Technical Any 6-71 blower tuners want to give me some carb help

Go with a good Quality , not a cheap one , you need live feed feed back ,
What is yr set up , Stock 350 with a Huffer ,
I have run a lot of blower combinations , one was a 6:45 et in 1/8
SBC 400, 10 pds boost ,timing 21 @ 1,000 Rpm , total 32 all in @ 2,500 ( stayed on safe side )
Car was drove 500 miles a week
"Sleeper "
Cam hunder .550 lift
2,700 stall
Pump gas
Twin 750 dp
3,700 pd car
3:55 gear
29 tall tire
9 wide ,
Switch over to Enderle injection , 6:28 et , violent !!! Was very hard to dive on street ,
Power is there if you R willing to tinker !!!

 

I struggled with a blower and carbs for 2 years. I have Boost referenced Quick Fuel 650 cfm blower carbs. In the end I trashed the power valves and square jetted the carbs. The power valves made tuning almost impossible at the track. Even on the dyno with an air fuel gauge on it it was all over the place. Lean to super rich to lean.

We drilled a small bleed hole in the butterflys which helped starting immensely. It also made for some decent idling manners and reduced the load up.

Keep in mind this was a race car that never saw the street. My timing was locked at 36 degrees. 7 - 9 lbs of boost on a fairly tame 406 with decent heads.

 

The ONLY time I EVER block the power valves on ANY STREET DRIVEN car is if I am running the carbs sideways on a tunnel ram. It will get horrendous gas mileage and be blubbery rich at pt. throttle as soon as it comes off the transition slots, and with a blower, the impellers will stir things up enough that the pt throttle fuel distribution issues you have with sideways mounted carbs on a tunnel ram are a non-issue with the blower.
JMO, but unless this is a track only car, I would NOT block the power valves, I would tune them instead.

 

Falcon George it is a little lean at a steady climb from 1300 cruising to 2000.flipping the 330 cams helped alot.if you stomp on it at idle it will still backfire once in awhile. I think it is getting closer.starts great,idles 8-900 no surge will cruise at 1300 rpm in overdrive at 60,j just half to shift to drive get above 2000 and nail it

 

I am running nearly the same setup w a 350.and 3:90 gear w a 700r4 transmission,2800 stall.only 5 lbs boost so far,will probably go to 8-9

 

Try changing to a higher power valve, like a 7.5 or 8.5. This will bring the enrichment in a bit earlier, I would try this first. If that doesnt get rid of it, I would get a wide range O2 sensor, then go in and drill the IFR's a LITTLE bit more at a time, like one number drill size at a time, you really want to sneak up on this. Be patient and really sneak up on it, you dont want to overshoot the mark and have it way rich at cruise, it knocks the shit out of your gas mileage.
I would change to the blue cams just as a matter of course, I mostly use the pink cams with sticks where I want the pump shot to come in a bit later so it doesnt use up as much shot staging the car. You can move the throttle a few degrees off idle with very little pump shot with the pink cams, I find they dont work well on automatic equipped cars.
Once you do all this, I would look at WOT.

 

Well my carb tuning went on hold.took the family for a ride 30 miles down the interstate and the right front wheel bearings went out.we were lucky brakes felt funny pulling in to the gas station.they were the only thing holding the hub on. I was looking at it and a friend pulled in with his trailer they just used at the parade.

 

Never a dull moment!

I notice that if I adjust the idle rich enough to just get the rolling surge at idle, it will be less likely to have an occasional sneeze.

 

It really has me second guessing my plan to drive it 3 hours to the meltdowns. What are the odds someone would pull in with a tilt bed trailer and straps so the paint didn't get scratched. Lucky day

 

I tend to do the same thing, even on naturally aspirated combos. A hair fat and a bit faster than it really needs to be. If the car is a stick, it makes it nicer to drive, and (separate issue from this thread) I tend to use very aggressive cam lobes, and the extra oil splash helps keep the cam alive as well ("aggressive" and "big" do not equate to the same thing at all, aggressive means that the lobes have a relatively higher rate of lifter acceleration off the base circle). I think at least some of the issues we see lately with pre-mature cam failure are caused by guys using the modern uber-aggressive lobes and trying to idle them down as low as they can for increased drive-in cred. I prefer a looser idle.

 

What is the best way to fatten it up at idle? I have the screws at 1-1/2

 

run them all out a quarter turn at a time, and see how it does.

 

I set the throttle plates with the carb off so I am exposing . 020 of the transfer slots (this is with a 4 corner idle, all four plates) set the idle in gear with a vacuum gauge to highest vacuum reading first without turning the idle speed screws (tip: on 4 corner carbs, I take the secondary idle speed screw all the way out and install it upside down, so I can tweak it with a small-blade screwdriver from the topside), then turn the speed up a little (way less than a turn), and back the idle screws out a little, like less than an 1/8 of a turn from the best vacuum reading. I just do the final setting by feel. Depends on the combination and so on, I have my truck at about 800 in gear, just under 1000 in park, with a 244@ 050 cam and a pretty loose converter.
I dont want to have any more than about .030-.035 of the transfer slot showing, if I cant get the idle speed where I want it within those parameters, I pull the carb and drill the throttle plates, I DO NOT just keep cranking the idle speed screw in! Generally, I wont have to do that on a 4 corner carb unless the cam is REAL big.

 

^^ two carbs with primary side idle, you can think of it pretty much the same way as one carb with four corner idle, you are still using 4 throttle plates and four idle circuits to adjust the idle, and the fuel/air requirements of the engine at idle dont really change just because you have more throttle plates. If anything, you could probably start with less than .020 of the throttle plates exposed, because the secondary plates should not be closed tight.

 

This is scary, Pete and Jake spindle.broke off right at the threads anyone seen this before

 

Just realized there could be room for confusion in what I posted, one more thing I gotta mention here.

On a carb that does not have a secondary idle circuit, DO NOT set the secondary throttle plates to expose the bottom of the transfer slot!!!!
The bottom of the transfer slot is located way higher in a venturi with no idle circuit, if you turn the secondary idle screw in far enough to expose .020 of the bottom of the transfer slot on the secondary side of a two corner idle carb the throttle plates will be WAY open, you will never get the idle speed down, and it will have a BIG bog when the secondaries open. On a 2 corner idle carb, the secondary idle screw should be turned in just enough so that the throttle plates arent fully seated in the bores, thats all, no further. You do NOT want to expose .020 of the transfer slot unless the venturi has an idle circuit!

 

Might want to start another thread with pictures if possible. New spindle, older spindle? This could be a safety issue.

 

Keep notes on all yr changes ,Very easy to get lost what you did,
I spent ,25 pluse hrs on a set of carb for a flatty,
If you are Runing pump gas , with the blend of today ,you can not trust what you see @ the plugs deep down the inside the porcelain ,the new blend's will give you Fase reading , ( more with ethanol blend ) this is why a Wide Band O2 is a must ,
There is a lot of experimenting,
This is a good read , ( link) one of many

http://members.tccoa.com/392bird/tuning.htm

 

PERFECT photo of where to bench set the throttle plates, from the link above...

 

Jim,
Just a question for ya. When you run holleys on a blower do run them power valve delete? That is what I have always done.

 

I left the power valves in mine, and left them stock. It ran fine, a bit rich on the wideband sensor, but still managed 12-13 mpg on the road with mild gearing. But only 6 in town with 4.11s

Scary about the spindle.

 

if its slightly rich at cruise, you can probably do better on the mileage by leaning the main jets, then opening up the PVCR's to compensate. Tip-in response will probably be a tad crisper too. Calculate the current total area of main jet and current PVCR combined, then lean the main jets till you get A/F ratio where you want it at cruise, and drill out the PVCR's to get back to the same total area with the new smaller main jet diameter.

 

X2 , this is where spending hrs add up on tunning carb or carb's
It will pay off when looking for performance, and gas mileage if you drive your car,
More than once a week ,further then 20 miles !

 

And its how I get 18 mpg with a 244@050 cam, a 750 double pumper, and 4.56 gears behind a 700R4...
If you optimize the A/F ratio in each circuit, a carb can do pretty much everything EFI can, with the exception of cold start characteristics.

 

Keep running that thing lean and backfiring it and see what happens to those power valves. Lippy

 

Holleys have had a backfire ball check in the power valve passage for like 25 years now. I actually dug up and posted the date of the revision on another thread on here a while back, it was sometime in the early nineties. Most guys were doing it themselves long before Holley started doing it. I used to use a 1/8" ball on top of a section cut from the spring in a ball-point pen. Drill the top part of the passage in the base plate out to 3/16, cut a section of spring about 3 coils, drop it in the passage, and drop the check ball in on top of it, then lightly touch the bottom of the passage in the main body with a countersink.

 

George well I'll be damned. Learn something new everyday, I'm going back to fuel injection. LOL. You know it's probably been 30 years since I ran carbs. And those were Braswell's, 660's with 850 baseplates. Lippy

 

Complete with pictures...
http://www.jalopyjournal.com/forum/threads/best-carburetor.1006925/page-3#post-11366380

EDIT: Just noticed, the original post has a typo. I said "drill the passage 1/16" bigger than the 1/8 ball" then I typed 5/16 for a drill size!! must be that new math...

 

Braswell....from Tucson, where I grew up. The company where my brother worked did some computer work for them in the early 80s

 

I have used a lot of Braswell products, best in the industry. I have their two-step undercut downleg boosters (say that three times fast) in a 650 double pumper, and I use their button-head throttle plate screws in everything, top shelf stuff.