Inliners International Forums General Discussion Hi Performance 3x1...needing some help

Hello, been a little while since i posted here last, but looking for a little help.
Here's the run down... 54 with a 235, powerslide car, not running a 700R4, i've been plaged with problems with my 2x1 setup and pulled if and got my offy 3x1 on. Built a progressive linkage setup, and running the stock rochester B's...i beleive actually the BC's because of the chokes, the stock carbs for the car. with all 3 carbs on it's misfireing, took 2 carbs off and it runs very good, also found a bad accelorater pump on one carb. Is there anything that needs to be done to the outter carbs to make them more of dumpers? I set them up so the idle adj screws were backed out and richened up the center, same problem. Just looking for some advice or suggestions on getting it back on the road.

Thanks

I have gone through this before. PLease search though previous posts.

Check out the tech tips to the left, worked for me. Armond

Thanks for the help. I found the post on page 4 and read it. I see i'm pulling out the power valve, but is there an easy way to plug/remove the idle circuit? I'm familular with Holley 4bbls, but these are kinda new to me

Thanks

maybe i should restate what i'm asking, after looking at it again...
If i unscrew the idle speed screw out, and bottom out the throttle blade, is that good enough? If i just tighten the idle mixture screw in will that seal enough? Other than the mixture screw is there anything else that is related to the idle circuit? With all that done, is there anything else I will need to do to the carb to make it a dumper?

Jeff

First, if you look at any 51-62 factory shop manual it will have a detailed explanation with cutaway drawings as to how the model B carb works. Study it...

Second, if you bottom out the idle screw, you will still have the secondary idle holes located just above the throttle plate that would still be active because you have not plugged the fuel source. It may not be a problem to do this. I would give it a try. You can always go back and plug the passageway later. I'm starting to wonder if it might actually help with minimizing the flat spot you will get when engaging these end carbs... Hmmmm....

Third, the throttle plate has to seal when fully closed or it will surge and idle like crap because there is no longer any idle circuit to add fuel to that air. A vary small amount of air getting past will still work ok, I guess you will know if its good enough or not if you can still affect a change by adjusting the idle mixture on the center carb...

Fourth, remove the power valve. Don't forget to remove the spring loaded ball that the power valve pushes on, or you won't be able to get any fuel past the jet...

Fifth, plug the vac source at the bottom of the carb that activates the power valve.

If you try to engage these modified carbs too soon, you will bog and shudder. I suspect that adding a weighted choke plate similar to the secondaries of a 4bbl Roch. or AFB may help to eliminate this, but I have not had the time to test this theory...

Thanks for the input, something to play with tomorrow. BTW, since you seem very knowledgable please keep checking this, i may need some more input.

Jeff

Got it working, thanks for your help!

Great!

I could use some help...

I am running Rochester M/MV on my 3x1, Chevy 250. Any input on adapting the carbs to work correctly? I am having some backfiring when in gear but off the throttle.
I rebuilt the carbs but the upper seal is soaked in gas on all three. Am I pushing too much gas into the carbs. I have a small electric fuel pump.

Does adding extra carbs affect the timing?

And should there be vacuum at the distributor connection on the carb during idle and acceleration, or just when you let off the accelerator?

It looks good under the hood, I just want to run that good.

I've never used the M/MV, but the same principles apply to whatever carbs you are using.

Backfires on deceleration are usually caused by a vaccuum leak or a lean out condition...

I can't see whats leaking, so all I can say is that the pressure only needs to be between 3-5 psi for it to work. A shop manual would have the specs for that...

Your base timing shouldn't need to change, but if you change the camshaft, you may want to experiment some. Recurving the dizzy may be needed to maximize performance...

Any time you open the throttle, you will loose vac signal, which in turn cuts back the total timing (when using a vac advance) which is how the engine adapts to a "load" condition (reduces detonation). Whether or not the vac advance sees vac at idle depends on if you have it hooked up to a ported or manifold vac source. You could try both and see which works better for your situaton, assuming the carb has both options on it...

The dizzy should be hooked up to the ported source and now that have the timing set correctly, some of the problem has gone. But, I found my number 5 plug was black while all the others were in the tan/white color range. Number 6 was darker, but within the color range of running within specs. I will be replacing the plugs, rotor, cap, and points this week to make sure everything is up to spec and hopefully solve the next problem

Next problem. My Tach will bounce around when I am holding the engine speed over 2500 with out a load and it matches the backfire(s) just about everytime. When attempting to acclerate, the truck will bog down, the tach will bounce around, and then will accelerate. I don't notice a change in engine speed during the bouncing. The bounce is between 500 and 1000 "rpm".
I am thinking my coil is going out. Any body else have any suggestions?