98 Ocean Pro 150 dropping a cyl at 4500 rpm?

[kevhed]

Still trying to get all the bugs out of this "new to me" boat. Engine was not going over 4500. Took to mechanic- said the recirc hose that goes in the top of the airbox was in wrong spot. Corrected and said it ran on the dyno fine @ 5000 rpm.
I water tested the boat and ran fantastic right up to 5000rpm (need to drop prop pitch)
but after about 10 minutes, dropped back to 4500 and that is where it stayed. Has awesome power out of the hole just won't get up past 4500 again. Mech says it seems to be dropping a cylinder- might be a bad recirc check valve, as his hose correction fixed the problem initially, although it was temporary. I did do a heavy decarbon when I got the boat-could be it clogged a recirc valve? Am getting pretty frustrated with the motor- any feedback would be appreciated.

I have replaced the power pack, plug wires, plugs , removed the anti-siphon valve all of which did resolve some other issues (surging, lean horn, etc) and got me to this point. This is the "last" problem I have to resolve.

 

[daselbee]

Re: 98 Ocean Pro 150 dropping a cyl at 4500 rpm?

Frankly, a recirc line as the cause of dropping a cylinder at 4500 rpm is crazy.

Get on the water with a timing light, and when it is dropping, put the light on each plug wire. Look into the light, and try to determine if spark is the issue, and which cylinder is the culprit. Also, the condition of your plugs can tell you which one is firing wrong.

 

[kevhed]

Re: 98 Ocean Pro 150 dropping a cyl at 4500 rpm?

Will do. In the meantime the mechanic is looking at it again.

If I have a spark issue would that point to a coil? They appeared to be original, with some cracking on the back. No burn marks on the old silver powerpack plate. I cheaped out when I did the pp and did not replace them.

I did check all with a timing light when on the muffs at home and did the spark jump test. All were fine. It appears this is a high speed or "when warm" issue.

Odd coincidence that it started working at his shop after he futzed around with the hose.

Thanks for your help