80cc bike engine not idling and overheating

S

SouthernOntarioBikeDemon

New Member
My engine seems to be overheating, the muffler is hot(scorching, and the engine head itself seems more hot then it should be) this is not a new engine, and i cannot idle i pop the clutch and it shuts off right away. do i need to tune the carb?:-||
 
When you say "pop the clutch", you mean when you pull the clutch handle in? If so, have you tried screwing the idle adjustment screw in more?

When I had the needle on my bike a little too rich it did not idle well and turning the idle adjustment screw all the way in did nothing. She would idle for about 20 seconds, then stall. Moving my needle one step leaner took care of the idle issue.

I know people say the needle affects off-idle to 3/4 throttle, but adusting mine on my NT carb definitely affected my idle too.

And with the stock head, these little guys run pretty hot. There is a thread around here where people compare running temps. You should pick up a cheap infrared thermometer (or borrow one if you do not have one) and check your head temps to see if they are in line with the others. Running lean can cause extra heat, maybe you have an air leak? That would explain your idle issues too.
 
yes, when i pull the handle in to stop the engine it just dies right away no idle, and smoke seems to come out of the engine head when i accelerate too, i will try to adjust the screw but is turning the screw right make it leaner? also i think there might be an air leak because when i throttle down completely the engine still revs like im giving it juice even though im not, how does one find an air leak? thanks alot for the help man!dance1
 
SouthernOntarioBikeDemon said:
yes, when i pull the handle in to stop the engine it just dies right away no idle, and smoke seems to come out of the engine head when i accelerate too, i will try to adjust the screw but is turning the screw right make it leaner? also i think there might be an air leak because when i throttle down completely the engine still revs like im giving it juice even though im not, how does one find an air leak? thanks alot for the help man!dance1
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If smoke is coming from the head, sounds like that is your big leak there. Are you using acorn nuts on the head bolts? If so, it has been seen that these can bottom out before putting enough torque on the head. They should be replaced with regular nuts to avoid this. Or at very least, and a washer under the acorn nuts to give them a little more grab room.

Also, a lot of times the head and cylinder mating surfaces are not exactly smooth, and lapping them a little using a piece of glass and fine grained sandpaper can help make them smooth.

You may have also just blown the head gasket.

You are right about the engine revving on as a lean condition.
 
i checked my gasket and it seems to be fine, but i noticed that there are some cracks in the piston rings, and there is alot of gunk on top of the piston head....idk what to think...:-||
 

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its just build up.. a bit more than ive ever seen. i usually clean the piston and jug every few months... clean it up and see if it helps.. it will also increase the life if the engine...
 
maurtis said:
I know people say the needle affects off-idle to 3/4 throttle, but adusting mine on my NT carb definitely affected my idle too.

And with the stock head, these little guys run pretty hot. There is a thread around here where people compare running temps. You should pick up a cheap infrared thermometer (or borrow one if you do not have one) and check your head temps to see if they are in line with the others. Running lean can cause extra heat, maybe you have an air leak? That would explain your idle issues too.
Click to expand...

The first part makes sense because you raise the throttle slide to allow just enough air to generate just enough power to keep the engine parts rotating.

X2 on finding the true temp.
 
Thanks for the pics. I am seeing a whole lot of oil, EVERYWHERE. I would still replace the acorn nuts. If you are losing compression and getting leaks at the head, the bike could still run, just horribly.

And I mentioned in your other thread, the "crack" in the piston ring, at least the one I can see clearly, looks like the regular split in the ring which fits over the locator pin on the piston. The rings are split, and form a circle when compressed. There should be a tiny locator in in each groove for the piston rings, the ring cutouts go over that pin.
 
maurtis said:
Thanks for the pics. I am seeing a whole lot of oil, EVERYWHERE. I would still replace the acorn nuts. If you are losing compression and getting leaks at the head, the bike could still run, just horribly.

And I mentioned in your other thread, the "crack" in the piston ring, at least the one I can see clearly, looks like the regular split in the ring which fits over the locator pin on the piston. The rings are split, and form a circle when compressed. There should be a tiny locator in in each groove for the piston rings, the ring cutouts go over that pin.
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the bike still has alot of compression, and by horribly you mean the engine is pretty much shot and i should give up trying, lmao.... i just want a working bike, its one thing after another, first i find it hard to mount, now the engines f'd,fml:-||
 
SouthernOntarioBikeDemon said:
the bike still has alot of compression, and by horribly you mean the engine is pretty much shot and i should give up trying, lmao.... i just want a working bike, its one thing after another, first i find it hard to mount, now the engines f'd,fml:-||
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I mean that it would run horribly while it was leaking, but fine after the leak was fixed.

