WOT RPM problem

[diver_down]

I got a 19 ft aluminum starcraft Islander 191 with a Johnson 140 (V6). The engine does not rev up all the way, at WOT I get 4000 - 4200 rpm. The boat is going about 32mph according to the rudimentary speed gauge.
I checked the carbs, they are clean, the plates open fully, there's nothing dragging off the boat, ...
The motor starts right up every time and purrs like a kitten.
Any sugestions would be appreciated.
Thank you,
Nick.

 

[Daviet]

Re: WOT RPM problem

Is this boat new to you, has the problem always been there or did it just start? Maybe a prop problem.

 

[diver_down]

Re: WOT RPM problem

Is this boat new to you, has the problem always been there or did it just start? Maybe a prop problem.

the boat is new to me.first time on the water this year.
I will try and get all the data off the prop and post in the prop forum as well.

 

[Chiliando]

Re: WOT RPM problem

Could have a fuel restriction. Use the search function on this site and you will find a great trouble-shooting procedure list.

 

[diver_down]

Re: WOT RPM problem

i tried searching for WOT or RPM but the search came up with NOTHING. If somebody remembers at least in which forum it was i'll start looking through posts.
Thank you!

 

[jonesg]

Re: WOT RPM problem

I got a 19 ft aluminum starcraft Islander 191 with a Johnson 140 (V6). The engine does not rev up all the way, at WOT I get 4000 - 4200 rpm. The boat is going about 32mph according to the rudimentary speed gauge.
I checked the carbs, they are clean, the plates open fully, there's nothing dragging off the boat, ...
The motor starts right up every time and purrs like a kitten.
Any sugestions would be appreciated.
Thank you,
Nick.

New to you, heres what I did,

get the manual first.
www.outboardbooks.com

Now, baseline the engine by the book, go through EVERYTHING, from the battery posts to the sparkplugs, fuel system , I would replumb the whole lot.
Compression test it before buying any parts.
Spark GAP test the ignition.
Change out lower gear oil, new seals on drain screws.
Remove prop, clean shaft check for fishing line, regrease and reinstall prop.
Change fuel filter on engine.
Rebuild carbs with new kits by the book.
Install water seperator.
Clean tank.
Water pump(change it) and check engine temps.
All the above is very simple, do it all in a day.
Thats what I did.

Then see what you get for rpm.

 

[cr2k]

Re: WOT RPM problem

If not over proped you would also need to check max timing. A lot of peeps mess with things under the cover that they have no idea what they do.

A lot of adjustments on OBs are inter connected or related to other stuff.
WOT may not be synced for max timing.

But for Max Timing you need a dyno, or be able to hang on on the water.

WOT should be around 5000.

Also check your re-circ hoses.

 

[diver_down]

Re: WOT RPM problem

already did ALL the maintenance, carbs, plugs, impeller, thermostat, lower unit oil, plumbing, fuel filter, vro sending unit, etc.
I can hang on on the water, the question is how do i adjust the timing (i even have the timing light). I beleive it might be the prop or the fact that the compression on the low end - about 80 in each hole on a cold engine, differences of 3-4 psi in between cylinders. The prop itself is quite banged up but i would hate to buy a new one and realize that i'm over or under propped.
Does anybody know what the gear ratio is on a 1985 J150TLCOS? (jonson 140, V6) I think that might help me determine if I am over propped.
Also, the boat is a Starcraft Islander 191, 1985, 1300 pounds dry weight, the engine is another 380 dry. I would assume the total weight would be around 2500 (gas, oil, kicker, gear), maximum 3000 pounds. The engine has a hydrofoil on it, no trim tabs.

If not over proped you would also need to check max timing. A lot of peeps mess with things under the cover that they have no idea what they do.

A lot of adjustments on OBs are inter connected or related to other stuff.
WOT may not be synced for max timing.

But for Max Timing you need a dyno, or be able to hang on on the water.

WOT should be around 5000.

Also check your re-circ hoses.

 

[jonesg]

Re: WOT RPM problem

Without the service manual you're guessing.

 

[iwombat]

Re: WOT RPM problem

agreed ^^^

Once you get the manual you can adjust WOT timing using the Joe Reeves method: http://forums.iboats.com/showthread.php?t=228183

Before doing that, you should really baseline the motor with a compression test (already done) and a spark check (didn't see it). 80psi is a little on the low side, but the crossflow V6's were lower in compression anyway. Since you didn't post your year or model # anywhere I don't know if that's what you have. (hint: please post year and model #)


You should be shooting for a prop that gives you 5800 RPM at WOT once you determine the motor is operating as it should.

 

[nymack66]

Re: WOT RPM problem

Are you sure its a 140 V6 ?

 

[diver_down]

Re: WOT RPM problem

Are you sure its a 140 V6 ?

The engine is a J150TLCOS, 1985, 150 HP, V6. I checked the spark, all the cylinders have spark, spark plugs look normal (at least for now).
If my memory is correct there's a place on it somewhere saying something about 28 degrees BTDC, I will have to souble check on that.
Is 5800 the target for WOT for this particular engine?

 

[nymack66]

Re: WOT RPM problem

The engine is a J150TLCOS, 1985, 150 HP, V6. I checked the spark, all the cylinders have spark, spark plugs look normal (at least for now).
If my memory is correct there's a place on it somewhere saying something about 28 degrees BTDC, I will have to souble check on that.
Is 5800 the target for WOT for this particular engine?

Ok because you posted 140 v6
The RPM target is contingent on a number of factors weight,prop etc.
Your Goal should be able to attain at lease 5500 to 6000 (Boat empty on smooth lake) this will allow you to cruse around with load at 5000 ..Some my say push for more RPMS its your call you need to post Boat weight and prop size . Prop matters ever increase in pitch size drops you 200 rpms at WOT
As for the BTDC you mentioned check for a sticker on top of the air silencer recommend settings will be 4 degrees less than posted for example if 28 degrees BTDC is posted you set the timing at 24 degrees See Joe posting on setting it best info out there ..

 

[James R]

Re: WOT RPM problem

Do you have the correct plugs and when were they last changed?

 

[iwombat]

Re: WOT RPM problem

As for the BTDC you mentioned check for a sticker on top of the air silencer recommend settings will be 4 degrees less than posted for example if 28 degrees BTDC is posted you set the timing at 24 degrees See Joe posting on setting it best info out there ..

Personally, I never trust the stickers. Silencers fit a whole slew of motors and get interchanged far too often.