Jetting a Holley

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I've posted about this here before and some members disagree with me. I disagree with Holley's Power valve recommendations, (PV# 1/2 idle vacuum) when it comes to most street driven carbs, especially when a larger then stock cam is involved. Using your setup as the example, at 12" of idle vacuum with a 6.5PV, it would seem that your just right. The problem arises at cruise rpm when your likely at 14-16"s and throw in the fact that with the manual trans when you decelerate in gear the vac is in the 20-22" range. Now for moderate acceleration, you need alot of throttle opening to get down to the 6.5PV for enrichment, hence the hesitation. Remember earlier i said that installing a bigger squirter is sometimes masking a problem.....well this was it. I believe you need a PV in the 9.5/10.5" range to bring your enrichment in sooner. I know it's not what the books say, but i've experienced this numerous times over the years and this solved the issue.

With all that said, if any timing changes are going to occur, do those first.
 
OldmanRick said:
Been busy for a few minutes bigtooth. I'll post something shortly.
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No trouble at all! I have a desk job so I just leave my FABO window open most of the time :blob:
I've got all day :glasses7:

I think I understand what you're saying about the PV. I may end up giving that a try. I'm going on vacation for the next week with the family, so It may be a while before I get to tinker on it some more. I'll be sure to update when I get somewhere.
thanks for all the help guys!
 
Stinky idle can be rich or extremely lean. Both usually give off high hydrocarbon levels. You may be on the lean side, especially with a boatload of advance using manifold vacuum. Use a vacuum gauge to set your idle mix screws, leanest idle, highest vacuum. This may be a case where you smell rich so you turn the screws in slightly and it really needs to go out. This may also help you lean tip in, just a little bit.

That cam is 230 at .050 so getting it to idle shouldn't be a huge chore. A 850-900 idle should be OK with that.

I'd turn the initial up to 20-22 see if it starts ok and check to see if the idle profile improves. You may need to buy or make a limiter bushing to hit your desired total #.

Tuning a PV really requires a O2 meter. As Rick mentioned, the 1/2 idle vacuum is just a decent starting point. I have/had cars that pulled 8-9 inches at idle, less in gear and had a 10.5 PV in them. If it has a lean spot when accelerating, squirter, cam and PV are where I'd make adjustments.
 
Are the floats adjusted properly?

Make sure there is no fuel dripping in from the boosters.
 
Yes do let us know how it goes. Have a great vacation:D. Oh yea, don't be too upset with me about not mentioning the PV while you were in the carb before. Just that all the other things have to be right first before knowing if changing the PV is warrented.
 
The primary float is good, havent checked the secondary - i will.


I just ordered a 9.5 PV and the quick change kit for the secondary - cheap enough to try :)

Not upset at all about you not mentioning it before, i' actually have a paper from the Holley website that says to go 2" below manifold vacuum for longer duration cams.

Okay, guys i'm outa here for the day, it will be awhile before i'm back on but...i'll be back... ha!
thanks again
 
Well, i'm still puttering with this. I've got the quick spring change conversion for the secondary spring and have the light yellow spring in it now. I don't think my secondaries are opening at all though. I tried the 'paper clip trick' with a semi loose zip tie and it didnt get pushed down the arm at all. I was quite surprised. I'm going to try the white spring and finally no spring to see if there is a difference.
I also have a 9.5 PV that I have not put in yet. Figured I'd try to get the secondaries figured out first.
 
bigtooth said:
Well, i'm still puttering with this. I've got the quick spring change conversion for the secondary spring and have the light yellow spring in it now. I don't think my secondaries are opening at all though. I tried the 'paper clip trick' with a semi loose zip tie and it didnt get pushed down the arm at all. I was quite surprised. I'm going to try the white spring and finally no spring to see if there is a difference.
I also have a 9.5 PV that I have not put in yet. Figured I'd try to get the secondaries figured out first.
Click to expand...

Welcome back bigtooth.

There's a little round seal/gasket that goes between the vac canister and carb body to seal the port. Could it have fallen off at some point during the r&r so that the canister is no longer getting a signal? Should also ask that the test was done while driving? They wont open by just free revving the engine.
 
OldmanRick said:
Welcome back bigtooth.
Click to expand...

Thanks Rick! Hope you're well.
The quick change kit came with a new cork washer but thats not to say I didnt botch installing it. I'll double check that, and I did take the car out for a spin.
I really just need to buy a mechanical or one of those Atomic EFI's, my wife thinks otherwise :)
 
bigtooth said:
Thanks Rick! Hope you're well.
The quick change kit came with a new cork washer but thats not to say I didnt botch installing it. I'll double check that, and I did take the car out for a spin.
I really just need to buy a mechanical or one of those Atomic EFI's, my wife thinks otherwise :)
Click to expand...

Thanks, doing ok. You'll get it right soon. I here ya' about the other half. When i was more involved she always looked at me like i was half nuts.....lol. Maybe she was right:D.
 
OldmanRick said:
I've posted about this here before and some members disagree with me. I disagree with Holley's Power valve recommendations, (PV# 1/2 idle vacuum) when it comes to most street driven carbs, especially when a larger then stock cam is involved. Using your setup as the example, at 12" of idle vacuum with a 6.5PV, it would seem that your just right. The problem arises at cruise rpm when your likely at 14-16"s and throw in the fact that with the manual trans when you decelerate in gear the vac is in the 20-22" range. Now for moderate acceleration, you need alot of throttle opening to get down to the 6.5PV for enrichment, hence the hesitation. Remember earlier i said that installing a bigger squirter is sometimes masking a problem.....well this was it. I believe you need a PV in the 9.5/10.5" range to bring your enrichment in sooner. I know it's not what the books say, but i've experienced this numerous times over the years and this solved the issue.

With all that said, if any timing changes are going to occur, do those first.
Click to expand...

Rick i went with your thoughts on this, i had a 6.5 pv in which according to the vaccum method is correct. However when the secondaries came in it was way..way.. to noticable, like something was missing before hand. I installed a 8.5 and put my primarys from a 67 back to a 68 and wow! What a HUGE difference. Thanks for the idea. I am curious as to maybe a 9.5.
 
chris17 said:
Rick i went with your thoughts on this, i had a 6.5 pv in which according to the vaccum method is correct. However when the secondaries came in it was way..way.. to noticable, like something was missing before hand. I installed a 8.5 and put my primarys from a 67 back to a 68 and wow! What a HUGE difference. Thanks for the idea. I am curious as to maybe a 9.5.
Click to expand...

Hi Chris. Glad you made some progress. I went back and looked at your engine specs and with that cam, i'm speculating your idle vacuum in gear is in the 11" to 13" range. Going up 1 size is really just a tweak. It may or may not make a small difference, but I wouldn't rush out to get one at this point.

I'll look over at your thread about the secondaries and post something there if i think I can add anything meaningful.
 
I'm back on this thing now that the nice weather's come back! and I've got and o2 sensor hooked up. Looks like i'm certainly running rich at idle ~12 and 13 on the sensor, it seems overall rich except when I get my bog off of idle, then I go real lean, like up in the 16 area, if I get it to bog to bad the o2 sensor maxes out at 22.4. I assume that's because I have a blast of unburnt air and fuel going through... Anywho, i'm going to revisit my timing and work on getting this thing running with no vacuum advanced hooked up, meaning i'll need to limit my MSD's mechanical advance and bump up my initial.
I'm still looking for an afforadable double pumper, but am a bit undesided on a 650 or 750, any input?
 
TOOTH,IM RUNNING A HOLLEY 750 street hp v.s. on my crate and it is night and day differance compaired to my 3310.
 
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