88 hp Johnson - rpms up & down

[dhardin78737]

Have 1992 88 hp Johnson. Recently rebuilt carbs and fuel pump. Motor runs fine at low speads but after getting up to high speed for about a minute, rpms will drop suddenly from 4800 to 4200 and will bounce back and forth. Motor bogs down more and more if I keep running like this but does not stall out. Strange thing is that 1) runs fine at low speeds and 2) it runs fine for the 1st minute at high speeds.<br /><br />I didn't feel real comfortable with the fuel pump rebuild when I did it. Could this be a fuel pump problem?<br /><br />One other thing that happened about a year ago - motor overheated and shut down because of ants in water system. Never seems to have been the same since.

 

[Dhadley]

Re: 88 hp Johnson - rpms up & down

Easy to check -- get the boat going and have someone squeeze the bulb. They then become the fuel pump. If it runs OK then we either need a fuel pump or enough beverages to keep that person happy while we ride around.<br /><br />If it has no effect then there are other issues to look at.

 

[jay gravely]

Re: 88 hp Johnson - rpms up & down

Do what Dhadley said. I certainly sounds like the fuel pump.

 

[TD_Maker]

Re: 88 hp Johnson - rpms up & down

I had a simular problem with my 89 88 spl. I purchased one of those cheap fuel lines fom Wally World, and I noticed that the hose was actually smaller (Inside Diameter) and the primer bulb never really seemed solid. Same thing, motor would lose RPM's at speed. I went back to a larger OMC fuel line and bulb. No more problems.<br /><br />Also, make sure the fuel tank is vented properly.

 

[andy6374]

Re: 88 hp Johnson - rpms up & down

Are you running a VRO or premix. If VRO, don't continue to pump the primer bulb after you figured out if that is the problem or not. This is a good way to pump lots fuel and no oil, and after that you will be posting more depressing questions <br /><br />Good luck

 

[dhardin78737]

Re: 88 hp Johnson - rpms up & down

Thanks for all of your help so far.<br /><br />I finally got out yesterday - squeezed bulb when rpms started falling and sure enough, rpms came back up. Replaced fuel pump last night and ran today and is still doing same thing. I also noticed that I have oil/gas drippings underneath my carbs.<br /><br />Do you think I need to try to re-build carbs again?<br /><br />Don't know if this has anything to do with it but I am also seeing black thick oil (almost like a grease) coming from engine running down front side of lower unit.<br /><br />Any ideas?

 

[dhardin78737]

Re: 88 hp Johnson - rpms up & down

One last shot - any ideas before I take it in to get it looked at?

 

[Privateer]

Re: 88 hp Johnson - rpms up & down

Had a similar problem with the leaky carbs and black goo from the exhaust. I was getting excess unburned fuel due to faulty recirc valves. These valves can also cause performance problems depending on whether they stick open or stick shut. Search all the forums for recirc or puddle valve. Good luck.

 

[Walker]

Re: 88 hp Johnson - rpms up & down

First you have to find and stop the fuel leak. Then if you still have the problem I'd check to see that the motor isn't overheating.

 

[TD_Maker]

Re: 88 hp Johnson - rpms up & down

DREW!<br />One last thing. You said your engine was an 88 hp. I would think it was an 88 SPL which was not oil injected.<br /><br />Under each carb, you will find small black fuel hoses which lead up to the primer/choke. They will crack and leak fuel. My carbs were leaking too, but I neglected to check these little hoses. Sure enough, they were cracked and leaking gas which caused the black mess on the engine. Repair these primer lines with the correct sized FUEL LINES, and see what happens. I think you may have found your problem.