89 Force WOT 4000RPM?

[jippie98]

89 Force WOT 4000RPM?

I just purchased an 1989 18ft mirrocraft cc with a 85 force outboard. The engine runs great and does not seem to have any problems. This is my first boat and it seem to me that it should do more than 4000rpm at WOT. Like I said, it runs great but i was curious if this sounds like a problem. I have not checked compression because it has never skipped a beat but given the size of the boat is this rpm normal? If not what should be my first steps in resolving the issue?

 

[roscoe]

Re: 89 Force WOT 4000RPM?

Re: 89 Force WOT 4000RPM?

Seems a bit low. You should be getting close to 5000 rpm.<br /><br />It motor is running well, and set up properly on the boat, then you need to get a new prop with less pitch. <br />About 3-4" less pitch.<br />Do you know the pitch of the prop that is on the motor now?<br />Do you have an aluminum or stainless prop?

 

[jippie98]

Re: 89 Force WOT 4000RPM?

Re: 89 Force WOT 4000RPM?

It currently has a aluminum prop. How can I tell what it currently has on it? Thanks for the help!

 

[roscoe]

Re: 89 Force WOT 4000RPM?

Re: 89 Force WOT 4000RPM?

Numbers should be stamped on the housing of the prop.<br />Usually on the outside, but possibly on the inside, against the lower unit.

 

[jippie98]

Re: 89 Force WOT 4000RPM?

Re: 89 Force WOT 4000RPM?

The only number found on the prop is 53323. Is this the right number?

 

[sangerwaker]

Re: 89 Force WOT 4000RPM?

Re: 89 Force WOT 4000RPM?

Also check where the motor is mounted vertically. The cavitation plate should be about even or slightly above the lowest point of the hull. Look at this relationship with the motor trimmed down fully. I had a Force as did my buddy on previous boats, and both had a 25" shaft. I was, shall we say, a little less informed then.<br /><br />Sorry Sir, I am not a prop guy, I'll leave the technical stuff to the large number of experts here. I do know you should be getting more than 4000 rpms. Is this with the motor trimmed up or down?

 

[jippie98]

Re: 89 Force WOT 4000RPM?

Re: 89 Force WOT 4000RPM?

I changed the plugs today and it seemed to run better but still only 4000rpm. What should be my next step to finding out the problem?

 

[JB]

Re: 89 Force WOT 4000RPM?

Re: 89 Force WOT 4000RPM?

I think you first need to confirm that the engine is making full rated hp, SC.<br /><br />Do a compression check and confirm that all cylinders are making power by pulling plug wires (very carefully) while at idle. Each removal should cause equal drops in rpm. A more accurate test is to have your dealer run it on a dynamometer.<br /><br />If compression is good and all cylinders are making power at idle you probably need a "shorter" prop. On an 18' CC with only 85HP I would start with a 15" pitch. If it reaches over 5500rpm go up an inch or two, if it still wont reach 5000rpm drop to a 13", etc.<br /><br />85HP is not much for that boat. My guess is that she is rated for 130 to 150HP and you are very likely over propped (too much pitch).<br /><br />Good luck.

 

[jippie98]

Re: 89 Force WOT 4000RPM?

Re: 89 Force WOT 4000RPM?

I will give it a shot......Thank you very much for the help!

 

[jippie98]

Re: 89 Force WOT 4000RPM?

Re: 89 Force WOT 4000RPM?

Just took the boat in to dealer. Prop info 131/2r 15 Is this a good size? Have not seen many props for this engine, any suggestions?

 

[rodbolt]

Re: 89 Force WOT 4000RPM?

Re: 89 Force WOT 4000RPM?

have the dealer dyno test it or run it with the test wheel. you must insure the motor is capeable of making the rated power before chasing ghosts.<br /> good luck and keep posting

 

[jippie98]

Re: 89 Force WOT 4000RPM?

Re: 89 Force WOT 4000RPM?

Had the comp tested 135 132 135.....Not 100% but still good right? Should my next step be a different prop? Will this make a difference in top speed or will it just rev more? Any advantages to have more revs for the engine? You guys have been great.....Thanks

 

[jippie98]

Re: 89 Force WOT 4000RPM?

Re: 89 Force WOT 4000RPM?

Any idea where I could get a 13 pitch prop for this motor? What kind of difference would it make? You guys have been great thanks.....