Saito .40 ragged runs

[Gerald Schamp]

Went out flying today with profile Corsair, with Saito .40 aboard. Had a hard time getting engine to smoothe out, one flight out of 4 was good. Engine has the adjustable choke screw, clunk tank, no muffler pressure, Thunder Tiger 11.3 x 6.8 prop. 15% Cool Power fuel. 10 minute flights on 3 ounces of fuel, next tank shortend to 2 1/2 ounces and it was just at 8 minutes, very saggy in overhead eights. Soon as it came down to level flight was okay. Any suggestioins. 

[Allan Perret]

Wait for the official word from Mr. 4-stroke (Bob Reeves),  but I would say you are set too lean on the needle,  need 20% nitro and 20% lube (mostly if not all syn).  Is the motor run-in  ?

[Gerald Schamp]

Yes motor is run in, has about 2 hrs runtime on it. Was wondering about fuel as well. The fuel is all synthetic, no castor, but only 15% nitro. I turned the needle until the motor started to fall off then backed off till it picked back up. Sounded good on the ground, but sagged right after launch. Is that still too lean? 

[proparc]

I own a Saito 40A but like Allan, I will wait to see what Bob has to say. Something like this, would be very easy for me to fix if I was there, but tough to call with no hands on.

I will chime in after Bob.

[Bob Reeves]

Yep, sure sounds like you are setting the needle too lean but the first thing that sets off bells is that you are NOT running muffler pressure. Please don't tell me you are also trying to run it with a uniflow plumbed tank.. The vent needs to go to the top inside front corner of the tank and be hooked to the muffler.

Once you get the vent plumbed and hooked up correctly, you need to continue going to the rich side of peak till you just detect a slight decrease in RPM. A that setting you should be running about 5 second laps on 60 foot e-t-e lines. If it's too slow, open up the choke screw and reset the needle. If you can't get there (with the needle set on the rich side of peak) you have a fuel delivery problem (hole in tubing, clogged filter... no muffler pressure) or that Cool Power fuel ain't working.

I've never been a great fan of Cool Power fuels but would bet your biggest issue is fuel delivery. Four strokes need all the help they can get sucking fuel and why we run all synthetic (lower viscosity), no uniflow (vent air has to bubble through fuel head) and muffler pressure.

If you stay with Cool Power you need to religiously use after run oil. I once had a ringed two stroke rust literally overnight after running it on a test stand with Cool Power. Thought I could get away with using C.P. for break in and was planning on running it again the next day so didn't use after run oil. Next day the ring and bearings were rusted and I had to rebuild it. I've neglected a few of my four strokes for several months after using Power Master 20-20 and so far never had a problem.

Good luck and hope you get it worked out..

[Gerald Schamp]

Bob,

Thanks for the help, no I am not running uniflow, just plain suction, but no muffler pressure. The tank is a Sullvan S-4 tank, found out very quickly that 4 ounces of fuel will last until lunch. 2 1/2 ounces seems about right. I will try to get some Power Master 20/20, no one sells PM around here very close. I did put after run oil in after I got home. I always use after run in all my engines, bushing and bearing engines.

My tank is plumbed like you say, just haven't been running muffler pressure, so I'll try that.

Thanks again,
Gerald

[Douglas Ames]

Is this Pat Johnston's prototype? How much tailweight did you end up adding, if any?
My Brodak Corsair is coming out a little nose heavy with no covering or finish so I'm not that worried about it yet.
Don't have a tail weight box. I suspect I'll need an oz. or two.

[Gerald Schamp]

Okay, I removed the tank and checked the plumbing, guess what I had it plumbed wrong, now its right I think. Haven't ran it yet but according to what I have read above, I was wrong. Have muffler plumbed in as well.

Yes this is Pat Johnston's proto type profile Corsair. With the Saito .40 it balances right the back edge of the leading edge sheeting, no tail weight. Has a terrific corner, hard to believe without flaps, tracks good both upright and inverted, it does fly nice. Got to get in some practice now and get back in the mix. Plane weighs 40 ounces with Saito .40, its all monokote covered. Nose has Rustoleum on it where I did some repairs to motor mounts. Wish I could build this light. Pat is a Master at light airplanes for sure.

Gerald

[Bob Reeves]

Is this Pat Johnston's prototype? How much tailweight did you end up adding, if any?
My Brodak Corsair is coming out a little nose heavy with no covering or finish so I'm not that worried about it yet.
Don't have a tail weight box. I suspect I'll need an oz. or two.

Fly that airplane before you start adding any tail weight, you might be surprised at how far forward the CG can be with a 4 stroke.

[proparc]

Okay, I removed the tank and checked the plumbing, guess what I had it plumbed wrong, now its right I think. Haven't ran it yet but according to what I have read above, I was wrong. Have muffler plumbed in as well.

Plane weighs 40 ounces with Saito .40, its all monokote covered.
Gerald

40 oz with a Saito 40A, man you could take on Doug Moon with that combo.
Attached is a link to a Saito 40A Bench run with muffler pressure as per Bob reccs.

[Gerald Schamp]

Got my Power Master YS 20/20 fuel from Tower on Saturday, today I ran two 8 ounce tanks of this new fuel through the engine on the test stand. Wow what a difference, the engine just purrs away. 8100 to 8400 RPM's, almost unbelievable how nice this engine run now compared to how it was running. Bob Reeves know his stuff for sure. Now, I really have the four stroke fever. Can't wait to get the engine back in the Corsair and get it in the air to see how that goes, plane flew great even with the ratty runs, so this should be really nice.  

[proparc]

Bob is the man.

[Mark Scarborough]

Gerald,, glad that beast is running better now,,

and dont forget, I can help feed that four stroke fever,, let me know what you want to do,,
in the mean time,, enjoy that feather weight corsair,, Pat is pretty amazing when it comes to building light!!

[Bob Reeves]

I'm working with Gerald to get his issues straightened out.. He flew the Corsair and still has run issues with the airplane. We are thinking it may be his tank set up. I sent him a couple photos this morning and thought it might not be a bad idea to also post them in this thread as it might help someone else.

The first photo is my Ringmaster 576 before I started modifying intakes. It has a UHP intake which I later abandoned for the better working spigot /nylon screw setup I'm using now. This tank only has two tubes, the clunk and a vent. I remove the pickup line to fuel it.

2nd photo is my Shoestring, not a great photo but you can see where the vent ends up in the tank (dark spot at the front top inside corner). You can also see the clunk at the bottom rear. Tank height ends up about centered on the intake. I usually end up with the tank filled to an imaginary line from the top of the stopper to the top rear corner. Can't see it and may not have done when these photos were taken but the rear of the tank is shimmed out 1/8 inch from the fuselage for a clean cut off.

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