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Linkage adjustment on QFT/Holley two fours
Question: what is a good start on adjusting /tuning the slotted opening of the second carb primaries coming into play. They are the Survival Motorsports/ QFT vintage carbs.
First quarter, Midway or last quarter of the slot? What is a good start?? 427, 282S, RPM heads, 10.3:1, Street driving but do not need it leaning out at partial throttle 90-100 mph with 3:54 at about 3,000 rpms. I guess I am answering my own question as I type, leading to the fuel/air mix FAST tool and welding bungs in the side pipes to really get the answer without holing pistons. |
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They should be pretty much setup from Quick Fuel... Open your idle screws up about 3/4 turn. Are you running the Blue Blunder version of the OEM progressive linkage? Here's a pic of my progressive linkage.. http://i140.photobucket.com/albums/r...alquads003.jpg |
Bought the linkage from Barry. To his credit I have sent a mail but he is pretty busy guy so just thought I would ask the forum as I got short break at work.
Setting the slotted progressive linkage on the right side, I am adjusting the slot which brings in the primaries of the back carb. |
I used the same photo's as a reference. The carbs are outstanding!! The real adjustments are all over. These carbs have adjustments for everything! Not just the idle and but underneath the carb too. I'm sorry as I don't remember all the adjustments as a friend was helping. He spent about two hrs and after wards the car is just killer! Regards, Matt
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Did not get the photos
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The best way to adjust ,IMO, is to set the linkage where the back carb if fully open when the front carb is too. That's the end product you want, at WOT both carbs are open 100% simultaneously. I think it works out to the front carb being open about 50% brfore the rear set starts to pick up. The rear carb opens about twice as fast as the front.
Make sure you adjust both front and rear idle jets, not just the front. Also make sure your accellerator pumps are adjusted properly, the actuator lever just touching the AP's diaphram. I had to use the lightest spring (I believe the white one) on both secondary diaphrams, also ensure both secondary diaphrams are tied together, vacuum wise. With no adjustments mine knocked down a 12.6 AFR on the chassis dyno, PERFECT! The "design" was originally worked out by me with Quick Fuel for my Pond 482 setup. I bought the setup through Barry. Afterwards I forwarded the carb "design" to Barry since it worked out so well and he had interest. |
With both right side adjustable rods I can get just about get any slot percentage and still both fully open at he same time. I just needed a good start at the 50% of total slot.
I am looking forward to seeing how they run with an 427 cu in application. I think they flow about 750 cfm each Undy, how are yours holding up with the E10 fuel ? Thanks Undy and Matt |
No problems to date with E10/15.
They're actually a tad too much carb but the adjustability allows you to still get spot-on. It was towards the end of the dyno pull before the rear set of secondaries came full open and that was with the lightest spring. I seriously doubt in street applications that you'll see the rear set of secondaries open all the way. |
Undy it looks like you pulled your upper fuel vent extentions out. Any problems??
The top of my oval air filter top comes awful close and with my last set of carbs, it was sitting on the air horns. My filter base is flat aluminum plate with holes cut out for the adjusting screws and other carb upper protrusions and then I used cut off spoons bottoms to cover the holes etc. The choke horns were milled off these. When the carbs were built I asked that the vent tubes be cut minimim height but it seems they are the stock height. Does anyone know what is a good minimin height and issues involved with shorter ones?? |
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