73 Johnson 135hp spark trouble

late Last year I got a 73 Johnson 135hp V4. After replacing a piston head, all new gaskets, all 4 coils, and a carb clean, it ran fine for the day. next time out it had trouble starting, like one cylinder wasn't firing, but did start and ran fine for a few minutes, ran rough,(like a cylinder died) then shut off and wouldn?t start. I pulled it out last week, charged the battery, and tested the spark with a spark tester. #3 cyl has a good spark, but the rest don't have any. I tried switching sensor wires #4 and #3, no change. I swapped coils #3 and #2, still no change. Am I looking at a bad power pack?


Just for the record these engines do get bad gas mileage.

Re: 73 Johnson 135hp spark trouble

You may find some good electrical ignition troubleshooting tips for this engine on the web at: cdielectronics.com. The spark plug coils don't fail that often, so you need to look at the timer base, stator and the power pack. All are expensive, so some time spent troubleshooting should payoff in the end.

Re: 73 Johnson 135hp spark trouble

Okay thanks. I tried switching coil wires #2 and #3 on the power pack, and the spark change with it. so I really thinking it's the power pack. I'm going to talk to a local marina guy, see what he thinks. Thanks for replying.

Re: 73 Johnson 135hp spark trouble

So I replaced the power pack and it ran great. We went tubing with it and it ran fine, but recently I went to a new lake and was driving all over at full throttle mostly, and after about half an hour it burned the same piston head that I just replaced. I talked to a local marina guy and he said that I never really fixed the problem in the first place I just got it running. He said it could be almost anything. So I got the thing apart and cant find anything wrong. It's only the one that burnt all the others look fine, the carb looks good for that cylinder, and I'm sure the gas mix was right. so my problem is I don't know why it burnt. and I cant find a replacement piston head. Any suggestions would be great.

Re: 73 Johnson 135hp spark trouble

Not sure just what you mean by "burned" the piston. Do you mean that the crown of the piston was damaged? Was it damaged similarly to the first piston you replaced? No damage to the actual face of the head? When you replaced the bad piston before, did you diagnose just what caused that failure in the first place?

Re: 73 Johnson 135hp spark trouble

both pistons look amost identical. The first time I rebuilt it I took the water covers off and they were full of what looked to me like some kind of salt buildup. the previous owner had it out in the ocean and it looks like it was never flushed out, so I figured that was the problem, now I'm not sure whats going on.

Re: 73 Johnson 135hp spark trouble

You've got an overheated piston. Causes can be that the block is actually overheated, or that the fuel mixture was too lean and it was not enough to cool the piston during the combustion process. Always possible you have too much timing advance. There are a couple of things you need to check before you reassemble anything. Remove all the jets out of both carbs and visually check to see that they are clear-will flow fuel. The original fuel lines on that engine were not made to handle today's ethanol fuels. It will break down the black fuel hose and black bits of hose debris can migrate into the carb jets and lean out the mixture. If you had the head covers off and found any buildup of material in the water passages, it surely is inside the block. Was it around the cylinders as well? There are 4 water deflectors which direct water in a circular pattern around the cyls. These deflectors must be in proper position. I'll attach a pic of proper diverter installation. The area by the rubber diverter is suseptible to narrowing-restricting water flow around the cylinders. This engine is a very high compression model. Probably 135 lbs. when new. With the original factory timing and these high compression heads, I would not run anything but premium fuel (93 octane.)

Re: 73 Johnson 135hp spark trouble

Really interesting case

Im gonna start running my v4 on premium fuel

Good luck

Re: 73 Johnson 135hp spark trouble

Okay thanks. When I cleaned the carbs they didn't look bad at all. the head covers were really bad, but around the cylinders looked okay. cylinder #1 overheated, cyl #3 looks like it got some heat from #1, the oil is burnt off the top side were the cyls are the closest but dosen't look bad. cyls #2 and #4 look great, plenty of oil, so that made me think it was isolated around cyl #1. I haven't been running premium gas through it 'cause I heard the high octane may damage it. Thanks for replying.