows out when the plane is level? Does it flow out when the outboard wingtip is 60 degrees down?

--Because of the unique single-vent design of the Mathis tank, are you absolutely sure that you are filling the tank to the top? Getting a syringe measurement going in that matches your increased-volume tank? Can you draw the FULL amount out when connecting the syringe to each tube? When the plane is tilted to the angle you expect would submerge the plumbing for a "good to the last drop" test?

--Are you positive that the pickup is in the center? If the tank will free-flow at the needle end of the tubing when full, will it stop flowing after you have captured half the fuel? And what about inverted? Half volume flow and then stops?

--Did you use 3/32" copper tubing on the tank or did you use 1/8"?

--If you can remove the tank, does it pass the "rattle test?"

--Did you have to squeeze the tank to get it into the plane? Did you cut an angle on the vent tube on the inside so that it cannot be obstructed by contact with the top of the tank?

--Do you have flex line that can kink in the bends and stop the flow? Is there ANY flex line inside the fuselage where you can't see it?

Of course, you can take the engine out and put it on the stand, but recognize all the additional things that are slightly--even if unintentionally--altered during the process.

A possible thought regarding the case where you had it needled on the ground but it died immediately after launch:  This is a classic symptom of an engine without enough fuel draw, and/or a needle that is set too lean. We look for this setting intentionally on CL glow-engine racing planes, then richen up just a tad.

I have built two of these Pinto tanks so far. One of them has not been flown yet. A friend has one that I believe was run on a balloon tank. It occasionally had issues.

Dave: Many great questions, so I've got some work to do! I'll give it all a go in the next few days and will report back. Thanks for your thoughtful consideration.

Dave Mo...

Hello All:


Back with a report. I put in a couple hours with diagnostics & attempts at running.

1) No leaks in tank or lines. Verified with serious bulb pressure tests in a quiet room.
2) With a full tank and ship at the level, I pulled the fuel line at the needle and could only get flow if I lowered it a half inch below needle.
3)The tank holds 1-3/4 ounce when full. It is plumbed with 1/8" pipes. No trouble getting it to fill completely.
4) When I installed the tank, it was a loose fit in the compartment. Loose enough so that I could pad it all around.
5) I did find that the needle was partially blocked, so cleared that out to great effect.

So, I attached an external 1-oz. uniflow tank with rubber bands. After many attempts to get the needle right for starting, I managed to get a run of less than a minute that left much fuel in the tank. I forgot to check if the exterior tank passed the flow test at the needle. I might try substituting a non-uniflow tank next if it doesn't.

I got a little burnt out, so that's where I left it. Will try again.

Dave Mo...

Quote from: Dave Moritz on August 15, 2026, 06:01:04 PMHello All:


Back with a report. I put in a couple hours with diagnostics & attempts at running.

1) No leaks in tank or lines. Verified with serious bulb pressure tests in a quiet room.
2) With a full tank and ship at the level, I pulled the fuel line at the needle and could only get flow if I lowered it a half inch below needle.
3)The tank holds 1-3/4 ounce when full. It is plumbed with 1/8" pipes. No trouble getting it to fill completely.
4) When I installed the tank, it was a loose fit in the compartment. Loose enough so that I could pad it all around.
5) I did find that the needle was partially blocked, so cleared that out to great effect.

So, I attached an external 1-oz. uniflow tank with rubber bands. After many attempts to get the needle right for starting, I managed to get a run of less than a minute that left much fuel in the tank. I forgot to check if the exterior tank passed the flow test at the needle. I might try substituting a non-uniflow tank next if it doesn't.

I got a little burnt out, so that's where I left it. Will try again.

Dave Mo...

   After reading your last post a couple times, I and that you found the spray bar partially blocked, I would return there and recheck that. The  Norvel engines are different and can be finicky to get the run satisfactory, but I have never had trouble just getting them to run. Check the spray bar again and how it fits into the case and the venturi. The ones I have experience with have a special shaped flange on the nipple end of the spray bar so it only goes in one position and the hole in the spray bar lines up in the direction it needs to go. Check howo that is all lining up. The fact that you have had issues with two different tanks now makes me thing the engine is the culprit. If you have another needle valve, compare it to the one you are having problems with and see if length, taper and such is the same. As a last resort, if you can remove the tank from the airplane, pull the back end back off and see what the end of the pick up tube looks like. Keep at it!!
  Type at you later,
   Dan McEntee

I meant to come back to this one yesterday.

