NHGuy

So, I am getting to the fine adjustments on my carburetor which is a Quickfuel Marine 750. It has mechanical secondaries and is a double pumper with front and rear fuel bowls, blocks etc.
I have the AFRs nice to around the top of the primary side at 12 to 13:1 then it goes lean when I crack it farther open. I am seeing high 14's which makes me back off.
Ideally I want 12.7 or 13:1. My boat isn't as heavy as some of you big multi engine guys and has no boost.
Think I ought to go up 2 jets on the secondary side?
I day dunk and have a 90 minute ride to the lake, So I want to try to minimize the changes and try to hit it close on this step.

TIA

ThisIsLivin

2 jet sizes might still be a little lean. I went 2 on mine and didn't seem to make that big of a step.

GLENAMY 242SS

iTrader: (1)

You also need to put a vacuum gauge temporarily to the dash. Mark on the throttle where JUST before secondary position is. If the afr's rise when just before the secondary's you may need a higher value power valve (vacuum gauge will tell you what you need). If the higher afr extends into the secondary's look at changing the jets (secondary).

SB

iTrader: (1)

Since you are boating today, (ie: not much time to do things) I’d put in 4-6 #’s higher in secondaries. See what happens.

Missed you by a week I guess. Was at Alton Sandbar mon and tues late afternoon last week few hrs each day. Went to Pop’s Mon eve. Yum.

NHGuy

i will be up Weds & Thurs in Moultonboro. But will be all over!

Baja Rooster

iTrader: (1)

I agree to jump up ~6 sizes and work your way back. 2 sizes can sometimes not even be relevant. The last time I was tuning a Quickfuel I believe I went up ten sizes at 2 at a time. Took forever day dunking.

SB

iTrader: (1)

If you are in need of parts you didn’t bring, I live in moultonboro.

NHGuy

Oops glenamy, I forgot to say it has mechanical secondaries.

GLENAMY 242SS

iTrader: (1)

That was in your original post. The need for the vacuum gauge is to monitor the power valve circuit. It is an internal fuel metering component that is vacuum operated. The number on the side of it tells you at what level it dumps additional fuel into the equation. I have seen some cases where the afr's go way lean JUST prior to the secondary opening, if that is your symptom you may need to adjust this circuit and only the vacuum gauge will tell you what the new power valve number needs to be.

NHGuy

The power valve has been properly set up and installed. And rechecked multiple times while verifying vacuum on a compound gauge..

This week the AFR was going and staying lean. Might not have said that very well.

I will do the simple jetting for now, but thanks for your input.

If I find out otherwise, appropriate amount of crow will be consumed!