Pro Street S10

I'm not a hot rodder, but for hesitation, I would see if something mechanical is holding the motor back. Lose the fan, put electrics on the radiator. In a standard clutch, the flywheel is very heavy. In an automatic, the torque converter is very heavy. An alternator takes lots of power to spin it, even when it is not making electricity. Is prostreet used on the street? If not, lose the alternator. Lose the air filter. Are you using the correct fuel for this motor? I presume you have headers, and the exhaust is free flowing. I hope you have not put big tires on it, or changed the rear end ratio.

Change the power valves way down to say 4.5. I leared the hard way that the power valve is the key to the transition to High speed jets. I run a 2.5 for hillclimbing on a single 650

OH yeh, the formula for power valves: 1/2 recorded vacuum = 2.5 YOU"LL FREAK

I assume you have done all the go stuff if your running PS. Sorry about the FREAK comment but low vacuum WILL NOT OPEN the power valve if it is to large a #. My parts guy told me wrong and I tried a 10.5. Stupid. We accelerate 2-300 times a day on race day and it took some consulting but more retard and lower power valve have cut down 60' time remarkably....... but it is a ford.

Listen to Ray. If you don't have his kind of racing experience with these machines you won't know what you're talking about. Not trying to insult you other guys. These racing machines are all different and each type of race engine setup has its own rights and wrongs.

BTW, I don't know a lot about these popular Holley high performance carbs. My thing is old Hilborn mechanical injector systems and I still have a lot to learn about them.

Ed Weldon

Try running on one carb, disconnect the throttle linkage from one carb and see if that helps the hesitation. Be sure that the linkage is free so you don't cause a stuck throttle,(ala toyota). Is this on a tunnel ram type manifold?

Hello c-stile

I am not into the hot rod scene any more, but way back when I was, I found that hesitation could be "generally caused by any of three issues being not correct, 1- not enough engine vacuum/ leaks around gaskets etc. 2- incorrect timing, and 3- faulty or improperly adjusted accelerator pumps in the carbs. By the way, the Nascar Cup engines are also 350 ci. and on one holly carb., they are making a bit more than 900 hp. 2 carbs., plus all that linkage, that could be improperly adjusted might also be an issue.

Check these options out!

TMF

Dumping a lot of fuel (multiple accelerator pumps) at low RPM can cause stumble for all sorts of reasons, one of them being lack of sufficient spark. What are you using for ignition? A multiple spark capacitive discharge system is a must.

Are the carburetors set up for progressive operation (street driving) or do they open simultaneously (drag strip).

Remember, high lift/high overlap cams are notorious for horrible running below 2000 to 3000 RPM (not enough steady vacuum to provide smooth fuel/air flow). That's why NASCAR engines sometimes stall pulling out of the pits if the driver isn't on it. It's the nature of the beast.

If you are certain your cam was correctly degreed in, valve lash HOT is correct, timing is not excessive (usually 36^o max at full advance (say, 4000-5000 RPM)_{38^o gets scary and can burn valves let alone loosing Hp by firing too early}) and you have plenty of spark, then grab a can of spray carb cleaner and check the entire intake/carb area for leaks with the engine idling (don't forget throttle shaft bushings, carb gaskets, any hose connections AND hoses and possible cracked manifold). I would do this first before disassembling anything, as it IS running now, just not well. Then make the suggested carb internal changes, Ray sounds like he 's been there and knows a bit about working with low vacuum engines.

Way too much carb...2 x 450cfm = 900cfm...that engine can't consume that much volume.

Try a 650cfm...you will be happier, the linkage will be simpler, you will go faster!

Just to be a little clearer

Theoretical CFM required for an engine is calculated as:

CFM= RPM x Displacement/3456

6000RPM X 350 CI = about 607 CFM.

I've always used 1.7 X cubic inches plus 100 at 5000 RPM as a base number to work with. The plus 100 is for a cushion when flat shifting. Then proportion as needed to your expected red line and choose the closest size carb as long as the closest isn't more than 50 cfm lower. You don't want to lose the cushion or you will be richening the mixture too much at red line. Over carbureting kills the vacuum needed at peak RPM for proper fuel metering and you will be running lean at wide open throttle.

I debated of putting post #6 off-topic

http://www.holley.com/0-7448.asp

I've used tri-barrels, 4-barrels, single barrels but think the 2-barrel is superior especially for pro street and multiples are fine if the linkages are geared.

My suspect ion would be to have the mechanical linkages checked by a professional mechanic to make sure that the carbs a synchronized, followed by checking the vacuum advances.

Have the jets ever been removed from the Holley carbs? Were the carbs ever rebuild? Also, may want to double check the floats in each carb for proper setup.....

Also, are the carbs dual feed double pumpers?

Ohhh, forgot one thing...how's the fuel delivery? Fuel pump, etc. working okay? Also, replace the fuel filter just in case! What type of high-rise intake manifold is installed. Is the 350 CID engine a LT-1???? Bored over??? Blueprinted engine?????

I offer you this bit of advice, if you're not experienced with working with carbs, then don't start now by tweaking with them of taking them apart...it'll cost you a small fortune to fix the mess you made. To fix this I think the trial and error method may be the best....having dual carbs complicates things 10 fold.

In all this we should aska couple of crude questions. What cam, What heads and what else was done to them, Plenum intake, Exhaust package? 5 pounds is low so I'm guessing your running a big duration cam which turns low vacuum. Take it to a pro and get them to varify engine specs or ...You could get thrown out of class if your racing. I gotta stop watching Pinks.