At this point I wouldn't blame the model's tank. I would encourage a good bit of bench running. I remember my Big Mig .074s were MUCH easier to start and much better (stable) runners after well over 60 minutes of running across many 1/2 ounce tanks. They were on a twin, so it felt like I was running these engines forever before I mounted them on the model.

I seem to remember a thread from several years ago that mentioned crank bearing tolerances can be a bit too tight on some of the NorVels...that is, beyond their normal, tight TDC pinch.

I think the find was running the engine to shut off and then probing the crankcase for excessive temps. The front of the case would exhibit higher temps than the rest of the case. The fix was to polish the crank a bit.

I think it was light finger pressure to probe the case.


Does this sound familiar?

Jim (and Dan):

I think we have an "a-ha" moment here! I too recall someone advising us to pull the crank and give it a good polishing, so good that the weight of the pin itself would float to the bottom when released (or something like that). Your suggestion, Jim, seems correct to me. Each time I ran the motor, it would bog down as if overheating in some fashion or other.

Polishing seems like an interesting winter-time project, and that'll be my plan assuming no other possibilities come to light here. As they say down under, "Good on you, Jim." And Dan, I picked up some pointers from your efforts at helping out.

Thanks a bunch, and I'll keep you all informed.

Dave...

As a follow-up, I hope to find the posting explaining how to polish the crankshaft. The trick will be how not to overdo it. If I recall, the grit was something in the thousands.

Dave Mo..

Mr. Dave
This should get you started. It is NOT an exhaustive list. Granted a thread is for the AP .061, but the premise is the same. Thank Mr. Larry Renger. The gist is to work the crank, not the case. Use sandpaper, not polishing paste.

https://stunthanger.com/smf/12-a-building/what-the-heck-is-'hypereutectic-alminal'/msg197537/?topicseen#msg197537

https://stunthanger.com/smf/12-a-building/cub-and-other-engine-hop-up/msg33594/?topicseen#msg33594

Check post #19 by Mr. Chuck Matheny here:

https://stunthanger.com/smf/12-a-building/norvel-061-big-mig-for-semi-serious-st/msg676990/?topicseen#msg676990

Check deep in post #5, Mr. Carl Cisneros:

https://stunthanger.com/smf/engine-set-up-tips/rpm's-okay-first-rookie-rebuild/msg476073/?topicseen#msg476073


https://stunthanger.com/smf/12-a-building/norvel-revlite/msg204561/?topicseen#msg204561



My "on-forum" search terms were "crank" and "polish," and set to display individual messages, not topics
There are other threads. I'm doing the copy/paste between tabs and rubbing my crossed eyes. Ouch!

Please forgive me for not doing the whole copy/paste of all of the relevant hits. I'm keeping an eye on this one!

You have to decide if you are changing the fit of the bearing, or are cleaning up the crank surfaces.

To clean up the surfaces, I polish the cranks on plain-bearing engines with SemiChrome polish (Happich) or Flitz. They perform about the same. If you are using a drill press, then get a stick with a good flat surface and "charge" it with the polish and use the stick to get where you want to go. The polishing removes very, very little material when used on steel. So you are cleaning off tarnish (or rust if the engine was REALLY neglected) and the peaks left behind by machining processes that probably should have been smoother. Using rags for polishing on any powered equipment (drill press) is asking for trouble. You can do it until there is a mistake and the rag gets caught. Human reactions are nowhere near fast enough to avoid that carnage. If you insist, try taking a jersey material like a T-shirt and cutting a 1/4" wide strip around 8" long. Charge the strip in the middle with SemiChrome and then hold one end with one hand (index finger and thumb) and the other end with the other hand. Yes, it will roll up when you pull on it. That's not a problem--it is just how the stuff is woven. The little strip gives you control, and it avoids most (not all) of the risk of wadding up the whole project--and your hands--in the drill press.

I always polish the crank and run it again to see if the problem was the tarnish and manufacturing peaks, first. If that fixes it, then I'm done and did not do extra work with sandpaper to "prematurely wear it out."

Larry Renger was specifically checking shaft roundness using his "pinch" technique. With the tools available at Cox, he was able to convince himself that his polishing technique was maintaining roundness. That is important. But roundness isn't the only issue. The whole length of the journal should remain constant diameter to achieve a constant fit. If you have a more aggressive metal removal scheme than just the SemiChrome polish (ie. sandpaper) it is more difficult to work the length of the shaft equally. Nothing shocking about that logic. Keep in mind that one person's "gentle rework" with sandpaper may be very different from another person's that results in the removal of .005".

