Adjust Carb Jetting for Colder Weather...

[threewood]

Winter in Yuma brings us low temps in the 40's and highs in the 70's / lower 80's. Going from 80-100+ during the summer.

I have been getting a lean burble, for lack of a better term. Off idle and med acceleration it will do it and I can watch my a/f gauge bump above 13.5 to 14.5. No stumble off idle and wot isn't affected. 800cfm AVS2

So, would it be acceptable to run my primary jet one size larger to compensate? Colder air = more dense so more air in = lean. Reasonable thinking?

Fuel pressure is steady at 6lbs. New fuel filter. 3/8" feed to regulator, 3/8" return to Holley EFI tank with in tank Walbro 255lph pump.

 

[beanhead]

You can, and depending on how dialed-in you like to get it you may want to adjust the idle air bleed and/or IFR size and re-adjust mixture seeing as how you're not on the main circuit yet 'off idle'. It might definitely want a bigger jet anyway, for when you are on the mains and smashing it, but around here I find tweaking the other areas of the carb usually cleans it right back up. I'm in the same boat we went from mid 80s to upper 40s and low 50s for highs, over the course of a week LOL.
You might try simply raising the float level a flat or so and see what it does.... I like tinkering with carbs but anytime I don't have to tear into them to get my desired result I'm happy!

 

[RJRENTON]

Yes, increasing the main jet by 0.001" - 0.002" may help. But what color are the plugs? Does the engine warrant a jet change...perhaps just decreasing the metering rods by the same 0.001" - 0.002" on the cruise step will be easier. But remember, ALL idle and off idle fuel metering origionates in the primary booster venturii via calibrated drilled orifices and are almost impossible to change. Check to see if these orifices are NOT constricted or partially clogged, as they will exhibit the issues you mentioned. REMEMBER...main metering jets and metering rods and step up pistons and springs do not effect idle mixture or off idle fuel transition circuit.
BOB RENTON

 

[threewood]

Thanks Bob. It's not an issue off idle as the transition slots are exposed, but further into throttle. I drive it often so it doesn't sit so I doubt anything is gummed up internally. No stumbles or issues during transition. But throttling further, lightly, less than 1/2 throttle it will burble until I get on it hard and it smooths out. Plugs are tan, look good to my eyes.

I'll try a smaller rod when I get home from work. Easier to do than swap jets.

 

[Don Frelier]

I would change the metering rods.
Maybe try the next stiffer springs as well, it might be late going to the step up position.
Remember: 1 change at a time.

 

[beanhead]

Sorry threewood I should have known you were talking about an AVS.... I had Holley on the brain

 

[Darter6]

Don has a good Idea ^^^^^ Mid range part throttle go to the next heavier springs for the metering rods.
Mine (750 Edelbrock did the same) I bumped it 2 sizes heavier to cure the problem.
Edelbrock has the spring and color chart on their web.

 

[threewood]

Don has a good Idea ^^^^^ Mid range part throttle go to the next heavier springs for the metering rods.
Mine (750 Edelbrock did the same) I bumped it 2 sizes heavier to cure the problem.
Edelbrock has the spring and color chart on their web.

I have orange in it now, going to swap up to the next stiffest. I also found a rod that should work and is a size smaller on the thin end.

 

[Don Frelier]

You might need a size smaller on the fat portion.

 

[threewood]

Well, with the limited rods I have in the kit I ended up swapping the main jets from .104" to .107"
And I replaced the orange springs with the yellow springs.

 

[mopar jack]

Don't know about Arizona but in California we have c.a.r.b (California air resources board) fuel requirements and winter grade fuel that has at least 10% oxygenates added that will make your car run leaner.

 

[Cranky]

I never did anything to mine but was usually running a little bit on the rich side to start with......

 

[threewood]

Don't know about Arizona but in California we have c.a.r.b (California air resources board) fuel requirements and winter grade fuel that has at least 10% oxygenates added that will make your car run leaner.

Same here I believe. The jet swap is working. The 6552 rod is what I am using and the 6252 wasn't included in the tune kit.

 

[Darter6]

Always have what ya don't need,Never have what ya need !

 

[threewood]

Always have what ya don't need,Never have what ya need !

Yep. And the set of rods is $15. Kind of price for two skinny brass rods.

 

[RJRENTON]

Yep. And the set of rods is $15. Kind of price for two skinny brass rods.

Good point...but...if that's what is needed....so what. This relates to the old adage: "if you need a tool and don't buy it, you pay for it, but don't own it". If $ 15.00 was spent on a few brown bottles of one's choice, after a hour or so, all that would be left is a memory...maybe...
BOB RENTON