It could just be the way the pictures look, but it looks to me that there is oil residue EVERYWHERE on that motor, especially on the head gasket and head.
 
SouthernOntarioBikeDemon said:
so how do i find/fix the leak?
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The first thing I would do, since you already have the head and cylinder off, is lap the mating surfaces smooth. You can search for how to do it on this site, there are tons of posts on making them smooth to help eliminate head leaks.

Then use regular or shouldered nuts instead of acorn nuts when reinstalling the head.

After everything is buttoned up and the engine is running (preferably idling, but as low an rpm as possible at first) spray various areas of the motor with WD40 or carb cleaner. If there is a leak and the spray gets sucked in, it should affect the rpms. If so, you found a leak.

Common places for leaks are at the head, intake manifold where it meets the cylinder, intake manifold where it meets the carb, and at the crank seals on the clutch or magneto side.

Good luck!

Also, what oil ratio are you running, and what plug?
 
maurtis said:
The first thing I would do, since you already have the head and cylinder off, is lap the mating surfaces smooth. You can search for how to do it on this site, there are tons of posts on making them smooth to help eliminate head leaks.

Then use regular or shouldered nuts instead of acorn nuts when reinstalling the head.

After everything is buttoned up and the engine is running (preferably idling, but as low an rpm as possible at first) spray various areas of the motor with WD40 or carb cleaner. If there is a leak and the spray gets sucked in, it should affect the rpms. If so, you found a leak.

Common places for leaks are at the head, intake manifold where it meets the cylinder, intake manifold where it meets the carb, and at the crank seals on the clutch or magneto side.

Good luck!

Also, what oil ratio are you running, and what plug?
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can you send me a link for smoothing the mating surfaces, or could i just use sandpaper to do it? i have no way of using a machine shop or anything like that to smooth it out so sandpaper is my only option in smoothing it out, and could you possibly send me a pic of the nuts i should use? and can i clean the gunk off of the piston,engine,cylinder head with wd40? the previous owner told me to run it at 20:1. but i have yet to fill a tank because i need a fuel on off valve...thanks for the help btw. also i think you or someone else said that the rings need to go a certain way, do you have any instructions or examples for me to use so i dont put them in the wrong way and blow my engine. lmao,thanks.
 
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SouthernOntarioBikeDemon said:
can you send me a link for smoothing the mating surfaces, or could i just use sandpaper to do it? i have no way of using a machine shop or anything like that to smooth it out so sandpaper is my only option in smoothing it out, and could you possibly send me a pic of the nuts i should use? and can i clean the gunk off of the piston,engine,cylinder head with wd40? the previous owner told me to run it at 20:1. but i have yet to fill a tank because i need a fuel on off valve...thanks for the help btw. also i think you or someone else said that the rings need to go a certain way, do you have any instructions or examples for me to use so i dont put them in the wrong way and blow my engine. lmao,thanks.
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20:1 is way to high for a motor that is already broken in. You should be closer to 32:1 if you are using regular or synthetic air cooled 2-stroke oil. Some people go with less, but 32:1 seems pretty safe. That would help explain all the gunk in there.

You can lap the head and cylinder flat with sandpaper on a piece of glass, there are tons of threads on how to do it, just search. The search engine on this forum works very well, as opposed to on some of the other forums.

WD40 should be fine for cleaning the crud off, just be sure to lube the piston and cylinder well with 2 stroke oil before putting it back together.

For the nuts, just any good quality nut that fits your head studs. Probably an 8MM nut, but some 66cc HTs (like mine) use 6MM. You can take one of your acorns to the hardware store and see what matches that size.

Good luck!
 
Oh yeah, and what kind of sparkplug is that? You might want to go ahead and replace it if it is in bad shape after cleaning it up and check the gap. I gap mine to 0.028", FWIW.
 
it doesnt seem to work for me , each time i search and use different key words the same stuff pops up over and over and over, here is some pics of my piston,I do not see the "pins" you are talking about but I do see a "5" and an arrow pointing towards the front of the bike, take a look at the pics, thanks,bikedemon
 

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