Around 1000-1200 under load the engine has a lean spot it seems. Basically, the engine hesitates a dead stop if I roll my foot slowly to accelerate. Once I get past 1500RPM is will pull smoothly to 4000RPM +. It's very noticable when driving around since whenever I come to a stop then go to accelerate, the engine just sits there for a second struggling to get from 1000RPM to 1500RPM, then its smooth sailing.

Jetted my carb down to a 63 primary and changed my PV from a 6.5" stock to a 9.5". Should I use an even bigger PV, like 10.5"?

 

1) Select power valve based on http://www.holley.com/HiOctn/TechSer...o/TI-222A.html - probably Paragraph #2 (all too many people only read Paragraph #1).
2) Jet primaries for proper mixture after completing #1.
3) Jet secondaries for proper mixture after completing #2.

 

use bigger squirters to cover the lean spot on the throttle transition

 

It's already a 30cc pump shot. Using a 50cc shot doesn't seem like the best way to go about this.

Why do they use inches of mercury? What is 2" HG equivalent to in inches of water column?

I get 15" WC @ idle in gear and 17" WC on the highway at 65MPH. So where should my PV be? I'm at 9.5"...should I go even higher?

 

i said use a bigger squirter, not a bigger pump diaphragm.

squirters are the accelerator pump discharge nozzles....the come in the thousandths just like jets.

my guess would be yours are between 28 and 31 if you've never changed them before

 

It's a 31, which should be more then enough. Any info on the HG conversion?

 

1" of mercury = just under 1' of water (1 atm = almost exactly 30" of HG, and 32' of H2O)

I would leave the accel pump alone except as a last resort. That's all it's supposed to be in the first place anyway, is a cructh, to get the carb over the period of time right after you move the pedal and air starts to move, until the (heavier) fuel can catch up. It's not RPM based, it's pedal-motion based; so if you have a RPM-based problem, it's the wrong answer.

Check your vacuum under all normal conditions; in particular, cruising in high hear at the lowest speed the car will comfortably go in high gear, and idling in gear. Use a PV that's about 1.5 - 2" lower than that. So right now, if your vacuum is over 13" under those 2 conditions, use a 10.5 PV.

If that doesn't fix it, go back up on jets.

 

all this is great, but whats it look like on a dyno graph with the a/f curve

vacuum is a joke compared to an accurate air fuel reading from a wideband, its like tuning EFI with a gameboy


thats what will tell you where you need to go, 31 isnt a very big squirter depending on the combination.

if there is a large spike in the A/F curve right at the point of throttle transition to wide open (smashing the pedal)

also known as the off idle hesitation/stumble you mentioned earlier......
then a larger squirter is needed to cover the lean spot.....try a 32 or a 33 i bet it solves the problem

 

http://www.holley.com/HiOctn/ProdLin.../TubeNzzl.html

I have a .31, now the next size is .35, is this overkill?

I think now that it may be a combination of pump shot and PV hurting me.

If I roll my foot very slowly, the car will accelerate smoothly for around town driving. By using very little pressure on the gas pedal I can get the car up to speed smoothly (to 25MPH) from a dead stop with almost no signs of hesitation. Once I hit 25-30MPH there isn't too much of a problem flooring it once the engine is above 1500RPM.

From a dead stop if I roll on the gas pedal 1/3 way quickyl it will fall on its face, then the car will jerk forward and the engine will rev and accelerate.

I haven't floor the engine from a dead stop yet, but before it used to just shut off.

I'm thinking this is a combination of lack of fuel and/or bog off the line. The 245's are pretty wide tires, possibly causing me trouble from dead stops when I want to accelerate quickly.

If I hold my foot on the brake, rev the engine to like 1500RPM, then launch like I would at the strip, it won't bog. But if I just want to take a left turn into traffic quickly and hit the gas to hard, it will fall on its face.

The pump shot will give 30cc no matter what, so if flooring the car from a dead stop w/o stalling makes the engine shut off, then using a bigger nozzle probably wont' help. But could this be a bog issue from the tires more then a fuel issue? I've heard that people with carbed motors sometimes find the car lauches better off the line at the track if they feather the gas, though I don't know if this is just a sign that the motor is not tuned properly. I don't know if the wide tires hooking could be making the bog worse. Maybe if I up the PV 1" in size and increase my pump nozzle, that I would be able to acceleate normally for regular street driving with no bog problems. But that no matter how I tune the PV/pump shot, the engine is going to have a bog issue from dead stops under hard acceleration due to the tires.

 

no i dont think so, i have holley 31, 32, 33,34, and 35 squirters in my tool box.....im using 33's right now

the symptom your describing mashing the throttle is EXACTLY what my car was doing, and i upped the squirter size, and it solved the problem.

the 30cc is delivered when you matt the gas, the size of the orifice in the squirter nozzle determines the rate at which the shot is delivered.

if theres a lean spot, you need to get more fuel to the engine quicker on the throttle transition, and thats accomplished by using larger squirters.....the power valve enrichment circuit is designed to work at part throttle under cruise and light load anyways, the accelerator pump circuit is specifically intended to cover lean spots on throttle transition.

 

I'll try a 35 nozzle (since its my onl choice pretty much) and see how much that helps then as a start. I take it from there.

Thanks