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Engine Air Leak?

Old 04-30-2019, 08:13 AM
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Default Engine Air Leak?

I read several ancient posts regarding this subject, but none of them answered my question. (Please no low end bashing - I own everything from Redcat to Kyosho)

After my buggy starts, the idle is stable for a few seconds and gradually increases to alarming levels. I found the other day that I can completely cover the air intake on the carb, feeling suction, and the car keeps running despite cutting all air off. (I figured this out when my car kept running even after adjusting the throttle to completely closed) My needles are set to factory specs, although I have tried leaning and richening. I removed a fuel filter and replaced the gas tubing, thinking it was allowing air in. I even took the back plate off and added a liquid gasket, all to no avail.
Yesterday I removed the carb and pull starter, and sealed those as well. I still have yet to see if this worked, as the gasket needs to set for at least 24 hours.
Another thing to note is that the engine seems to run a little hot - which indicates an air leak as well.
Any ideas?
Old 04-30-2019, 09:13 AM
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Well, I'm an airplane guy...but what engine? I assume nitro and not gasoline?
Typical leak points, more or less in order of likelihood:

1. carb to body - o-ring or gasket leaking.
2. Bad o-rings on the rotating carb barrel
3. Worn threads on the high speed needle.
4. Crankcase to main body - bad gasket.
5. Backplate, as you noted.
6. Leaking head gasket.
Old 04-30-2019, 05:38 PM
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If the carb is sealed to the crankcase and the slide or barrel is not overly worn within the carb body, the front and/or rear bearing(s) could be allowing air to enter through the front of the engine. The rubber seal isn’t what seals the crankcase, but rather the fit of the crankshaft inside the crankcase. If the crank isn’t running true, air can get past the crank through the front bearing.
Old 05-11-2019, 04:47 AM
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It's a brand new GO .21 engine - It was already mounted to a VRX2 buggy. I sealed everything I could and it still ran crazy. I contacted the seller who said "It may have been old stock". Since then, he sent me a fat refund and I purchased a Dynamite Mach 2 .21 engine I just finished mounting yesterday. Now I'm trying to figure out what to do with the GO engine - As I said, it was nearly done with break in, so it's pretty much brand new. I don't want to send the thing to Europe - Perhaps my local hobby shop can help, although they don't seem to be experts in anything really. Thank you for your responses!
Old 05-17-2019, 01:26 PM
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had you possibly checked the fuel tank for leaks? is there any primer apparatus? those tend to leak. you can test the engine air leaks much like a fuel tank and submerge it in a soapy water (if you do this make sure that right after you rinse all of the internals, i do say that again ALL OF THE INTERNALS out with either fuel or DNA as you would when cleaning out anyways.) then blow into the carb while plugging the exhaust port. with your thumb.

rotate the motor over while it has fuel/DNA in it to make sure all of the soap/water (if any made it in) is out of the bearings, crank etc. i know for awhile there Composite carbs were terrible about leaking, had you checked your carb O-rings? if it was old stock i wouldnt doubt that they would be dry rotted and stiff. if possible when getting new ones put some factory team green slime on them. might double check the HSN mount/banjo fitting as well have had one engine that had an air leak there.

since everything went brushless, nobody at my LHS knows anything specific about nitros... just fuel, what glow plugs are, and put ARO in it.

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