Lean condition with a old Holley 4150

[70bigblockdodge]

I have a 400 in my car currently with some milled and ported 516 heads old aluminum Wiend intake and some generic headers. Runs reasonably well under normal driving. Problem is if I slow to turn from one road to another or someone slows to turn off when I step back in the throttle 1/3-1/2 throttle running on the primaries once the accelerator pump shot burns off the car goes very lean, runs flat like filter is clogged (it is not). I have played around with main jets with little effect slightly better with 78s over the original 72s. When secondaries come on car runs like a scalded cat. Everything points to power valve not opening but it is new this spring along with a good cleaning and new gaskets (Holley kit). It never seemed to do this on the 383, and the 400 is not much different has a 284/484 Mopar cam in it. It has basically done this the whole time it has been on the 400 about a year, before and after the rebuild. Has anyone ever ran into this problem I know it's probably something simple that I'm overlooking, this is killing my 330- 1/8 mi time and I am still pulling 98-99 mph. Looking for some things to check, second set of eyes. Thanks in advance.

Btw it is a dual feed 3310 list Holley from waaaay back.

 

[bm02tj]

What power valve do you have and have you tried a lower one to open sooner

 

[70bigblockdodge]

It is a 6.5"hg and vacuum below that when lean. I have not tried a lower vacuum PV.

 

[lewtot184]

i'd do a fuel pressure check .

 

[70bigblockdodge]

What power valve do you have and have you tried a lower one to open sooner

This has to be what the problem is. I will get some vacuum readings this weekend. I think I overlooked this because of how bad of shape the gaskets were in when I took it apart, then trying to dream up a more complicated problem after it was back together.

 

[Bigal75]

I wouldn't go any lower than 6.5 you want a higher number for it to open sooner.

 

[Bigal75]

How do you know you're lean?

 

[Cranky]

And how long does your squirters squirt? I like to check them with quick opening and slow opening.

 

[70bigblockdodge]

I wouldn't go any lower than 6.5 you want a higher number for it to open sooner.

This is what I thought. However I duct taped a vacuum gauge to my windshield and also borrowed a OOTB stock 1406 Eddy just to see difference. I also finally got off my but and welded the slots on my dizzy to only allow a 11° swing 25 initial an 36 total in by 2700. Car ran okay with Eddy but I could not get it to idle anything other than pig rich, I'm sure this could be tuned out but not my carb to modify. I put the Holley back on unchanged and immediately ran better at idle from properly set initial with some driving I learned that my thinking about the power valve is backwards. When you are in 1/3 to 1/2 throttle the vacuum drops off to ~2-3" and as soon as the accelerator pump shot burns off it feels like it is running out of fuel, watching the vacuum gauge start to recover as soon as it approaches ~6" of vacuum the car wakes up and pulls well. My conclusion is just what the experts say half your idle vacuum in gear (automatic) and pick the next lower power valve. Mine is ordered.

 

[Bigal75]

What's your vacuum at idle and when cruising? And yes it sounds like it's running out of fuel.

 

[Bigal75]

Let us know how it goes. What you're doing by installing a lower vacuum power valve is delaying the operation of that fuel circuit.
For example I have 5 inches of idle vacuum and run a 9.5" PV because my cruise is at 12" or so. It adds fuel as you start to curl your toes and get into it without opening the secondaries. But as we all know every set up is different.

 

[70bigblockdodge]

I have around 7" at idle so half that puts me at 3,5" power valve. A Holley works backwards holds it shut vacuum pulls it open, mine now at 6.5" power valve I wait, wait, wait once the vacuum gauge passes about 6" the engine wakes up and pulls. I am waiting for the vacuum to enriched the primary circuit.

 

[Bigal75]

Yes I have a holley as well. What I'm saying is anything less than 6.5 inches will show an enrichment in the main circuit. If a 6.5 isn't adding enough fuel neither will a 3.5. Unless the 6.5 installed now is defective. But then the enrichment will only be after the engine reaches 3.5 of vacuum or less.

 

[WileERobby]

You may want to adjust your accelerator pump arm & using a 50cc pump.

 

[70bigblockdodge]

Yes I have a holley as well. What I'm saying is anything less than 6.5 inches will show an enrichment in the main circuit. If a 6.5 isn't adding enough fuel neither will a 3.5. Unless the 6.5 installed now is defective. But then the enrichment will only be after the engine reaches 3.5 of vacuum or less.

I'm sorry but you are backwards the power valve is opened by vacuum my power enrichment does not turn on till 6.5" I need it to turn on around 3-4". I should also add that this was exacerbated by added restriction in the idle feed restrictors to correct a very rich condition at idle and make the mixture screws more responsive.

 

[Bigal75]

Yes but vacuum goes down as rpm climbs. So you will reach 6.5 before 3.5.

 

[70bigblockdodge]

Yes but vacuum goes down as rpm climbs. So you will reach 6.5 before 3.5.

I went back and read my Holley book per their description the vacuum closes the valve and spring opens the valve, so this follows your logic and my original thinking, I'm doing a good job at confusing myself. Now I need to go back and recheck my passages because my 6.5 should work fine. Back to basics.

 

[Bigal75]

It's easy to get confused with this stuff.
At what rpm is the engine going lean? You said there isn't a change when increasing jet sizes? Main jetting usually comes in around 2300 to 3000rpm.

You say it gets better when the engine gets to 6.5 vacuum. Maybe try an 8.5 or 9.5? What's your vacuum when at cruise?

 

[70bigblockdodge]

Vacuum at anything over 1800-2000 steady state cruise is 15-18", 3000 about 60 is 22-23". I am going to disable the secondaries to make sure it is not contributing to this problem.

 

[Bigal75]

Try an earlier opening valve or more main jet. That's where I would start.