[hvy barrel]

I have a 350 SBC with a set up a 650 BG mighty demon carb.
I had the carb tuned in pretty close over the summer, a little on the lean side.
I drove it last weekend & it was so rich you couldn't ride behind the car.
The only thing that I can think of that could have changed would be the switch to the "winter blend" fuel.
any suggestions?

 

[eric32]

From what little bit I can maybe help you with is maybe if its running a little rich like that and what you could do is re do your idle mixture screws just a hair if its rich at idle but for crusing I would maybe go down two jet sizes on the main jets and that should put you in the ballpark of what your looking for. I had my carb set up really good on my other motor and from reading my holley book it might just need a little tweek too the idle mixture and the main jets and secondary's should not have to be touched. Hope that might help I am not a carb genius like Fbird and others on here but am learning.
Eric

 

[smartparts312]

Just my thoughts but I wouldn’t think the winter blend is going to change your mixture much.
However with the cold weather you would want to richen the mixture to adjust for the air being denser.

 

[BogiesAnnex1]

I have a 350 SBC with a set up a 650 BG mighty demon carb.
I had the carb tuned in pretty close over the summer, a little on the lean side.
I drove it last weekend & it was so rich you couldn't ride behind the car.
The only thing that I can think of that could have changed would be the switch to the "winter blend" fuel.
any suggestions?

I wouldn't think winter blends would have that much effect. The refinery juggles some of the specific amounts of high vapor pressure (less volatile)for lower vapor pressure (more volatile) to make the fuel evaporate faster making it easier to light off on cold days. This shouldn't have much of an effect on mixture ratio.

However, some winter blends also include a lot of alcohol for an oxygenate, these can attack some plastic and rubber carb parts, though these days they shouldn't, but if it went after the power valve damaging it or if the fuel picked up some dirt keeping the valve from closing, it could be leaking fuel into the main-well. This would be my first place to look for a problem.

Bogie

 

[cobalt327]

it was so rich you couldn't ride behind the car.

Your problem isn't w/the winter blend gasoline.

First thing, check the float level/ dirty or sticking needle and seat assembly. Then, besides the power valve (which if fully blown, would make for a pig-rich condition) look for a plugged air bleed.