engine has low compression and backfires thru carb...

[oonighttrain]

i have an engine that has low compression on 2 of 4 cylinders.. cylinder walls look fine.. it also backfires thru the carbs..

whats the cause of this? timing off????

anything else?

 

[switchback]

Sounds like your timing chain/belt is off. What engine is it?

 

[oonighttrain]

hey troy,
its a yamaha 4 stroke 50 hp outboard. its got very low compression on 2 of 4 cylinders. it will run but rough and loss of power. i took the head off, cylinders look fine.. i took th ehead to a machine shop and they did a vacuum test on all the ports? the dude said the head was fine..

after much thought i had the same idea as you, maybe the belt jumped a tooth? or some shmuck was in there trying to adjust the valves and got it all fugged up???

if it had bad rings or something in the cylinders causing the low compression, it wouldnt backfire thru the carbs would it???

 

[oonighttrain]

1= 20 psi
2=125 psi
3=125 psi
4=90 psi


btw, 1 and 4 run together and 2 and 3 run together...


whatcha think?????

 

[switchback]

Should have watched the thread closer Would have saved you a call. Nice to hear from 'ya again though. March................

 

[captain_stuck]

check your cam. Sounds like a lobe might have gone round.