Author Topic: Venturi for AP 061 ? ? (Read 9364 times)

Larry Renger · « **Reply #50 on:** May 18, 2009, 10:35:17 PM »

The carb can be reversed to have the needle point down! You will burn your fingers from the exhaust if you are not using a muffer, though. An old trick is to use a dowel with some rubber tube as a temporary extension/tool to adjust the needle, then pull it off when flying.

Bill Adair · « **Reply #51 on:** May 19, 2009, 12:39:13 PM »

Ran my Wasp again yesterday, and it continues to pick up RPM as it breaks in. It's turning over 17K now, with the 5.7 X 3 APC, on my make shift fuel blend.

A short length of medium fuel tubing under the needle valve, cured the touchy needle settings I was seeing before.

It starts by hand flipping now, but is still not easy to get running when cold.

Bill

Larry Renger · « **Reply #52 on:** May 20, 2009, 12:46:24 AM »

Did you remove the sheet metal spring stop when you added the fuel tubing seal? Photos, perhaps?

I am using the "001" NV assembly for my venturis, but have to turn special washers .0625 thick and .22 diameter as spacers to clear the heads of the retaining screws and center the hole in the spraybar.

I hope to turn out the next version tomorrow. I had failed to subtract the obstruction of the needle and jet from the bore of the carb in my calculations and it was significant! My first versions are WAY oversize, and the engine hates it! I have a spreadsheet where you can plug in the venturi bore and spraybar diameter and get a really accurate passage area output. I can add an equivalent unobstructed bore size column to compare to things like the Tee Dee venturi. Drop me an e-mail if you want a copy.

I suspect that a standard setup of venturi and spraybar will never match the clean flow of the Tee Dee. But it will be more reliable and compact than the stock carb setup.

Vincent Corwell · « **Reply #53 on:** May 20, 2009, 01:40:29 AM »

Hi all
I started this thread and I am waiting patiently
to buy 2 assemblies, I dont see the small needle
assembly on RSMs web site,
Is there a small version
will Eric be offering the complete unit to convert
to control line please?..........cant wait as I have
2 of the AP 061 engines in a stretched Baby
Flite Streak twin, cant get both to run reliably
and I reckon the venture/needle conversion will
solve the problem

thanks to all for the replies, some very good tips there

Photo now included below

Vincent

Larry Renger · « **Reply #54 on:** May 20, 2009, 10:44:55 AM »

Neat model!

Development of the venturi for RSM is not complete. I hope to turn a new test article today and test it this weekend. After I am satisfied, I expect it will be several weeks before Eric would have the conversion kits available. For the time being try the fuel hose trick mentioned above, or get some plumber's teflon joint compound and seal the needle thread area.

Stan Tyler just completed a twin Flite Streak for two Tee Dee .049s. His is a scale of the Classic legal design, I don't recall the designer. Joe Bellcrank (John Miller) has the plans. Stan is having trouble keeping the outboard engine running the full flight. I suspect overheating. My contention is that the centripital (or centrifugal, I never could keep them straight) force on the outboard engine is greater, so it leans out more. I think he needs to send the plane off with the outboard engine noticeably richer than the inboard one.

minnesotamodeler · « **Reply #55 on:** May 20, 2009, 02:01:08 PM »

...also to insure the outboard runs out of fuel and quits first!

I built a twin using two McCoy .19s many years ago, a real blast. At least once the inboard engine quit; it continued to fly on the outboard only, but very scarily...line tension was virtually undetectable. Just enough control to keep it out of the ground.

Bill Adair · « **Reply #56 on:** May 20, 2009, 05:54:05 PM »

Quote from: Larry Renger on May 20, 2009, 12:46:24 AM

Did you remove the sheet metal spring stop when you added the fuel tubing seal? Photos, perhaps?

No, I just estimated the length of medium fuel tubing it would take to seal up against the needle detente spring at the carb side, and to ride up onto the taper of the internally threaded needle outer housing, an eighth of an inch or so.

I cut both ends of the fuel tubing square, forced it over the threaded spray bar, and screwed the needle back in. The tubing is small enough to fit under the detente spring without interference, but large enough to let the tapered end of the needle outer housing squeeze into the tubing. Seals at both ends of the fuel tubing, and holds the needle solidly in place, but the needle can still be turned to fine tune the mixture.

Not sure how that will hold under flight loads, but it ran quite steadily on the bench, and just touching the needle no longer changes the mixture.

Quote

I suspect that a standard setup of venturi and spraybar will never match the clean flow of the Tee Dee. But it will be more reliable and compact than the stock carb setup.

