1987 Johnson 30hp running on one cylinder at idle

[jdoug]

Morning Gents,

I was hoping y'all could help me out. I have a 1987 Johnson 30hp and the other i had it running in the drive way and notice it was only running on one cylinder so I checked the plugs and everything seemed fine, even switched the plugs and the same cylinder was dead. I took it out to the river the next day and still on one cylinder at idling but when I give it throttle I can hear the second cylinder try to fire and it kicks a little bit and then engages and runs perfectly on both cylinders until i let off the throttle and it gets back done to an idle and then the same one dies again.

thank y'all

 

[JB]

Re: 1987 Johnson 30hp running on one cylinder at idle

Do a compression test. Then clean the carb jets. Tell us your results.

 

[jdoug]

Re: 1987 Johnson 30hp running on one cylinder at idle

I've done both, dead cylinder is at 30-40 and good cylinder is around 95

 

[alldodge]

Re: 1987 Johnson 30hp running on one cylinder at idle

I would be thinking valves

 

[racerone]

Re: 1987 Johnson 30hp running on one cylinder at idle

Reed valves have nothing to do with compression in the cylinder !----Take cylinder head off for inspection.--Could be a blown head gasket.

 

[Bosunsmate]

Re: 1987 Johnson 30hp running on one cylinder at idle

Have a look at your sparkplugs, it could have blown the head gasket meaning waters got into the cylinder and a sparkplug will look muddy.
Sometimes as the rpm increases and the poppet spring opens the cylinder strts firing again. Im not sure of the dynamics of that happening but it seems to be what can occur.
You will want to get on to this quick as if water has got in things will start rusting internally

 

[JB]

Re: 1987 Johnson 30hp running on one cylinder at idle

I've done both, dead cylinder is at 30-40 and good cylinder is around 95

Dead cylinder is low on psi. Inspect to find the reason. Blown gasket, broke ring?

 

[jdoug]

Re: 1987 Johnson 30hp running on one cylinder at idle

Thanks guys, next question, I'm pretty good with a wrench but I've never pulled a head before. Is there anything I need to make sure I do/don't do?

 

[jasper60103]

Re: 1987 Johnson 30hp running on one cylinder at idle

Thanks guys, next question, I'm pretty good with a wrench but I've never pulled a head before. Is there anything I need to make sure I do/don't do?

I have the same motor. Be sure to cleanup the gasket surfaces. There is a procedure in the manual for prepping the head and torque requirements. Take your time. Good luck.

 

[racerone]

Re: 1987 Johnson 30hp running on one cylinder at idle

Just take out the bolts and the head is off.-----Nothing will jump out at you.

 

[daselbee]

Re: 1987 Johnson 30hp running on one cylinder at idle

"Nothing will jump out at you".....unless it is a broken head bolt....then you can consider yourself "jumped out at".

Seriously, don't break any head bolts. You will be in a world of hurt unless you are skilled at removal.

 

[boobie]

Re: 1987 Johnson 30hp running on one cylinder at idle

If you're in a salt water area be gentle and use some heat if you have to.

 

[jdoug]

Well boys I'm back again, I had to put the boat in storage for a little bit so I couldn'g work on it but I'm back at it now.

Got the head gasket changed out and tested her yesterday and she is still running on one cylinder. Any other ideas? Is it not getting gas? Do I have a bad power pack? Please help!! duck season is fast aproaching and i need to get out on the river!

 

[racerone]

Was the head gasket blown ??----Was cylinder in good condition.?---Have you tested compression again ?

 

[itsaboattime]

How did the head look? How did the piston look? Were the rings intact? Carbon build up? Did you clean the head and piston? Scoring? Were the rings loose in their grooves in the piston?
Did you check the head for warpage? How did the water passages look?

 

[jdoug]

Head gasket didn't look blown, cylinders looked good and testing compression tonight.

The head looked good, no scoring and I didn't think to look at the rings while I was in there but I'm starting to think the rings are the problem.

 

[racerone]

Only with some inspection and testing will you get results !!

 

[jdoug]

well I tested compression last night and both cylinders are around 90ft/lbs so I put new plugs in it and she runs like she did back in 87. Looks like the head gasket and bad plugs were the problem.


Thank y'all for the help, much appreciated