I just bought a 69 camaro with a 350 in it. I have a recept of the Holly 650 Carb from 1995. My question is how do you know it is time to rebuild the carb? I am presently getting reasonable power and about 10 miles to the gallon. I have know idea on the cam size, but I am assuming a mild performace cam with stock heads. I also have 350 Turbo tranny.

The Carb is clean, and looks ok. One guy told me you need to rebuild these carbs yearly. Is this true? The Carb probable has less them 6000 miles on it (pervious owner did not drive the car much). I have put 2000 on it this summer. Any help would be greatly apprechated. Thank's

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69 SS

At 8000 miles it should not need a rebuild as long as it has been run with an air cleaner and fuel filter in place. If the car sat with fuel in the bowls for any length of time you could have some varnish build up.

As far as rebuilding once a year that would depend on mileage.

You might check the power valve, an engine backfire can blow the diaphram and cause the car to run rich at part throttle. That could be some of your mileage problem.

If it were mine I would order a non-stick gasket set and take it apart to clean it just for piece of mind. With the non stick gaskets you can reuse them when changing jets. The first time you take a holley apart the original gaskets are usually a pain to get off, but other than that they are not that difficult.
Stephen

if it runs and performs well and doesn"t give you any problems, run it. you don"t need to rebuild it every year, some cars have 50-100k on them and they still run ok. it might need a little carb cleaner now and then to keep the throat and flaps clean. if you store it in the winter like i have to, add some gas stabilizer to the tank "full of gas so you don't get moisture" and run it for a while so the stablizer works it's way through the whole system. this will prevent varnish in the carb while it sits, and helps keep the gas fresh.

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You will have the best luck if you run a paper fuel filter before the carb.
The main thing is to keep the fuel clean and if it sits and dries out enough times you will get some residue plugging in the idle circut.

You will notice a funny lean smell coming from the exhaust when there is plugging, or poor performance. Almost allways it's the idle circut because that has the smallest orifices in the carb, and they plug up the easiest.

You need to keep the air bleeds near the venturis clean too.

If it aint broke, don't fix it!
Usually double pumpers are not recomended for auto trans use, and not for street use either. If it's small enough like yours, it will work OK with lower mileage the only penalty.
The DP carbs do have a little better response when you stab the throttle. If it's sized right.
Get a book and learn what the proper settings are for the carb so when you do have to clean it up you can set it right.
They are very easy to work on.
David

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Check my web page for suspension info:
David's Homepage (http://ourworld.compuserve.com/homepages/David_Pozzi/)
67 RS 327
69 Camaro Vintage Racer
65 Lola T-70 Can Am Vintage Racer

If double pumper are not typical for street use, what is? I have a Elebrock 600 CFM on a second car of mine and it is not really that impressive. How do you know if your power valve is blown on the 650 double pumper?

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69 SS

Articles I've read state that the double pumpers are sensitive to sizeing in that if you go too big they bog easily.
If you use a vaccum secondary carb the secondaries will open more slowly and are controlled better than the double pumper carb which just opens wide.
With the vaccum secondaries, the manifold vaccum does not drop too low under full throttle and you don't get a bog. The vaccum opening of the secondaries can be dialed in by changing a spring.

I'd say if you have a stock auto trans with stock rear gearing and stock type torque converter, a vaccum secondary carb looks good.
If you have a looser converter, gears, and other mods. A double pumper looks better but you have to size it just right.
I would guess that a 650 DP would have more jump in the lower gears once rolling. And if it is sized very well, it might be better off the line from a standing start.

If that is the case, then I'd be wondering if the top end performance would be better if I went up a size to a 700 DP or a 750 vac sec carb.
I think you could easily go 50 to 100 cfm larger on a vac sec carb over a double pumper.
Because the vac sec carb is more forgiving, you should only compare a larger vac carb to a smaller double pumper carb.

You absolutely have to go with a carb that feels the best on your car. That's reality, everything else is just theory.

If you have a friend that has a larger carb try swapping and see what the difference is. Think of it as an experiment.
I think the 650 DP carb you have now is small enough to stand a full throttle stab at fairly low rpm's and run well. You are probably getting a little worse mileage than with the 600 would get.

The power valve is fairly durable in my experience. If you have a lot of backfiring on an older model, their life can be shortened. People say one backfire can blow them out but the backfire pressure has to blow thru a vaccum passage and into a chamber, this softens the pulse, and I don't think they are as bad as some people say.

If your power valve goes bad the mixture will go too rich at part throttle. Possibly at idle too. Plugging of the air bleeds inside the air horn and plugging of the idle feed restriction are more likely problems to develop. If you get a rough idle, and when you try to adjust the idle mixture screws you don't get much response out of them or only one screw makes a difference that's plugging of the idle system.

A squirt of carb cleaner into the mixture screw holes (remove the screws first) usually does it.
If I were you I'd work on a good advance curve for the distirbutor and make shure the carb is jetted correctly, and all adjustments like float level, and accelerator pump, are correct. You should have #66 primary jets to start.
David

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Check my web page for suspension info:
David's Homepage (http://ourworld.compuserve.com/homepages/David_Pozzi/)
67 RS 327
69 Camaro Vintage Racer
65 Lola T-70 Can Am Vintage Racer

[This message has been edited by davidpozzi (edited 07-29-2000).]

A little accel. pump tuning, and a double pumper will not bog regardless of gear and converter. My chevelle has 2.73 gears and a stock converter. Have no bog with my 383 or 350 with a 650 DP. I do agree that a vac sec would be better with this combo, I'm just saying I have no bog or hesitation.

I also agree that powervalves are not as delicate as most people think. In 17 years, I've only blown 2. One when I broke a pushrod and had a huge backfire thru carb. The other when I was cleaning the metering block with carb cleaner, and the powervalve installed. If you do have a blown one, your plugs will foul quickly.

I've had a double pumper in my daily driver forever it seems. I didn't build the cars for milage, but I have taken the chevelle on many 400 mile, each way, trips. Average 14.5 mpg with 383.

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67 Camaro 410sb 11.63 @117.6
67 Camaro 388 ET-???
website (http://www.geocities.com/lonnie67_1966)

Sounds like I need to buy a Holly carb book to really understand my Double Pumper. When I hit the gas, I have good (not as good as when I bought the car 5 months ago) acceleration, but after I slow down I get a gas smell going into my car. I do not see any visual leaks in the carb. I am getting about 13 miles to the gallon on the high way. I would like to be getting more power for the crappy gas milage I am now getting. Thank you for your input.

If I bought a air to flue ratio gauge, how much would that really help in my cars tuning and is it worth it? Worth it for a carb amiture tuner like myself. thanks