Johnson 9.9 has no top end

[TXSTDU]

I have a 91 Johnson 9.9. It had sat up for tow years until about about 2 months ago. For preparations for this duck season I added a new gas tank and fittings, new primer bulb, new fuel lines, new spark plugs, and had a OMC shop complete a fuel pump rebuild and rebuild the carb.

Prior to all this the motor would start, now after all this work it starts and runs ok. When I first got it back I took it out and it would run poorly. I took it back to the OMC shop and he said it was carbon build up. So I bought a can and did a decarb, this made a small difference. Next found a decarb on here where you put a whole can of Seafoam in 3/4 gal of fuel mix and run and let it rest in 10 min. intervals. This got alot of gunk out.

The motor on the muffs run great and revs up perfectly, but when I put it back on my 15 ft. aluminum boat it wants to bog down at WOT. I can only get a top speed of 6.5 mph. It also requires a small shot of starter fluid to get it going when it is really cold outside.

Please help before I pull my hair out

 

[Rick.]

Re: Johnson 9.9 has no top end

I'm sure you don't want to hear this but it sounds as though the carb. still needs more cleaning. Or, when your trying to go WOT and it is not responding pull a plug wire and see if it makes a difference. If not put it back and pull the other. If the engine dies with either removed you have a spark problem. You may well be running on only one cylinder. You should not rev the motor very high on the muffs. That can blow it apart when it has no load. Don't pull your hair out! Keep us informed. Best of luck. Rick.

 

[HighTrim]

Re: Johnson 9.9 has no top end

If the engine dies with either removed you have a spark problem. QUOTE]

Actually you want a noticable drop in RPMs. IF there is no drop, that cylinder is not firing and dead. I prefer to use an inductive timing light to test for spark at various speeds. Check the compression as well and let us know what you find. Will choking it pick it back up? Pumping the primer bulb?It may very well be a clogged high speed jet as mentioned (carb issue). If so, bring it back until they rectify the issue.

Also, stay away from Quickstart, it does not have the necessary lubrication for 2 stroke outboards, use pre mixed fuel instead.

 

[TXSTDU]

Re: Johnson 9.9 has no top end

I checked the compression and I got 85 in each cylinder.

I will try the spark plug thing in the next few days and will keep you informed.

 

[TXSTDU]

Re: Johnson 9.9 has no top end

Ok so I put it on the muffs and pull one plug and then the other. Both times it really dropped in RPMs and barely ran. So I don't think that is the problem.

Also as a note the motor runs great on the muffs but it runs poorly when in the water pushing the boat.

 

[HighTrim]

Re: Johnson 9.9 has no top end

There is likely a fuel delivery issue then.

Did you try pumping the primer bulb to see if it picks up? If so there is likey an issue with the fuel pump rebuild. Spraying pre mixed fuel into the carb throat? Choking it? Look back to the carb.

Bring it back to the shop that performed the carb work.

edit:The tank vent is open isnt it? What type of tank is it?

 

[nightstalker]

Re: Johnson 9.9 has no top end

There is likely a fuel delivery issue then.

Did you try pumping the primer bulb to see if it picks up? If so there is likey an issue with the fuel pump rebuild. Spraying pre mixed fuel into the carb throat? Choking it? Look back to the carb.

Bring it back to the shop that performed the carb work.

edit:The tank vent is open isnt it? What type of tank is it?

What he said. Check that tank vent closely. I've seen that vent cause a lot of problems.
Nightstalker

 

[TXSTDU]

Re: Johnson 9.9 has no top end

I thought the vent early on so I ran it with no cap on and it acted the same.

Also when I stop the boat in the water it forms an "oil slick" that is rather substantial.

 

[HVSTRINE]

Re: Johnson 9.9 has no top end

If the engine dies with either removed you have a spark problem. QUOTE] Will choking it pick it back up? Pumping the primer bulb?It may very well be a clogged high speed jet as mentioned (carb issue).

My 9.9 did the same thing after sitting for a couple years. But when i would choke it it would throw you back in the seat(the increase in accel.) I ran it choked for a while and whatever was in the carb blew out finally.