Help with Quick Fuel accelerator pump linkage adjustment

[Lee Patterson]

Hoping some here can advise. Just replaced my aging Holley on my Pantera 351C with a Quick Fuel HR-600 carb (mechanical secondaries). Went through all the set up and tuning. Got strong vacuum of 17+ inches and set 4-corner idle. Quick Fuel installation guide says nothing about setting or changing factory settings out of the box on the primary and secondary accelerator pump arms. So, watched the videos on YouTube (probably a mistake) and adjusted the lash on the arms to less pre-load (supposedly you are to set to zero lash). Upon doing, car throttle response was shit. Falls flat on its face with any throttle advance. So I adjusted back to the pre-load that came out of the box and it responds well again. So my questions for this group are:

1. Should accelerator pump arm have some amount of preload? (when I push arm up against the actuator arm spring, I get about 1/8" to 3/16" inch travel of threaded rod / nut above the arm.
2. Is this actually the case of the arm should have zero pre-load but my pump nozzles are undersized and creating that flat spot? (nozzles are 0.28" from factory)

I appreciate your insights on this.

 

[DaveM]

I set my Quick Fuel with just the slightest play on the pump arms. Probably less than .010". You may need to change the accelerator cams. Buy Holley 20-12 that has an assortment of cams. These alter the depth and duration of the pump shot. I think Quick Fuel puts the pink one in standard but I changed mine to red (main) and green (sec). It will be trial and error for what suits your engine best. Changing mine really perked up the response and eliminated flat spot.

 

[Lee Patterson]

thanks. yes, QF has pink installed P and S. did you change pump nozzles as well?

 

[DaveM]

I have a QF 750 on a 427 Windsor. QF sends the 750 with .031" nozzles. I did not change these. Since you're running a 650 on a 351 Cleveland I wouldn't change the .028" nozzles unless you can't dial it in with the cams.

 

[Lee Patterson]

before you changed cams, what was your throttle response like - dead spot from idle? once I tightened the pump linkage springs to essentially zero lash, the throttle response went to shit. that's what I still dont get.

 

[DaveM]

Yes I had a big flat spot before changing cams. That will make a much bigger difference than pre load or nozzle size. Once you get the cam kit look at the fuel delivery diagrams. The difference between different cams is dramatic.

 

[DaveM]

Check this out Lee:

https://documents.holley.com/pumpcamgraph.pdf

 

[Lee Patterson]

Thks guys

 

[Jim Dewar]

I run a Holley 650 (4150) “0” accelerator pump lash. First try opening your 4 corner idle mixture 1/8 turn at a time, you may have idle mixture too lean. If that improves your throttle response but not quite what you need go to 31 pump nozzle. Primary main jet size?

 

[Neil]

Hoping some here can advise. Just replaced my aging Holley on my Pantera 351C with a Quick Fuel HR-600 carb (mechanical secondaries). Went through all the set up and tuning. Got strong vacuum of 17+ inches and set 4-corner idle. Quick Fuel installation guide says nothing about setting or changing factory settings out of the box on the primary and secondary accelerator pump arms. So, watched the videos on YouTube (probably a mistake) and adjusted the lash on the arms to less pre-load (supposedly you are to set to zero lash). Upon doing, car throttle response was shit. Falls flat on its face with any throttle advance. So I adjusted back to the pre-load that came out of the box and it responds well again. So my questions for this group are:

1. Should accelerator pump arm have some amount of preload? (when I push arm up against the actuator arm spring, I get about 1/8" to 3/16" inch travel of threaded rod / nut above the arm.
2. Is this actually the case of the arm should have zero pre-load but my pump nozzles are undersized and creating that flat spot? (nozzles are 0.28" from factory)

I appreciate your insights on this.

I would follow the factory recommendations. The quick fuel is not the same carburetor as a holly it has many improvements over the old Holley design

 

[Lee Patterson]

4 corner idea mixture has been set very carefully using the procedure from QF using a vacuum gauge. Idle mixture isn't the issue. I am getting the cams and going to try Dave's recommendations before changing the pump nozzle.

 

[Lee Patterson]

Primary main jets that came with it are 66. Secondary 72. Primary nozzle is a 28. the problem isn't idle but anything off idle up to about 2500 RPMs. It at least is running with throttle response as I have it set right now with a small amount of pre-load.

 

[Jim Dewar]

No preload, you’re just compensating for a lean idle mixture! Try the four corner as I recommend, you can always adjust back to your original settings. The 4 corners affect the mixture through the entire range of throttle.
The carb I own is the same technical build as your QF built by AED, I have owned and tuned a QF.

 

[Lee Patterson]

ok will do. thank you

 

[Lee Patterson]

ok update, re-adjusted both primary/secondary pump levers back to zero pre-load. When adjusting, I set it to essentially zero interface when the pump arm just has pressure on it to start the downstroke. Started car let it warm up. seemed to warm up and had throttle response. Was about to look at mixture screws and noticed fuel leak. Appears to be at the front bowl. Tried to tighten bowl screws to the spec of 30 in pounds and still leaking. Back is tight and dry. Front dripping. I confirmed not from my fittings (same as yours pictured here - Fragola). Any thoughts on this new adventure?

 

[Lee Patterson]

Update. Rookie mistake. Fuel leak was at the front bowl inlet fitting. Had torqued them per spec, but front was loose. All tight. Adjusted idle mixtures out 1/8 turn. Idle speed increased and much less bog. Will test drive and see latest results. thanks for your input so far guys.

 

[Lee Patterson]

Dave, Jim: I thought I had stopped the front bowl leak. It continues to be moist even after retightening. Curious on the Fragola fittings it you used the metal washers or the Holley nylon type. I am going to have to uninstall it most likely to see what the heck is going on. Any experience in sealing these would be appreciated. Back fitting dry. All the ANs are fine as well

 

[Terry Oxandale]

Very little preload to zero is the designed intention, no? The purpose is to richen the mixture in conjunction with the opening of the throttle plates, so any gap provides a delayed enrichment (undesirable as observed by the poster), and any preload is either wasted in that the cam doesn't do anything until the plate shaft starts turning, or reduces the full designed volume for injected fuel used at full stroke.