1988 Force 35hp backfired and wont run now

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Htnelson

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Joined
May 13, 2019
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6
I have a 1988 35hp as the title suggests it backfired and wont start anymore. Well not for more than a few seconds. It cut out on me in the middle of the lake a few days ago and stranded me. Got back to my dock and went to a local mercury specialist and brought the carb to him to look at. He said the carb looked fine and it was probably a Fuel pump diaphragm. Bought the kit and replaced the gasket and diaphragm in the order they came off(old one had some tears in it). Cranked it over and it started right up and idled better than it ever has while iv owned it, for 30 seconds. Then it idled way up, backfired, and stopped running no matter how much i manipulated the butterfly. Primer bulb gets hard and the plugs look fine too. At least they look like 2 stroke spark plugs. Not overly wet or fouled and not dry either. One last symptom i noticed is smoke coming from under the cowl near the mounts after it ran for a few seconds. And im at a total loss as to what that can be. It doesnt sound like a powerhead gasket to me. Any help would be appreciated because id like to have a boat to use on the rest of my vacation if possible. Thanks!
 
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Nordin

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Do as raceone suggest.
Check the flywheel key, if it is sheared the flywheel has moved and the timing is off.
Back fire and no start issue regardless of spark and fuel at the engine is a common issue if the key is sheared.
If you have a 0 mark at the flywheel and a timing point plate at the power head (just above the carb) you can check it very easy.
Set the throttle at idle, pull the plugs and put a screwdriver in top hole.
Turn the flywheel CW and find the TDC for the piston, then the 0 mark at flywheel should line up with the 0 mark at timing point plate.
If not the key is sheared.
 
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jerryjerry05

jerryjerry05

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You said: Then it idled way up, backfired, and stopped running.
The flywheel key would be suspect until you said it ran again.
One last symptom i noticed is smoke coming from under the cowl near the mounts after it ran for a few seconds. And I'm at a total loss as to what that can be. It doesn't sound like a powerhead gasket to me.

The first line, that sounds exactly like the motor ran out of gas.
Next: the smoke under the cowl: that also sounds like the gasket blew when it backfired.
Under the pack/coil are 2 port covers. It's possible when it backfired the gasket/s blew and now the motors sucking air and won't start.

The bulb gets hard, does the bowl fill? undo the screw on the bottom of the carb and see if a tiny bit of fuel o r a bowl full drains out?
 
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Htnelson

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May 13, 2019
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jerryjerry05 said:
You said: Then it idled way up, backfired, and stopped running.
The flywheel key would be suspect until you said it ran again.
One last symptom i noticed is smoke coming from under the cowl near the mounts after it ran for a few seconds. And I'm at a total loss as to what that can be. It doesn't sound like a powerhead gasket to me.

The first line, that sounds exactly like the motor ran out of gas.
Next: the smoke under the cowl: that also sounds like the gasket blew when it backfired.
Under the pack/coil are 2 port covers. It's possible when it backfired the gasket/s blew and now the motors sucking air and won't start.

The bulb gets hard, does the bowl fill? undo the screw on the bottom of the carb and see if a tiny bit of fuel o r a bowl full drains out?
Click to expand...
It sounds like it ran out of gas to me too. But the gas tank is full, and the carb bowl was filled even with a damaged fuel pump diaphragm. I assume its still filling it now that its been replaced but ill check again. Theres also oil and stuff in the cowl from me being a messy mechanic so i thought maybe that was where the smoke was coming from but since it came from outside beneath the cowl im not so sure.

But yes to reiterate after the fuel pump was rebuilt it fired right up for 30 seconds then idled up, backfired, and died. About 20 minutes later it cranked back up again but only ran for about 10 seconds
 
H

Htnelson

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Joined
May 13, 2019
Messages
6
Upon investigation, it fired for just a second one more time after sitting overnight. Then i took the fuel line coming from the fuel pump to the carb and there was nothing coming out except for fumes. I just rebuilt that FP. Could the new diaphragm have failed that quickly???!!! “Mercury precision parts” lol
 
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