271 SR1 low rpm issue
 

I have am having an issue with my RPMs on my 1995 Formula 271 SR1. The boat has the 454 EFI 385hp with a bravo 1 drive. It also has a drive shower. The prop is a 21 pitch mirage which is the correct prop for this boat according to Formula. I was expecting to be turning around 4400-4800 rpms at WOT. However, the best I have been able to get is around 3,900. I know this is way low. I am running two people on board with half fuel.

Any thoughts on where to start looking for issues-

Thanks

Check the following stuff . . .

Fuel pressure/fuel system
New gasoline
Throttle linkage and full throw to WOT
Engine 'codes', if any
Base timing
Engine alignment
Compression test
Cylinder leak test

Is this boat new to you, or do you have some history with the boat for comparison purposes?

Thanks, yes the boat is new to me this summer. Spoke to the previous owner who said it would run normally between 4400-4800 rpm depending on how hot it was.

How do you check the throttle linkage?

Also, what is meant by “engine alignment”?

Thanks for the help so far.

Does the boat just stay at 3900 RPMS or does it start to break up? How is everything else below 3900.

It runs pretty much consistent at 3900, it doesn’t break up. When throttling up it runs good too, at least to me it does. I know these are heavy boats and the 454 is not going to have as much power as the 502. But he power is consistent.

Also, when was last tune up. plugs, fuel filters, plug wires etc...

Just had the fuel filter cleaned, going to check compression, plug wires, and plugs today.

With the engine off . . . take the throttle up to WOT and check to see that the air intake plates are opening all the the way. If they are not, then the throttle linkage may be catching on something, preventing you from really getting to WOT.

Google "Mercruiser Engine Alignment" - the engine has to be properly aligned with the outdrive shaft. Otherwise it will cause excessive resistance and eventually wear out the coupler that is attached to the flywheel.

Just got the compression test done, only 100-105 in most and one had only 55. Does this mean rebuild or new engine?

Those numbers are really low . . . assuming you had all the plugs out, etc when you did the test and a fresh battery charge?

Can you post the specific cylinder results?

Your next step would be to do a cylinder leak test to give you a better idea of where the problem(s) is/are. It is always good to know as much as you can before you start taking apart the engine