If you are trying to change the fit of the bearing, since you don't know (or state) the actual clearance fit you are trying to achieve, and since most people are not going to have inspection equipment anywhere near accurate enough to measure the bore properly, we are stuck using a "feel" criteria. All I can suggest is go slow, expect lots of iterations, or be sure to have a lot of spare parts. If it ran at all before, then you probably don't want to remove more than .001" if that much.... Before I even took it apart, I would probably try running some all-synthetic fuel thru it just to see if the crank and/or piston was all varnished up. A Cox engine will behave like your description. So will a Fox .35.

https://happich.de/en/products/simichrome-polish


https://www.walmart.com/ip/Simichrome-390050-All-Metal-Polish-Tube-1-76-oz/5229982330?wmlspartner=wlpa&selectedSellerId=101017072&adid=22222222222000000000&wmlspartner=wmtlabs&wl0=e&wl1=o&wl2=c&wl3=10352200394&wl4=pla-1103028060075:aud-821217196&wl5=79192&wl6=&wl7=&wl10=Walmart&wl11=Online&wl12=5229982330_10001036451&wl14=happich%20simichrome%20polish&veh=sem&gclid=36c068e0173c11269edf026811f7385d&gclsrc=3p.ds&msclkid=36c068e0173c11269edf026811f7385d

Man alive, you guys - ask here and ye shall most certainly receive! Jim, your Cyclops work beats my double eye approach by a long shot. Great search results and much to digest there from some guys really in the know.

Dave: I'm inclined to use your less aggressive Simichrome approach. The tolerances inherent in Larry Renger's skill level are well beyond my "shade tree mechanic" aptitude and tool selection. Appreciate your mention of the drill press caution. This hobby can be hard on the fingers and hands and we can't be too careful.

Much obliged to both you gents!

Dave Mo...

PS: I'll mix up a trial batch fuel sans castor oil and see if that makes any difference.
D...

Hmm..., I just finished a short run of the Norvel with synthetic only in the fuel mix (30-20); it again bogged down. I noticed that the cylinder was way too hot to touch after the short (10 seconds) run. The crank bearing, not hot at all. Not sure what to think other than I might have goofed up the break-in routine in that I used castor in the fuel at that time. I'll read up on what Jim's links above might suggest about a cylinder or piston problem.

Dave Mo...

Curly Moe,

Not sure you can blame yourself for a break-in procedure using castor as a cause of the problem. If you didn't blow the rod out or break the crank, then the worst the all-castor might do is varnish up the cylinder or the journal bearing. If the journal was not getting smoking hot, I wouldn't expect varnish. If you were able to run a fair amount of all-synthetic thru the engine, then that would also remove much of the varnish. So I don't see any reason to think that you goofed up much.

Not sure if you can see the piston very well, but I think it is time to take a very close look. In the best-fitted engines the OD of the piston at the top gets shiny when running in. It is the "wear band." The rest of the piston should have more clearance. You can get this if you taper the bore of the cylinder and use a "straight" piston. This is best case. Note that the head of the piston runs the hottest, and it expands the most. This effect is really minimized with the hypereutectoid aluminum piston material--but it is still there--probably about half. (Varies with alloy.) If the barrel and skirt of the piston have shiny spots BELOW THE WEAR BAND one option is to get out your 1500-grit paper glued to a very flat substrate and start lapping the piston by hand. (You can use a 1/4" wide strip of .062 aluminum cut like a popsicle stick, for example.) If you see sleeks on the piston, polish those to. But never the wear band. This is an extremely iterative process but it acknowledges the actual parts and the actual fitup, not a bunch of measurements. There was a pretty good writeup about the technique by Glen Lee(?) years ago in the magazine (probably pre-Model Aviation?) called "Tiger Tuning.)  As I recall, he was hand-fitting a SuperTigre .15 for a scale racer. But the techniques listed might be used if you really have too tight a piston fit and continued running won't loosen it up.

One of the problems with plating is controlling the thickness. Plating a bore with chrome you have to deal with the "throw" of the anode. With anodizing it is not a simple matter of a time-function to buildup. Anodize actually goes into the metal, converting it as you go to something akin chemically to sapphire--some kind of Al2-O3 base compound plus whatever "magic" that this particular engine maker decided on. And sapphire is dang hard. Which makes break-in dang hard if the fit is even just a bit too tight.

If you wanted to lap the bore, then you would need to make a tapered brass lap. You never use the piston. The best lap would be adjustable diameter. You start small, charge the lap and start to gently work the bore in a back-and-forth-while-round-and-round motion. Put a handle on the bottom of the lap to make this easy. The lap needs to be near-perfect shape because the bore won't end up any better than the lap. I've done crude versions of this on engines that were donated to me because they were "dogs." In some cases, the liner was buckled from mishandling and all I had to do was "bump out" the defect--usually near a port. Often because someone used the screwdriver-in-the-exhaust-port trick to try to jack out the stuck liner. These engines usually have the pliers marks on the liner flange, too. I have a Brian Gardener P/L set that I bought from someone here in the states that has the bottom of the liner pushed in from being dropped. I haven't messed with it yet because I didn't need it, but it is going to need some help.

