Johnson 88 SPl 1993 low RPM problem

SteuryLover · Nov 19, 2008

I recently bought a center console and am having issues getting the motor to run correctly. I am only getting 3000 rpm under load with 2 men in the boat and 40 gallon bait tank in the middle.

Here is what I have done

-Rebuilt carbs
-new fuel pump
-new fuel filter
-test fuel tank used
-onboard fuel used freshly vented with new fuel lines
-fuel lines replaced from primer to carbs
-new wires
-new champion plugs
-13.75x17 3 blade aluminum boaters world new prop
-boat weight 1200 lbs dry and has a reasonably deep V hull
-boat is 18'4" in length
-motor does look to be mounted a little low considering the weight from the bait well and batteries in the rear
good compression from 125-130 on all cylinders (had boat shop check this)
good spark (had boat shop check this)

They put it on a dyno and said it created 1500lbs of thrust but only pulled 3000 rpm. They wrote off the low rpm to a bad tach. New tach reads correctly so they were never able to pull more then 3000 rpm on the dyno. I have lost faith in them to solve this problem. Does anyone know how much thrust a Johnson 88 SPL (basically a 90hp) should make? Any ideas would be great. I am thinking of doing Joe Reeves timing procedure tomorrow although the marine shop claimed it was fine. Thanks for everyones time on this.

tashasdaddy · Nov 20, 2008

Re: Johnson 88 SPl 1993 low RPM problem

do Joe's timing, and then do a link n sinc. hope you have an OEM manual. that is a fantastic motor, i have had several.
did you do this in your carb cleaning?

http://forums.iboats.com/showthread.php?t=244013

are you sure you got the jets back in there respective places. i have swapped the low and high speed jets before.

Dhadley · Nov 20, 2008

Re: Johnson 88 SPl 1993 low RPM problem

How does the motor idle?

emdsapmgr · Nov 20, 2008

Re: Johnson 88 SPl 1993 low RPM problem

The engine should be mounted so that the anti-ventilation plate is level with the bottom of the boat. If it is mounted too low on the transom, the drag from the engine increases and can have a significant impact on speed. A crazy question, but are the carb butterflys opening all the way?

SteuryLover · Nov 20, 2008

Re: Johnson 88 SPl 1993 low RPM problem

Idles rough when cold, once warm pretty good around 700rpm. The butterfly pins are perfect when throttle it wide open. When I bought the boat the engine was supposed to be on great shape low hours (reading forums, that seems to always be the case but never reality). I did go through some grounds cleaning and reattaching. I want to take it out again so I can take a photo of the motot height while running. Thanks for the fast responses.

SteuryLover · Nov 20, 2008

Re: Johnson 88 SPl 1993 low RPM problem

As far as the jets I am sure they went in the correct place when reassembled. This really being my first time digging into an outboard I may take the carbs apart and really go through them again spending a little more time. I have heard this is a good motor and hope this will push my 18' center console well, hoping for 35 mph WOT. Thanks again for the time on this.

emdsapmgr · Nov 21, 2008

Re: Johnson 88 SPl 1993 low RPM problem

Did you open up the airbox to check the full throttle position? It is hard to tell exactly where the butterflys are from the external pins on the shafts, since they are at an angle when closed. The only true way to tell is to open up the airbox and have a look their position at full throttle.

SteuryLover · Nov 21, 2008

Re: Johnson 88 SPl 1993 low RPM problem

I will take a look this weekend, honestly it feels like that is the problem. It goes to 3k pretty quick and planes the boat fast. Just wont go any faster. Thanks again for all the help on this.

tashasdaddy · Nov 21, 2008

Re: Johnson 88 SPl 1993 low RPM problem

are you sure the tach is accurate? and not on the wrond setting. if on the wrong setting it could be reading 1/2 the rpms.

