demoke

Plz help this non-mechanic:
3 years ago i acquired a 1980 4/speed Corvette with 82,000 miles. The engine was rebuilt at 89,000 miles, keeping and rebuilding the original block.
The engine was built with 9.5 to 1 Speed Pro Hypereutectic Pistons, a Comp Cams .500 lift Hydraulic Roller Camshaft, Professional Products Typhoon Intake and a 750 CFM Holley Carb.,and a new Ram clutch.
The original quadrajet carb was taken off and boxed. Here is my problem: I want to drive this car more for enjoyment,take some trips, not just for "freeway" racing. I am having problems with the car sometimes stumbling from a dead stop. I have had the holley tweeked several times but still sucks lots of gas and doesn't really seem to be set right for too long. Several different mechanics have suggested that, for what I want the car for, i am better off putting the quadrajet carb back on my car. They said it would be better on gas, just as much HP and alot less headache. I do have a gentleman in my area that is a "quadrajet expert" so i believe i could have it set up correctly. I would really appreciate any feedback you all might have. I am in Charlotte, NC. Thx Robert

TheSkunkWorks

My favorite Lars'ism is that 90% of carb problems are ignition problems. So, before you blame the carb, make certain your ignition system isn't at fault. In addition to the usual suspects, this includes ruling out spark scatter (erratic timing).

With ignition issues eliminated, the next questions are 1) do you have an auto or manual trans, and 2) does that Holley have mechanical or vacuum secondaries?

If the secondaries positively open when you operate the throttle by hand (with the engine off), they're mechanical, which given your stated purposes would be a mis-match IMHO, especially if you have an auto. In this case, you may want to have that Q-jet tuned up in lieu of buying a new carb, but is that intake for square bore carbs?

If the secondaries are vacuum, assuming everything else has been set properly, the secondary diaphragm spring is very possibly too soft. This can be remedied rather easily by picking up a Holley secondary spring kit (# 20-13 IIRC) and installing the softest spring which doesn't bog under load. Lots of guys miss this one.

There are more possiblities, of course, but always rule out the easy stuff first. My $.02

demoke

thx for the info...i have a manual transmission. i did have some timing issues with this carb before. rs

Vette5.5

Sound's like your engine may be set up for higher rpm power than your intention's, and as mentioned the Typhoon intake is for square bore Holley's. You said very little about the cam, but duration @ .050" and lobe center line spec's will tell a lot about streetibility. For what you're doing, probably go a moderate cam, Cyclone(or similar) intake and well set up Q-Jet. If really going the next step, a Kiesler or Hurst 5 speed o.d. tranny.

snoopykissedlucy

My two cents:
A Holley is sexy........yet most people rebuild them wrong and tune them wrong.
A Qjet is ugly......and most people rebuild them right (idiot proof)

Bottom line: if you buy a Holley and mount it straight out of the box...it will work like a charm. If you're buying a used one.....make it a Qjet.

I also agree....I bet if you buy an MSD box and rebuild your dist with electronic points...it will cure your problems.

baxsom

it was kind of touched on before but if your current intake is a square bore and you want to go to a qjet you will have to change out the intake and probably the fuel line and throttle cables. Holleys are a lot easier for the backyard mechanic to rebuild. It may just need to be put back into oem specs. The #1 problem I have seen people talking about is that they immediately put jets that are too big in. You will find a lot of really knowledgeable people here are saying that a MSD box is in no way necessary to proper running of a street engine.

jerome1979

holley carb are tune rich out of the box !! you must probably change jet!!
More than that, a 750cfm carb is too big for a 350ci in 90% case !!!
So IMO:
1) check ingintion
2) setting carb correctly (wideband, change jet, use good secondary spring)
3) Enjoy your ride !!!!

Buddy1980

I have used many of the Holley #3310 750 cfm vacumn secondary carbs over the years on engines similar to the one you built. All my engines ran fine and I never remember any problems with the carbs. The 750 cfm carb may be a little large for a 350 engine, but the vacumn secondary system should only supply what the engine needs if it is working properly. I currently have this carb on a 383 small block, and previously had the same carb on another 350 and 383. The 73 convertible with 383 and Richmond 6-speed trans. would get 18-19 mpg on the highway at cruising speeds of 65-70 mph. These results were with stock out of the box Holley 3310 750 cfm carbs. I am not against a good quadrajet, just have found it more economical and less trouble to buy a new Holley for $269 than rebuilding a old quadrajet. I am assuming that your carb is the 3310 vacumn secondary model. If it is, you might want to get a secondary spring kit from holley and experiment with a weaker or stronger spring and see if that cures the problem.

baxsom

That is weird. Most of the time you read here that when you get a holley you need to move the bigger back jets to the front and then up the back jets by about 8. I have read a lot that they can run rich at idle and need a brass inset in the idle circuit but jets wont affect that.