1999 Johnson 90 Hp. J90PLEEB Carb Rebuild Questions

[83mulligan]

Ok, I'm pretty sure the carbs on my 1999 Johnson 90 need to be pulled and cleaned. Its a new to me boat that had a lot of neglect. The engine runs fine sometimes and gets real laggy others. I've been through a lot of other things including replacing old fuel lines, plugs, adding my fuel water seperator from my old boat, running some sea foam through, etc. I've pulled the drain plugs on the carbs and ran a wire up in there. In a nutshell, i'd just like to start with fresh carbs and never run ethanol gas through it going forward. I fish on big water and want the peace of mind that everything is clean and up to date. I'm going to pull the fuel pickup from the tank and clean that.

My question is if i buy the carb rebuild kits, how complicated a job is this. I'm not a marine mechanic, but I've been around engines enough to be able to do things. There are 4 of them and I have a guy that will do them for 400 - 450 labor but I'm really considering doing it myself and having him to fall back on if I mess something up. So, anyone with experience on this carb want to chime in and give me some advice? Also, what kind of things will I need to do the job aside from the basic tools to pull and replace them?

 

[Woodonglass]

Do you have a OEM Service manual for the Motor. You WILL need one. If you have one then I suspect you could rebuild the carbs. This is some more good info...http://forums.iboats.com/forum/engi...aq/250235-carb-cleaning-instructions?t=244013

 

[racerone]

Remove one carburetor.---Then remove the float bowl.------If everything is clean then the problem might be something other then the carburetors.------What other steps have been taken to try and sort this out?

 

[83mulligan]

Racerone, I listed most of the things I have done so far. New Plugs (the old ones were running black), replaced fuel filter, replaced fuel lines, added my fuel water seperator. I removed the drain screws from each carb and fished a wire throught he hole and then blew out with compressed air. I have not run it since then. It's an intermittent problem. At times it runs like a new motor. Other times, it lags, then breaks free and runs, then lags. When it is running good it runs good the whole time until i shut it down. Then, It usually the next time out it is back to struggling and lagging, particularly over 3000 rpms. My thought is things in the tank or the carbs are floating around and getting sucked into screens or jets or something. Any suggestions on what to test next?

 

[83mulligan]

Wood, thank you for the link. I do not have the oem manual yet.

 

[racerone]

Sudden / instant changes in performance are usually ignition related.

 

[83mulligan]

Sudden / instant changes in performance are usually ignition related.

well, give me some steps to follow to diagnose. I don't see it as being sudden or instant though.......

 

[racerone]

Well, I see lots of posts where folks say " rebuilt the carburetors and motor still runs the same " -----or " replaced the powerpack and coils and motor still runs the same "

 

[83mulligan]

Well, I see lots of posts where folks say " rebuilt the carburetors and motor still runs the same " -----or " replaced the powerpack and coils and motor still runs the same "

I'm not disagreeing with you. Again, I'm asking what procedure to follow to diagnose the problem.

 

[83mulligan]

bump for diagnosing possible ignition issue

 

[Chris1956]

The only tricky part of cleaning the carbs, is adjustment of the idle mixtures. On your carbs, there is a side plate that covers the idle mixture screw. I was able to blast it clean (no adjustment changes) after removing the cover. The carbs are real simple, Just a float bowl and a couple of jets. The throttle plates and part of the carb passageways are in the throttle bodies. One could argue that you have either 4 carbs or two (vertical) 2 bbl carbs.

Did you clean the main fuel strainer? Does it seal well? Air leaks in the fuel system will cause the motor to burn lots more oil, and other issues.

 

[83mulligan]

Chris, thank you. I did clean the main fuel strainer. Actually, I replaced it when I got the boat last summer. It was filthy. I looked at it again a couple days ago and it is pretty clean. It appears to be sealing well. I haven't checked the seal with the engine running but when i pump the ball it holds.

 

[83mulligan]

I think what I will do is pull the fuel pickup in the tank and clean that up and then run some ethanol free gas through it and see how it performs and make sure there are no leaks anywhere. Then go from there.

Anybody have any other suggestions on things to check? Trying to figure out why my plugs are running black and not dark brown also.

 

[Chris1956]

Black plugs are usually from carb flooding.

 

[83mulligan]

How do I fix carb flooding? What would be the cause? Thanks for the response!

 

[Chris1956]

Carb flooding is usually caused by a bad float, incorrectly set float or bad inlet needle. Rebuild the carb that corresponds with the black spark plug. Better yet, rebuild all four of the carbs. Set the floats to the correct height, and install new gaskets and inlet needles and seats.

 

[racerone]

If a cylinder is running " cool " then plug will not look good.--What are the results of a compression test.