10.5 power valve ???

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65-440

65-440

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Has anyone had to run a 10.5 power valve in their holley ? I just got my 340 back together and have been running it for a few days now. Was running great with an out of the box 770 street avenger but I room that off to use on my fresh 383. I tried to match that carb to this one I got from a buddy. Perfect off idle, perfect WOT, been fighting a lean stumble during throttle tip in during cruising. 12" vac at idle, 14-15" while cruising steady. AEM 750dp, pink cam up front with 30cc pump, 31 nozzle, 50cc secondary with 35 nozzle. 65/77 jets. Originally started with 4.5 power valve and was not drivable. Going by holley guide I went to 6.5 according to my hot idle vacuum of 12". Still had a nice stumble at same spot. Drive with vacuum gauge and notice the stumble happening around 7-8" vac so I ordered an 8.5" power valve. The stumble is so close to being gone but still there. Before I order a 10.5 PV, I figured I'd ask those with more experience than myself ..... would a 2" quicker enrichment cure the lean stumble? Stock bore '70 340, eddy heads, comp .484 cam, 4spd... 18deg initial timing, starts and idles great, prefect throttle response from a stop ....
 
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I had to run a 9.5 in a tunnel ram (single 4 barrel) to get it to respond properly. just keep an open mind and keep swapping out the power vales until you find the one that works the best. I have about 8/10 power valves that I keep handy because you never know which one will work best. I've also had to order special ones that aren't carried by the local parts store. If you have time to wait you can order them through ebay and save money. Once you find the correct PV you'll notice a big difference!!!:steering:.

treblig
 
Just spoke to the local Mopar engine guru, said to leave the PV I got and go up 3 jet sizes in the primary. Said the 65's I have now are way too small
 
I would check the metering blocks to see if the idle feed restrictors are replaceable. if so, i would increase them by .002 or whatever the next drill size is and see how that works.

i think the 7.5 PV you have now is probably good.
 
65-440 said:
Just spoke to the local Mopar engine guru, said to leave the PV I got and go up 3 jet sizes in the primary. Said the 65's I have now are way too small
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that was my other thought, 65's are way small unless you have annular boosters.
check the metering blocks for adjustable IFR's while you swap the jets..
 
If the car runs well at part throttle (no surge) on the main circuit, upping the jet only make it run richer all the time.

If you have a lean stumble as you roll into the throttle, try the higher number PV.

You upped the PV numbers and it's been helping... that should tell you something.
 
If it's only throttle TIP-IN that's a concern and steady part throttle acceleration A/F in the range of 4"-8" is good, then you should be using the primary accel pump to fix it.

The PV should not be used to address transient fuel since it's intended to add fuel during a steady throttle.
 
with a 4speed this might be hard to do, but does the motor run perfectly smooth if you steadily drive just off idle? or does it do a little bit of lean surging? just the slightest amount...

i'd guess lean in the transition...so your IFR's
my truck is doing thing now but i've been too lazy to adjust it yet. i dropped the IFR's down from .033 to .029, it's almost good but, but it does the slightest amount of surging just off idle, cruising down the street or through a parking lot at 10mph.
it also has a slight lean tip in stumble that showed up when i leaned the IFR's. it's most noticeable before the motor has about 20 mins of drive time in it (carb still coming up to op temp). i'm going to drill the IFR's a step larger.

Surprisingly, this HR650 (mech secondary) quick flow carb i put on my 318 in a powerwagon was almost perfect out of the box. i thought i was gonna be over carb'd and way rich...the thing was undriveable cold before i hooked the choke up. lean backfire through the carb so much...
i mention this because the AED carb might be similar to the QFT carb i got...as in not pig rich in the transition like everyone says holley 4150's are.

on the main jets, the 65's do seem small but if the car doesn't lean surge at highway speeds then they might not need to go richer.
 
No off idle stumble or surging whatsoever.... I'd say 40% throttle no matter what gear or speed. Same vacuum reading each time it stumbles. I'll go up to 68's and see what happens....
 
65-440 said:
According to spec sheet, it should have 70's primary ....
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That's a starting point. Doesn't matter now that you're tuning it to your engine and car. Its good to keep in mind so that when you start tuning the secondaries, its likely you'll be able to lean them the same amount as the primaries.

The folks above gave good advice on the Primary main jet - make that as lean as it will tolerate when cruising at mid rpm, highway speeds. Something like 3000 rpm, 60-65 mph. It will surge and die when its too lean at moderately light load. If that happens, slow down , drive home at 55 and jet up. :)

Powervalve opening point is to provide extra fuel into the main circuit only when the load gets too high. Whether this is at 10" of vacuum, or 6" will depend on your combo. If its a flat spot or a little doggy when your rolling along at a good clip and squeeze down to 10", then it definately try the 10.5 PV. If that's not it, then go back cause its wasting fuel and washing down the cylinder walls.

A couple other possibilities you can test to eliminate.
1. At 40% throttle, the secondaries might be cracking open. Test by disconnecting. If it's the secondaries at their opening point, then adjust the secondary idle mix (idle feed restriction and idle airbleed). If it's unstable, relocate the idle feed restriction to the lower position. see Idle feed restrictions and placment for more information and direct to pictures here
2. Primary air correction issue. If its not the secondaries, and its not the transfer/accelerator pump, then it could be too much air correction. Air correction should gradually bring in the main system and then keep the AFR steady at any given throttle postion. But too much air can do strange unpredictable things. To be in the ballpark, follow what the old Holley's did...
Detailed explanation here: http://racingfuelsystems.wonko3.myfunforum.org/Emulsion_Tuning_about42.html
From there you can just poke around the forum with the search to find a starting point for your emulsion and main air bleed. It will be something like one .027" dia. e-bleed near fuel level and another at or near the bottom. Then use the main air bleed to get the AFR to flat line at the top.
 
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Absolutely, all sound advise. Once I get back in town I'll play around with it. I've matched everything except the Jets to the 770 that I took off the car, they were 72 on primary. I'll go up in primary jet and see what happens. All I gotta say is thank God for reusable gaskets !!
 
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