My friends camaro that I work on developed a very strange issue when we went to race it yesterday. the motor is in a 74 Camaro and is a 468 with a 177 supercharger. I just rebuilt the 750 dbl pumper that's on it. Ordinary rebuild...except I put the Holley Adjust-A-Jet system on and blocked the power valves. When we first ran it on the car (about two weeks ago) we dialed it in using an 02 sensor in the exhaust with a digital A/F meter. We set idle to a perfect 14:1 then managed WOT and cruise very close to 12:1 under load. Car ran better than perfect up until yesterday which were our first base runs on the new carb. First pass the car broke out of second so bad we let off a babied it to the traps (still ran a 14sec. E/T). Next pass in the burnout box car stumbles pretty bad then dies when staging. Start it back up...seems to run okay and we try to make a pass. The second that WOT ocurred, the car stumbled all over the place and did not clear until about mid second gear but was puffing black all the way down the track. Heres the problem...pull the plugs and they're all pig-rich. Thought maybe I had a needle and seat valve stick on the primaries but no gas or carbon was in the main block when I pulled the air cleaner off. After checking the pressure regulator and pump and wiring we made two more passes with exactly the same results. It didn't drive to the track like this....we made a few test passes on our way and the car was fine.
The fuel system is a 5/8" line all the way from the tank to the carb. The fuel pump is a electric Holley Blue (brand new) that is right next to the tank and the pressure regulator is set at 7psi and does not fluxuate at all under WOT....
What's weird is that the car idle's and drives fine and is even okay under WOT when already moving...but try and do a burnout or launch at WOT and it's a very nasty stumble while it just dumps fuel in. We're going to replace the plugs and set the A/F ratio on it again but I'm concerned something failed on the carb....any suggestions??? Something to look for? Thanks.

Hook a piece of fuel hose between the two bowl vents. Cut a slot in the top to allow the vents to work. What is happening is the fuel is comming out of the front vent and going into the primary throttle bores when you launch. Causing your flooding problems.

Jesus...I never thought of that!!! Thanks...I'll let you know!!!

why did you decide to plug the power valves? sounds like if you decide to replace the pv plugs with a 1.0 power valve, it may run good. I know if you do remove the pv's, you must jet up the carb by about 10 sizes. Also sounds like when you launch, the vacuum drops, then becomes boost, and you may need that extra fuel that the power valve system provides. I know of Holley using these 1.0 power valves on all of their supercharger carbs. After the burnout and when you are on the trans brake, the plugs could be getting fouled. Good luck.

Does the carb have the plastic vent extensions on the metering blocks ??
Why would it dump fuel out of the vent during the burnout ?
What do you mean by " broke out of second " ??

Broke out of second means we lost traction on a poorly prepped track :(
No, I don't have the extensions but thought they were merely for hard braking since fuel pressure never drops.....didn't run the power valve because this is 95% a track car and it has the holley adjust-a-jets on it so tuning to compensate is no issue and wasn't. Like I said the problem just occured on track day.
The whole burnout box issue kindof weirds me out too. I think by that time the plugs were already fouled so trying to clean the tires under load was making it worse.....to compound the issue we discoved a charging problem in the electrical system so I'm sure that helped. :eek:

Did you buy fuel at the track?

It may seem odd, but I have had bad fuel cause a similar problem, as if the engine were flooding out.

Try some fresh fuel and see what happens before you pull your hair out hunting for other issues.

Kind Regards!

Thank you guys for all your help. comination of slosh from the vent and a slowly deteriorating charging system was the culprit. The alt. is only charging at 11.8 volts idle and 12.2 reving the motor at 4K. Definitely caused the plugs to foul and now that we fixed the above issues all is well. Thanks again..... :cool: