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Old 05-14-2010, 07:21 AM   #1
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Questions?? Starting a HOT engine

Sometimes when my engine is very hot and it stalls, such as running out of fuel, it won't restart (after refueling) until it cools off. Are there any tricks? I have tried priming it again, steps to unflood it in case it was flooded (it was not), etc.. This only happens when it's really hot. For example last time when the engine was off, when I open the throttle it sounded like someone frying bacon in a pan, so I assume the oil inside the motor was bubbling? Maybe the carb is getting too hot and the fuel is boiling? After it cools for a few minutes it starts right up and runs fine again until it runs out of fuel. It is warm here (ambient temps around 90F in the shade) so the motor gets much hotter now than it did in the winter.
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Old 05-14-2010, 07:32 AM   #2
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don't let it run out of fuel then.


Could very well be vapor lock though. And if that is the case your motor is approching or surpassed 300 degrees. Not good at all.
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Old 05-14-2010, 11:03 AM   #3
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A motor that's difficult to start when hot, but gets easier once it cools down is a clear symptom that you've lost compression, and it's time to have it pinched, or get a new piston/sleeve.

If you're heard a "sizzling sound" more than once, I'm pretty sure you've gotten the motor way too hot a number of times, and it's done. Incidentally, do you have a temp gun? Probably not a bad idea to get one when you buy the new parts for your motor.
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Old 05-14-2010, 11:11 AM   #4
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First of all, how HOT are we talking here? And what engine is this? Does it have an all metal carburetor? It very well could be vapor locking. Or it could just be that you're getting the engine too hot to begin with.
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Old 05-14-2010, 11:32 AM   #5
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The sizzling is usually fuel boiling in the carb. Happens with metal carbs if you run em too hot. I'm ALL too familiar with engines with minimal pinch. Stubbs is right on with his diagnosis. TRUST ME. He ran a good 5 miles last season pitting for me with worn out motors ;-)

Everything inside expands with heat....so if you have pinch when cold, and it disappears when hot.....you need a new piston/sleeve or at least a fresh "pinch" to the piston/sleeve you have if they are still in good condition.
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Old 05-14-2010, 11:36 AM   #6
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I had this issue with a motor, for some reason i could start it cold but not hot. Turned out to be a leak in tank.
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Old 05-14-2010, 12:52 PM   #7
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Thanks for the tips, maybe it is just getting worn out?.. The engine is the stock engine in a Kyosho DBX, it does have a metal carb. I don't have a heat gun.. It still runs great with good power. It seems to have good compression when cold and hot, though it has zero pinch as far as I can tell (had buckets of pinch when it was new). The head cools down quickly, but even when the head has cooled it won't start if the engine cases are still very hot. I have about 2 gals through it so far and it's just my back yard toy so I'll probably run it till it blows up then shop for a fancier motor. Maybe an O.S. .18 or something that's a good durable "daily driver" motor. Suggestions welcome.
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Old 05-14-2010, 02:07 PM   #8
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I hate to say this, but I think that your engine, carb, and bearings are toast. That sizzing sound is never good.
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