V. Sharp

This old timer needs HELP!!, PLEASE!

Although I have been messing around with these little engines for 40 years off and on, it has been much too long since I have run them. They have been cleaned and re-assembled, with new gaskets and reeds.

Engines start fairly easily, and I set the needle valve to a rich two-cycle (breaking back and forth). When I release the plane, they run about one lap like a scalded dog, then lean out and die, time after time. The fuel is Byron 25% nitro, 20% castor. Any ideas why I can't get a consistent run??

Thanks,

V. Sharp

HighPlains

My Feedback: (1)

What size prop?

V. Sharp

Re: prop sizes --

have tried Cox black 6X3, Cox grey 5 1/2X4, Graupner 6X3, all to the same effect.

mclintock

My Feedback: (3)

Is the fuel pick up tube on the outer edge of the tank, so it gets fuel when the fuel all sloshes to the outside of the plane, away from the (control) lines?...or The tube could be hard and leaking at the nipple so when it's sitting on the ground getting adjusted full of fuel it's fine, but going round, the engine starves as the nipple sucks air.. you are talking control line right??

V. Sharp

Both Controlline and R/C -- I have reintroduced controlline to a bunch of R/C fliers, and am flying a 24" 2-channel biplane that I built in 1978. Having the same problems with both!

combatpigg

My Feedback: (3)

A close inspection of the piston and liner with a jewelers' lens can show up some pretty ugly stuff. If you prime the engine, bring it up to compression and hold it there, the cylinder should stay pumped up for at least 5 seconds. If it passes this test, then you have something to work with. I have worn out a few backplate/needle valve seats and small fuel tubing over the needle has bought me more time before the part was totally useless. The torque applied to the screws when the engine is reassembled can cause random airleaks. A crankcase pressure test with a blow tube hooked up to the intake, and duct taped exhaust ports might reveal a leak. If you get bubbles out the front bearing, it's time to pick another engine up from an auction website!

V. Sharp

Thank you all very much -- I will try all of the above!

I really appreciate the assistance, guys!

DICKEYBIRD

Hi Vaughan, welcome!

Good suggestions were given already but you also might try less prop load. Those props you mentioned are a pretty big load. Try a 5x3 Cox black or it's equivalent. The 25% nitro without extra head shims at our altitude might be causing overheating. Less prop load and/or 2 or 3 more head gaskets might help. Also the little venturi gasket has to be fresh for the reedies too run.

Good luck!

V. Sharp

Dickiebird --

I have added a head gasket, a smaller prop and a fuel line seal on the needle valve, but I will have to wait until I can get to a hobby shop for a new glo head, (only have a couple of TD high compression heads left) some more head gaskets and fresh fuel -- I have let kids have most of the 1/2 A stuff I have had over the past year or two. I feel as though I am on the right track to get my last two engines running right!

Thanks -- will keep everybody posted on my progress.

V. Sharp

combatpigg

My Feedback: (3)

What gets confusing is when there is about 6 things that are wrong at the same time!

gcb

Vaughan,

Check the seal on the venturi tube between the backplate and the tank. These are easily pinched or lost. I think this is what DICKEYBIRD was referring to. A small "O" ring or section of fuel tubing can be used as a replacement.

George

Edit: Additional thought. Once you have made the changes, run a full tank of fuel without releasing the plane to see if it will bench run.

Edit2: Just realized I mis-typed your name Vaughan...sorry.

V. Sharp

GCB --

I make venturi seals out of silicone fuel line and a brand new razor blade. It squeezes down to a good seal -- been doing that for years. Have ordered lower compression heads and more props, will have to wait for smaller props to try much more. (85 miles to the nearest hobby shop.)

Everybody has given me a lot of great ideas to try! I really appreciate it.

fireman7875

My Feedback: (7)

Another common problem to the reed valve engines that I don't think anyone has mentioned yet is a spinning needle valve. Over the years metal fatigue weakens the needle valve spring and they can spin causing a rich or lean condition. The fix is as simple as a new spring or a good tug on the old one.

V. Sharp

Fireman, I hadn't tried that one, but I think the fuel tubing over the whole needle valve is helping hold the needle valve still -- that might be one of the reasons I got a better run after I tried all of the above and reassembled the engine! Just waiting for a lower compression head and smaller pitch props now. Thanks! Not quite there yet, but getting better!!

V. Sharp

Fellas --

Just one more question - (like Columbo, probably) -- which exhaust set up will give the best performance, exhaust facing front to back, or exausting out the sides?

Thanks,

Vaughan

fireman7875

My Feedback: (7)

I don't think it will matter much if any. Besides, I doubt you'll really have a choice in the matter as the cylinder screws into the crankcase and wherever the threads stop will determine what position the exhaust is in.

gcb

Actually, you can grind or mill off the top of the crankcase a bit and/or adjust with gaskets. Just be careful that you get the surface lined up perpendicular to the crankshaft (not tilted in any way). Also be aware that you are altering port timing when you do that...and add head gaskets if you lower the cylinder.
By doing this you can adjust the max power for higher or lower RPM (Affects prop size). Is it worth the effort? Only you can answer that.
For most (including me), fireman has it right.

George

BMatthews

I seem to recall that some testing was done with the exhaust openings at various orientations to the airflow and it was found that their was very little difference. I do seem to recall that fore and aft was best.

V. Sharp

B. Matthews --

Thanks for the info -- Both of the engines I have left are exhausting from the sides, and I figure it ain't broke, so I'm not going to fix it! I have just received heads and props in the mail, and am going to continue trying to get good runs. (OH, for the good old days when everything worked the first time!!) Or so we thought!
Thanks,

Vaughan

V. Sharp

To All -- you have been a great help!

A little follow-up -- Good weather in Ky. and a a LONG honeydo list have slowed progress :-)

I have broke the engine down, and reassembled it with careful attention to all gaskets and seals, have a piece of silicone tubing over the needle valve, 2 gaskets under the replaced, now standard, (not high compression) head, and made sure the fuel pickup was where it is supposed to be. Fired it up a few minutes ago, and got a flat screeming full tank run on a Cox 5 X 3 prop.
Will try to fly probably Sunday. Thanks again, fellas!!!

Regards,

Vaughan Sharp