Why would this happen???(no compression)

[joshualeeusmc]

This is long so bear with me...
I have a 1990 yz250 that was running great, I parked it for a week with out starting it> I went to start it yesterday morning and it had absolutely no compression. I kicked it over a few hundred times still no compression or starting. Frustrated I walked away and let it sit for a couple of hours, when I went back to tear the top end apart I kicked it just to see what would happen if anything and it chugged a little (still no compression) so I kicked it agian and it ran very rough at first then it spit out a fountain of premix and started running normal, now it has normal compression and runs great agian. Any Idea why it would do this, and could it be a sign of something wearing out?

 

[Rider 007]

Did you leave the gas petcock turned on when you last parked it?

 

[joshualeeusmc]

I honestly do not remember, it is a good possibility so lets say yes.

 

[YZ165]

Sounds like sticky rings to me. I'd inspect the piston, ring grooves, and ring end gap to see if anything is amiss. My .02, YZ165

 

[Rider 007]

Quite often what can happen when the gas is left on is that the float valve in the carb won't seal properly and will let fuel leak into the throat of the carb and run into the engine.

This would account for the stream of premix when it started.

I've seen the bottom end completely fill up and overflow into the exhaust pipe.

:ride:

 

[joshualeeusmc]

How would that affect the compression?

 

[YZ165]

I don't think a bottom end full of gas would result in no compression. It wouldn't run, but it would still have compression. YZ165

 

[Rider 007]

I didn't kick it over and therefore don't know exactly how it felt, so I can't speak to that.

However, I do know that bad rings, etc., wouldn't fill the crankcase with fuel.

It's possible that you have more than one issue going on here and leaving the gas on is merely one of them. That would explain the raw premix that came out of the exhaust and a sticking ring that became unstuck would restore compression and explain the other.

If it was mine, I'd turn the gas off every time I parked it and see if it does the same thing again or exhibited the other symptoms minus the raw fuel in the engine.
Proceed from there with what you find.

Or, as mentioned, you can go ahead and open it up now.
Your call.

Hope it helps.

:ride:

 

[YZ165]

Good points 007.

 

[sick 96 250]

my buddies 125 sat for this winter and when he went to kick it over it had no compression also. We put a little oil in the spark plug hole and slowly kicked it over to get the oil around the rings so they would seat themselves and its been fine ever since.

 

[joshualeeusmc]

Thanks for all the replys, I think the raw premix that came out was from kicking the engine so many times trying to start it. Sounds like a sticky ring was the culprit. I am not going to tear it down right now, I will see what happens next week end. Once agian thanks for all the input.

 

[liverpoolphil2130]

mine was similar about a week or so ago, I dont think it had 'no compression' but it sounded like it had no compression

Checked my air filter and it was filthy, cleaned it and the bike started first kick and sounded great

A guy local to me said I should be cleaning my filter after every ride? Is this right?

 

[Rider 007]

A guy local to me said I should be cleaning my filter after every ride? Is this right?

If there's no dust when you're riding and the filter is still clean, you can leave it alone.

If it's dirty, clean it!

You can't go wrong by erring on the side of caution.

:ride: