Logo
FULL SITE MENU

Johnson 9.9 backfiring at rpms

L

Lppp

New member
Hi I have a 1987 Johnson 9.9, when advancing the throttle it is bogging down and backfiring constantly, just replaced the cam follower as it was broken off and I linked that up with the mark and isn't changing anything. Also one spark plug comes out slightly damp with fuel and one comes out dry covered in black residue each time after running. Thanks for ur help
 
From latest tests have learnt both cylinders have 80psi compression ,have switched coils over and made no difference, have pulled sparkplug boots one at a time and both cylinders are running, the bottom one maybe sounds slightly stronger but hard to tell, nothing I've tried has made it run any different
 
Are you sure you have the right cam follower replacement part? Kind of sounds like your timing is off and that part plays a big role in setting the timing as the throttle is advanced. Certainly an interesting coincidnence.
 
optsyeagle said:
Are you sure you have the right cam follower replacement part? Kind of sounds like your timing is off and that part plays a big role in setting the timing as the throttle is advanced. Certainly an interesting coincidnence.
Click to expand...

Yes I am worried that this area is still the problem, the only difference with the old and new parts is that the roller is around 2mm bigger in diameter on the new one, apart from that they look the same and I can't see that really making a difference but not sure. I did have to screw in the adjustment screw quite a long way into that piece to get it to hit the timing plate at the right point, probably screwed about 2/3 in not sure if anything seems wrong with that.
 
Rwbutler said:
How was this motor running before the cam roller replacement?
Click to expand...

Not sure, only just bought the motor cheap and was broken off in the cowling when I got it, motor does have signs that someone tried to mess with parts before so they could of broke it off trying to adjust a problem or it could have started the problem I'm not sure. Owner I bought it off hadn't touched it only had it to get the boat it was on.
 
Back
Top