Hey yall.

So my monza is ready to hit the roads and tear em up...only I got a problem.

Im running a tunnel ram (weiand street ram) with dual 600 single pump vac sec. holleys.
Both carbs are identical with the same jets, cams, squirters, and pumps.

Intake is heavily modified...so I know everything is working together.

But...I seem to be getting some problematic backfiring through the carb whenever I stick my foot in it hard...this equates to a giant fireball through the carb followed by a mushroom cloud of black smoke at around 3000rpms...So i am assuming I need to replace the power valves.

but I dont think I have any vaccum leaks  and I would think that 1200 cfm of carb wouldnt run lean anywhere.

Does anyone have any experience tuning tunnel rams?
Please help if you can.

PS: before you tell me that running one carb would be easier...this I know...but the harder it is to do...the cooler the results...so Im sticking with the ram...plus I have about 20 hours of labor in the intake alone.

God bless
-Shred

I wouldn't assume that it's not lean.

Could it be that the secondaries open prematurely, causing velocity at the venturis to drop and thereby leaning out fuel flow through the jets?  (remember, carbs are simple pressure differential devices). 

A tunnel ram is also not going to have the best low-speed velocity because of its short, fat runners.  Overcarburetion together with a low velocity manifold design may be what's causing your  "lean backfire" problem.

I'd experiment with the secondary opening rate and the power valves.

You have alot of plenum to fill up up with air fuel mixture before it gets to the intake valve. It sounds like a lean out backfire. Try larger accelerator pump nozzles, like 31's or 37's. Then go with stiffer springs in the secondaries. Also, try using power valves that open with lower vacuum like 45's or 55's.

Timing could also be an issue.

Take one step at a time so you know what each steps results with.

Stick with the duals. Look great and perform great. I am running 2 660 holley's on a tunnel ram and I am very happy. I take my car to a dyno tuner regularily to keep thigs running well. I don't know why, but things change a lot with two carbs