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

I have a 6-71 on a 350 chevy, pair of boost referenced 600 Holley. off idle lean condition. 6.5 power valves.drilled the power valve holes .010 larger to .052, drilled idle feed restrictor from .o33 to .035, primary jet 70,secondary 78, nozzles.035. it idles good,timing 20 all in at 2000 to 36

 

If you keep it above 2000 rpm it runs pretty well but 1000 to 2000 it sneezes through the carb. Do I keep drilling the power valve holes? Or bump up primary jet? Or both jets? I am running out of time for the meltdowns, can't get it on a dyno. Before then

 

what are you running for initial timing?

 

19-20, 35,36 total

 

I have an adjustable stop in the distributor I can play with if needed

 

Jim is your man on the carb blown stuff. I personally block off the power valves, bump the jets a couple sizes, timing would really have to be messed up to cause sneezing at constant speed. I am not familiar with drilling power valve holes? I wouldn't run vac secondary carbs on a blower. So it is sneezing at idle? Or just cracking the throttle? Sorry missed idle was ok. Lippy

 

I don't know...do the idle mixture screws have any effect? When I had the holleys on mine, it was plenty rich at those engine speeds. I just had pretty much stock 650 double pumpers, no boost reference.

should still be on the idle and transition circuits, you can try adding more jet, but 70 should be plenty.

 

There not vacuum secondary.the holes under the power valve. I read it in a old Holley book. Just sneezes when you stomp on it off idle. if you have it 2000 and stomp on it it runs ok. Jim has been a ton of help on alot of my dumb question's.

 

put a air fuel gauge in the car. you can see whats really happening without guessing.

 

that's for sure.

If it's just when you open the throttle, might play with the pumps. Are they double pumpers?

 

25 yrs. Ago I built my first blower motor, I found that the advance curve was one of the most pivotal parts of the tuning, 283,6-71,single point distributer, I messed around with spring's for day's, But in the end my fine tune ultimately came down to the advance curve, But I was running Carter's.. Everyone told me to "lock" it up...I just kept changing springs/weights an Finally got it dialed in an regularly spun it up to 7300 , I bought a old allenyzer distributer machine since )

 

One other thing.. I had to deal with was even though my blower was new (Dyer's) I had back fire's an come to find out, it had diesel seals in it, Which are different than gas, An was pulling the drive oil in fouling plugs, only realized it when I smelled gear oil on the plugs, just mentioning because you can chase your tail for a Minute on that one...

 

I was thinking more pump squirt also.

 

X2
Wide band O2 is a must , for tunning
What yr set up ,
BDS has a chart , Engin size , Rpm , boots = cfm's ,
Two 600 are not much on 6:71 unless under 5 psi , 5,000-5,500 rpm's

 

I agree with others that what you describe is linkage / acc. pump timing / acc. pump shot size. You are not yet where the power valves come into play. You said the pv was boost referenced. Where are you picking up the reference signal?

 

Sounds like doublepumpers. Then I'd crack open the secondaries, turn the carb upside down and you'll see a small screw to open the secondary blades a little, you open them to the edge of the transition slot so you can just see it with the throttle blades closed. With the secondaries opened a little you can close down the primaries so the transition slot is a square hole or so.
The transition slot is what provides fuel as the throttle blades open, it operates in milliseconds and is the 'transition' providing fuel until the squirters give their shot. Sometimes the primaries are open a little too far for the transition circuit to work right, so you close the primaries down a little and open the secondaries a little to get your idle speed back.

 

I'd be looking more in the direction of accelerator pumps - try bigger squirters, will tell you straight away whether thats your problem.

 

Yes double pumper, I have the pumps adjusted so there is no play.330 pink cams in

 

If I get an air fuel gauge what does it tell me? Sorry, I have never even seen one

 

I have an extra set, I will keep drilling.easy enough to try

 

Below the blower,in the back of the intake

 

Primaries are pretty well closed, it idles at 900 starts good and doesn't load up or surge. I had played with those before to get the surge out

 

this is the type of gauge he's talking about.

https://www.innovatemotorsports.com/xcart/product.php?productid=16373&cat=0&page=1

there are a bunch of different varieties, but this is probably most hamb friendly

 

Jim is there a book or somewhere to read on what the gauge tells me?

 

I don't know. Stoichiometric air/fuel ratio is 14.7, but most carbs seem to run around 12 to 13.5:1 at cruise, and richer (around 10 to 11) at WOT. The gauge will show you that the AFR fluctuates in strange ways with a carb...if you have EFI, you can adjust the fuel map to make it pretty, but carbs only let you do so much. But if you see it jump up over 15 when you wing the throttle open, you know it's leaning out, so that is something slightly useful. If it is high at low rpm part throttle cruise, then you probably need to richen the idle transition circuit, and you can play with jets and see if that affects it.

It may or may not be useful for you.

 

I flipped my accelerator pump cam's,so they come on instantly.it helped alot.in overdrive it cruises at 1200 rpm I thought we had it and it sneezed 1 time.before you has to run it in drive to stay above 2000

 

How big is the cam?

I keep mine 2000 or more cruising, don't shift into OD until I'm going 55 or so

 

It runs good enough I need to repaint both rear fender Wells. Evidently I need heavier springs and some stops on the rear end.

 

Setting up suspension is tricky....especially if you have tires that stick out past fenders, or something.

 

You were probably on the right track opening the IFR's, but I would use a wide range O2 before you go further, its easy to lose the rabbit drilling the IFR's by the seat of your pants, and because the restrictions are small, one increase in drill size is a big increase in terms of percentage of total area.
#330 cams give a lot of volume, but are lazy off the base circle, I'd try #427 blues.
One thing thats not completely clear here, and ABSOLUTELY CRITICAL to any advice given, is the lean issue steady state or transitional? In other words, is it lean at low rpm steady state cruise or does it go lean when you blip the throttle? If its steady state, you need to continue to work with the IFR's and transition circuit, if its when you are blipping the throttle, you need to work with the accelerator pumps and main circuit enrichment.
If its lean on transition, I would go up one on the power valves. Dont go bigger on the main jets to cure the issue you are describing. Main jets control steady state WOT mixture.