88hp Johnson loses power at full throttle

[Jack B]

My 88hp Johnson loses power after about 5 seconds of running at 3/4 to full throttle. I have checked from the fuel tank all the way to the fuel pump. I did find a tear in the diaphram on the fuel pump and I replaced the pump. The motor still had the problem so I pulled the carbs and checked for any blockage. Everything looked OK but the motor still has the same problem. Whats next? http://www.iboats.com/ubb/confused.gif

 

[12Footer]

Re: 88hp Johnson loses power at full throttle

Check the compression. If you don't own a compression gauge, you may be able to borrow or rent one from an auto parts store.<br />If the fuel system, carb and fuel pump are clean, you might have a problem with compresion.No compression = no fuel being pumped, and no fuel being drawn into the engine. (Runs good until it heats-up a bit,then looses compression,and then runs rough.)<br />Some engines have a rev limitter that kicks-in when the engine overheats, so make sure the cooling system is werkin.<br />Good luck, and post what you find on the test.

 

[Jack B]

Re: 88hp Johnson loses power at full throttle

Compression and h2o pressure are all fine. But the motor does not have any alarms. I don't know how to tell if this motor has a RPM limiter.<br />Thanks Jack

 

[clanton]

Re: 88hp Johnson loses power at full throttle

What year or model number, and what are the compression numbers,<br /> Temp sensors should be on each head close to the top, 1 on each head with single tan wire for each sensor, tan wire goes farward in control harness and should connect to overheat horn. Check the power pack/s for a tan wire same as temp sensor, if no tan wire pack does not have function that reduces rpms when over heat. Power pack has tan wire, disconnect tan wire and try engine again.

 

[rwise]

Re: 88hp Johnson loses power at full throttle

Jack<br />is the tank vent open and venting?<br /><br />Richard

 

[Jack B]

Re: 88hp Johnson loses power at full throttle

Captain, It is a 1992 88hp spl. The guy who checked out the compression said all the cylinders were at 150 psi and the cooling system was working properly. I have run the motor with 2 different tanks and different fuel lines and I have checked the vents on both. Thanks, Jack

 

[pioneer]

Re: 88hp Johnson loses power at full throttle

blocked filter<br /><br />worn connections to tanks(lets in air during high suction)

 

[mtp]

Re: 88hp Johnson loses power at full throttle

Had the same problem. Will it rev up in neutral, but not "in gear". If so, high speed jets in the carb may be plugged. Mine had the fuel bowl gasket deteriorating into the gas - into the jets... drove me nuts. Would go in idle, and only 1500 RPM at hi - throttle. Cheap fix. New carb bowl gaskets (if your bowls are plastic, get the metal ones - they don't warp), and time to blow back the jets.....

 

[Jack B]

Re: 88hp Johnson loses power at full throttle

I rebuilt one carb and probably shoud have done both. I bought another carb kit today. The carb that I did not rebuild has a little seepage around the bowl gasket. I hope this fixes the problem it really is getting on my nerves. Oh yeah, it does have plastic bowls, how much are the metal replacements?<br /><br />Thanks, Jack

 

[Jack B]

Re: 88hp Johnson loses power at full throttle

Well I rebuilt the other carb and found a little piece of the fuel pump diapham lodged in the needle seat. clean the carb and it runs like a champ!