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Charles
Charles, Marine Mechanic
Category: Boat
Satisfied Customers: 3342
Experience:  US Navy (Ret) Certified Mercury Marine Tech with over a decade of repair experience.
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I have 1990 larson with a gt 175 johnson 1989 it has a miss

Customer Question

I have 1990 larson with a gt 175 johnson 1989 it has a miss fire at low rpms ( water hooked up ) when it missfires ,standing behind it running ,the left bank , a puff of exhaust comes out someware at the base of cylinders , can't really tell due to all the electrical in the way any ideas
Submitted: 6 months ago.
Category: Boat
Expert:  Charles replied 6 months ago.
Hello, my name is***** will assist you.Do you have the full model number off the engine?
Customer: replied 6 months ago.
J175STLCEB
Expert:  Charles replied 6 months ago.
Thanks, ***** ***** could be coming from gaskets 21, or 37, or 39. The best way to locate it is to move the electrical wiring and look for some water as well as exhaust. Let me know what you see, and we can go from there. http://www.boats.net/parts/search/BRP/JOHNSON/1989/J175STLCEB/CYLINDER%20&%20CRANKCASE/parts.html
Customer: replied 6 months ago.
I've replaced gasket 37 and 39. I didn't go farther into the motor. I've been a diesel mechanic for 31 years, but this is the first time I've worked on an outboard.
Expert:  Charles replied 6 months ago.
Still getting the puff of smoke, if so, do you have the equipment to do a leakdown test on the port side. Take out all 6 plugs, install the gauge, then use a 1 7/16" socket to roll the engine over to bring the pistons to TDC. Lister around that cylinder head to see if you can hear the leak.
Customer: replied 6 months ago.
I did a compression check on each cylinder and they were at 100 to 103 wide open throttle.
Expert:  Charles replied 6 months ago.
but a leaking exhaust gasket will not show under compression.

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