Hope to have the Wasp broke in soon, so I can get some baseline RPM readings, before the Tee Dee mod.

Bill

Larry Renger · « **Reply #57 on:** May 27, 2009, 10:10:29 AM »

Well, I am now satisfied with the venturi design and will turn it over to Eric Rule for production. He has a source that looked at the preliminary drawings and says it will be no problem.

Bill Adair · « **Reply #58 on:** May 27, 2009, 11:30:02 AM »

Larry,

That's good news!

I'll be watching for the release announcement.

Bill

Bill Barber · « **Reply #59 on:** May 27, 2009, 02:48:25 PM »

   Larry , I have to ask, how did your new venturi compare to
  the Tee Dee venturi ?
   Bill

minnesotamodeler · « **Reply #60 on:** May 28, 2009, 05:58:06 AM »

Hey Larry, price? And can we pre-order? And can we see a picture? And...

Larry Renger · « **Reply #61 on:** May 28, 2009, 08:54:22 AM »

I'll have to beg for some time on both the above questions. I need to tach the two engines with the same prop and fuel. I expect that Eric hasn't a clue yet on what the carb setup will cost.

I can, at least do some photos. I'll post some later today.

Larry Renger · « **Reply #62 on:** May 28, 2009, 09:44:01 AM »

Here it is!

don Burke · « **Reply #63 on:** May 28, 2009, 10:18:09 AM »

I suggest getting an NVA from Doug Galbreath. They're a lot more compact and made for small engines. And as anything fomr Doug, super high quality.

http://www.the-printer.net/DookCat.html#rossi

Bill Adair · « **Reply #64 on:** May 28, 2009, 12:04:10 PM »

Larry,

Very nice!

Did you use the original carb mounting screws?

Bill

minnesotamodeler · « **Reply #65 on:** May 28, 2009, 07:31:30 PM »

I finally took my Wasp out and ran it today, 1st time. Typical of these pinched-top engines, the first start was kind of a bear, took a little while, but it got progressively easier to start with each run. Not the equal of a Norvel .061 yet, but maybe after it loosens up a little more. I'd estimate it's putting out about the power of my good Black Widow, maybe a skosh better, not much more than that right now.

But I gotta say, those RC carbs on these things stink. Yes, touching the needle changes the setting...you can wobble the NVA back and forth and see the needle tip moving inside the venturi. This can't be good! I tried the seal-it-with-fuel-line trick and it helped, but still pretty erratic. I'll be needing one of those new venturis. Or I'll have to make my own. But there's no way I'll use the stock carb, wired open or otherwise. Anyone wanna buy it off me?

Graham Collins · « **Reply #66 on:** May 29, 2009, 05:28:42 AM »

Larry,that's a nice looking venturi set up - looks the part and like it belongs.

Doug Galbreath and Larry Driskill both have some smaller needle valve assemblies that are at least available. I still have a small (very small) stash of small OS needle assemblies but when gone will be gone. Trouble with trying to shop around is that a picture may be worth a thousand words but if the critical dimensions are missing or some sort of reference is given, you really have a clue on how "big" or "small" the thing is short of buying one of each and sorting through them.

cheers, Graham in Ottawa Canada

Larry Renger · « **Reply #67 on:** May 29, 2009, 08:40:53 AM »

Yes, the needle assembly is big, but it is what Eric stocks, and thus, what I designed around. What the heck, it works beautifully. For improved performance, I suspect a smaller diameter spraybar would be a good thing, but I would have to start development all over again! Even so, the Tee Dee carb setup will probably always be the ultimate choice for top performance.

minnesotamodeler · « **Reply #68 on:** May 29, 2009, 11:08:59 PM »

I disassembled the carb tonight and modified it, put a washer shim on the needle side to tighten against, locking it wide open and trying to stabilize the assembly. Still, even with the fuel line seal, the needle can wobble inside the jet, seems like the male threads are a little undersized or something...but it is better, I'll try running it tmw and see if there's any improvement. Seems a shame to put such a cruddy little carb on an otherwise really nice engine.

john e. holliday · « **Reply #69 on:** May 30, 2009, 08:42:30 PM »

Hey Ray, try some teflon tape on the threads of the needle valve. We used to do on the Tee Dee needle valve/body when we used them in F2C years ago. DOC Holliday

minnesotamodeler · « **Reply #70 on:** May 30, 2009, 10:07:58 PM »

Well Duh, why didn't I think of that...I can make the threads as tight as I want, that should take most if not all the wobble out. Thanks Doc.

