Engine running rough

[steve-0]

have you tried backing out the idle mixture screw on that side of the carb?


and instead of pulling the carb just shoot some starter fluid down the carb and if it smooths out for a sec and then you have a fuel problem.

[R.E.Co.]

have you tried backing out the idle mixture screw on that side of the carb?


and instead of pulling the carb just shoot some starter fluid down the carb and if it smooths out for a sec and then you have a fuel problem.

I concur.

[emptyhead]

Got around to buttoning things up again and ran a compression test while the engine was running on all the cylinders and that tells a different story. 1,2and 3 between 115 and 120. 4. Is at 40 to 50 5 and 6 are between 60 and 70. So I'll put one more head gasket on otherwise crack in the head somewhere I'm not seeing crack in the block somewhere I'm not seeing. Cylinders where bored and sleeved so if cracked maybe in valve area. Hooked up a vacuum guage and low vacuum needle bouncing all over the place. Any of you guys ever play with the valves on these engines.  Also checked the carb while it was running and the outboard barrel was a little weak on fuel delivery as opposed to in inside barrel. Took that apart and cleaned it but couldn't find anything wrong. Thanks guys for the input.

[8683jb]

You might try a differential compression test instead of static. You get the cylinder to TDC on compression stroke and typically put 80 PSI on the gauge. The second gauge will indicate how much leakage there is in the cylinder, but the bonus is that you can hear where it's leaking from and how bad. Put an ear to the exhaust pipe and if you hear air, the exhaust valve isn't sealing. Air at the carburetor, intake valve. At the breather, it's rings. It's a quick, easy way to pinpoint a problem without a bunch of trial and error. Make sure the piston is at TDC before applying the air! If it's on either side of TDC, when you put 80# on it, the piston will go down and if you have a wrench on the damper to turn the engine it can spin pretty quick and break fingers, so be careful!

[autocar925]

The tester he is talking about is called a "leak down tester" and is very common in the racing world.  Not real expensive and are available from any high performance store-Jegs, Summit, etc.

[8683jb]

If you're near an airport and know an A&P mechanic you might be able to borrow one. I have lent mine to trustworthy folks. Tell them it's for a half track and you might be able to borrow the whole mechanic! You'd need a 14MM adaptor as his would have an 18MM for aircraft engines. It would be easy to make one from an old spark plug base.

[steve-0]

might also try checking your valve lash before you pull the head

[HenryVIII]

I agree with the valve lash idea. When I had my engine rebuilt by a professional he did not check the valve lash. One of the valves was being held slightly open and I had a miss too. Before you take too much apart again I suggest you check the valve lash on the lifters. When the valves seats were ground the valves sit lower and you loose the clearance on the lifters. Sounds to me like one set 4,5,6 might need checking. If the valve is held slightly open you could burn a valve if not corrected. I would have to check for sure but I think the clearance should be around .020 cold.

Good luck   Henry 

[emptyhead]

If you could check that would be great. I can't find any info on the valve train in my books. Thanks

[HenryVIII]

Here is a copy of the page with the valve specs. It is from page 203 in manual TM9-1711.    Hope this helps.  The clearance was a bit more than I thought. .040-.080

Good luck
Henry

[emptyhead]

Thank you very much

[Smadge]

Did you figure out what the problem was??

[spec4don]

Check your air cleaner oil level too. Water gets in there and also causes the engine to run rough.
Also I had my little foam seal slid down into the carb!

Don G

[Robert Cassin]

Remember, I am 20 miles north if you need help!!! Not that i know what I am doing! I can perform gopher duties!  Ha Ha...

[emptyhead]

A little update started playing around with the engine again. Made up a plate to block off the hole in the intake manifold where it bolts to the exhaust manifold and brazed a air fitting on it. Pressurized it and had a big air leak blowing into the intake side of the manifold so hopefully that solves a lot of my problems. Thanks all,the suggestions guys will keep you updated