[BadDecisions619]

Turns with all 3 plugs.. can turn by hand with what feels like reasonable resistance.. but wont start. It really struggles.
But if I remove the bottom plug (3?) it will fire and run and idle (roughly).

When I put my thumb over the plug hole, I feel the compression AND that will bog it down and die if I dont remove my thumb.

I am worried I have some valve issues??

Suggestions?

Thanks everyone.. new to this forum, but forums like these are what encourage me to make bad decisions, like buy this boat with a wonky motor.

 

[jaguar]

If it has valves then it's a 4 stroke and you should of asked on a different forum. But I'll be nice and give my opinion any way. Probably that cylinder isn't firing due to an ignition problem, or it has worn valves or rings. Yeah I know the valves and rings on the other two cylinders are just as used but not everything wears down equally. Check for spark at that cylinder and if it's there then take it all apart to check the valves and rings.

 

[BadDecisions619]

If it has valves then it's a 4 stroke and you should of asked on a different forum. But I'll be nice and give my opinion any way. Probably that cylinder isn't firing due to an ignition problem, or it has worn valves or rings. Yeah I know the valves and rings on the other two cylinders are just as used but not everything wears down equally. Check for spark at that cylinder and if it's there then take it all apart to check the valves and rings.

Thanks for the reply.. I am a total kindergartener when it comes to 2strokes.... Im a 4stroke engine guy by experience (not necessarily preference). In doing some google'ing I saw some stuff on valves with 2 strokes, but that apparently was just very large marine diesel engines or something?

This is def a 2 stroke... oil and fuel separate... 1983 Force 85 3 cyl chrysler 2 stroke.

I am doing a compression test on it this weekend and spark test too. I was pretty sure about the spark, but not sure I recall how strong it was.

Is there anything (reeds?) that could have obstructed the exhaust?

My theory until I can do a compression check is that the compression in that cyl is too high (similar to a hydrolock) for it to turn over with the plug in.

I know I have some basics to check - compression/spark - and any additional things to check would be good to hear if you have em!!! THANKS!

 

[jaguar]

the only other thing to be aware of is the possibility of a leak at the crankcase seal. Usually those leaks change the air/fuel ratio which affects everything.

 

[BadDecisions619]

Ok... so with some testing and trouble shooting, I have determined that one of the black CDI boxes is dead. The one that fires #3.
I wouldnt have thought it would be enough to keep it from running with the 1 dead cyl, but then again my frame of reference is V8 motors and they can run on 7.

These CDI boxes are pretty pricey.... and its a pretty crappy boat from 1983 to begin with, are there cheaper compatible modules? I dont mind making/fabbing changes to the bracket.

Suggestions?