Wot RPM

[boat4fishin]

ok, all fuel filters changed (1). no kinks in lines, clear pick up tube. still only getting 2200 WOT RPM with 17 Pitch, sure a little small for my 1984 mercruiser 140, 19 pitch on the way. looking at compression test numbers this week, i notice some blow by, but it ran at 4500 WOT RPM 3 times, also hit 32-35 MPH 3 different times. could all this be just weak spart? distributor counter weights not advancing the spark as they should.

 

[jtmarten]

Re: Wot prm

Re: Wot prm

distributor counter weights not advancing the spark as they should.

There's your answer. No advance = no rpms.

A 19p is going to yield about 300rpms less than your 17p. If you ran 4500rpm with nthe 17p, it sounds like the right prop. With the 19p you'll only run 4200 and take longer to plane.

 

[boat4fishin]

Re: Wot RPM

thats when it did run good. the last time was a week ago right off the trailer it hit 4900-5000 RPM. i turned it off got some fishin gear, backed away from the dock, went to go foward and it just stopes at 2200 RPM now, RPM comes up and just levels off. i tried evey posioton you can on the trim adjustment, it wont change and its just me and 1/2 a tank of fuel.

 

[jtmarten]

Re: Wot RPM

If you were hitting 4900-5000, the 19p would be a better choice.

Sounds like something broke or quit working. All you can do is systematically check the things that could cause a drop in rpm. Most likely ignition or fuel system.

 

[boat4fishin]

Re: Wot RPM

distributor counter weights still work the same as car, right. its just mechanical advance, weights not swinning out enough to advance more timing for more revs, there is no knocking and pinging, or weak fuel pump. pump half the fuel go half as fast.

 

[jtmarten]

Re: Wot RPM

Usually if you pump half the fuel, it'll go fast until the usage overtakes the bowl(s), then she'll bog down, let her idle a bit and refill the bowls and she's good for a short burst again.
You'll need to get a light and check the advance at idle and 3500-4000rpm.

 

[boat4fishin]

Re: Wot RPM

the motor to out drive coupler is not slipping, and the prop is not slipping on the lower unit, so my lack of WOT RPM is not caused by the failure of those two parts. i will see what timing is with muffs and what timeing is at WOT under load on the river which lately has been around 2200 RPM with 17 pitch prop.

 

[full stringer]

Re: Wot RPM

put a timing light on the indicater mark rev the motor and see if the mark advances