If nothing on your engine is broken yet, you are doing ok. You just have a little farther to go. I'd look at the piston next to try to understand the wear pattern.

Good Luck!

The Divot

Yup! Inspect the top end. I remember my NorVel .074s being absolute beasts in the early runs. They were well-behaved after quite a long break-in.

I'm curious, so I may have missed this one:

How many head gaskets?

Can you try a Cox "normal-compression" glow head (same threads)?

Are you running the engine rich, or leaned out to max rpm? Or, somewhere just fat (rich) off of the lean run?

Ah, ask and I shall receive!

To the Hullmeister: a capital suggestion on the wear band. Also am glad to hear that I've not likely deep-sized this engine yet.

Jim: One standard head gasket. Yes, I ran it some time ago with the Cox head and it did all right. You might have a point on needle stinginess. This mill is such a beast to clear out when flooded, so I might be erring too much on the side of caution.

Will return here with results.

The not so curly Moe...

Yeah!!! Got a run this evening that went through a full tank of 30N-20O; I'm in a celebrating mood big time! It's a screamer, finally. Thanks to you gents for all the encouragement to keep going.

So, I finally found a needle setting that would allow for a good start without flooding. 'Twas a bit tricky as I didn't want the immediate overheating that I got in the past. At any rate, I found a sloppy 2-stroke setting that kept it running adequately. When it would start to load up, I'd dial in a couple clicks to keep the same RPM. A few more clicks yet would eventually (30 seconds) bring it up to much higher Rs. I alternated this up and down pattern to get a feel for needle response. Very slow to lean out but quick to richen up.

I've got to head to the basement now to clear out the smoke.

Thanks again.

Dave Mo...

Progress!  Good work Moe!

El Maximo Divot:

I did take a gander at the piston through the exhaust port and found its surface uniformly shiny, sans the (optimal?) wear pattern you mentioned. But the dang thing runs predictably so I'll go with that.

Thanks.

Moe...

Gents:

Can't win 'em all. I took the Pinto/Norvel combo out this eve for some fun flying. On start-up, the Norvel gave me a run of a second or so, and then promptly gave up the ghost. No compression. I suspect past operator abuse.

I've got some alternate motors to consider for the Pinto. The TD .051 would keep it in the same high-performance league and it'd bolt right in. I've also got an OS .10 and an OS .10FP in the stable but would have to modify the front end quite a bit.

I'll stay in touch as this goes along. Thanks for all the help!

Dave Mo...

Moe,

Sorry to hear about the demise of your Norvy....  I am puzzled how it could go from "too tight" to "no compression" in the blink of an eye...?  You checked for loose plug/head/cylinder?

If you have to change, I would sure try to go with a Cox Medallion .049. Or, if it has to be the Cox TeeDee then consider "hopping it down." Install the Medallion intake and needle system. And the Medallion crank if you have one laying around. Don't mess with the pulse-timed case pressure.

Hoping you get your Pinto up and flying!

Divot

You're most certainly correct. Methinks the operator likely had a screw loose as he found that the head was loose. You're the best! By the way, that's a great suggestion on an alternate power source in the Medallion - sure beats what I had in mind.

Much obliged, my friend.

Moe...

Quote from: Dave Moritz on September 14, 2026, 09:19:24 AMDivot

You're most certainly correct. Methinks the operator likely had a screw loose as he found that the head was loose. You're the best! By the way, that's a great suggestion on an alternate power source in the Medallion - sure beats what I had in mind.

Much obliged, my friend.

Moe...

   Almost any 1/2A type engine can have the head come loose at any time. I'm guessing it has to do with expansion and contraction rates of the steel cylinder and the aluminum head??? Just guessing but in my memory if was a leading cause of flame outs and starting issues when we were kids. Keep working with it!! And i would vote for the Medallion also as an alternative. I think that's the engine that Mathis used in the prototupe.

  Type at you later,
  Dan McEntee

Yup, Dan! So easy to forget the basics when burrowing down into minutia. Didn't know about Medallion / Pinto matchup; it truly makes sense. Thanks!

D Moe...

did you hook up the external tank to muff pressure

I find when a top end keeps coming loose, it is work-hardened gaskets, or damaged threads.