SteuryLover · Nov 21, 2008

Re: Johnson 88 SPl 1993 low RPM problem

The tach is set on 6, I am aware that the Teleflex brand tach I bought has a inconsistent problem reading 88SPLs correctly. On their website they claim to install a specific capacitor on the gray wire from the tach to correct the problem if there is one. from the sound and speed of the motor it sounds correct. i will have more info once I put it back into the water this weekend. Thanks again.

SteuryLover · Dec 21, 2008

Re: Johnson 88 SPl 1993 low RPM problem

Finallt dropped my boat off at the shop. They said the carbs where rebuilt wrong (my fault). They said it is good to go now, I will take it for a test run tomorrow. I also raised the motor a couple holes, I hope all is well.

SteuryLover · Dec 23, 2008

Re: Johnson 88 SPl 1993 low RPM problem

Problem solved, carbs rebuilt wrong. No if I can only solve this cavitation issue!

SteuryLover · Dec 27, 2008

Re: Johnson 88 SPl 1993 low RPM problem

Well im back, problem not solved. The boat ran great for about 30 min. After that I went to take off and only 3k. It would surge forward for a moment as if it is a fuel starvation issue. The boat also took some extra time to plane. I just got it back from the marine shop and they rebuilt the carbs and checked everything else. Little frustrated here as the boat had now been to 2 different outboard shops with both stating it is good to go and now this. Any ideas here? Thanks for the help.

HighTrim · Dec 27, 2008

Re: Johnson 88 SPl 1993 low RPM problem

Just to throw out a possibility....its not going into SLOW is it?

The engine is not overheating in any way is it? Try disconnecting the TAN temp wire from the pack and retesting it. If the engine now performs as it should, replace the temp switch. Finally, make sure that the TAN temp switch wire is not located next to a spark plug wire. This may cause issues.

Also, have you had an inductive timing light hooked up to ensure that all cylinders are firing?

DJ · Dec 27, 2008

Re: Johnson 88 SPl 1993 low RPM problem

You say it ran good for 30 minutes? Which fuel tank were you using?

If it was the onboard tank, I would suspect the anti siphon valve.

SteuryLover · Dec 27, 2008

Re: Johnson 88 SPl 1993 low RPM problem

Yes spark was tested as well as timing and all is in right order. A link and sync was just done. It ran great this morning, besides only getting 4500RPM (but that may be a prop issue). The shop does not reopen until after new year, so I may just bring it back. It really feels like a fuel issue, the RPM is too inconsistent to be in slow mode to me. I will pull the plugs in the morning to see how they look and go from there. Thanks for the response.

SteuryLover · Dec 27, 2008

Re: Johnson 88 SPl 1993 low RPM problem

It is a permanent fuel tank. You could be correct. When I do hit the prime it will jump up in RPM. Slow speed was also rough when going through the harbor (6mph). How can I check the valve? Thanks for your time.

HighTrim · Dec 27, 2008

Re: Johnson 88 SPl 1993 low RPM problem

Just take it out and knock the guts out of it, if that fixes it, you can then replace it.

DJ · Dec 27, 2008

Re: Johnson 88 SPl 1993 low RPM problem

SteuryLover said:
It is a permanent fuel tank. You could be correct. When I do hit the prime it will jump up in RPM. Slow speed was also rough when going through the harbor (6mph). How can I check the valve? Thanks for your time.

That's a HUGE clue.

The valave IS the tank outlet. As HighTrim said, take it off, knock the innards out and try it.

BTW, 4500 RPM will KILL that engine. Once you get it running good, prop it to turn 5500-min.

SteuryLover · Dec 27, 2008

Re: Johnson 88 SPl 1993 low RPM problem

Great, I will take care of that in the morning. I am aware I want to be in the 56-5800 range with today's fuel. I started a thread about the prop sizing and style for this boat, any response there as far as RPM range and propping would be appreciated. I will check back in tomorrow afternoon with an update.

Johnson 88 SPl 1993 low RPM problem

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