1991 Johnson 140 does not make WOT rpm

[firefighter384]

I have a 1991 johnson 140 it is hard to start I have to hold the throttle open about 1/2 inch. Once I get it started, and it warms up it idles fine. at WOT it will only do 4000 RPM, and that is only with help from the other engine. It wil runn all day long at 4000 with no problems. Same prop as the other engine, only difference is the slow one is the counter rotating prop. Compression is good 115 all cylinders. The right hand engine does 5200, and you can feel a diefinite acceleration when you hit the right hand throttle, as where I do not feel a strong throttle response from the left hand slow engine. Have held the throttle wide open by hand with no better results.

 

[ezeke]

Re: 1991 Johnson 140 does not make WOT rpm

Your motor has a QuikStart ignition, which automatically advances the timing and should make cold starting very easy if it is functioning properly.

Try keeping the key pushed in while cranking until the engine fires for your cold starts. Don't let the engine run faster than 1100 RPM during warmup.

Check the gear ratio on the engine that will only run 4000 RPM - there's a good possibility that you have a V6 drive on that motor and there is no way to tell the difference by looking at them. The V4 drive propshaft will turn 12 revolutions for each 27 revolutions of the driveshaft. The V6 drive propshaft will turn 14 revolutions for each 26 revolutions of the driveshaft.

BTW: You should consider re-prop so that you can reach 5800 -6000 at WOT when everthing is working correctly.

 

[firefighter384]

Re: 1991 Johnson 140 does not make WOT rpm

The lower unitis correct. Basically I was wonder what would be a logical trouble shooting progression? Maybe what to look for.

 

[Faztbullet]

Re: 1991 Johnson 140 does not make WOT rpm

If its been running correctly and just started this check the basic's, some of these are visual checks:
1) Compression
2) Spark on all cylinders
3) Sync and link
4) Timer base not advancing (see sync & link)
5) Cable from controls not advancing throttle & spark( see sync & link)
6) Carb problem (trash in high speed jet or needle swollen shut)
7) Vro problem ( not enough fuel supply)
8) Fouled plug or defective plug wire or cracked coil.

 

[firefighter384]

Re: 1991 Johnson 140 does not make WOT rpm

Think I have solved the problems. Slightly clogged water seperating filter, and a very weak VRO pump. Troubleshoot with a vacum gauge in the fuel line when I bypassed water filter vacum cut in half. Did the pressure test on VRO pump, and it is puking air like crazy. Can't wait for new VRO to get here!! Thanks for the help!!!!