Is my carb too big???

MaximusGluteus · 03-14-2005, 06:01 PM

Hey everyone! I'm new to this forum and I have a question about my carburetor setup on my 73 Nova SS. The carb is a Holley 750 Double Pump (I think it may be the Dominator series) sitting on a rebuilt 355 with 10:1 compression, rebuilt TH350 trans w/shift kit, 350 Corvette cam, ported and polished Camel Hump heads from a 69 Corvette, Performer RPM intake, and Dynomax headers running to 2.5 inch dual exhaust with Flowmasters. I bought the car with the engine built like this, and it seems like this engine should make a ton of power, but it really doesn't seem to have all that much (especially when compared to the very MILDLY built 350 in my 78 Camaro Z28 w/4-speed, which is a faster car than the Nova and both cars have a posi 3.73 rear end). Could my carburetor be too big (bogging the engine down)? It seems to have more power when I DON'T put my foot to the floor.

Anybody have any ideas/advice? Thanks a lot!

Fyter87 · 03-14-2005, 08:45 PM

Well I dont know too much about carbs, but ill try to give you some advice. A 750 Double Pumper does seem like alot. I have heard that holley's take awhile to tune and prefect, so I would take some time and hopefully get some more advice about tuning holley's. Good Luck

-Cliff

rumrunner88 · 03-15-2005, 10:47 AM

bigger the better bro

nova68 · 03-15-2005, 08:33 PM

when you step on it does it feel like to much gas for the engine does it bog down? right now i need to get a bigger carb, when i step on it it sputters and stalls. i messed with timing and checked everything has to be my carb?

Robs71Nova · 03-16-2005, 06:52 AM

Any idea on the actual specs of you cam? If you can find those, I can give you a better idea, but as it Is I would say no. I ran a holley 750 double pumper on the 355 in my 71 Nova without any problems. If it comes to it you can jet the carb down, but I personally don't think that the carb is too small.

Rob

MaximusGluteus · 03-16-2005, 10:50 AM

Quote:

Originally Posted by nova68

when you step on it does it feel like to much gas for the engine does it bog down? right now i need to get a bigger carb, when i step on it it sputters and stalls. i messed with timing and checked everything has to be my carb?

Well what happens is it steadily increases in acceleration as I push the pedal farther down (like it's supposed to do), but when I get to the floor it actually seems to lose power, like it's being bogged down (like you suggested). It's not super noticable, but I can tell something just isn't right. It has more power at 3/4 throttle than at full.

As for the cam specs Rob, all I know is what is in the receipts folder when I bought the car, which is a piece of paper that says the cam is a 350/350 Corvette cam, whatever that means. I was thinking about maybe changing the cam anyway. My 78 Camaro has a huge cam that makes it sound like it's fighting to stay alive, but once you hit the gas that car explodes and it feels like the front end is going to come off the ground. I thought about having the carb jetted down, but I want to keep that as a last resort, just in case it's something other than the carb (i.e. timing, ignition, fuel delivery, cam, etc.).

jrbabboon · 03-17-2005, 03:39 PM

What RPM are you at when that occurs? Perhaps you have passed peak horsepower when you are at full throttle.

MaximusGluteus · 03-17-2005, 08:38 PM

Quote:

Originally Posted by jrbabboon

What RPM are you at when that occurs? Perhaps you have passed peak horsepower when you are at full throttle.

It happens no matter what the RPM is. It actually seems to not be as bad at higher speeds (like when I'm on the highway and I punch it). It could be that I just don't FEEL it as much at higher speeds.

jrbabboon · 03-18-2005, 06:44 PM

What octane rating of fuel do you burn? For your case, I would suggest around 100 octane. Generally, to find out what octane requirement your car needs, just add a zero to the end of your compression... Example 8.5:1 is 85 octane or low grade. 9.5:1 is 95 octane, or high test. Your case, 10:1 is 100 octane, similiar to what light aircraft burn =c)

Octane boosters will do the job, just try to hit the proper ratios listed for fuel and booster. Higher compression requires fuel to combust at higher temperatures to burn correctly, and if you don't have a high enough octane rating, your fuel burns less efficiently, causing loss of power. Your full throttle syndrome sounds like it might be due to this.

Should I happen to be a fool and you are burning the correct fuel, it almost sounds like your Holley just needs a little tuning tailored to your Nova's needs.

AlmostStock · 03-25-2005, 03:17 PM

Quote:

Originally Posted by MaximusGluteus

It seems to have more power when I DON'T put my foot to the floor.

With the engine off have a buddy slowly press the accelerator down to the floor while you watch what happens at the carb butterflies and linkage. Full pedal should equal full butterfly opening at the same time. If it doesn't then adjustments are necessary. You still will probably need to tune the carb for the engine. Get a Holley book for this. If it is a dominator I wouldn't use it on the street. It's made for racing and I would be surprised if you were happy with it for normal every day driving.

ace27 · 03-25-2005, 06:30 PM

What size of fuel pump do you have, is it mechanical or electric, mabey at high rpm your pump has a prob. keepin up to the demand. I had that prob with my car, had to put in an electric pump.

MaximusGluteus · 03-26-2005, 12:39 PM

Thanks for the help everyone!

To answer the question about what octane level fuel I'm using, the answer is the highest the gas station has, which is usually 97 octane I believe. I'll buy an octane booster to up it to 100 and see how that works out. I've had the carb adjusted by a mechanic and he said it was right on, but I'll get a Holley book and see what else I can do with it.

Oh and I apologize, but in my first post I said I thought the carb might be a Dominator series, when I meant I think it's a Street Avenger series. Hopefully that helps a little bit.

As for the fuel pump, I'm not sure what size it is or if it's electric or mechanical. I'll check that out, and if it is mechanical perhaps I'll give an electric a try.

AlmostStock · 03-27-2005, 10:39 AM

Quote:

Originally Posted by MaximusGluteus

As for the fuel pump, I'm not sure what size it is or if it's electric or mechanical. I'll check that out, and if it is mechanical perhaps I'll give an electric a try.

If a stronger fuel pump is necessary you may want to consider a high output mechanical unit. It will be cheaper and easier to install than an electric one.

jrbabboon · 04-01-2005, 05:12 PM

I got the stock Rochester 2V on mine and recently has the same problem, except mine was to the extreme of stalling completely...I recently fixed my gas tank (which required dropping it) and all the 30 year old crap on the bottom of it got sucked into the fuel filter. $2 later she was running better than ever. I know its a brand new carb, but maybe you got some sludge pumped up to it.

miltystu · 04-09-2005, 04:05 PM

I'm not 100% sure but it sounds to me like the cam specs would be:
GM part number 3896962 Hydraulic Flat Tappet
This hydraulic flat tappet is used on the 68-81 L-46 and L-82 Corvette. The duration at lash point in degrees (intake/exhaust) is 312/312; duration at .050" tappet lift (intake/exhaust) is 222/222 and maximum lift with 1.5:1 rocker ratio (intake/exhaust) is 450/460. Valve lash is zero/zero and lobe centerline is 114 degrees.
Have you checked your fuel filter? The carb should be ok. See if you can borrow a friends 750 DP or vac ssecondary and try it. I had this cam in a 73 Nova 350 and a 750 vac. and it worked awsome.

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