I have 502's with Blowershop 250's in a Cig TG.
runs and idles fine but the last couple times I drove it, I noticed that the port motor is not making more than about 4200 RPM's

I checked the prop, spark plugs, wires, (has MSD boxes)
that all seems fine... plugs look ok.
Anything else I should be looking at here?

the boat is slightly under propped - at WOT throttle its at like 4900 - 5000 RPM....

I want to say it is smoking just a little bit at idle after its hot, but I honestly cant tell if it is smoke or steam - its very minor... im probably being hypersensitive to everything I am seing but was curious what I should be looking at here.

The boat is getting pulled out next month for top end rebuilds, blowers to get redone, carbs, etc...

Any ideas here on things I should be checking here? thanks

Thats a good rpm hit i would move to fuel pressure maybe a quick bowl pull then compression leak down . Which wouldnt be a bad idea anyway before motors come out for baseline ,reference and identify areas for potential upgrade - improvements when they are out

I agree. Check fuel pressure. Is boost psi even with other engine ?

boost psi is a little less on the port motor - the one in question here.
only getting about 3 psi to the 5 I am getting on the other side... but I don't keep it at WOT throttle long to watch it because this situation is making me nervous.
fule pressure looks good. I have gauges that are both reading about 6-7 psi (not sure where that is reading from though) and I have gauges on the rails going right into the carbs and both are at about 8-9 psi.

so it sounds like the first thing that probably needs to be done is a compression and leakdown test??

If down boost pressure, i would start by checking to make sure carbs are opening all the way at full throttle. And make sure blower belt isnt slipping.

I used to get exact same thing on my 525SC when the 10 rib supercharger belt started getting bad.

I didn't think your engines had that many hours on them since your rebuilds a few years ago.

Hi Griff, correct, there is probably less than 100 hours on the new builds and the blower belts did get replaced then, but that doesn't mean that's not the culprit either....
so, whats the best way to check them if they seem ok? check for a difference in tension between the two belts?

There really was no way to tell looking at the belt. I used get 60-100hrs out of a belt before it would start slipping. I would just try a new belt.

right on, thanks! Anybody stock these locally at the lake that you know of?? I believe we ordered these last time but I have no idea where they came from!

I used to just get my 10 rib SC belts from NAPA. We have a big warehouse here, so I never had an issue.
I did have to get one at the lake once, but don't remember which auto store actually had one in stock.
Trust me, you don't want one shredding at 5000rpms. It was a huge mess.