Hello all, can you help ? RPM's 1972 240

[Kurt 240]

I have a 1972 240 cc that is only getting about 3500 rpms on a OMC 225 e shift, Clean all filters, changed over to electronic ignition, good fuel. but it will not get over that. I have changed props. I have three to chose form the smallest is a 14 1/4 x 12 and it will not even allow the higher RPMs. at the dock with no load.. it is 6k.. running.. No go. any thoughts. here is a pic.

PS.. I love this little boat.. :thumbsup:

 

[Matt89GT]

Check the distributor for rusted springs and weights, sounds like they might be siezed and not letting the timing advance, or you can just replace it with a new distributor and know what you have, just sayin

 

[Kurt 240]

What should I be getting ? OMC guide said 4600 with a 14 x 14 prop.. I could never imagine getting that high.

When you peg it to the wall, all 4 barrels open up and she drinks a lot of fuel.

While setting the timing. The timing TDC mark moved in the advance direction as rpm's went up at the doc, I set the timing at about 12 degrees. I don't know if this is right.

 

[Matt89GT]

I would start at 10 degress although you might get away with 12 degress but while putting the engine under heavy load listen for poping and knocking sounds ( detonation ) if you would hear that back off the throttle immediately, and back your timing back to 10 degress, every engine is different and some will take more than others. I dont know exactly what engine your OMC 225 is but I'm assuming Ford and 4600 sounds right, 4400 to 4600 max is what I would shoot for. As for a 14 x 14 prop I dont know. Myself I would start with a 14.5" x 17P and see where that gets ya but if that didn't get ya in the ball park you just might need to drop down to a 14, but that dont sound right to me.

 

[Kurt 240]

Ok.. :smt024 here are some numbers, I think it is a GM motor, not a ford. Seeing a 4600 rpm on this boat sounds impossible. :smt021 At WOT i am seeing 3400 and she is moving fairly well. I will need to GPS the speed as my speed meter is not working.:smt089 Please let me know if these numbers match anything anyone can decipher. :smt100

I have to thank my children for helping me with the smiles. :smt101

If you know any other locations on the engins to get numbers please let me know and i will look.

 

[kybishop]

Welcome aboard, Nice looking cuddy.

You have come to the right place.

 

[ScottyC]

We have a 75 240 with a 351 ford, gears in the IO could be different but the best prop I have found is a 16" X from 13 to 15 pitch (I have tried a lot of others). The SeaRay prop chart said a 16" X 15 pitch. I normally can only get 3800 - 4000 RPM's, best I have seen was 4250 (1 time). I had a 14.25" and could overpower it and make it cavitate(?) the prop. Hope this might help, it's not the same as yours but...

 

[ScottyC]

We have a 75 240 with a 351 ford, gears in the IO could be different but the best prop I have found is a 16" X from 13 to 15 pitch (I have tried a lot of others). The SeaRay prop chart said a 16" X 15 pitch. I normally can only get 3800 - 4000 RPM's, best I have seen was 4250 (1 time). I had a 14.25" and could overpower it and make it cavitate(?) the prop. Hope this might help, it's not the same as yours but...

 

[Matt89GT]

post some pictures of your engine, I see its a GM V8...that engine should turn 4600 no question about it. If it dont turn what it needs to turn its gonna tulip a valve or even throw a rod sooner or later with such a load on it something will happen. Take some pics and somebody here will tell ya. No one can give you accurate answers without seein what you got.


On the port side of the engine at the rear, just below the intake manifold there will be a casting number, for example something like a 3970010 number that will tell us what engine you have.

 

[Kurt 240]

Thank you.. I will take more pics when i get there. I am out of town at the moment and will be back in a few days. thank you all for your help. If you think of something else. please let me know.