4.3l Low RPM

[SeanDavis42]

I purchased the boat with bad 1991 4.3L V-6 2 brl, alpha 1 gen 2 running 17 pitch prop., previous owner reported 30 - 35mph. Replaced motor with remanufactured 4.3L V-6 added edelbrock 4brl (1409 w/ v-6 kit), same outdrive and prop. New motor uses electric fuel pump, old had a mech.Test of boat showed max RPM -3200, adjusted timing and rpm reached 3700. Noticed 'steam' from valve cover breathers to flame arrestor and white slime in tubes. I've have read Don S. post on low rpm but I'm not sure where to start, I'm afraid changing the prop will get the rpm up but could mask another problem. Any advice would be great. Thanks.

 

[SeanDavis42]

Re: 4.3l Low RPM

I forgot to add that motor will rev to at least 4000rpm when in neutral but max with load is 3700rpm. Thanks

 

[joewithaboat]

Re: 4.3l Low RPM

hello
I have a 1996 4.3 merc, alpha 1 gen 2, factory 4barrel, 19p 3 blade ss prop
19 foot 2600 pound v hull it runs 48mph, gps confirmed, trimed up a little. tach says 4800rpm but never checked it against anything. Only owned it for this season and have never run any other props on it. Sorry

As to the white slime.... how much is there.
Sometimes when the weather and temp is just right... condensation burning off will steam and show some white foam up in the breather tubes. Pull the dip stick and oil cap and look for water here. You might need to pull a valve cover if you find any more water.
Like you stated i would make sure you dont have a water problem before messing with props. Where your exhaust manifolds in good shape?

 

[SeanDavis42]

Re: 4.3l Low RPM

hello
I have a 1996 4.3 merc, alpha 1 gen 2, factory 4barrel, 19p 3 blade ss prop
19 foot 2600 pound v hull it runs 48mph, gps confirmed, trimed up a little. tach says 4800rpm but never checked it against anything. Only owned it for this season and have never run any other props on it. Sorry

As to the white slime.... how much is there.
Sometimes when the weather and temp is just right... condensation burning off will steam and show some white foam up in the breather tubes. Pull the dip stick and oil cap and look for water here. You might need to pull a valve cover if you find any more water.
Like you stated i would make sure you dont have a water problem before messing with props. Where your exhaust manifolds in good shape?

We checked the oil at the dipstick and the oil fill and had no indication of water. The exhaust manifolds were suspect on the old motor so I replaced them with new units when the motor was replaced. Thanks.

 

[joewithaboat]

Re: 4.3l Low RPM

I have seen some posts here with brand new manifolds leaking, i believe they were GLM ??
Good luck.

 

[Bt Doctur]

Re: 4.3l Low RPM

Are you positive you have the correct drive gear ratio?

 

[SeanDavis42]

Re: 4.3l Low RPM

Are you positive you have the correct drive gear ratio?

I used the same drive that was on the boat, but I plan to check the drive ratio. I believe that the 1.62:1 is the correct ratio but i need to check mine out.