G2 suddenly lost compression

gregm227

My in-laws G2 has been running fine all summer.Yesterday it barely moves,just creeps along.It's getting gas and has good spark but won't go above an idle even when chocked. If a valve was bad wouldn't it be a gradual thing. I mean this was running fine Friday and barely running on Saturday. What should I look for??? Thanks...Greg

BGW

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jmz

I would pull the valve cover . When i bought my cart it had a push rod that was not under a rocker arm. Not saying that is what it is but it is easy to check.

GMB74

Plugged air filter? plugged exhaust? Did they take it through some water and soak the air filter? Hit the exhaust and flatten the tailpipe? Animal build a nest in the air filter or muffler?

bigstik40

Is it actually running?? It may be just creeping along on the starter only and not actually starting up. You said it had good spark, but is the spark plug ok?? A fouled plug could cause a running cart to not run (all of a sudden). Replacing the spark plug would be a good thing to try (easy and fairly inexpensive). Good luck and report back with progress. - RAY

gregm227

he said he changed the plug ,no help.I guess I'm going to have to start tearing down the engine. I've got no clue, is there a diagram for the g2 engine online anywhere? I've looked and can't find any.

gregm227

it's the pushrod not under the rocker....thanks JMZ

bigstik40

OK, that's good you found problem!! Good catch by JMZ !!! Not sure why that would happen "all of a sudden", but there you go. Valve setting is .004 cold, in case you're not sure. -RAY

gregm227

adjusted it to .004 and turned it over .push rod came off again. i think the lifter is bad. it's not seating properly. does that sound like i need to replace the lifter?? thanks for your input guys...as you can tell,i'm not to mechanical.

bigstik40

I have no "hands on" experience with the Yamaha engine, but I took a look at the parts explosion in my manual and can offer these suggestions: 1. the Rocker Arm could be damaged in the area where the "ball end" of the push rod seats into it causing the push rod to slide out. 2. Another scenario could have a valve sticking open causing the push rod to fall out. 3. Check for a broken valve spring. 4.You need to examine the valve train closely looking for any of these or other possible problems. Something is definitely wrong!! We're in need of one of the more experienced members here. Make sure you let us know what you find.-RAY

smallblock450sl

Have never had a "lifter" go bad, but there is always the first. More likely the carbon on the valve stem is "sticking the valve". Valve guides could be the problem, but I would take the head off, remove the valves,decorben them, do a "lap job" and new head and valve cover gaskets adjust both intake and exhaust to .004 (when cold) and you should be golden.