I have a weiand roots 177 supercharger on a chevy 350. The carb. I am using is a 750 cfm edelbrock. When I hit full throttle, the engine backfires throught the carb. sometimes. It doesn't seem to run correctly. My setup: Running standard 4-7 psi boost. 8 degrees initial ~30 degrees total. I changed secondary jets from .107 to .113. I kept standard primary jets, but replaced the metering rods with .065 x .037. (stock is .071 x .047) Am I getting too much fuel? Please help with expert advice for setting up an edlebrock carb. for roots supercharger use.
Thanks

The first thing I would try is more initial advance. Blowers love timing at idle and lower rpms. I'd start with 14-16 degrees initial. You will however have to cut back the total timing to keep it in the 30-32 degree range.

A lean condition would also cause this; the Edelbrock carb would not be my first choice for a blower motor, but with some tuning it can be made to work.

Jody

Malibu,
I second Jody. From the BDS web site:

"Blowers love ignition advance. Especially initial advanced. For most blower applications, the initial timing should be set at 16-26 degrees initial advance with a total of 32-36 degrees advance, in all by 2500-2800 RPM. More advance can be run if there is not a detonation problem. Some vacuum advance systems will have as much as 45-50 degrees total advance under part throttle, cruise conditions."

I agree with these guys. You need about another 6 degrees under full advance. And speaking of full advance, have it come in around 2,400 rpms' and fast. Might want to make sure you aren't running out of fuel on the top end either. That 'issue' was chasing me for a few weeks after first firing the motor. Couldn't figure out was causing the fuel pressure to drop down to the 3 and 4 psi range while at WOT. And man - it would let you know...KA-BOOM!! :D It turned out to be a 10 micron billet fuel filter still plumbed near the fuel pump out back. Overlooked it completely, but it was the choke hold in my fuel system. graemlins/clonk.gif It wasn't an issue with the n/a 502 before, but like your blower, this thing has an appetite. I swapped to a larger 100 micron filter and the severe backfiring thru the carbs was gone. Fuel pressure stays right at 7psi under WOT now. Hope this helps some.

Like the others, I dislike your initial advance. I'll even go one step further on the ignition advance - run it locked, with a start retard as needed. With a supercharger, especially a roots type, you can build cylinder pressure faster than any normal advance curve can keep up with. On my 468 the exhaust temps went down 100 degrees after locking the advance (mostly locked at 28 to 32 degrees depending on fuel/boost psi).

I've seen plenty of street rods with the 177 blower and a Carter/Edelbrock carb. A high volume fuel pump is a must. Also make sure that fuel tank sock is fresh and that there are no undue restrictions in the fuel system. If you only have 5/16" fuel line now would be a good time to upgrade to 3/8".

Thomas

Normally a carburetor would have zero or near zero vacuum just below the throttle blades when it is at wide open throttle and at a fairly low engine rpm. The blower all but eliminates this no-vacuum condition and instead causes the carburetor to experience a slowly increasing vacuum signal from just about any rpm and any throttle position.
What you are experiencing is the result of a continuous vacuum to the pistons which operate the metering rods in your Carter AFB, I mean,,, Edelbrock Performer carburetor. The blower doesn't allow the carburetor to operate the power enrichment circuit properly and runs lean at wide open throttle.
The fix is to modify the carburetor so that the passages are connected to the plenum area beneath the blower and also re-calibrate the little springs that are under the power pistons. I believe the good folks at The Carb Shop, www.customcarbs.com (http://www.customcarbs.com) can help you if needed.

Good luck,

Louie

Malibu, I would agree with all of the above and emphasize that my supercharged motor (running a B&M 144) really likes a lot of fuel and timing on the low end. I recently switched from a Holley 750DP to a 950 HP which was not specifically tuned for a supercharger and instantly noticed an inconsistent backfire sometimes when I would try to stomp it from idle. I eliminated the backfire by changing to the proper accelerator pump cams (more fuel, quicker).

Additionally, I have observed that the more agressive I get with the timing curve the more responsive the motor gets. I started real conservative with 10 initial, 28 total, all in by 3000 and after several tuning sessions at the track/street driving I have ended up with 18 initial, 32 total all in by 1800. All I can say is the more agressive timing curve (changed by using springs from a moroso timing kit) really woke this motor up (like night and day). I gained an honest 2 mph (113.x to 115.x)in the 1/4 this past sunday by adjusting timing over the course of 5 runs.