Low RPM's on 86 force 125

[JDP]

I finally got my tach installed and got the boat on the water yesterday. The idle is good at around 750 but WOT all I get is 4000. My top speed was right at 30 with the speedo from the boat. Any ideas on what to do to get my rpm's higher. I currently have a 15 pitch prop, I was thinking about maybe trying a 17 or even 19. What do think?

 

[jkp1]

Re: Low RPM's on 86 force 125

Going from a 15" prop to a 17 or 19 will not help increase top end RPM.

If the current prop got to rated max RPM on that boat before, it should be able to do it again.

Carbs, compression. timing or ignition. Start with compression & timing check.

 

[JDP]

Re: Low RPM's on 86 force 125

I don't kow if the boat ever got to max RPM with this prop. When I bought the boat it wasn't running right. I rebuilt the carbs and had to replace one of the cd modules. The compression is ok in all 4 cylinders. (100 psi across all) I just checked the timing 2 weeks ago when I replaced the cd module. I have also checked the reed valves and replaced the diaphram in fuel pump. Gas has been emptied and plugs replaced. I'm running out of ideas here.

 

[roscoe]

Re: Low RPM's on 86 force 125

A 17 or 19 pitch prop will kill your performance and the engine.
You should try a 12p if you want to raise the rpm.

 

[QuadManiac]

Re: Low RPM's on 86 force 125

What boat and size of boat is this on? Not reaching RPM's with a 15" pitch makes me believe that it's either a large boat or you have engine problems.

 

[JDP]

Re: Low RPM's on 86 force 125

It's a 86 Bayliner 19' cuddy cabin. Let me ask you this. Is it bad for the engine to not reach max rpm's when at WOT? The boat runs good except for not reaching max rpm. To be honest I don't have any complaints about the way the boat runs. I only use it to mess around on with the family and sometimes friends. The wife and I are already talking about selling this one and getting something different

 

[Frank Acampora]

Re: Low RPM's on 86 force 125

I would expect more RPM on a 19 footer --even the heavier cuddy--unless of course, you are carrying a lot of weight or people. If you continue to run below recommended RPM, eventually the rings will carbon up, stick, and you will lose compression. BTW: 100 psi is low--should be up around 140-145. Might just be your gauge or might really be low. Try a little Sea-foam decarb and see if compression and speed come up. Check other threads here to learn about Sea-foam treatment.

 

[jnk111]

Re: Low RPM's on 86 force 125

JDP, did you happen to buy the Sporqster tach? I bought that one myself and am starting to think that it may not be accurate. I have a 1988 17' bayliner cuddy with a 85hp, 17 pitch prop and also only see about 4200rpms at 33-34mph on the speedo (it seems to be pretty accurate, I made a river run and timed distance over 10 miles). I noticed on the tach that my manufacture date was in 1995. I have done the same things, fuel pump, carbs, plugs, timing verified that the butterflies are fully open on WOT. I seem to be in the speed range I should be from what I have been told. So I am wondering about the tach at this point. Do you have access to a different pitch prop? You could change the prop and check speed and rpms to see if either changes. ( Typing this I just realized that I have a 19 pitch as a spare, next time I am out I may swap props and see what happens to the rpms on the tach.)

 

[JDP]

Re: Low RPM's on 86 force 125

Yeah I have the sporqster tach. I was wondering about the accuaracy of it as well. I know the book says idle should be around 750 rpm. If I try to set it at that rpm the idle adjustment screw doesn't hit the side of the motor like it should. I have set the idle pretty much by ear and the tach reads around 1500 rpm. That is with the idle screw just barely pushing the tower rod out. I did recheck the timing again last night when it was easier to see the marks. It was off a bit. So I reset it and I'm going to take it out here in a little while.
One quick question for those of you with the 125. Is the locking nut on the timing adjustment screw in between the 2 pieces that move apart when adjusting? The book shows it this way but on mine the nut is on the outside of the peices. Just wondering if this could be causing my timing to go out. I know when I reset the timing a couple of weeks ago it was right on. Also when you set the timing do you follow the STATIC timing procedure or the DYNAMIC timing procedure or both? I don't have the test wheel that they refer to for the Dynamic timing procedure.

BTW Frank, I did the decarb that you mentioned. (What a smoky messy produre.) My one neighbor is a fireman and came out thinking I caught the motor on fire. I also borrowed a different compression tester from my other neighbor. (I got mine from Harbor Freight) After the decarb and on his tester the comppression is now reading about 135 an all cylinders.

 

[JDP]

Re: Low RPM's on 86 force 125

Well it seems that after the decarb and readjusting the timing my problems are gone. She's running WOT right at 5000 rpm with a top speed of 38-39 mph. (going off what the dash mount speedo says) It has also fixed my planing issues as well. I am getting on plane really quick now. Oh and I found out what a hole shot is. I don't think I would have any problems getting a skiier up now. Thanks to everyone that helped me out with this. This board is great.