Quick Fuel Slayer -poor transition

[57 210]

The ignition and timing are spot on as the engine runs perfect with other carbs, as1850's or 3310's. I thought I could get this carb to run with it's own original parts. During my work on this carb, I did try a throttle plate an 1850 Holley. Guess what? It ran good. I didn't try to fine tune it as I wanted to keep it original. I think that indicates I will have to change throttle plates. I've chased this mutt a lot and got no ware.

[rgalajda]

[rgalajda]

I should add here that I usually start with IFR sizing and leave the air bleed as is.

Air bleed system behavior and its effect on low flow. They don’t always do what you would expect. 

This also relates to main air bleeds.

You haven't mentioned camshaft specs

[57 210]

I will try the .033 idle restrictor. the throttle plates seem to be good but I will check them. I don't think the shaft is twisted but I did true up one transition slot with a welders cleaning tip. It had a small burr that made it look angular. It's now square and even with the other. The problem is the engine goes lean right off or very soon off idle and stays until the mains come on. The cam specs are Crane hyd roller with.222-230 @ .050 and lsa. It's a 406 sbc in a 3800 lb car with a 200-4r and lock up and 3.42 gear. So it can load the engine at low speed and high gear. This problem also happens during low gear starts. This is not my carb so I will ask my friend if I can drill the transfer slot for the .081 restrictor. This is all helping my knowledge base; but since I did try with success the Holley 1850 throttle plate it indicates transfer slot width problem. The .004 th's difference doesn't seem like much but it is 17% bigger. that is a lot.

[rgalajda]

Transfer slot restrictor is to lean up the transition slot . If you are already lean, this won't help.

Are the idle mixture screws 1.5 turns out ( 2 corner Idle ) and close the secondary throttle blades 1/8 to 1/4 turn after contact of the screw.
Try richening the idle mixture screws.

220-230@.050" needs more fuel. Maybe more than .033" IFR
What is the LSA?

[57 210]

jmarkaudio. Can you explain how a t slot restrictor works. Does it lessen the proportion of slot air/fuel to the amount from the idle air/fuel mixture after the idle mixture screws are reset.

[GTO Geoff]

As I said earlier in this thread, a long[r] T slot will make the off idle mixture leaner. Performance carbs of the same family I have looked at have short T slots, emissions versions [ leaner ] have longer slots. The long slot allows more air in & bleeds off signal, result leaner mixture.

I see two 'fixes'. Either used singularly or together. Reduce the size of the IAB so that the idle cct functions higher into the rpm range. And/or reduce the size of the MAB so that it starts earlier.

[rgalajda]

Holley 3310-1 780 cfm
transfer slot .023 x .220

Holley 3310-2 750 cfm
transfer slot .026 x .210

Holley 80557 750 cfm
transfer slot .022 x .240

Holley 4803 780 cfm
transfer slot .024 x .210

Quick Fuel 770 cfm
transfer slot .028 x .225



Holley 850
transfer slot .024 x .200

Holley 750
transfer slot .027 x .230

Holley 600
transfer slot .024 x .260

Holley 1850-3 600 cfm
transfer slot .024 x .270

These are carbs that I measured the transfer slots on . I used pin gauges to measure the width of the slots. Notice how they vary so much. And look at how long the slots are on the 600 cfm carbs.

[57 210]

LSA is112 and it idles at 15 inches at 800 rpm in neutral.

[JedIEG]

This is the same carb I have and it does as you say. Lean transition off idle. I have messed with it for years and not been happy-its infuriating. However, QFT's best suggestion to me was to raise the float level so fuel is at the very top of the sight glass. It made the car drivable, but then you have to chase the ultra rich idle and main circuit. I have changed about every bleed and jet on the crab to get it to behave ok. Also if you have the pink pump cam still on there ditch it. You need the orange or blue cam that deliver a decent volume right off the hit. That got me to the point where there is only a little stumble when accelerating slowly.