[18 Shabah]

Hello again,

So all the consistency that I had on my last trip did not transfer over to this trip. The amount of time in idle made no difference. Idle mixture adjustments made no difference. It seemed totally random. Both my son and I noticed how random the performance was.

It starts and idles perfectly.

Sometimes it would buzz at full HP right from the start. Most of the time, it would chug for a while and then jump to buzzing. I did notice that upon acceleration, when I bumped the RPM up a bit by bringing up the trim little, it tended to reduce the time it took to jump from chugging to buzzing.

Sometimes, when pulling a towable loaded with kids, it would chug. I could quickly pump the throttle from idle to WOT a couple of times to reduce the time it took to buzz. This worked sometimes. Other times, I’d have to drop back to idle and try again. Sometimes it would chug, and other times it would buzz right from the start. I could always get it to buzz eventually and once it was buzzing, it did not return to chugging until the boat had returned to idle.

It seems that it is a problem when at WOT and low RPM, primarily at start.

The fuel filter/separator has less than 10 hours on it now so I don’t think that’s the problem.

I discovered that I have a Mercarb 2 BBL that only has 1 idle mixture screw.

My next step is to check the carburetor fuel inlet filter and then ensure that the accelerator pump is working consistently. I’ll also put some cleaner through the fuel system before my next trip out.

Any other ideas?

[18 Shabah]

Hello Larry,

So after much frustration, I got it fixed. The engine manual detailed that this motor came with 2 different Thunderbolt Ignition systems. One without a timing control module and one with both a timing control module and a knock control module. Mine fooled me because it has the engine control module, but not the knock control module…so it looked like the other system. So when I set the timing after changing the distributor, I set it to the wrong spec. I finally figured it out, set the timing correctly, and it is running perfectly now. Thanks for your help with this. I just thought I’d close the loop with you.

Take care ~ David

[ColoradoDiablo]

Glad to hear everything came out good for you David.
Mid year changes in the system can sure be a pain in the butt for sure.