Carburetor general questions

Seems like there aren't many people anymore that know much about carburetors.

I've become pretty proficient on my 2 barrel rochestor varajet II in the past 8 months or so.

1st: At what altitude was considered "high altitude"?

2nd: If by chance anyone knows, I have 2 spare varajet II's and both have adjustable power piston-needle assemblies. I am not 100% sure what the factory setting is, but I've read to bring the needle all the way up, then 2.5 to 3 turns down. Is this correct?

3rd: I have 2 varajets that are fixed power piston needle assemblies. Would I be better off with these?


(The engine is a v6 2.8l gm being used at 2500 - 2800 ft)

 

can't help you with your questions. i know nothing about these carbs. if you have the time, could you tell me the advantage these carbs have over a fixed carb such a Rochester 2GC? Especially since your altitude varies so little. thanks, jack

 

You are not at high altitude, use the adjustable carb not the fixed carb always.

 

I'm guessing you're using non ecm controlled carbs, like ones that were on S-10's. You should be about right on the adjustment, but you are .5 mile above sea level so a little bit of compensating might be necessary.

 

Question number 1:

Carter (lean calibrations listed for some models only):

Standard calibration - sea level ~ 4000 feet
One size lean - 4001 ~ 6000 feet
Two sizes lean - 6001 ~ 7000 feet
Three sizes lean - 7001 ~ 8000 feet

Holley (AA series carbs):

Standard calibration - sea level ~ 5000 feet
One size lean - 5001 ~ 10000 feet
Two size lean - 10001 ~ 15000 feet

Rochester (some models):

Standard calibration - sea level ~ 5000 feet
One size lean - above 5000 feet

Stromberg (some models):

Same as Holley

In the FWIW category:

E10 (because of its reduced energy) seems to work fairly well at the "one size lean" altitude with the "standard" calibration. Of course that means for best results, carbs using E-10 in the "standard" calibration zones would perform better with a "one size rich" calibration.

The Holley AA series, Rochester B, 2G, and 4G series carbs used jetting changes to effect the different calibrations. Carter, with their superior metering rod calibrations, used thicker rods to effect the leaner calibrations. Carters, because of the extra steps on the metering rods, handle altitude more efficiently than the non metering rod designs. And yes, I am well aware that Rochester used metering rods in the Q-Jet, but Rochester normally released a different carburetor (Q-jet) for altitude use.

Jon.

 

I truly appreciate the replies!

I did forget to mention that the vehicle is in fact the last year model for the non-ecm.

At the moment, I am using a 2se that has the fixed power piston. It seems to run decently, but there is always that thought that I think it could run better albeit it may be running its best.

 

Unfortunately, I've not had much luck in finding much on tuning these 2se's.

The stamped numbers on the jets seem to match the diameters, but the numbers on the needles don't. I.E. jet stamped "177" is .077 diameter.

The needle is stamped "63". The tip measures .025 and the big end measures .045.

 

well, after taking some diameter and length measurements, it does not look like i am going to effectively use the adjustable needle jets.

the adjustable needles are smaller in diameter by a couple thousandths and the jets are larger than the fixed.

based on the measurements, i would not have any adjustment to lean out the adjustable needles since my elevation is about 2800 and the fixed needles are larger and the jets being smaller.