[360Camaro]

My good friend's Impala's 2BBL carb went south. He plans to install a warm 383 stroker. So the idea we came up with was to use the "future stroker carb" on the stock 350ci Chevy for now while the other motor was built.

This is a rebuilt 3310S Holley VS atop a 4-2BBL adapter with stock 2BBL manifold on 1972 Chevy 350 (factory stock, with true dual flowmaster 40's).

Trouble is, idle RPM is too high. I've practically screwed in the mixture screws fully & adjusted timing to lower the RPM; but alas it's too high and the timing compensation is ridiculous (backfires with load).

Obviously the carb is large for stock cam/compression. And the 4-2bbl adapter is hardly ideal. But I've taken stock 305's and slapped a 600cfm Holley atop a 4-2bbl adapter and the wheels smoked & engine adjusted fine.

Is this rebuilt carb (freshly ordered) defective? I don't know the jet sizes. Are the 600cfm idle circuit vastly different from 750cfm causing this?

Thanks

[Blazin72]

This probably isnt much help but I can tell you this. I loaned a 3310 of mine to a friend because his truck needed a carburetor and it worked great. Only one difference...his engine was a completely stock 400 (except we later found out that the engine was bored .060 over so it was a 412) Just a little bit larger.

[Arcuden]

Only other thing I can think of would be the throttle adjustment screw. Kind of obvious, I know, but make sure it's not too far in and keeping the blades open at idle.

[DoubleVision]

the open adapter is junk and the best place for it is the trash. You can screw the idle adjustment all the way in and it has no effect because since the adapter is the open type each cylinder is drawing off the entire mass of the carb, same way at cruise and there on. The adapter also disrupts the fuel and vacuum signal. Best thing to do is install a 4 bbl intake a aftermarket would likely be the best choice since they`ll accept the Holley, a stock 4bbl intake will only accept a Q-jet which will work fine also if you can find one in decent shape. For a stock 350 the 750 is too big but would work if tuned properly. I would just rebuild the 2 bbl carb or go to a 4 intake.

[baddbob]

2 barrel rochester rebuild kits are usually only about $15. I'd rebuild the 2 barrel and put the 750 away till the 383 is built. Those adapter plates are junk. Been there, tried that years ago.

[360Camaro]

Originally Posted by DoubleVision

the open adapter is junk and the best place for it is the trash. You can screw the idle adjustment all the way in and it has no effect because since the adapter is the open type each cylinder is drawing off the entire mass of the carb, same way at cruise and there on. The adapter also disrupts the fuel and vacuum signal. Best thing to do is install a 4 bbl intake a aftermarket would likely be the best choice since they`ll accept the Holley, a stock 4bbl intake will only accept a Q-jet which will work fine also if you can find one in decent shape. For a stock 350 the 750 is too big but would work if tuned properly. I would just rebuild the 2 bbl carb or go to a 4 intake.

Thanks for the input so far. Concerning the adapters, yes of course they suck, but in my 17 years of using them I've never seen one not work in temporary solutions or even permanent.

So a 3310 ran on a stock 412 chevy... larger engine but interesting since I can barely get below 2000rpm at idle on a 350ci (I looked up the engine block code).

So I'm getting 2000 revs because of "open plenum" mixing due to the carb adapter?? It worked great on a 305 smogger, peanut cam, and 600cfm VS on 4-2BBL adapter. Idle adjust was fine.

Swapping to 4BBL intake, many would say there's not enough cam/CR in the stock 350. True but that's mostly running conditions. I'm talking about idle & the need to know if this carb is a dud. Intake swap alone to stop the open plenum mixing I doubt would drop the 2000rpm idle enough; it's just way to high.

VS carbs are more forgiving when "over-carbing" (during running condition I'm sure). Even tho this case is somewhat extreme, I still think the idle screw should stall this motor with proper working carb idle circuits.

I notice I can lower idle RPM by pressing the throttle back with my hand (and I have "double-return" springs, i.e. stiff pedal, & even unhooked the pedal cable), but it's still not enough, as if the carb is defective and slightly open even at backed out idle (the butterflies looked closed at passing glance before install). This Holley rebuilt carb came with e-choke, that I have unhooked (temporarily) at the air-horn. Before install, I noticed a slight gas odor and traces of teflon tape on fuel bowls. Even "buggered" float level screws. I've seen plenty of Holley remans without this stuff. Did Summit send us a used turkey (not necessarily blaming them, plenty of fine orders there...)? Personally I've seen the same #'s of defective new and reman units (local speed shops also agree here) which is why we ordered the reman to save $50.

Rebuilding the 2BBL (for $16 & some time) can make the car drive for cheap, but I have serious doubt about this 750 Holley now as I feel it should have idled down. Since it was ordered online we need to know if it's good or not (the 377/383 won't be ready for perhaps months). Only "testing" option I can think of is swapping with a known good 3310 from my built 360ci 400hp Camaro (currently in use by wife tho). Perplexed.

[360Camaro]

Problem fixed... I told my friend to unbolt the e-choke for now and set the fast idle screw behind it backed out. Now it runs great, stock 350 & 4-2BBL adapter.

[lluciano77]

The original 2 barrel mounting pad is different than a Holley 2 barrel. You will get a huge vacuum leak that way. It is not like a Ford where you can bolt that 4 to 2 barrel adapter on.

[360Camaro]

Originally Posted by lluciano77

The original 2 barrel mounting pad is different than a Holley 2 barrel. You will get a huge vacuum leak that way. It is not like a Ford where you can bolt that 4 to 2 barrel adapter on.

?? The 2 barrel to 4 barrel carb adapter is from Trans Dapt, it's quite generic with 2 supplied gaskets. It went on without a hitch. I mean as it sits on the 2 BBL intake, it's quite solid using all 4 bolts. The Holley 4BBL side fits just as good. Vacuum gauge is steady at 20psi even on 33year old 350 stock chevy.

It's only temporary, but since my friend needed that carb anyway (for future 400HP+ plans), neither of us felt like scraping on the old Rochester 2BBL to rebuild it.