<div id="post_message_987782">Hi, I'm running a Zenoah G62 in my dragster.I can't get it to run smooth.Since this is a airplane engine I thought you knowledgeable guys here will have the answers.I'm running 87 octane for fuel and a 40:1 ratio.That's what I run in my gas cars.The high speed needle is about 1 1/4 turns out.She idles fine.When i pull the triggerthe rpms goup but itseems rough not asmooth transition.Is it the octane? How high a octane and what fuel /oil ratio should I run. If that's the problem.I have since switched to 91 octane and 32:1 ratio.I did rebuild the carb and replaced the spacer between the carb and head.Any info will be appreciated. Thank you. (Oh just a foot note ,I ran the car in May on my street and being useto the smaller Zenoahs with a fan and shroud .I ran the dragster up and down the street forgetting this engine does not have the fan or shroud on it.I'm thinking it overheated. It never ran the same after that.)I removed the head today and everything looks fine inside.No scoring ,no signs of overheating on the parts.The onlything I found was the gasket between the head and the carb spacer was breaking down.It was new when I put the new spacer on.There was a little fuel on top of the spacer.Also when I removed the head the head gasket it was wet on the case side.Maybe the surfaces are uneven.I also run a straight header pipe.Could the lack of back pressure be a problem.Thanks.</div>

the first thing that is a no-no is not having any cooling system. you'll know if you smoke the engine when it either seizes up or looses power. you can overheat an engine to the point of tempering the piston ring without the engine seizing or gawling the piston.this would cause a major loss of compression. but that depends on your lubrication type. in order for these engine to run smooth at an idle generally they need a flywheel of some type. the stock one just doesn't have enough mass. i'm not sure how they set these up in dragsters , but i can see when a flywheel could hinder a quick engine ramp-up time in your case.it sounds to me like your high speed needle is to rich. the best way to set it is to get the engine full throttle and tweak it there. once you have a good high speed mixture then go to work on the low end. you might have to go back and forth a couple of times. i run straight 89 in all my gas planes with no problems and i run Stihl 50:1 ratio oil. stihl has an additive that helps off set the effects of today's ethanol. awesome oil ! i would try leaning the top end out first if you feel you have a good idle ,but don't be fooled ... a rich idle setting will load up the engine and cause the same effect as a rich high speed needle. i hope this isn't to confusing,but for me it's easier to do it than explain it. you should post a video on you tube to show what you talking about , that would be a big help. hope this help at all WB_1

after rereading your post. i would first check to see if it has good compression . you may have over heated it. how long did it run when you did run it? running a open header is not as bad as running a restrictive muffler. i don't see a problem there. as far as the carb insulator block goes ... you could have distorted it from to much heat. the fuel you saw my have been oil that bled past your bad gasket. not surprising.usually when you have a bad seal on the carb side ,you'll have a lean problem from sucking air. i have been around small engines my whole life and feel i'm pretty good at trouble shooting. if you want , i can provide my number and maybe we can figure it out.

Hi, Thanks for the reply.The engine is completely stock.It has the stockrotor or flywheel.I ran it I think twice down the street (100 ft.).As soon as I order a new head gasket i'll do a compression test.I will do the needle settings again. I did the high speed needleby adjusting it while going full revs but didn't do the low speed adjustment that much.I'll make sure the carb spacer is flat and put on a new gaskets.I'm also going to make a heatsink for the top of the head.If it still runs poorly then I'll give you a call. Thanks.

After you set the high speed needle, the low speed needle is generally set as lean as possible and then still be able to accelerate to high speed correctly.

Thanks for the help.Problem solved. I couldn't wait for Thursday.That's when the new head gasket comes. So I put the head back on with the old gasket. I guess I didn't adjust the low speed needle enough.So I adjusted one then the other and now the engine revs up nice.Now what temps should I be watching for. Someone told me to use theinfra redat the rear of the engine where the head meets the casing. Another said directly on top. Measuring the first way I get 135 degress + -. On top I get 240,250.+-.What would be the max. Thanks again for replying.

was it too rich?

You run past 250 very much and you will eventually have trouble.

Yes it was still rich on the low needle.Which location should the temp be taken from?Thanks.

Right around the exhaust side of the spark plug on the head