Throw some fresh Cox head gaskets in there and run it again...on the bench.

Or is the engine broken now?

Bob: Yes. The muffler pressure is essential in getting any kind of run at all.

Jim: Holy moly, but I maybe should have taken your advice on more bench run time. I tried starting it in the basement again today without any luck. Getting the correct prime has been a tough nut to crack and it showed today. After three attempts, I ended up over priming it and it threw the prop. The spinner backplate took a hike, so has to be in the nether world. A half hour of searching everywhere with a flashlight turned up nothing. Will have to make a new one.

This venture is detracting from my flying time, so I may put it on hold and revisit it this Winter with a hope that 2027 is kinder.

Thanks, all.

Dave Moe...

Moe,

A few questions about HOW you are priming the engine and a few ideas to consider:

--I assume you are finger-flipping it to start it?

--Are you priming by choking it with a finger over the venturi?

--Are you priming it by squirting some fuel into the venturi?

--Are you priming it by squirting some fuel into the exhaust port? The muffler?

A real issue exists with sensitive engines in being extremely repeatable about procedures. And small engines need small, controlled amounts of prime. Not like a bigger engine that might be able to swallow a pretty good slug of fuel and kick back once or twice, clear itself and run.

So a couple of thoughts that you might consider:

--The "thumb over the venturi and forward flipping" is highly inconsistent because you aren't counting how many flips it takes THIS time just to get the fuel up to the spraybar. And one vigorous flip may pump more fuel that just "pulling it thru."

--Fueling the plane (but almost certainly not a "two line Pinto tank") can flood fuel into the engine, making it too wet even before choking starts.

--For practice, you might try a series of starts with a completely empty tank and investigate priming methods. When you have it down to the point that it fires and runs out the prime with the minimum number of flips every time, now you have a much better feel for what it likes, now the challenge is to avoid letting the tank and the fueling process alter this recipe.

--Something that we do occasionally with .15-sized racers (and others) is refuel the thing with the intake closed (prop back against compression), but push the fuel all the way up to and out the spraybar. Then tip the plane to pour out any fuel from the venturi. Apply the clip and flip. Just the "whiff" of fuel in the venturi is what it wanted. Some OS engines (especially their car engines) are like this, but it is very much an engine-specific thing.

--For sport/stunty stuff, I always consider exhaust prime. Most guys won't do that because they have a muffler. But if you are already standing up (with a helper) to start the engine to save your knees and your bad back like me, just back it off of compression (BDC and open exhaust port), tip the plane nose down, add 3-4 drops down the exhaust (to suit engine size, like perhaps a .40?), then level the plane followed by tipping somewhat to outboard tip up Wiggle the prop back and forth off of compression. You are just giving the cylinder a whiff of the fuel that vaporized in the muffler. And for some engines that is all they need, and all they want. (Not usually true of Fox .35s and McCoys....) After wiggling, run the prop forward so it is barely up against compression. This traps your "whiff" in the cylinder and gives your buddy time to finish telling the joke about the frog and the barman without losing your prime. Now level the plane off, add the clip and flip forward. This first flip is your very best chance. Don't pull thru "to feel the bump."  That feel the bump" technique is useful mostly if you know you are overpriming and are doing that routinely. It works fine on a lot of engines; less so on very fuel sensitive engines. But after going thru the routine to get just a whiff of fuel into the cylinder, why burn the whiff out with no starting attempt?

--I like to use a little eyedropper bottle with a metal tube tip. I can count the exact drops used. No guessing how much. I use it on sensitive engines for venturi priming and for exhaust priming. More consistent, more consistent starts. I use it to prime Cox engines. Way better that squirting fuel all over with a syringe that doesn't go, doesn't go, then REALLY goes.

--Forward flipping draws more fuel; back flipping does not.

--I have an old ST.35C that will start if warm, without a battery. It is a good test item to see how close I get on the "right amount of prime." If the prime is just right the engine will start sometimes with a back bump. Without the right prime, you can flog it quite a few times with the battery attached before it will light off.

--Small engines can be very sensitive to weak or poor battery connections. What at first might seem like priming (or other issues) can be poor power to the plug element.

If you have already considered stuff like this and solved your issues, my apologies for beating a dead horse....

The Divot

Stick with it, Mr. Dave.

After my .074s were broken in, they started this easy:

Right friendly and generous you both are. Presently, excess priming and insufficient run-in time are my diagnosis. I'll copy your suggestions to a file and revisit the Pinto after the flying window closes in the not-too-distant future. Will stay in touch.

Dave Moe...

Jim: Nice "Skeet" video.

DM

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