SeaSideLife
Member
- Joined
- Apr 2, 2025
- RO Number
- 36935
- Messages
- 10
Update: It seems I've fixed the problem. TLDR: I think it was the timing.
I was about to take out the carbs and switch them and check the reed valves while they were out. But a buddy was having the EXACT same issue on his boat, (I literally witnessed it firsthand a few days ago.) and he fixed it by changing out a plug.
So that told me it had to be an ignition-related issue and wasn't as likely to be a fuel delivery problem.
So after a little research I realized the timing could affect how a cylinder fired due to the spark happening too early or too late in relation to the position of the piston. That could, theoretically, result in the issue being somewhat intermittent and worse while at speed and trying to accelerate.
Did a timing reading and it was firing about 6 degrees after TDC. But it's supposed to be 22 degrees *before* TDC. So I adjusted it. The screw on the magento control link could only go so far, but that got the timing to around 7 or 8 BTDC.
For a brief moment when I took it out to test it, it trembled again. Then I tried it again and it ran perfectly for 70 seconds without any problems at all. Did it again for about 90 seconds no problems at all.
Tested again yesterday evening and no problems. Runs like an absolute dream now.
After adjusting the timing, out of curiosity, I tried another test: I tried starting it using only one plug. I did this with every plug, and it fired up perfectly with each one.
Interesting note: It also started fine on the plug that failed the cylinder drop test (number 4). Did the cylinder drop test on that plug again, and it still "failed." There was no change in engine performance when removing it and no "surge" when putting it back in. I don't get that.
A few more side notes for anyone reading this 15 years into the future lol...
- While working on it, the impeller failed and stopped putting water out of the telltale. The Woodruff key had eaten through the inside of the impeller. I replaced it. I don't think that made a difference with the issue I was having though.
- While taking out the lower unit, like a genius, I chipped the anti-cavitation plate. Smh. So I put a hydrofoil on, a Doelfin, that I had already bought anyway. That was before I tested it after adjusting the timing. I truly don't think that made a difference with the issue, but the urban myths are 100% correct: That thing is a miracle. Gets up on plane crazy quick and seems to just skim the water now. At speed, it handles like, idk... a jetski. Super agile.
So yeah, problem fixed. Thanks to everyone for the help and insights.
I'm still confused about how the cylinder drop test could be a fail but it could start up on that plug. But it's running WAY better and smoother now after the timing adjustment. And the problem is gone. So
