Max Rpm

[danny9696]

Can anyone tell me what the idle rpm and the max rpm should be on an 89 force 125 ob? just bout this boat and I took her out today but could only get about 4000rpm out of her trimed out, and about 30mph

Thank you

Danny

 

[pnwboat]

Re: Max Rpm

Idle RPM should be approx. 800 - 900 RPM. Max. RPM is 5500. 4000 RPM is low.

Could be over propped. Do you know what pitch prop you have? There should be some numbers stamped somewhere on the prop itself.

Also what model boat and what size is it?

 

[roscoe]

Re: Max Rpm

Yep, 4000 is too low.
Could be too much boat, too much prop, or not firing on all cylinders

 

[danny9696]

Re: Max Rpm

Thank you for your input, the boat is a 19' bayliner capri modle 1901 ski boat, the boat was ran at 2500' I just bought it and we are running it at 6000' could the elevation chage causing it to be to rich also be a contributing factor, it has a 19 pitch prop on it and I have a 15 that came with the boat as a backup.

Thank you all again

Danny

 

[jerryjerry05]

Re: Max Rpm

Do a compression test and get back with the results.J

 

[roscoe]

Re: Max Rpm

Carbs will have to be rejetted to run at 6000'

That will make it run better, but it will still be down on power compared to 1000' elevation.

You will likely still need to use the 15p prop.

 

[danny9696]

Re: Max Rpm

I have not done a compression check but I will get one done this week and post the results, I did put the 15 pitch prop on and ran the boat and got 4300 rpm, But I was changing plug wires and noticed the #1 plug wire was loose coming out of the coil, way loose! I threaded it back in but have not ran the boat yet, I don?t know if what I did is even something I should have done or If I messed it up more, but the #1 plug was way clean and oil washed compared to the others. My new jets will be in on 5-26-09 and I will be out the following weekend to try her out, I am way concerned about the plug wire I hope I did not brake the core!

 

[john from md]

Re: Max Rpm

If the #1 plug is clean it can be a variety of things. No spark, lean mixture or a head gasket leak. Even if the spark plug wire was loose, it will still fire. You should check for spark while motoring on the starter with the plugs out. Make sure you ground the plugs when testing or you will ruin the CDI unit.

John

 

[pnwboat]

Re: Max Rpm

I'm assuming you have the Prestolite ignition system with the Blue coils and CD units. The core on the coil wires is solid wire. Pretty hard to break. The wires are molded into the coil. Can't replace them. From your description of #1 plug, sounds that cylinder is not firing properly. This will affect max. RPM.

I'll bet that someone has been trouble-shooting number one cylinder in the past and probably tried to pull the spark plug wire out of the coil thinking it was replaceable, thus the loose wire.

 

[MikDee]

Re: Max Rpm

Danny, if you're compression were real good, and you had no other motor issues, a 19" pitch prop would work for that boat, but if your compression is a bit low, a 17", or 15", pitch prop is needed. Make sure your engines firing good on all four first Wait,I just noticed you're running at 6000ft elev. forget it I doubt the 19" prop will work for you, probably a 17", or 15", once you get rejetted.

 

[danny9696]

Re: Max Rpm

Hi all I am sorry it has taken me so long to get back with you all, I did the compression test and all cylinders were within 4psi with the highest being 115 and the lowest being 111, all cylinders have good spark, I put the 15 pitch prop on and new plugs but I have not been out to the lake to try it yet oh ya and I jetted it all so, the OEM jets were 101 in the top and 94 in the bottom, I put 94 in the top and 88 in the bottom to try to keep the spread between the two. Does this help anyone with any idea Y my rpms are so low? because I just don't understand it myself.

Thank you all again

Danny

 

[danny9696]

Re: Max Rpm

Hi all I finally got to take the boat out, I have the .092 jet in the top and the .088 jet in the lower, propped down from a 17 to a 15, and new plugs in. boat started right up and started out great, but then it fell on its face and started loading up and bogging down, also I used a 1/4 tank of fuel in about thirty min. I think I have a fuel pump that may have been causing some of this problem, or could it?

 

[john from md]

Re: Max Rpm

Your compression is very low. I suggest that you decarb the engine real good.

I also suggest that you verify that your trigger, CDI and coils are all wired properly. You may only be firing on two cylinders.

As to the fuel pump, it wont cause you to use more fuel than you normally would. That may be a symptom of only firing on two cylinders. However, if it hasn't been changed in a while, I would replace the diaphram anyway.

John