'99 90hp Johnson missing

[paradise1]

I have a 1999 90 hp Johnson on a Riviera Cruiser Pontoon that runs good at low RPM's but at random times runs really rough at higher RPM's. It is very random and doesn't happen everytime but does most of the time. We have replaced the spark plugs, fuel filter, fuel lines, and completely emptied the fuel tank of all gas in case there was water in the gas. We were told by the local boat repair center to put alcohol and Sea Foam fuel conditioner in the tank. No help. It runs a little better but after a few minutes starts missing intermittently. There is no rhyme or reason to when it decides to start missing. It is very strange. Any ideas on next steps?

 

[ccnstlr]

Re: '99 90hp Johnson missing

Did you try to squeeze the bulb or hit the primer to see if it straightened up? Or could be a heat related issue of electic parts or loose connection possibly to be so intermittent as you describe. That's very broad I know, but you need to start with the basics. Check wiring connections, coil pack mounting 'strap' cleanliness, etc.

 

[paradise1]

Re: '99 90hp Johnson missing

I have squeezed the bulb and that does nothing at all. Could it be water in the gas tank? It is very often that this happens but sometimes I can drive it all day and it is fine. Most of the time it is not.

 

[ccnstlr]

Re: '99 90hp Johnson missing

Well, you stated you emptied the tank of all gas so that would seem unlikely in this situation.

 

[paradise1]

Re: '99 90hp Johnson missing

Where is the coil pack mounting strip located?

 

[paradise1]

Re: '99 90hp Johnson missing

My husband is saying that the tank was not completely dry but we could see the bottom of it in places....we were unable to get the last 1/8 of an inch or less out. It is very hard to see in there. He is still convinced that the small amount of liquid in the bottom could have been water and is still causing this problem. After the tank was "what I call" empty, we put 1 bottle of alcohol and a 1/4 can of seafoam in the tank along with 5 gallons of gas. It still missed.

 

[ccnstlr]

Re: '99 90hp Johnson missing

Most coils have a strap that is at the bolt hole where the coil is bolted to the crankcase. Just a preventative type thing to ensure the connection is clean between the coil and the block.

 

[ccnstlr]

Re: '99 90hp Johnson missing

Maybe you could try to isolate the miss to one bank or the other while it's happening. A timing light while running may show which cylinder is missing if it is a firing issue. If it is on one bank of cylinders, you could swap coils and see if the issue moved to the other bank. Just a long shot.