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  Rough idle on 90HP Johnson

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Author Topic:   Rough idle on 90HP Johnson
rathersailing posted 11-09-2001 12:22 PM ET (US)   Profile for rathersailing   Send Email to rathersailing  
The idle on my johnson is pretty rough. I "power tune"ed the carb, replaced the plugs, and revamped the dash ignition wiring. Runs better, but still a little rough at low RPM. Top end/power is excellent, above 2000 RPM. Anyone have one of these, with a similar problem? Any sugguestions?
ratherwhalering posted 11-09-2001 01:03 PM ET (US)     Profile for ratherwhalering  Send Email to ratherwhalering     
As you can tell, I've been bitten by the Whaler bug...I even changed my screen name! I thought I might add that the engine is a 1987.
csj posted 11-12-2001 11:13 PM ET (US)     Profile for csj  Send Email to csj     
I HAVE A 1985 90 HP JOHNSON ON A 1977 WHALER AND UPON PURCHASING THE MOTOR IT TO RAN ROUGH. MY BROTHER RE-BUILT THE CARBS AND IT HAS RUN PERFECT FOR TWO SEASONS.
reelescape1 posted 11-13-2001 09:51 AM ET (US)     Profile for reelescape1  Send Email to reelescape1     
Rebuild the fuel pump...the small rubber check valves have a tendency to crack. One small crack WILL cause that but will sometimes run at higher rpm.
ratherwhalering posted 11-13-2001 11:45 AM ET (US)     Profile for ratherwhalering  Send Email to ratherwhalering     
Thanks guys...I'll have my mechanic check out both the carbs and the fuel pump. It also looks like there is some oil seeping from the lower engine cover. Should I be worried?
Bigshot posted 11-13-2001 03:03 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
have the carbs redone. Is the VRO connected or running 50:1? When carbs get funky they will leak and therefore you get oily gas crap leaking out from under the cowl, makes a mess.
Timo posted 11-13-2001 03:27 PM ET (US)     Profile for Timo  Send Email to Timo     
I had (have) the exact same problem with my 88 Suzuki 85hp. (on a '77 15 Sport, I know...overpowered but its nice to have). I bought it from a friend who had not used the engine for two years...went through a nasty divorce and forgot to winterized it after the last use...

Needless to say, when we put it in the water it would turn over then die under throttle. I took it to the local Suzuki dealer who promptly rebuilt the three carbs. I took it out, it started right up and ran great. However, after a about 7 hrs. on the water, it started to idle VERY rough, and even began to stall when pushed from idle. I brought it back to the mechanic and, same as you, they noticed oil leaking from just under the cowling. Their diagnosis? Because the engine had sat for so long (without internal part being lubricated with usage), once they had fixed the carbs and the engine started producing peak compression, the compression seals in the power head gave way. According to the mechanic, i could still run the boat; it runs great at peak throttle, but the minor compression loss it amplified at idle; when the two-stroke engine needs compression most.

The short of it? I will be paying someone to remove the power head and replace the seals. The engine only has around 100 hours, so i feel the investment is worth it.

Has your engine sat such that the seals could have dried out?

Bigshot posted 11-14-2001 10:32 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
huh? I would get a second opinion but it could be your base gasket(mine is going on my Yamaha). If it is your base gasket you will hear exhaust leaking from under powerhead. If it is your lower crank seal then it would also drip but the reason it is not idling is due to water being sucked into your lower cyl(not good). Both require powerhead removal and about $20 in parts. to check crank seal, see if it runs good on muffs. If it does then crank seal. If you hear and see water coming from under the engine, then base gasket. Do a compression test to be sure it is not something more serious.

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