1991 Rude hitting rev limiter

[racefan2]

I have been making changes to my setup. I have a 20HP rude with a 28HP carb and TNT on a 16' boat and run a 13 pitch prop. I hit 5000 RPM by myself in boat and 4400 with a 180lb passanger. I switched to a michigan marine 11 pitch and I am now slaming the rev limiter at 5200 rpm at 3/4 throtle and no trim on motor and hitting the rev limiter at 5200 rpm with the same 180lb pasanger at 95% throtle and very little trim minute at most.<br /><br /> Shouldn't this motor have a 5500 rpm limiter on it from the factory? Would I be better going up to 12" pitch or the 13 and live with it or could I change the rev limiter to a 5500 rpm unit.<br /><br />It would run only 21mph spedo with myself or 2 people . It was at 27 mph with the 13 and 1 person but started porposing with a weight balance. I am looking to go stainless in the very near future with a turbo hot shot or a powertech so I want to be right on with the size.

 

[G DANE]

Re: 1991 Rude hitting rev limiter

As I remember it, your motor doesnt have a rev limiter, but I dont know all the 1991 features. If it has, its set at 6000 and not 5200. The sweet spot for the 35's,( same block ) I worked on mostly is just aroung 5750 RPM. But I think the exhaust tune pipe from the 20 will limit it from getting there. It will perform like a 25 - 28 HP now, especially if you changed the intake manifold, if this wasnt upgraded to the larger type thru the years, I dont know. My 35 did 28 MPH on a 16' footer, like yours, maybe a tad lighter.

 

[Silvertip]

Re: 1991 Rude hitting rev limiter

Have you verified the accuracy of the tachometer? IF that engine has a rev limiter, as mentioned earlier it would not be set at 5200 but rather closer to 6000. If the engine is sputtering at 5200 RPM you have an engine problem.

 

[racefan2]

Re: 1991 Rude hitting rev limiter

It should have a 5500 rev limiter and I wonder if the OMC tach is correct. It hits 5300 and sounds like it is dropping a cylinder or only firing on 1 cylinder for the time it is at 5300 rpm and the second it drops to 5200 it runs smooth.

 

[G DANE]

Re: 1991 Rude hitting rev limiter

Forgot to add: It will not overrev doing 27 MPH with a 13". The gear ration is 13:28 teeth. 6000 Rpm *13/28 * 13 ( Pitch = travel forward pr turn ) * 60 ( min/hr ) / 62990 ( Inches/mile )Which gives a possibility of 34 miles in theory, but with lets say 10 % slip, you still get 31 mph theoretically. By this formula 27 MPH with 10 % slip would be around ( 6000/31*27) 5200 RPM.

 

[racefan2]

Re: 1991 Rude hitting rev limiter

I was changing the plugs and found the top plug loose. It was not tight as I took it out with my fingers as it turned trying to remove the boot. These were my winter plugs for fogging and I must have not tightened it after fogging. I will run it again and let you all know.

 

[racefan2]

Re: 1991 Rude hitting rev limiter

I just run it again after changing the plugs and tightening them and it is still the same it seems to start missing or cutting out at 5200rpm @ 21 mph with the 11 pitch prop. I put the 13 pitch back on and it run fine at 5000 @ 26 mph. I will have to check the tach but the motor was idleing at 600rpm so if the tach is wrong them the motor is idleing at 900rpm which is a bit faster that the motor is running I beleive. Could it be something in the powerpacks? I hit the 5200rpm in a turn with it trimmed with the 13 pitch and it did do the same thing it missed a bit till the RPM dropped a tad and then it was fine.