Is there a RPM limiter in my Merc 135V6?

[Chris1956]

My Seloc manual doesn't seem to know. Does the Idle stabilizer also limit RPM? Do the switchboxes limit RPM?

My speedboat runs right up to 6100RPM or so, with lots of pep. I was wondering whether something was limiting the RPM.

 

[Dukedog]

Re: Is there a RPM limiter in my Merc 135V6?

My stuff calls it an idle stablizer. Says nothin' 'bout advance 'cept at idle. Take it off, stick a LITTLE prop on it and TEST IT. wooh whoo

Last 135/150 2.0 I ran would turn 2 ta 1's and 22 inline chopper well over 7 (jacked up xr6 gearcase)

 

[j_martin]

Re: Is there a RPM limiter in my Merc 135V6?

If it's the same one that's on the XR4, it advances the timing at 5000 rpm, then retards it at 5500 rpm.

If you pull it off, set the WOT timing at 23 degrees. The porting and reeds on that engine pretty well limit the torque band to a little over 6000 rpm. You can spin it higher, but you won't get any more power. The VRO oiler is more prone to failure over 6500 rpm.

I run my XR4, with 1.78 gearing into a 24 pitch high five up to about 6100, 61-62 mph. I run the prop right at the surface on an 18' Tracker bass boat.

 

[sschefer]

Re: Is there a RPM limiter in my Merc 135V6?

If it's the same one that's on the XR4, it advances the timing at 5000 rpm, then retards it at 5500 rpm.

If you pull it off, set the WOT timing at 23 degrees. The porting and reeds on that engine pretty well limit the torque band to a little over 6000 rpm. You can spin it higher, but you won't get any more power. The VRO oiler is more prone to failure over 6500 rpm.

I run my XR4, with 1.78 gearing into a 24 pitch high five up to about 6100, 61-62 mph. I run the prop right at the surface on an 18' Tracker bass boat.

Works just like John say's. There's a wire going down to one of the switch boxes that senses when the idle rpm (it's just a tach) is low and it advances the timing to bring it back up. Once it's stabilized it returns the inital timing to normal. When the engine reaches 5000 RPM it kicks the timing up to 21 degrees and at 5500 it brings it back to 19.

25 is about all the useful advance these motors can handle but due to some minor inconsistencies in the crank grinds and crank case volumes and pressures, the max recommended after removing the advancemodule is 23.

At about 6100 rpm the power curve has all but run out so going from 5800 to 6100 will get you a few more RPM but it usually fluctuates because the engine doesn't have the hp to hold it.

Reducing pitch to get more RPM has much the same effect as increasing pitch to get more MPH if you're stressing the engine. The common result is that your boat becomes a floating island and your best friend is U.S. Boats Towing service.

 

[Dukedog]

Re: Is there a RPM limiter in my Merc 135V6?

Reducing pitch to get more RPM has much the same effect as increasing pitch to get more MPH if you're stressing the engine. The common result is that your boat becomes a floating island and your best friend is U.S. Boats Towing service.

This is only true when if you're tryin' ta string one out. It has all ta do with quick instead of top end. Your puttin' a lot more stress on one tryin' ta turn a big prop. I had lot rather have one turnin' a 24 6500 as opposed ta one turnin' a 28 5500. But thats just me. Don't be scared ta experiment with 'em. There's no fun in being scared. I've been expermintin' with tha V6 since '76 and only popped three motors due to my stupidity and/or tryin' somethin' diffferent...................JMO

Don't know where ya'll are gettin' you're info. All my stuff (up to '94) only shows tha IDLE timing part on tha 2.0 motor. Doesn't say anything 'bout max timing. But who knows. Its Merc/Mariner and old like me...............D

 

[j_martin]

Re: Is there a RPM limiter in my Merc 135V6?

My data's out of the manufacturer's maintenance manual for my engine. Initial timing is 19 degrees. Advance is 23, setback is 17. (advances 4, then retards 6) Idle advances 4 degrees below 600 rpm.

I run mine at 23 degrees, and 91 octane no alcohol fuel.

You can run the engine up to 6500 with impunity with the oiler, much higher without it. It would much rather rev than lug, being an oversquare engine with about a 2 million BTUH fire in it. Stock porting, reeds, and carbs runs best right around 6 grand, and falls off rapidly after that.

 

[Chris1956]

Re: Is there a RPM limiter in my Merc 135V6?

Thanks for the info. I am running a 16 footer with a 21" Rapture Prop, and she will run 61MPH at 6100 RPM (4% slip according to the prop calculator).

That is fast enough for me, so it was just a question on whether the RPMs were "held back" by some device.