Need some advice on tuning quickfuel dp carb. - Hot Rod Forum : Hotrodders Bulletin Board
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Old 08-09-2009, 12:01 PM
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Need some advice on tuning quickfuel dp carb.

Hello guys I am still having some minor issues getting my carburetor just right. Its a quick fuel double pumper 650 q series drag racing carburetor.

Engine
350 sbc (9.5 to 1 cr)
Voodoo roller 231/239 @ 50 535/550 lift.
edelbrock rpm performer air gap intake.
HEI 65000 volt distributor with medium springs.
Timing is 18 initial and 34 by 3000
Vacuum advance is hooked up
Dart iron eagle 200 cc cylinder heads

I guess that should be enough info so you know about my motor. I currently have on the quick fuel carb 70 jets primary and 78 secondary. Pump cams are both pink primary and secondary. Power valve is 4.5 secondary is plugged. I went down two jet to what is stated above.

My spark plugs are not as bad as before but some are a little more black then the others. It seems like its still running on the rich side but I have an off idle stumble and sometimes it will die if I lightly tap the pedal. Also if I go to wide open throttle it has a big quick bog then it takes off like I stole my truck. I just bought a pump cam assortment and don't know anything about them on what to use etc.

I know the off idle and WOT throttle is a lean stumble cause my plugs are still black. With my cam change its helping me a lot and it runs great in idle and goes in too gear and still runs good just don't know what to do about getting it a little leaner but also to get rid of the bog. If I had a holley street avenger vacuum secondary I probably would have a more tuneable carb for street but I don't know. I feel this double pumper carburetor is killing my engine a slow death. Any help or suggestions.
Thanks
Eric

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Old 08-09-2009, 05:14 PM
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Well I took some of my spark plugs out and some are still rich with unburnt fuel on them. So I am going to put the quick fuel q series on ebay for a cheap price since it's almost brand new and has less then 200 miles on it and look at getting me a holley street avenger vacuum secondary to replace it with and hopefully have better tuning for a street motor and better fuel burning manners.
Eric
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Old 08-09-2009, 05:31 PM
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There is nothing wrong with the carb other than you need a bigger accelerator pump SHOOTER to cover the lean hole at launch, then work the jetting and idle circuits leaner to clean up the plugs. Just buying another carb will give you the same problems, they all have to be tuned out of the box unless you buy a custom hand built carb, and they may even still need adjustments once on the motor.
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Old 08-09-2009, 06:02 PM
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Hello Eric good to hear from you. Well I have already adjusted the idle mixture screws as best as I can and got them as lean as possible already. All IMS screws are all set the same and the primary and secondary idle screws are both the same with both butterflys approximately .020 and have already got my timing dead on. I went down two jet sizes and its still on the overly rich size. I will try two more jet sizes and see what it does but I feel like the double pumper is a little too much for street use.

The quick fuel drag racing series carbs seems tailored more for more track use then street. I wish I would have done more homework but I previously had a way bigger cam and went down in size quite a bit and now the carb seems to be too much. I used edelbrock carbs and one holley vacuum secondary on two previous 350 builds with a more agressive cam then what I have now and they ran a lot better and did not give me all the tunning issues I have now.

They only required a few turns of the screws and one jet change and they where good to go. Thanks bud for your help. I will try one more jet size change then other then that there is not a whole more I can do. Idle is good as it is now. Screws are only 1 1/4 to 1 /1/2 turns at the most at idle. The accelerator pump is just a 30cc and the 50cc would work nice I am sure but I got a pump cam kit to use but don't know what to do with it. The quick fuel carb has both of the pump cams on the passenger side of the carb. There is nothing on the primary linkage.
Eric
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Old 08-09-2009, 06:21 PM
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Now you've got me confused, I looked at the QF carbs, ALL of them have an accelerator pump cam on the primary side throttle linkage. What is the # for the carb?? If you are missing the primary pump cam I can see how you would have accelerator tip-in response problems. You are saying BOTH pump cams are on the secondary throttle shaft arm?? And there is nothing on the primary throttle arm??
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Old 08-09-2009, 06:32 PM
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Yeah I know it sounds weird but on my primary throttle shaft on the drivers side there is no pink pump cam wich is on my carb. On the passenger side there is two pink accelerator pump cams one facing the fire wall and the other one beside it facing the front of the carb. They are both on the secondary throttle shaft. I would post a picture but I don't have a digital camera. It states on my sheet both have pink cams and my main throttle shaft on the primary there is no cam there like the holley 4150 carbs have. I have looked at it several times. It has black plastic on it but nothing in the shape of a cam. There is number only on the passenger side that says number one and number two position. To make it worse holley did not have any chart to tell me wich cam is the lightest to the strongest.
Eric
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Old 08-09-2009, 06:42 PM
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Does the black plastic cam actuate the front accelerator pump lever?? This is sounding like a really weird deal. Wish I could see this carb. Is there a pump nozzle over each pair of barrels adjacent to the bowl vent tubes?? Do both bowls have accelerator pump housings??
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