Bill Adair · « **Reply #71 on:** June 10, 2009, 03:38:53 PM »

Was going to continue the break in of my AP Wasp, but found one of the carb retention screws was missing!

Haven't checked to see if it backed out during previous bench running, or simply sheared off. I torqued them down as much as I dared for that size screw, so I think re-tapping for a larger screw size is the next step.

Bill

john e. holliday · « **Reply #72 on:** June 11, 2009, 07:46:11 AM »

Go to your local Ace Hardware and check out their machine screw bins. Take your engine with you. That is where I get mine when I am in a hurry or it's metric. DOC Holliday

Larry Renger · « **Reply #73 on:** June 11, 2009, 09:15:33 AM »

Loosening of those screws is a problem. They are 2mmx.4mm, 2.5mm long. I think you can drill and tap for 2x56, or just drill and run a 2x56 bolt all the way accross the venturi. I may try that. Definitely use locktite!

Bill Adair · « **Reply #74 on:** June 11, 2009, 12:55:00 PM »

Larry,

Thanks for the screw size info.

I'll check ACE for the screws, as I noticed some really small metric sizes there.

The case is drilled large enough for a 3X48 screw to pass through (with room to spare), but a 2X56 should be more than adequate, and won't require drilling out the carb screw holes.

Out of curiosity, I pulled one of the venturi retaining screws out of a Norvel, and found it's the same thread size. The Norvel screws go all the way through, and use a nut on the other end.

I was going to check the fit of a Norvel carb/venturi on the Wasp case, but they apparently used some adhesive to hold them in place, in addition to the machine screw.

Bill

Larry Renger · « **Reply #75 on:** June 11, 2009, 04:47:38 PM »

I am finding that at the rpm I run, glue and screw would be a good thing!

Bill Adair · « **Reply #76 on:** June 12, 2009, 01:20:25 AM »

The Wasp carb is now mounted with a 2X56 machine screw, with a little coaxing from my tap to chase the threads in the carb base. Found there is no room for much of anything under the throttle arm, so I ran the screw in from the other side, and locked it snug with a thin 2X56 nut. There isn't even room for a washer under the nut, but I think it will hold.

Next time I try this, the throttle arm will be removed first!

Hope to run it again tomorrow, to see if it stays in place. Also want to see if performance is effected by the screw through the carb base.

Since all the later Norvel engines use a 2mm screw straight through the carb base, and they run circles around the Wasp engines, I don't expect to see any effect at all.

Bill

Bill Adair · « **Reply #77 on:** June 12, 2009, 06:08:05 PM »

Ran the Wasp several times today, and it runs fine with the 2X56 bolt Through the carb base!

I did notice that the needle valve is still sensitive to movement, which I thought had been improved by the fuel line under the needle. Pushing down on the adjustment knob as before still had little effect, but pushing up, forward, or back, had a very pronounced effect on engine speed!

Oh well, that much more to be gained with a fixed venturi.

Bill

minnesotamodeler · « **Reply #78 on:** June 12, 2009, 08:29:02 PM »

Bill, that is what I had found too, the thread tolerance is just not close enough to prevent the needle from wobbling in the jet. It was suggested that a guy could wrap the threaded portion with teflon tape. I haven't tried that yet but intend to, it's bound to at least help. What we really need is a better NVA. I believe that's being developed as we speak (write, type, whatever).

Bill Adair · « **Reply #79 on:** June 12, 2009, 10:08:40 PM »

Ray,

I'm not sure that tightening the needle valve threads would be enough. On my particular engine, the rotor is a sloppy fit in the carb body, so I would have to fix that source of air leaks as well.

Hope Eric can market Larry's venturi design inexpensively. Other than that, he could reverse engineer the Norvel venturi design, and sell enough extra needles to Norvel owners to make them more cost effective.

Anyone tried a Norvel venturi in a Wasp yet? My Norvel venturi all appear to be cemented in, and I'm reluctant to pull one.

Bill

minnesotamodeler · « **Reply #80 on:** June 13, 2009, 07:02:57 AM »

I think the Norvel venturi is flattened where it inserts into the case, whereas the Wasp is round. Don't think it would fit. (I knocked one of mine out in a crash once. Definite, significant flats on 2 sides.)

Bill Adair · « **Reply #81 on:** June 13, 2009, 03:51:51 PM »

Ray,

It was just a thought, but the Norvel venturi is nearly impossible to find anyway, so no big disappointment.

Checked ACE Hardware today, and they have lots of 2mm screws, so replacements for the Wasp carb will be no problem for you folks.

Bill