1992 johnson 30 hp miss fire

[nauticool]

hi guys,

Have the above engine which has a bad missfire. rebuilt carb numerous times and using brand new fuel 50:1. also checked fuel pump and fitted new spark plugs. lower cyl is leaving plug black and oily. the missfire is really bad when cold, to the point where its only running on the top cyl. when it warms up both fire and just get a cough every 2 to 3 seconds and normally idles ok. could this be a weak coil on cyl 2? Not sure on the history of engine, just bought it. Please help

 

[blimp]

Re: 1992 johnson 30 hp miss fire

Get a manual, do the "link and sync" procedure. Mine had a really bad lean sneeze, now she purrs.

 

[nauticool]

Re: 1992 johnson 30 hp miss fire

Doesn't that apply to engines with 2 or more carbs? Mine is single with 2 cyl.

 

[nauticool]

Re: 1992 johnson 30 hp miss fire

anyone else??

 

[ENSIGN]

Re: 1992 johnson 30 hp miss fire

Check the reeds,a chipped or broken one can create your symptoms

 

[blimp]

Re: 1992 johnson 30 hp miss fire

Doesn't that apply to engines with 2 or more carbs? Mine is single with 2 cyl.

Mine is an '88 of the same motor, the 'link' is the important part here, the linkage is adjustable and if the timing is not synced up to the movement of the carb slide, it can cause engines to misbehave.

 

[psteurer]

Re: 1992 johnson 30 hp miss fire

Link and sync is important for all motors including a motor with only 1 carburetor. To test the coil you think is weak, just swap the two coils and see if the problem follows to the other cylinder. If it does, then replace the coil. From your description, it sounds like your problem is still in the carburetor. Did you remove the high and intermediate jets and clean behind them?

 

[nauticool]

Re: 1992 johnson 30 hp miss fire

Thanks for your response, much appreciated. I did clean both jets and removed the gauze on both sides. I stripped it down as much as possible. It's like new inside now.
With regards to the sync, the roller just touches inbetween the two points as the butterfly opens, i believe this to be correct?
i did change the two coils over but it ran worse, wouldnt rev or idle. I now have a new coil and will try it on saturday..... fingers crossed!
Any chance it could be poor points? never taken a flywheel off but it looks like it may be heading that way if the coil doesnt work. once the timing is set can it move? otherwise i guess we can assume its faulty parts.

Thanks again, any other ideas would be great

 

[nauticool]

Re: 1992 johnson 30 hp miss fire

Thanks ensign. the reeds look perfect... as new even! All have a good seal too.

 

[blimp]

Re: 1992 johnson 30 hp miss fire

Thanks for your response, much appreciated. I did clean both jets and removed the gauze on both sides. I stripped it down as much as possible. It's like new inside now.
With regards to the sync, the roller just touches inbetween the two points as the butterfly opens, i believe this to be correct?
i did change the two coils over but it ran worse, wouldnt rev or idle. I now have a new coil and will try it on saturday..... fingers crossed!
Any chance it could be poor points? never taken a flywheel off but it looks like it may be heading that way if the coil doesnt work. once the timing is set can it move? otherwise i guess we can assume its faulty parts.

Thanks again, any other ideas would be great

This engine has no points, it has electronic ignition and an electronic trigger under the flywheel.

 

[nauticool]

Re: 1992 johnson 30 hp miss fire

Thanks blimp. So when something goes wrong under there it just dies or could there be something that is causing this miss fire?

 

[psteurer]

Re: 1992 johnson 30 hp miss fire

This engine has a power pack, which delivers the timed charges to the ignition coils. This electronic ignition system replaced the points as was used in the older engines. I am not an expert on power packs, but I would think that if the power pack starts failing or fails, you would see the problem occur in both ignition coils and not one. Since you have the new coil, the next step would be to replace it and see what happens. For your question on the link and sync, the roller is suppose to touch between the two cam marks, at the exact instant the throttle plate starts to move. Another step in the link and sync is to check the timing.

 

[nauticool]

Re: 1992 johnson 30 hp miss fire

Thanks Psteurer,

It's making more sense now. I will try the coil and also test the compression on Saturday and let you know how I got on.

Thanks again

 

[nauticool]

Re: 1992 johnson 30 hp miss fire

FIXED

Turns out the plastic fuel tank that used to be used was breaking down. found loads of orange plastic strands in the cowling connecter which must have been feeding the fuel pump and carb. so everytime i cleaned them out they would block again! took all the fuel system apart cleaned.... again.... and now it runs perfectly. Have it fitted to a 3mtr rib and it flew yesterday. 30knots (gps)!!!! may be over propped though. feels like it should do more but at the least the engine is now sorted, didnt miss a beat. Will be fitting a fuel filter this week Thanks or all your help.