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Discussion Starter · #1 ·
Motor:
360, 10.5:1, hydraulic roller cam (no exact specs, mildly lopy), turbo 400 w/3000 stall

I called Holley and spoke to a few very reputable engine builders here. All agreed that for what I have and want, the 650 double pumper was the way to go...so, my shiny new carb is bolted on and I've started some initial tuning on it. It's idling very nicely. Float levels are perfect. I adjusted the idle mixture screws based on highest manifold vaccuum.

Issues:
It has a fairly substantial stumble from dead stop to WOT and the plugs are reading lean.

I've got about 20" ov vac at idle in gear. The stock powervalve is 6.5. Based on reading I've done, I should be using a PV that is roughly half of the vaccuum reading, right? SHould I bump it up to a 8.5 or higher and see how the plugs look or should I work the jetting. The stock jets are 68's in the front and 73's in the back. The previous carb had 68's in front and 74H (what does the H stand for?) BUT I think that carb was never quite right. I think some fuel was getting by the transfer slots.

What is the appropriate difference between primary jets and secondaries? I've heard everything from 2 sizes to 6 sizes.

In addressing the stumble, I haven't touched the accelerator pump spring yet. I move the throttle slightly and I get a bit of fuel from the squirters. Should I adjust it or move up on the jets and if jets, to what size?

Thanks everyone
 

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I have always used a jet spread in my 750 dp of 7-9 sizes between primary and secondaries . Before you mess with the PV , I would properly adjust the accelerator pump shots and play with the squirters, increasing the numbers starting with 28 and 31in increments of 2 until the stumble goes away. Then you can mess around with the cam colors blues and reds being the best throttle response for a streetrod.

SK
 

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Bill
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The H on the jet size just means it is a Holley jet. Did you need to adjust the idle screw in to get it to idle? If you turned it in more than a quarter turn, the idle transfer slots need checked under the throttle blades with the carb off. You can read up on that or we can discuss further if needed. If this is not the case, then like SK mentioned, I would bump up the accelerator pump squirtters a couple sizes. The main jets are not a concern for this problem. They might be an issue for the lean plugs but I would start with the stumble problem. You could try the 8.5 PV too. What is your timing set to; initial and total?
 

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Change the squirters in both sides to a 31's and use the orange pump cams. Drive it and see how it goes, if still persist step up to a 35 squirter that should help.
 
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