my malibu is stumbling(hesitating)off the line.it has a holley HP 750,jetting is at 63/73 w/ rear extensions,fuel pressure is at 9,could use any and all suggestions,thanks
stumbling off the line
- Thread starter polchiks1980malibu
- Start date
Need some more details first to get a better response, this is what I have off the top of my head:
- Are you leaving from Idle or a certain RPM with your foot on the pedal some
- What cams do you have on the secondaries (the plastic inserts that determine when the secondaries activate)
- What squirters Front & Rear
- Power valve? If so, what #
- Fuel pressure #
- Are you leaving from Idle or a certain RPM with your foot on the pedal some
- What cams do you have on the secondaries (the plastic inserts that determine when the secondaries activate)
- What squirters Front & Rear
- Power valve? If so, what #
- Fuel pressure #
What kind of stumbling, at the hit of the throttle? You are looking at either accelerator pump, or uncovering of the rear jets. Where are you located, I am over in Mountville. I should be at Maple Grove this weekend with the Chevelle.
Please give some engine specs. We will be able to help you allot more..I would say go down in squirtter size, and see what your timing is at
Here is all the information. The holley is a 750 HP right out of the box. Intake is a Weiand Team G with a 2" Plenum gasket matched to a set of AFR 227 (2.100 intake and 1.600 exhaust). Mallory electric fuel pump. Howards Mech. Roller cam (.630 lift on intake and exhaust) duration at .050 is 252/258. Pistons 11.7:1 Compression. Forged Crank. Splayed Four bolt Eagle mains. 1 7/8 Full lenght Headers. Th-350 with 8" 5000 stall converter. Hughes Manual valve body. MSD 6al Ignition. MSD pro billet distributor. Ford 9" rear with 4.57 moser gears. Full spool. 35 spline axles. Best et 11.0 at 125. with 60 ft. are lagging at 1.6 plus. Car weighs 3150.
First off, 9psi is too much. Possibly overpowering the needle and seat. Try 6-7psi. Secondly, the HP carb series is more for street driving as evidenced by the 63-73 out of the box. My "other" brand 750 mech. secondary came out of the box with 76-83 which I've tuned to 81-86. Perhaps you adjusted the fuel pressure up to mask the lack of fuel delivery by the carb? You have extensions so that isn't the prob. Is all that hardware on a 350"? She's gonna' want to spin crazy rpms so you need a kick butt-dialed in fuel delivery system to keep it fed. Give us a detailed breakdown of the entire fuel system including line diameter everywhere, pump specs and location, filter size and location, cel or stock tank, etc.
Small Block Chevy 358 ci. Five gallon fuel cell. Goes to Fram canister filter. To a Mallory 140 Comp fuel pump.( all that has been mentioned is behind the rear differential) 1/2" stainless Steel braided (entire fuel system). Goes into a Holley Fuel regulator to Holley 750 Pro Series HP Carb. (Squirters , front and Rear are both 31) . Using Sunoco 110 octane fuel. Leaving the line at 2700 (foot braking)
I'm running 80 square in my 355 now, no power valves in a Quick Fuel P850..3/4" fuel line w/ BG280 Pump. 6000 Stall leaving from Idle. Granted, the current headers are scavenging fuel (2" primaries). Best et is 11.50. You say it's stumbling and still goes 11.00..not bad, you are way ahead of me.
You are about 100# less than I am, what time of year/weather conditions did you run 11.0?
I'm struggling with 1.6X + 60' times also, we need to get together and fix them both at the same time : )...What are you doing November 6th...?
You are about 100# less than I am, what time of year/weather conditions did you run 11.0?
I'm struggling with 1.6X + 60' times also, we need to get together and fix them both at the same time : )...What are you doing November 6th...?
I was just posting in another thread that better heads are probably what I am lacking to get the last bit out of my motor. I am running ported Pro Comp 210cc heads with 2.055 1.60 valves, the AFR 227's are definitely helping you...
What are you shifting at?
How do the plugs look after a pass? If you're running at MG, the scenic drive on the return road might hurt the plug reading, however.
What cam do you have on the secondary diaphragm arm? Is it set to open later since you are leaving from 2700RPM? If it is set to open instantly, you could be getting a lean stumble because some of the fuel is already blowing in when you are staging and isn't there when you leave.
What are you shifting at?
How do the plugs look after a pass? If you're running at MG, the scenic drive on the return road might hurt the plug reading, however.
What cam do you have on the secondary diaphragm arm? Is it set to open later since you are leaving from 2700RPM? If it is set to open instantly, you could be getting a lean stumble because some of the fuel is already blowing in when you are staging and isn't there when you leave.
