Hot Rods Rochester Varajet

Gentlemen,
We are planning to try pikes Peak 14,000 foot summit with a GM V6 Rochester Varajet carburetor. People suggest the car will not be happy in the thin air. Any suggestions on adjusting/adapting to make it run leaner? Thanks!

 

I thought one of the features of the Varajet was al***ude compensation, but I could be wrong.

 

Interesting point I was not aware of. The Varajet does have a adjustable idle jet that people have suggested adjusting in to reduce flow. But that sounds like just at low rpm. I thought I may try disconnecting the accelerator pump. If it would run at all I'd guess that may reduce overall fuel flow. Thoughts?

 

Disconnecting the accelerator pump will just make it bog/stall on acceleration, nothing to fix running rich at steady speed.

 

X2 accelerator pump does nothing for air fuel ratio once running down the road, it is only for throttle tip in to prevent bogging. After that no effect on air fuel ratio.
A sort of interesting fact, the idle circuit still puts fuel into the air stream at speeds above idle. It has more effect at lower throttle, but it is adding some fuel all the time, less as the throttle is increased.
I don't know about the varijet functions. As a comment I have had my vehicles from seal level to 10K plus elevations and never did a thing with any mixture screws or jets. Sure it might be optimized if staying at high elevation, but they still ran fine.

 

Isn't the Varajet a computer controlled mixture carburetor, similar to the same era Quadrajet with the vibrating needle idle mixture control ***********? I had to rebuild one of those on my O/T El Camino and spent two days getting that POS adjusted so it would idle. I nearly threw it away and put on one of the older Q-jets that don't rely on the computer to control the idle mixture.

 

I think a rule of thumb is reduce one main jet size for every 1000 ft. of al***ude increase. So if you are starting at 5000 ft and are climbing to 14,000 ft you should be 9 main jet sizes smaller up top. But I offer another solution if this is a one-time event.

Put a large vacuum hose on the intake manifold with an adjustable bleed valve, so as you gain al***ude you can start to introduce air in a controlled vacuum leak, increasing the bleed valve opening as you ascend and closing it off as you descend.

You can start with it jetted a few sizes leaner than stock so the A/F ratio correction will be smaller as you go.

Sounds like fun.

 

Jet for the middle of the course.

 

That is a novel and interesting suggestion.
The non computer carburetors have a "second" ****erfly above the secondary ****er fly. It is attached to a longish taper needle valve that pulls out of a jet as engine speed/vacuum increases adding additional fuel. I'm wondering if I restrict how far the ****er fly/ needle pulls out, how the engine will run. I haven't found jets to replace with a smaller size.

 

VaraJets existed for a few years ('78, '79, '80?) before GM's C3 system added the electronic carburetor controls in '81. Essentially a Q-Jet split down the middle, lengthwise, with small primary throttle bore and a considerably large secondary. Even had a similar spring loaded secondary air valve to regulate air flow when the throttle was mashed.

Always wondered if a pair of them might work good on an inline 4 or 6 cylinder. Of course, they probably wouldn't look cool enough though . . .

 

You replace the needles with fatter ones to lean the mix.

 

Have a second fuel tank with E85 in it (or a mixture of E85 and regular), switch to this at the appropriate al***ude.

 

They were a smogger carb at the end of the does not have a computer to control it era.

I'm thinking that is what a V6 Chevy Citation that I bought off Ebay for 99 bucks back in the 90's when you sold your beaters on Ebay. We drove it for a year or so and the carb acted up and the local shop that actually could work on it wanted 350 to rebuild it at that time. I turned around and sold it and bought her another car.
Truthfully if there was a manifold available to put a different carb that was a bit more "normal" on the engine it is on I'd be doing it. Otherwise expect it to run like **** for a few miles at high al***ude like most engines with a carb that isn't prepared for al***ude do and gear down and call it good. A lot of rather suspect old family cars have limped their way to the top of that mountain over the past how many years and many more will in the future.

Some info here that I think a couple of the others looked at My Website (ednutter.ws)

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Regarding French Town Flyer's and Mr. 48 chev suggestions, might adding a controlled air tube to my blanked off EGR manifold location supply additional air to lean the "over rich fuel mixture" at al***ude? French Town Flyer's inspiration and Mr. 48 chev's web site info are very interesting!