Holley 650 double pumper spread bore - Chevelle Tech

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post #1 of 11 (permalink) Old Apr 14th, 10, 12:05 PM Thread Starter
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Joe
 
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Holley 650 double pumper spread bore

Anyone ever got a spread bore to run good? I'm having a problem getting my secondaries to kick in good. I have a 350 bored 30 over. Voodoo cam 219/227@50. 62cc Camel hump heads with 2.02 intakes. Flat top pistons. Edelbrock performer intake, headers. The carb has 64's in the front and 81's in the back. When I kick in the secondaries it boggs down and I have to throttle out and gentle get into it. Are the secondaries too big or is this just common with spread bores. I don't really know anything about the air mixture screws.
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post #2 of 11 (permalink) Old Apr 14th, 10, 12:30 PM
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Bobby
 
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Re: Holley 650 double pumper spread bore

I have one of those I ran on the Chevelle for about a year, it ran pretty good overall with decent mileage, but them I got to tuning for the better and make the primaries all screwed up. I pulled it off and have not messed with it since.

A few things to think about or check is to make sure you rear squirter is working properly, You may need to tune the amount of fuel it dumps to cover the large secondaries.

You need to make sure the motor is good for the airflow and power the large secondaries will produce, if the motor is not strong enough your not going to tune the bog/stumble out.

Check your secondary pump cam and squirter, then check what holley put on there stock. It's normally a good starting point.

-Bobby-
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post #3 of 11 (permalink) Old Apr 14th, 10, 5:22 PM
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Re: Holley 650 double pumper spread bore

Holley jet size chart !!

http://www.race-cars.net/holley3.html

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post #4 of 11 (permalink) Old Apr 14th, 10, 9:02 PM
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Re: Holley 650 double pumper spread bore

List # 6210?

No, never heard of such a thing before.
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post #5 of 11 (permalink) Old Apr 15th, 10, 1:31 AM
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Re: Holley 650 double pumper spread bore

I had the 800 cfm version of that carb on a 402. Same problem. Never could get rid of the bog. I was told the secondaries are just too big. Ended up putting a 780 vac. secondary on. Ran much better, no more bog.
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post #6 of 11 (permalink) Old Apr 15th, 10, 1:52 AM
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Re: Holley 650 double pumper spread bore

Do they have a 50cc pump in the back?
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post #7 of 11 (permalink) Old Apr 15th, 10, 10:10 AM
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Bobby
 
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Re: Holley 650 double pumper spread bore

Mine does, I never had a problem with the secondary bog, had some problem keep the tires hooked when the secondaries opened, but no bog!

Like liked the carb because it ran off the small Primaries on my 327 and got as much as 19mpg with a 3.08 gear and 4 speed.

I have read a bunch about nightmares to tune them, I feel that is what happened when I tried to lean out the idle circuit.

-Bobby-
1965 SS 331 Muncie
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post #8 of 11 (permalink) Old Apr 15th, 10, 11:59 AM
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Re: Holley 650 double pumper spread bore

Quote:
Originally Posted by 19-joe-68 View Post
Anyone ever got a spread bore to run good? I'm having a problem getting my secondaries to kick in good. I have a 350 bored 30 over. Voodoo cam 219/227@50. 62cc Camel hump heads with 2.02 intakes. Flat top pistons. Edelbrock performer intake, headers. The carb has 64's in the front and 81's in the back. When I kick in the secondaries it boggs down and I have to throttle out and gentle get into it. Are the secondaries too big or is this just common with spread bores. I don't really know anything about the air mixture screws.
John, 650DP are good if you have big gears and a 4 speed tranny. Your better off using a 750 VS. I ran into the exact problem you are having.

Louis
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post #9 of 11 (permalink) Old Apr 15th, 10, 1:27 PM
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Re: Holley 650 double pumper spread bore

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Originally Posted by lg1969 View Post
John, 650DP are good if you have big gears and a 4 speed tranny. Your better off using a 750 VS. I ran into the exact problem you are having.
I agree. I ran one of these on my old stock 327 ( stock intake/exhaust manifolds, presume a stock cam), and it ran pretty well... But I had already swapped to a 4-speed and 4.10 gears... Instead of bogging, it would just smoke the tires

It was just a temp situation where the Q-jet was toast, and my brother offered the near-new DP...


Whats the rest of your combo like?

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post #10 of 11 (permalink) Old Apr 15th, 10, 3:17 PM
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Re: Holley 650 double pumper spread bore

The spreadbore double-pumpers IMO are one of the best all-around street cars ever built. Great gas mileage, make excellent power, they FIT THE CAR unlike some other carbs (*cough* Edelbrock *cough*), and are extremely easy to work on.

The whole "bog" thing is usually driver education. Never forget, it's a MANUAL SECONDARY carb! You can't just stomp on it like a cockroach and expect the same results you get with a vacuum secondary carb. Once you learn know how to drive with a trace of finesse, you'll see.

To tune it:

Get your timing set right. Which is, about 36 - 38° of advance at 3000 RPM, with the vac advance unplugged. Make sure your timing mark is accurate; they usually aren't, and can be WAY WAY off of you have an aftermarket timing pointer and a stock crank damper. That combination usually results in about a 35° error. This will cause the motor to "bog", have no response, run hot, get poor gas mileage, and generally run "lazy".

Tune the primaries by first leaning the jets down until it just begins to barely surge going up a slight hill in high gear at the lowest speed you would realistically do so; usually 35-40 or so. Then go back up 2 sizes. Then raise the power valve (stock is a 6.5 IIRC) until the tip-in sag with light throtlle goes away, then go up 1 - 2 more #s. It'll usually end up with a 9.5 or 10.5 in a street car.

Set the curb idle speed to where you want it (700-750 or so), then take the carb off and turn it upside down and look at the transfer slot. If there's more than about .050" of it exposed, back off the curb idle screw to set it to about .030", and open the secondary idle stop screw by an approximately equal amount. Put the carb back on and adjust the idle speed, then the mixture screws for highest vacuum (you'll probably have to turn the idle speed back down as you do this). Turn them both all the way in, counting the turns, and turn them back out to their average, plus ¼ turn. Repeat this whole paragraph until the transfer slot has less than .030" showing below the pri throttles, the idle speed is where you want it, and the idle mixture screws are within 1/8 turn of each other and ¼ turn out past max vacuum.

All of that should make it run ALOT better. Then all you have to do is learn how to roll into the throttle a little bit, instead of just stomping it to the floor. If it still has issues, post back up, and we'll try to help.
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post #11 of 11 (permalink) Old Jul 18th, 10, 1:03 AM
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Re: Holley 650 double pumper spread bore

I know this thread is a couple months old. We finally got the spread bore Holley on the '70. After feeling how much better the car runs with the Holley I don't see any reason to go back to the Q-Jet. It pulls harder ,and gets there faster, than the Q-Jet ever did. No issue with a bog, even when punching it from low RPM. I really like the way this double pumper makes that 402 run. The secondary jets may need to be taken down a notch or two, but it really runs well the way it is.

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