Johnson GT150 drops a cylinder intermittantly

[tournyangler]

1990 Model J150STLES-B with 35 amp charging.<br /><br />The problem is intermittant. <br />When accelerating from idle, the motor will sometimes not reach full RPM's. RPM's top out at about 4,100 with wide open throttle (WOT). Once the boat is on plane, the RPM's go to 4,300 for several seconds, then the RPM's jump, suddenly, to 5,400 WOT.<br />I have had the boat to two different OMC shops. They replaced the rectifier and power pack. After each repair the motor ran well for a couple of trips, then the symptom returned.<br />I recently replaced the stator, spark plugs, and ignition wires myself.<br />I still have the problem. Could it be the ignition coils or timer base? How can I test them?<br />Could this be a fuel problem?<br /> I need help!<br /><br />Tournyangler

 

[dewley]

Re: Johnson GT150 drops a cylinder intermittantly

tourny angler, I know how you feel I fought it for a long time on a 92- 120 Evinrude, found it was the timer base. Would run as you said, the miss , what a thrill when it came in at top speed then perfect for a period. Finally loaded motor with long run under load on trailer, miss became apparent, used meter to find base breaking down and not feeding the power pack. Good luck, Dewley

 

[tournyangler]

Re: Johnson GT150 drops a cylinder intermittantly

Dewley,<br />Thanks for your advice. I had suspected the timer base could be part of the problem but I do not know of a way to test it.<br />Does anyone know of a method to check the timer base?<br />Tournyangler

 

[clanton]

Re: Johnson GT150 drops a cylinder intermittantly

You should have 2 connectors Port and starboard to power pack/s marked A B C D. Check each termial for short to ground on both connectors. Check output from A B C with black lead connected to D . Spec is .2 volts with peak reading meter. Connect the 2 D termials with jumper, check output from A B C with black lead connected to D. Spec is 1.2 with peak reading meter. Ohm readings between A B C and D with black lead connected to D is about 970 ohms+- 100.<br />Between the 2 D termials 230+- 30 ohms. This is the short version. All results should be same for <br />each test of termial A B C. Meter connections must be good.

 

[tournyangler]

Re: Johnson GT150 drops a cylinder intermittantly

Thanks Clanton,<br />I will test it.<br />I just wonder if the timing base is sticking and the vibration of the motor finally "shakes it loose" resulting in 5,400 RPM.<br />I think I will pull the flywheel and look at it.<br /><br />Tournyangler