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1987 johson 150 gt

B

basspro62

New member
last few times out motor starts up let it warm up. go to take off wont i belive running on maybe 3 cylinders . if i keeping trying clean out with warm up leaver seems like all are firing but looks rich . then give it full throtle it might go ,might not but 2 or 3 times of that then it goes is it power packs , or coils . i did put new plugs and fuel pump in. any help please thank you.
 
Basic trouble shooting starting point.

Remove all spark plugs. Check compression. What are the readings of all cylinders?

Plugs still removed. Check spark. Spark should jump a 7/16" gap with a strong blue lightning like flame... a real SNAP! Does it? If not, explain as good as possible what type spark you're getting. The gap is important... do not waste your time using the spark plugs to check the spark! No Tester? Read on........

(Spark Tester - Home Made)
(J. Reeves)
A spark tester can be made with a piece of 1x4 or 1x6, drive a few finishing nails through it, then bend the pointed ends at a right angle. You can then adjust the gap by simply twisting the nail(s). Solder a spark plug wire to one which you can connect to the spark plug boots, and a ground wire of some kind to the other to connect to the powerhead somewhere. Use small alligator clips on the other end of the wires to connect to ground and to the spark plug connector that exists inside of the rubber plug boot.
Using the above, one could easily build a spark tester whereas they could connect 2, 4, 6, or 8 cylinders all at one time. The ground nail being straight up, the others being bent, aimed at the ground nail. A typical 4 cylinder tester follows:
　
..........X1..........X2
.................X..(grd)
..........X3..........X

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ok all cylinders good 7/16 spark snaping .dont know cylinder numbers but both center ones seem to only fire every 2nd or 3rd. all others fire every crank. looking at cylinders from back starting with left side top88,center 80 bottom 85, right side top 80 center 80 bottom 85lb compression. i hope this is enough INFo. if not let me know . ty
 
Okay, from what you've said, the spark is as it should be. The compression is slightly low BUT that could simply be due to a slow cranking engine. The difference between the cylinder readings is within specifications, that is the reading between the lowest and highest reading cylinder is only 8 psi (okay).

Engine not running but in gear..... have someone slowly advance the throttle while you're observing the timer base under the flywheel. It should move smoothly from the idle fully retarded position to the full throttle full spark advance position. If it should stick anywhere, that would cause the problem you're encountering.

If the timer base moves as it should, then suspect that the carburetors are somewhat fouled. In which case, remove, clean, and rebuild them.
 
The two center cylinders hesitating their spark could be simply due to the engine not cranking over fast enough or the gap setting is a little too wide. However, if that stator is a 35 amp stator, look under the flywheel at the two large black coils at the rear portion of the stator.

Those two coils supply approximately 300 AC volts to the powerpack. Should they be melting down a sticky looking substance down on the timer base and powerhead, that would result in a voltage drop to the powerpack which in turn would result in weak, erratic, and eventually no ignition (spark).

If those coils appear to be okay, I would still be suspecting fouled carburetors.

Another thing.... I believe the flywheel on that model has magnets that are epoxied in. look closely under the flywheel to make sure that none of the magnets have come loose and slid together. all of them should be spaced evenly, approximately 3/8" apart.
 
ok i looked under flywheel by coils seen shinny stuff below coil was hard and dry to touch wasnt sure if that was what u ment or epoxy. so took off fly wheel for better look . i belive it is epoxy or somthing now fly wheel was hard to get of with puller.was tapping on puller and bumping fly wheel til released. and 3 loose magnets is that problem or did i knock loose that easy? are they repairable can i reglue them? if not let me know price of one if u have one .so what do u think about those coils clue epoxy ? or bad coils ? thanks.
 
Epoxy glue especially for those magnets can be purchased at your dealership... or other epoxy glue purchase elsewhere. Use a short piece of 3/8" OD fuel line to space between the magnets. That may be the cause of your problem pertaining to spark but I seriously doubt that it's the cause of all your problems.

Those black coils, even when new have a hard looking drip on the bottom of many of them... this is normal. However, if the cols are actually leaking, melting down, this should be easy to decide as it would have dripped down upon the powerhead and timer base area.
 
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