Thread: 350 SBC 6-71 Blower Carburetor Adjustments

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whats IPA?

Also, an alternative to a timing retard is a toggle on the ignition. You engage the starter and switch on the ignition after it's spinning.

India Pale Ale. It's for those who really REALLY likes the taste of hopps.

I personally don't care for a locked distributer on the street. But I think Jerry is recommending that to help keep you safe from detonation. Having a locked distributer makes the ignition timing a little more stable.

"......open idle mixture screws to 1 3/4 turns and adjust from there......"

Just to expand a little bit on what Jerry said.

The initial adjustment on the idle mixture is just that an initial setting.There is no set "turn them out so many turns and it is right". Carburetor, engine specifications, manifold design (both intake and exhaust), fuel, air pressure and humidity all have an effect on the engine idle.


You want the initial idle mixture rich enough to keep the engine running until it reaches operating temperature. General rule of thumb is to screw the adjusters in until they [I]lightly[I] seat and them back them out 1 1/2 to 2 turns (the amount you initially back them out usually depends on experience and preference).

Once the engine has reached operating temperature then you start adjusting the the mixture screws until you achieve the best idle. Some people us AFR meters or a vacuum gauge but most end up going by feel.

Start on one side or the other and adjust the mixture until you get the best idle then move to the other mixture screw. As I normally use 2 turns out as my initial setting it's generally a bit rich so I start by turning the mixture screw in until the engine starts to stumble just a bit and then back the screw out until it runs the smoothest, then move over to the other mixture screw and do the same thing. You might also have to reset the idle speed screw a bit as your adjust the mixture.

With dual carburetors I do one carb first then move to the other and them back to the first one etc etc until I'm happy with it.

Don't be concerned if the idle screws aren't set exactly the same once you're done. Manifold design and the different distances the fuel mixture has to go to get to the cylinders often requires just a little bit different settings.


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Originally Posted by firebird77clone

I'm not so much a fan of IPA, but it makes an interesting change of pace on occasion.

Hahaha! It took me a minute to understand what you were talking about,...my radiator overflow tank!

Originally Posted by jerry clayton

whats IPA?

He was referring to my radiator overflow tank. Took me a minute to figure it out too!

Originally Posted by Mike P

"......open idle mixture screws to 1 3/4 turns and adjust from there......"

Just to expand a little bit on what Jerry said.

The initial adjustment on the idle mixture is just that an initial setting.There is no set "turn them out so many turns and it is right". Carburetor, engine specifications, manifold design (both intake and exhaust), fuel, air pressure and humidity all have an effect on the engine idle.


You want the initial idle mixture rich enough to keep the engine running until it reaches operating temperature. General rule of thumb is to screw the adjusters in until they [I]lightly[I] seat and them back them out 1 1/2 to 2 turns (the amount you initially back them out usually depends on experience and preference).

Once the engine has reached operating temperature then you start adjusting the the mixture screws until you achieve the best idle. Some people us AFR meters or a vacuum gauge but most end up going by feel.

Start on one side or the other and adjust the mixture until you get the best idle then move to the other mixture screw. As I normally use 2 turns out as my initial setting it's generally a bit rich so I start by turning the mixture screw in until the engine starts to stumble just a bit and then back the screw out until it runs the smoothest, then move over to the other mixture screw and do the same thing. You might also have to reset the idle speed screw a bit as your adjust the mixture.

With dual carburetors I do one carb first then move to the other and them back to the first one etc etc until I'm happy with it.

Don't be concerned if the idle screws aren't set exactly the same once you're done. Manifold design and the different distances the fuel mixture has to go to get to the cylinders often requires just a little bit different settings.


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Thanks for the post. I currently have them set at 1 turn out, and the AFR is reading saturated rich. Since there are dual carburetors, maybe it's just too much fuel for idle on a 350?

I'm still interested to understand why there is a surging idle, and a stumble between idle and off idle. These were not there when i had the carburetors set at ~1/4 turn out on the idle mixture screws.

From doing some reading, it looks like blower surge is caused by too rich of an idle.

One possibility is that the floats are set just a bit too high and are dribbling fuel at idle.....could explain the surging and over rich condition.....something else to check anyway.



.

I thought it was dental floss!?!?! LOL.

Locking the timing can solve many issues. But it can create others.. there's ways around those too..
As said, you need to establish a baseline and control what's happening, through the entire curve / rpm range.
So when you say it's running like a pig, is this at idle? or cruising at 1800 - 2000?

Like I said - make a change, note it, and note the results.. that way you can explain to us what's happening and you can un-do those things that have bad results. Jerry has a lot of experience with supercharged motors, so lean heavily on him while you can.