What could cause piston rings to break?

[Glenn Herlong]

O.K. I don't know if this is where I should post this but here goes.

I got my engine installed and it actually ran. I was supprised but very glad also. I still have questions though.

The engins is backfireing when I let off the gas. It was doing this before the rebuild but I just drove it anyway. I want it to run as good as possible so any info or suggestions would be appreciated.

I think the back fireing was what led me to think timing or fuel mixture could be the problem with the rings breaking. But after the previous post and looking at the pulsar coil behind the fly wheel, I don' t see how the timing could get off.

I think some other threads on this subject indicated it could be the carb. Please help

[ruredy]

Very possible it's a fuel mix problem, it could be running lean. Carbs do wear out and start leaking air causing engines to run lean. This will cause engines to run hotter than normal and lead to premature failure. You should be able to tell if it's running lean or rich by looking at the spark plug after you've ran it awhile.

[Glenn Herlong]

Running lean? Does that mean too much oil? Also, what should I look for on the plug to determine lean or rich mixture.

[ruredy]

running lean means not enough fuel to air. carbs wear the parts that move, over time this will let more air into the engine than gas compared to what it was new.
Just about every manual for any engine repair being cars, motorcycles lawnmowers, whatever will have pictures of how plugs look in different conditions. Ie: running lean, running rich, oil fouled, normal, ect. You can probably find this info online, I don't have any pics of this handy or I'd post them.

[ruredy]

I got one, lean would be the too hot plug

[pizzamaker]

Originally Posted by ruredy

I got one, lean would be the too hot plug

nice
gray to white in color=lean and dark brown to black=to rich, tan is the color you want

[DEWDIGGLER]

make sure you hooked up the throttle cable right.
the butterfly should not start to open till the micro switch opens.
if it does then your sending gas before spark causing back fires.

good luck, Dew

[DOOmsman]

Glenn, you said a lot of carbon, that would make me think rich. The clutches don't drop out as soon as you let off the gas and the engine pushes a little unburnt fuel into the exhaust and if you have some carbon buildup it could be glowing in the can and when enough unburnt fuel builds up it back fires. faster than I can type this. Be sure and keep us posted how you do

[DOOmsman]

Here are to pics of pistons the clean area around the edge is what we call wash, the black piston is rich the tan is nice. In a race tune we will look for that build up to be no bigger than a quarter.

[Glenn Herlong]

Lots of good info. The top of my piston was absolutly, totally black.

All of the top of the piston was black. So, does that mean that my engine was running rick. (too much air) Keep in mind the engine is out of a 1986 and probably has never been into. Could the amount of time and usage of the engine cause the whole top to be covered in carbon. Also, mine is a two cycle. Should a 4 stroke and 2 stroke piston color be the same since one is mixed and the other is not.

I will check the throttle connection also.