74 85hp Johnson will not run high RPM

[larryfarley2001]

will idle ok new floats and needdle and seats but dies when in gear coming off idle speed will try and pick up if hitting the choke but still dies, will run high RPM when out of the water <br />

 

[Joe Reeves]

Re: 74 85hp Johnson will not run high RPM

Larry... What is the compression on all four cylinders? Should be approx 100+ psi and even on all cyls. Also, with the spark plugs removed, does the spark jump a 7/16" gap on all cylinders?<br /><br />Spark plugs should be Champion QL77JC4 or L77JC4 plugs, gapped at .040 . Are you using new s/plugs?<br /><br />Let us know what you find on those two checks.<br /><br />If the above checks out okay, I can only assume that you have overlooked something in the carburetors.

 

[ob]

Re: 74 85hp Johnson will not run high RPM

Larry ,If the above procedure Joe has laid out checks OK,your symptom may also be attributable to improper idle mix settings or link and synch of carburetors out of adjustment.<br />Another possibility since you say it tends to try and settle out if choke is applied is a failing fuel pump.Have you tried squeezing the primer bulb when engine won't pick up?

 

[larryfarley2001]

Re: 74 85hp Johnson will not run high RPM

4 new plugs firing on all 4 check with a timing light have tried squeezing the primer bulb while tring to pick up RPM also the carburetors have no adjusting screws

 

[ob]

Re: 74 85hp Johnson will not run high RPM

As Joe states ,you need to insure strong spark on all cylinders that will jump a 7/16" gap and known compression of all cylinders.Spark ,fuel delivery through carbs,and carb linkage to ignition synchronization are likely areas of your problem.<br /><br />Has this engine ran fine recently and this problem suddenly arose??

 

[larryfarley2001]

Re: 74 85hp Johnson will not run high RPM

No I just got the boat 2 weeks ago and was told that it ran ok last year,

 

[ob]

Re: 74 85hp Johnson will not run high RPM

I'm beginning to get a clearer image.If engine doesn't pick up when squeezing bulb we may have ruled out the fuel pump.The process of elimination needs to continue.

 

[zj-jeepster]

Re: 74 85hp Johnson will not run high RPM

Larry,<br />I have the exact same engine, same year. I had your exact problem.<br /><br />I went with OB and Joe's advice and looked at my motor without the cover at night. I had a really bad arcing problem to one of the cylinders.<br /><br />The coil for that bad cylinder was like falling apart. I could actually rattle the round part around in its mount. I replaced with new coils from seilersmarine.com and changed to new plugs and now she's strong as ever at WOT.<br /><br />Hope this helps you some.