Fuel delivery/crank seals

ckr74

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I need some guidance on my 1985 Johnson 35hp outboard. This problem has been ongoing for a couple of years but I want to fix it before winter crappie fishing this year. The problem is that it bogs down at wot. I've rebuilt the carb, replaced fuel pump,and changed ALL the fuel lines. It still runs at low to med. throttle but if you open it up it runs lean. It still gets me where I need to go but it's annoying. Squeezing the primer bulb helps. I'm thinking that maybe the crank seals are bad and the crankcase pressure (pulses) are too weak for the fuel pump to deliver enough fuel at wot. Am I on the right track here? I've tried most everything. Thanks!
 

nccatfisher

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I would really doubt it was crank seals. It isn't impossible but that would be a last resort. I would really lean toward #1 Try another tank to rule out the pickup #2 fuel delivery since you say squeezing the bulb helps. I would check for loose clamps or suspect a minute hole in the fuel pump. #3 I would revisit the carb and make sure it was spotless, especially the main jet and all channels. #4 I would do a compression test with a known good gauge.
 

ckr74

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Thanks for the reply! I think I'm at the last resort. I forgot to mention that there is a lot of oil running down the leg also. The power head removal looks like it will be fun.
 

Pappy

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If the upper crank seal is leaking it will leave a visible trail from below the flywheel all the way down. If the lower crank seal goes it normally will really affect the running quality at idle. In fact both the upper and lower can affect idle quality. If your engine idles well you have a well sealed crankcase.
Change fuel tanks and eliminate the tank.
If you think the fuel pump is not pumping enough simply squeeze the primer bulb! The engine should pick right up and go.
Let me ask you a question that I want an answer to. When going to WOT does the engine initially reach WOT then sag back down a bit?
 

ckr74

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Pappy said:
If the upper crank seal is leaking it will leave a visible trail from below the flywheel all the way down. If the lower crank seal goes it normally will really affect the running quality at idle. In fact both the upper and lower can affect idle quality. If your engine idles well you have a well sealed crankcase.
Change fuel tanks and eliminate the tank.
If you think the fuel pump is not pumping enough simply squeeze the primer bulb! The engine should pick right up and go.
Let me ask you a question that I want an answer to. When going to WOT does the engine initially reach WOT then sag back down a bit?

Thanks for the reply. I pulled the flywheel yesterday to take a look at the top seal. It appeared to be in good shape with no oil around it. I did spray some soapy water on it and it didn't leak in around the shaft. The motor idles good with no hesitation when throttled up. At WOT it doesn't really sag any but the RPM's fluctuate a little and then starves for fuel. It will only go a couple hundred yards at WOT before having to back off the throttle. WOT is 5200 RPM but it seems labored if that makes sense.
 

DaleH

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… but … does pumping the primer bulb bring the RPMs back up, whilst @ WOT????
 

ckr74

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DaleH said:
… but … does pumping the primer bulb bring the RPMs back up, whilst @ WOT????

Yes. I'm going to look at the carb and fuel pump again. It almost acts like the tank isn't venting because it will run a ways before it bogs. We loosened the cap but it made no difference. It also appears that there are several variations of the fuel pump.
 

Pappy

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Do NOT use aftermarket parts on the fuel pump if you plan on rebuilding it. There are differences in the diaphragm material and spring rates that can make a big difference. Same thing with aftermarket fuel pumps. Pretty much hit and miss.
When you were in the carburetor did you replace the high speed nozzle gasket? Should be a thick round gasket, usually made of a brownish red material if it is OEM.
 

ckr74

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Pappy said:
Do NOT use aftermarket parts on the fuel pump if you plan on rebuilding it. There are differences in the diaphragm material and spring rates that can make a big difference. Same thing with aftermarket fuel pumps. Pretty much hit and miss.
When you were in the carburetor did you replace the high speed nozzle gasket? Should be a thick round gasket, usually made of a brownish red material if it is OEM.

Yes. It's a Sierra carb kit part# 18-7042.
 

Pappy

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If you shop around you can get an OEM kit that is absolutely complete. Float, packing washers, plastic compression washers, etc. for about the same price as Sierra and sometimes less.
 

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