90 HP Force won't idle after teardown

[jeburr1]

I just replaced the pistons in my 1990 90 horse Force. It is hard to start, & won't idle. It dies at anything below 1500 RPM, acts like it runs out of gas. I took it to the lake, set the timing (wide open throttle, in gear) retarded 2 degrees like everyone says it should be. The boat runs great at higher speeds, but idles down for short periods only, then dies. I'm thinking maybe vacuum leak, but can't find one. I'm also wondering if maybe I have fuel recirculation hoses wrong? There is 1 hose that runs from the carb cover to the crankcase, one from the bottom of the crankcase to the top of the intake.
Some dummy (that would be me) took it apart without taking pictures to help get it back together right. Can anybody help?

thanks

 

[Frank Acampora]

Re: 90 HP Force won't idle after teardown

One hose runs from the bottom of the triple recirculation plate to the intake manifold between the top and middle carb. One hose runs from the bottom of the air box to the bottom of the intake manifold.

Timing at idle should be somewhere around 0 degrees plus-minus 2 deg.

Low speed needles (brass screw in the top of each carb)should be no less than 3/4 turn out from lightly seated. Start at 1 1/4 turns out and adjust. usually the correct setting is somewhere between 3/4 and 1 turn out. Too lean and the engine may run out of fuel at slow speed. Too rich and it will load up and stall. With either condition it will run well at high speeds because the low speed circuit in the carbs only fully functions below approximately 1500 RPM. Above 1500 RPM, the main venturi has enough air flowing through it to supply fuel to the engine. The low speed circuit DOES function some at high speeds because there is always manifold vacuum and if you set it too lean (less than 3/4) you run the very high probability of melting at least one piston due to detonation.

Lower carb roller should just contact the cam when the mark on the cam is aligned with it. However, at idle the mark may not be aligned but rather may be slightly advanced.

 

[jeburr1]

Re: 90 HP Force won't idle after teardown

Thanks for the info. I'll check it out tonight & let you know how it works

 

[jeburr1]

Re: 90 HP Force won't idle after teardown

I checked the hoses, they are correct. I pulled the idle screws out, flushed the with carburetor cleaner, put them back in & turned them out 1 1/4 turns. The motor started, was running pretty rich, so I turned them in so that they are about 1 turn out. The motor then idled with the ear muffs on, so I thought it was ok.

By the way, the bottom idle screw was only out about 1/2 turn to begin with. Oddly enough, that was the cylinder that had a big hole in the piston that caused the teardown. I've had this boat for 10 years, never adjusted it. That may have contributed to the failure, although the nut that locks they timing screw had also worked loose (prior to the teardown), & the timing was way off.

I took the boat to the lake. It still won't idle, but still runs great above 1500 rpm. I also noticed that the ignition key no longer stops the engine. This may have been since I put things back together, I don't know, since the motor has been shutting itself off every time I idle back.

Any ideas?

thanks
John

 

[jeburr1]

Re: 90 HP Force won't idle after teardown

I found the problem, but not where I expected. I pulled off the carburetors & cleaned them. When I looked inside the reed vale plate, there was a gasket hanging inside, broken. I pulled the reed valves off, made a new gasket, & it runs great!