supercharger carb mods?

Seeker1056 · DOURO, ONT

supercharger carb mods?

RacerRick · TORONTO, ONT

You need more accelerator pump shot if it is going lean when you first get on the pedal, then evens out as the main jets get involved. That's what the accelerator pump is there for - to cover up the fuel "hole" when the butterflys are opened rapidly but the isn't enough flow through the venturi to pull fuel from the main jets.

Are the carbs list 4224 center squirters or another list number? The 4224 is the most common 660 center squirter carb and are designed for use on tunnel rams and other large plenum intakes, so they are very fat on the bottom end, and have 50cc accelerator pumps. They should work fine on your blower motor once tuned.

On a holley carb, the accelerator pump cams position determines when the accelerator pump comes in, the pump cams shape determines how the fuel pump shot behaves as the throttle is opened, and the squirter nozzle size determines the amount of fuel.

The blower motors I have played with all required a really large accelerator pump shot. I would start by moving the pump cam to the most aggressive position on the throttle linkage and see if that helps. Also make sure there is no slack between the pump and the pump arm. If going to the more agressive position on the pump cam helps but doesn't fix it, then your squirters are just too small or and you may have to go to a more aggressive cam. I believe the squirters are 25's from holley - I would start with 28's and go up from there before messing with the cams. The last 6-71 blown small block I tuned ended up with 35 squirters in it IIRC, or it would pop back if you snapped the throttle open under load. Backfires are really bad for blowers....

Seeker1056 · DOURO, ONT

Racer Rick - thanks for the reply

That's why I chose the 660s - no power valve to deal with, and fat on the bottom end - just like a supercharger likes.

so yes - fine tuning

I will check the pump cams and see what can be done there

the accelerator pumps are tight set, (well with in a couple thou - so maybe I will tighten them to zero)so maybe the pump shot from the squirters does need enlarged

the backfire is so slightly off idle the squirters don't get a chance to help by the look of it

I had someone tell me that the actual idle circuits needed addressed to increase fuel flow but this thing is already very fat according to the gauge?

once there is heat in the motor/blower is doesn't happen much if at all

It could be my starting strategy - I read yesterday one is sposed to bring idle up to like 2k for at least 2-3 minutes immediately so the blower gets some heat in it - I have only been catching the throttle and slowly letting it back to 850rpm - all in the space of like 30-40 seconds

-- Edited by Seeker1056 on Monday 1st of December 2014 10:31:21 AM

Cat in the Hat · BRANTFORD, ONT

Ken,

I agree with Rick

You might want to look at holley part # 20-12 accelerator pump cams

I had the same issues and bought the cams (about $20 a set)

and kept changing untill i found a set that got rid of the stumble/back fire

could be cheap fix aside from buying new carbs

lmao......backfires are bad for blowers.....yup....that about says it

Seeker1056 · DOURO, ONT

yes - I know about backfires being the bane of superchargers - the blow off on mine works very well lol

so I will get to the pump cams and adjustments tonight to see exactly where I am at.

So what pump cam did you wind up with when done - these ones - that you gave me the part number for? - just checked - that's a kit of various ones - I would be more interested in knowing what you used so I can just buy a pair and be done with it - Ebay price on the kit is $41 plus shipping and dollar exchange

-- Edited by Seeker1056 on Monday 1st of December 2014 10:42:07 AM

Seeker1056 · DOURO, ONT

so Holley now only makes a .025 squirter or at least that's all they list on their website - you have to drill out to get larger

So not being a machinist - if I want say a .038 or .040 hole what drill size is that?

given this thing will never see the back half of the carbs - would one just drill out the front two squirters and leave the back ones alone to preserve volume?

Cat in the Hat · BRANTFORD, ONT

I ended up useing the brown ones....they worked for me....not saying they would be the best for your application

$23 from summit

I have included a pump cam chart for you to take a look at

as for drill sizes...im sure slim will jump in and tell you what size a .038 or .040 drill would be

holley pump cam chart.jpg

Seeker1056 · DOURO, ONT

thanks Cat

Seeker1056 · DOURO, ONT

I checked at lunch time - I already have the brown cams installed, however the rear carb does need a slight adjustment on the pump arm... smiles
so maybe a slight increase in shooter size is in order if the adjustments don't cure it

slim · DUNDAS, ONT

.038 =#62

.039 =#61

.o394= 1 mm

.040= #60

smile smile smile

Seeker1056 · DOURO, ONT

thanks slim

my bad - it was sposed to read .028 ... smiles

slim · DUNDAS, ONT

.028 =#70 ... you will need a pin chuck and spin it as fast as you can

slim · DUNDAS, ONT

This will be easier

https://www.imperialsupplies.com/pdf/I_DrillSizeDecimalEquivalent&TapDrillChart.pdf

forget that one this is more complete

http://www.gfii.com/images/Greenfield_Decimal_Equivalents.pdf

Other useful stuff

http://www.gfii.com/content/technical.asp

-- Edited by slim on Monday 1st of December 2014 08:36:03 PM

RacerRick · TORONTO, ONT

I would try the yellow or blue cam first, before drilling. You used to be able to buy squirters for that carb.

What lobes does the blower have? Traditional GMC straight 3 lobe design?

Seeker1056 · DOURO, ONT

twisted rotors design

will let you know how I make out with some adjustments first before tackling cams