Bog @ 3400 rpm

[gtfireftr]

So I was comfortable enough to get her up on plane today after my 4 hr breakin.
New 4.3's with new 1409 Edelbrocks.
I used Ricks final setup from his thread regarding jets, and springs.
Port motor seems to rev up with little issue. Stbd engine had a flat spot around 3400, maybe wven lower. Once the bow comes over it seems to catch up.
Any thoughts??

TIA

 

[alldodge]

Are they both new motors, or only one?

 

[gtfireftr]

Both new.... Both identical set-up.....new everything....

 

[alldodge]

Both new.... Both identical set-up.....new everything....

In that case I would first think the adjustment in the carb or linkage for the starboard motor is a bit different. Here is the troubleshooting guide
http://www.edelbrock.com/advertising/Literature/Posters/EDL_Carb_Warranty_Poster_0309.pdf

 

[gtfireftr]

Thanks.... I think I have mixture issue... Not sure if lean or rich.... I think I will pull the plugs and take a look see.....
Linkages are perfect..... both max out at the same time....

 

[alldodge]

Agree its probably not getting the right amount of fuel, but above 2000 rpm's it won't be the mixture screws. My first thought is a bit to much fuel

 

[gtfireftr]

Agree its probably not getting the right amount of fuel, but above 2000 rpm's it won't be the mixture screws. My first thought is a bit to much fuel

Any advice as to how to proceed?

 

[alldodge]

Any advice as to how to proceed?

It won't be the first time the carb straight out of the box was not adjusted correctly. With everything being new it shouldn't be something like fuel pressure, I would look at float level, needle and seat, and accelerator pump setting. Also check for vacuum leak. Put a vacuum gauge on the motor

 

[gtfireftr]

Ok... will do....
Where should I put the vacuum gauge??

 

[alldodge]

Ok... will do....
Where should I put the vacuum gauge??

You got me there, probably don't have the ability to do it being a 3.0, the intake doesn't have any ports

 

[GA_Boater]

GT said a pair of 4.3's. Any ports on a V6? I have no idea.

I would be tempted to swap carbs between the pair.

 

[alldodge]

GT said a pair of 4.3's. Any ports on a V6? .

Woops, to many threads, I don't see any on the 4.3 either. Did look back with previous post to note the original motors were original 98 models. So unless you change manifolds with ones that have a plug on the intake runner side, guess were out of luck

 

[gtfireftr]

No ports that I can see...
I may swap carbs....

 

[gtfireftr]

What controls mixture above 2000 rpm?

 

[alldodge]

What controls mixture above 2000 rpm?

The main carb jets and valves. As the carb opens the air passing causes fuel to be drawn out of the bowl. As the throttle opens the needle valves are lifted out of the main metering jets.

 

[Rick Stephens]

I agree with the baseline check, make sure the float level is right and that everything is tight. The Edelbrock carb is build such that vacuum leaks internally are not usually an issue. I would worry less about that than with a Roc.

First quick fix is stronger springs on the needles. The needles are pulled down by higher vacuum against the springs. As a motor speeds up to match a given throttle setting, the vacuum raises up and the needles settle back down against the springs. A set of stronger springs keep the needles up longer and sooner (Viagra for your motor :^). Up in that throttle range, halfway open or so, you are running on main jets. So if stronger needle springs doesn't get it then either a larger main jet or smaller diameter/shorter needles are used to richen up the mix.

 

[gtfireftr]

Is it normal that one motor would act differently than the other..? There is definitely a difference between the two....
Are you thinking that I am lean, or rich?

 

[Rick Stephens]

I would add that if the stronger springs don't get it solved, then the diagnosis would look at what part of the throttle is too lean and where the bogging happens. If the bogging is on acceleration, but once spun up the motor runs good at 3400 RPM, you know the mains are about the right size. Only perfect way to check that is run at 3400 RPM for a bit then turn off the motor and pull a spark plug, see if it is running rich or lean.

If the problem is that at a certain throttle setting the motor bogs and falls flat, and even pumping the throttle a little to get it running still leaves a flat spot, then we probably have to get larger mains or smaller needles.

 

[gtfireftr]

So you are thinking that my flat spot is a lean condition?

 

[Rick Stephens]

So you are thinking that my flat spot is a lean condition?

First guess is lean. Usually rich won't bog out. But you need to describe it a little more completely. And test it using the throttle, like a car with a carburetor, if you pump the throttle you get get more fuel from the accelerator pump. If you do that with the boat and it revs up, then you know you are running lean. Only really accurate method to be certain is run it at 3200 or 3400, shutdown quickly and pull a plug.