If gas is an issue the motor would not run clean or perhaps not at all. It would not just be a matter of less power particularly with a carb (no detonation sensors). That engine should easily pull a 23p M+ but the speed and rpm numbers don't match very well (as mentioned above, a lot of slip or the difference between actual speed and theoritical prop speed). This leads us to ask a couple of questions. 1) Is the drive a 1.5:1 ratio? I bet we are all assuming that it is. 2) Are the trim limits on the drive set correctly? If the drive ratio is higher (numerically) or the trim is set too high then speed will be limited, but you should also be pulling a lot more rpm in those cases. 3) Is there a rev limiter on the engine? Does the engine miss at top speed? 4) Check your jetting. Run it wide open (4800 rpm) for several seconds and then as fast as you safely can pull the throttle back and kill the engine. Pull a plug and take a picture of it, let us see it. With unleaded gas it should be a very light tan. If it is black or sooty you are way rich, white way lean (this is a drastic simplification here). Any soot on the transom after a run?

I am suspecting that the prop is bad or you have a drastic out of trim condition. If the prop has one or more blades dinged or tweeked etc and you are getting cavitation or ventilation there will be a significant loss of performance and attendant slip. You will know a lot more when you put the R1 on from BBlades. That should be too low a pitch though (as previously mentioned). A 502 powered 272 (Islander or not) should be a 60+ mph boat.

One other thing to check is weight up front. Any heavy stuff stored up there or water in the ski locker that is not draining etc? A bow heavy (high drag) condition will give the symptoms you are describing as will a drive that is trimmed down too much. Again, check the trim limit switch settings.

Good luck. A 272 Islander is a very nice (and rare) boat. You will love it.

Dan

It does have stabilizer, but I'll add some fresh stuff and run it out of there. Troubleshooting with stale gas - talk about a "duh" moment. *facepalm* lol.

Thanks, Dan.

It is the 1.5:1 ratio Bravo 1 drive. I tried trimming it out every which way and that was still the best I got. The prop looks absolutely cherry without a single ding or nick in it, but 31% slip seems ridiculous on a very common prop/boat combination. I'll check the jetting this weekend, but no soot on the transom.

The jetting would be a long shot I would think, but relativly easy to check. Assuming you are making rated HP then it is a weight, trim or prop problem. You are not running a shorty or anything like that are you that would cause you to have a lot of slip are you? Running a drive shower? The pickups for those have been known to disturb the water at the prop on occasion. Remove anything that might be questionable and try again. Before putting the boat in the water visually eyeball the position of the drive to make sure it has some tuck when fully down and tilts slighlty up when on the trim limit.

Dan

OEM lower, so it shouldn't be a shorty. It does have a drive shower. I'll take pictures this afternoon and post them up.

Did you ever try that Rev 4 prop? Any improvement for that or any other reason?

Dan

Ordered the prop yesterday, and will try it out over Labor day, and I've also ran enough of the old gas out and added some fresh stuff to take that out of the equation. BBlades recommended a 21p with the 4 blade prop, but they didn't have one in stock so I went with the 23p, which is what I think should be about right with 502HP. I'll keep you posted!

Good luck. I borrowed a Rev 4 23 from a friend after successfully running a B1 22 and 24 as well as a M+23. The Rev 4 was much heavier than any of the others. I could not turn it past 4600rpm when getting 4800 out of the M+ and 4700 out of the B1 24. There are few things in life as fun as testing props though so you will find it interesting no matter the outcome.

Of course my 496 is only rated at 375hp and I don't believe I'm making that. At least you will be able to tell if you've got a dud M+ for some reason or another.

Dan

That's helpful info, Dan.

The 4 blades are heavier, but in theory 502hp outa be able to swing that thing. At the very least I'll be able to rule it out and not always wonder the "What ifs..." Lol.

Please keep us posted. With 500 HP you should be running closer to 70 than 60 (or 48) @ 5000 RPM. I have basically the same power, EFI. Dan has paced my boat real close to 70 himself.

I do have an extensively worked M+ 23 that measures to 24.4 pitch per Bblades.