3.4 L v6 chevy @ 8psi with holey carb

I finally get the rail out this weekend and it ran great... sort of.
In the higher rpms she stalls. Only when I change gears though. When I am balls out she is fine, unless I am going up hill, then she backfires.

if I on the flats and in the higher rpms every time I change gears, she stalls. I usualy have to pop the clutch and I am fine, but I am loosing a ton of performance.

Any ideas?

It almost sounds like it is starving for fuel at WOT.

I thought it was fixed.....

Fuel pressure/pickup problem?

Float leval, too low

There's your problem, right there

Holley makes a carb for offroad use, the Truck Avenger. It's designed for off-camber situations like Jeepers would get into, oughta be perfect for a rail as well. It comes in three flavors, 470, 670, and 770 cfm.

[attachmentid=160179]

The backfire during hillclimbs is more than likely raw fuel spilling over the float bowl and going down the throttle bore. You didn't say how steep the hills were, if it's just Olds or if it's every dune you go up. You might get rid of that by adjusting the float level in the bowl DOWN, but it's a real fine line to being too low.

The stall at gear change, does it stall at WOT, or during the shift, or when you engage the clutch?

Edited to add pic...

In the dunes, I have to be going balls out, WOT up a good sized hill for it to backfire.
For stalling in the flats, it happens mostly in the higher RPMs, not always WOT though.

You do not mention what model Holley carb you have. I have had, and set up many Holley double pumpers for the dunes over the years. Hopefully this info will help. I will only use center hung float bowls with brass floats. I always use spring loaded needle and seats and the thread in jet extension. I then remove the vent tubes from the air horn (use a small pair of vise grips and twist slowly and they will come right out) and I then replace them with 5/16 hard line and make them about 3/4 shorter than the air cleaner lid. It is hard to explain but hopefully you get the idea, the tube usually ends up being about 4 1/2 inches tall. I then set the float level about 1 1/2 turns down. I know that sounds like a low float setting but I have had great success. One other thing that I have done is to use a Holley red pump with no regulator and feed straight into a fuel log. On the back side of the fuel log I would run a glorified ball valve with linkage connected to the throttle shaft. I then would place a jet in the output side of the valve and then plumb it back to tank. At idle the ball valve is open and returning fuel back to tank. You can set your idle fuel pressure with the return jet size; I would usually end up about 3 lbs. As you accelerate the ball valve closes off ad at W.O.T. you will be at full pump pressure of 9 lbs. This really helped with the flooding over at low rpms in the woops.
Good luck, I hope this helps.

Thanks for the reply
PM sent

I called the shop that built the engine. The only thing they said was to bring it in so they can adjust the jets.
Said that the backfiring is over boost. Does that sound right?

I run a card and to fix these problems I run a Barry Grant 220 gpm pump with a bypass fuel regulator. The regulator goes after the carb and it lets everything over the set PSI return to the tank.

In a way yes, too much boost for the amount of fuel being provided. Need to find out if the carb has the power valve modified for boost reference and if the power valve channel restrictions are stock.

You don;t happen to live in AZ do you?

If you are looking to do the cross over mod to your holly an easier way is to use a piece of fuel line and connect the two vent outlets, just cut a V in the top by the carb stud.

8psi might be a tad too much imo.drop it down to 6.5psi you will get more volume also.Might also want to lower float bowls a tad.

IMO carbs can work well in the dunes they just need to be set up right which ain that hard to do.