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

Hi,

I had the local mercury dealer do the test. He told me that number 4 was only 55 psi the other 7 were between 100 and 105. Then he said the cheapest way to go would be to just get a new long block rebuilt from merc. Not sure if there is any other way to go. He did tell me I could still run the boat as much as I wanted and that it was just a tired engine.

I would not buy a new long block from merc. I would get the engine pulled and take it to a good marine engine builder. I'm sure there are plenty in your area, go to the general Q&A section and post your question. In the end the engine will be balanced, hand assembled and be a much stronger engine than an off the shelf merc engine and most likely 1/3 the price.

Ok, I just posted a thread in the Q and A section.

Thanks

The 'best' way to fix it really depends on the source of the low compression. If it is valve issues, then a valve job could fix it without the replacement of the engine, so long as the lower end is good. A cylinder leak test could get you that additional information as to where the cylinders are leaking. If it is valves only, then maybe a top-end rebuild. If it is rings and valves, then maybe go for the longblock.

As mentioned, a local engine rebuilding shop might get you more diagnosis and options. I would check out their background and reputation as best you can before you commit.

I have a similar issue with my 84 272LS mine may be over propped 23p props with 350 motors that were rebuilt a couple years ago I run on the muddy Missouri river most of the time and 3900rpm is it it seems I can get a few mor RPMs going down river but not much when I go to a lake I can get about 4300 RPMs that heavy muddy river water makes a big difference!!!

If the 350's are Standard Head Pre Vortec models you're not developing enough power to swing 23's. My 355 Vortec engines with Comp XM 272 Rollers are turning 23" Mirage Plus over 5000 thru Bravo I's in my Formula 255 Liberator which is very similar to your 272.

Try a set of 21" Mirage Plus...I think you will be happy with the performance and you should see 4700~4800 RPM.

What will the 21p props effect be on my cruising speed and fuel economy ? It cruises at 40mph Luke a dream and I very seldom see wot!! Would 21p props give me more top end speed or just more RPMs at the same speed? I see 55mph with normal laod of fuel and people on board on a good day with no kansas wind Friday night we hit 52mph on my hummingbird gps going up river with 4 people and half tank of fuel!! Will I hurt the boat if I leave the 23p props on it? I've only owned the boat for a year but I assume the props have been on there a long time and I have 3 of them!!
Sorry to hijack your thread!!

Hi, Does anyone know what the correct RPMs should be at idle for this boat? 1995 271 SR1 with 454 efi.

Thank ou

Hi, to revisit this issue, I am taking the engine to have a leak down/blow down test to check the valves and the rings. However, I have been thinking of upgrading to a 502 or 496HO. In this case, would it be cost effective to sell the 454 as is fully dressed and use the money to put towards a used low hour 502 or 496HO? Is the 454 worth anything as is? Any parts of it that I should keep?

rebuild the 454. Throw a cam at it and bore it .30 over and work the heads. Throw on some stainless manifolds to let it breathe. youll be increasing the power for much less money.

I.M.O. dont rebuild it and make it a 454 or 469. Put a stroker kit in it and turn it into a 496. I did and my boat with a fresh motor would run 72 any day and 74 with just me. BTW it sounds just plain Nasty! I get a lot of compliments on the way she sounds. Best of luck!

Decided to maybe try to sell the boat as is. Then move up to a newer 292. Anybody know what it would be worth?

Let me know when you have a number in mind.

Hi guys, any thoughts? I can send pictures also.