Lean out QF 850 cruise

[Right hand drive]

[i82much]

is this a pressed-in restrictor?

[rgalajda]

[i82much]

We might have a few more days when I can drive the car, once we get the first decent snowfall they put the deicer down and then I put it away. But not sure if I will get around to drilling and tapping it before then.

i am not entirely familiar with the procedure, but I'm guessing a # 21 drill bit and a 10/32 tap? Can I just use a bottoming tap? Seems small enough that I might not need to start with a plug or taper tap.

Also will these blanks work? Not sure if they are the correct length?

https://blp.com/cart/index.php?main_pag ... ts_id=1495

[rgalajda]

3/16 is the correct length. Usually an 8-32 for most main body Holley carbs. Since yours already has a pressed in restrictor you would have to remove that and measure the hole.
I use a normal tap that has been marked for correct depth so the set screw bottoms out flush. You will have to tap shallow, screw in the set screw and test for depth. .064" is what I ended up with in my Quick Fuel carb. I don't know if you were going to oder blank or predrilled set screws? I ordered mine from McMaster Carr in all 3 sizes 6-32 , 8-32, and 10-32, 3/16 length.

[i82much]

thanks! i just ordered 50 of each in all 3 sizes, will pull the carb off and get to work. should be fun! and i will feel a lot better about going on long drives if my AFR cleans up.

[jmarkaudio]

.081 is a fine place to start. As far as idle jet and bleed sizes, it really depends on the engine its going on. I had to go to .039 on a 600+ HP Pontiac, same carb on my engine was fine with a .037. Vacuum at idle, timing curve, how the cam pulses, texture in the intake tract... lots of things will affect how the idle circuit needs to be tuned. Lean it until you get a stumble or surge in light throttle positions, give it just enough to run clean. Engine temps need to be consistent, gas has multiple chemicals that evaporate at different temps, pump gas can be really temperamental. Sometimes only a 10 degree change will have an effect. Large swings in ambient temps will change it as well, so you may need to make an idle bleed change from summer to winter.

[rgalajda]

For a true street car ( not a race car ) the IFR should sized for more than just consistent engine temps, unless you like a stalling engine while it is warming up and feathering the throttle while you back out of the garage , even with a choke. Car cools off somewhat when your somewhere and idles like shit until heat is back in it. Also I think the .081” TSR will be to large to make a difference to your cruise AFR. Easier to drill it larger than keep making new ones.

But what do I no . I tune street carbs , not race carbs.

[treyrags]

Mark suggested .081 as a starting point. We all have our own personal preference for cold start behavior. I personally don't mind tickling the throttle a little to to get the engine to operating temp to ensure a nice clean mixture once it warms up. That's what thermostats are for.