Jetting a Holley

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bigtooth

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I have a Holley 80508-3 ([ame]http://www.holley.com/data/Products/Technical/199R9934-3.pdf[/ame]) on my 390hp 360 magnum crate engine, I want to up the jets in it a touch, because the plugs look a bit lean. The porclins white around the electrode and the groud stap is pretty light.
I have the stock 70 primary jets in it, and, i'm sure, the stock metering plate (I have no idea what this is , but i'm going by the manual in the link).

My question is do I need to up the size of this metering plate or do I just up the size of the main jets to offset a lean condition?

thanks!
 
Here's a oriface size chart........http://www.junkyardgenius.com/holley/jetsize.html

Looks like just going to a #71 gives a pretty good jump in fuel. As for the secd. plate, the choices you have are buy a different plate or do a block conversion. I would suggest you try a lighter secd opening spring first. The black spring is the heaviest and is set to never fully open (period). I would go to a plain spring and if you have 3.91 gear or higher # i like the yellow spring. Getting them open a little earlier may be enough if your only slightly lean.

Below should be a link to the spring opening rates......if it works? Scroll down some and there is a chart.


http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=1&cad=rja&ved=0CEUQFjAA&url=http%3A%2F%2Fwww.holley.com%2Fdata%2FProducts%2FTechnical%2F199R8219-2.pdf&ei=JxQtUNTLBZPY9ASryIDIDA&usg=AFQjCNGv_wLeNEkwrgJoi7uDJusP0aXNQg
 
two good books to have for a holley

[ame="http://www.amazon.com/Holley-Carburetors-High-Performance-Emanuel/dp/1884089283/ref=sr_1_1?s=books&ie=UTF8&qid=1345131890&sr=1-1&keywords=holley+carburetor"]Holley Carburetors (High Performance): Dave Emanuel: 9781884089282: Amazon.com: Books[/ame]

[ame="http://www.amazon.com/Holly-Carburetor-Handbook-4150-Hp473/dp/0895860473/ref=pd_bxgy_b_img_b"]Holly Carburetor Handbook 4150 & 4160 Hp473: Mike Urich: 0075478007509: Amazon.com: Books[/ame]
 
here is a conversion for the rear metering plate. it allows you to use normal jets there instead of having to buy new plates or drill your existing plate. worked out very well for my 750..


http://www.forabodiesonly.com/mopar/showthread.php?t=72939&highlight=quick+fuel




berfore:

sept1001.jpg





after:

sept1012.jpg





.
 
thanks rick. its a 4 spd car, with 3.91s
I'll give that a try. I do have a secondary spring kit already.

Once characteristic of it currently is if I have the rpms anywhere under ~2k and try to get them up it will come up slow then after 2 it will really turn on (I liken it to the 'kick in the pants' feeling the carb manual talks about)
If I try to really step on it anywere under 2k there is an instant bog till I back off and get the RPMs up.

I was going to try messing with the secondary spring, but was not sure which way to go.
 
I was going to try messing with the secondary spring, but was not sure which way to go.
Click to expand...


does your carb have a spring quick change kit on it? if not it would be a wise investment.. make changing those springs cake.

i would go right to the short yellow spring and see what happens. then if needed work up through the stiffer springs..:)
 
bigtooth said:
thanks rick. its a 4 spd car, with 3.91s
I'll give that a try. I do have a secondary spring kit already.

Once characteristic of it currently is if I have the rpms anywhere under ~2k and try to get them up it will come up slow then after 2 it will really turn on (I liken it to the 'kick in the pants' feeling the carb manual talks about)
If I try to really step on it anywere under 2k there is an instant bog till I back off and get the RPMs up.

I was going to try messing with the secondary spring, but was not sure which way to go.
Click to expand...

With that gear and if the black spring is still in there i believe going lighter will definately help. Also make sure the accelerator pump arm is adjusted correctly. Looks like that carb came with a #31 shooter so that should be enough. Here's a pump video if that help's........
[ame="http://www.youtube.com/watch?v=w3F3ssOb8lg"]Accelerator Pump - YouTube[/ame]
 
I' glad you said you think the 31 shooter should be enought, I was thinkin of upping that...

I have mesured the pump arm at WOT and can get my feeler gauge in there. But one thing that I was noticing this AM when messing with it is when the throttle is closed the pump arm is already quite a way into its stroke. Almost like I could tighen up the bolt with the spring that pushes the arm and get a longer duration pump out of it.

If the stock secondary spring was the balck one, i'm sure its still in there.
 
bigtooth said:
I' glad you said you think the 31 shooter should be enought, I was thinkin of upping that...

I have mesured the pump arm at WOT and can get my feeler gauge in there. But one thing that I was noticing this AM when messing with it is when the throttle is closed the pump arm is already quite a way into its stroke. Almost like I could tighen up the bolt with the spring that pushes the arm and get a longer duration pump out of it.

If the stock secondary spring was the balck one, i'm sure its still in there.
Click to expand...

I like to set the arm so it's just making contact at idle so as you said it gets the longest shot. The wide open measurement is just to make sure your not bottoming the diaphragm so it wont be damaged.
 
I should say as far as the shooter, if you need to go bigger there, it may be covering for another issue. I do have some thoughts on that but i'd like to see how the jet/spring changes do first.
 
abodyjoe said:
does your carb have a spring quick change kit on it? if not it would be a wise investment.. make changing those springs cake.

i would go right to the short yellow spring and see what happens. then if needed work up through the stiffer springs..:)
Click to expand...

It currently does not, I will add one of those to my next parts order.
I'll try the lighter springs tomorrow as soon as my primary bowl gasket arrives, the one on there was less than intact after I took it apart to check my mains.
 
Just for giggles,check out Quick Fuel Technologies.They have a billet adjustable vacuum secondary diaprahm.Nothing to swap,it has an adjustable needle/seat setup.Kind of like an air/fuelmixture screw.Summit part no.,QFT-63-1,about 40,45 bucks.No more swapping springs/diaphrams.Check it out.
 
Abodybomber said:
Just for giggles,check out Quick Fuel Technologies.They have a billet adjustable vacuum secondary diaprahm.Nothing to swap,it has an adjustable needle/seat setup.Kind of like an air/fuelmixture screw.Summit part no.,QFT-63-1,about 40,45 bucks.No more swapping springs/diaphrams.Check it out.
Click to expand...

Good idea bomber, he really could use a 750DP but who has a extra 400+
dollars burning a hole in there pocket....lol. A well tuned vac carb can still get the job done, i've done quite a few.
 
oh that is sweet, I might just have to get one.

I did up the primarys to a 71 and swapped in the short yellow spring and backed the springed screw that hits the pump arm so the pump starts at the begining of it stroke.

Seemed to help a bit, it smells like i'm burning a bit rich, but still need to check the plugs. I drove it on the interstate today for a bit an noticed that at no matter what rpm if I take my foot completely off the throttle and then push it, as soon as the blades open there is a split second of hesitation/bog still, then it clears up. Is this just the nature of the beast or is something still wrong?
 
Since it's rich at idle I assume, what's the initial timing?
 
I dont even have a spring in my secondaries,, with gears and everything else,, it's absolutely perfect .. no bog.. no hesitation,, it just squats and goes like heck..

BUT you MUST make sure that the piece of linkage on the driver's side, that connected to the secondaries, absolutely shuts the rear throttle plates when at idle,, requires a little tweek with a pair of pliers,, cuz with no spring, that's the only thing closing the secondaries,.. do it gently (bend).... try it,, you may like it.. I sure did..

I acts like a big one barrel, no hestation, just puts you back in the seat,, .02
 
initial timings at like 16 BUT I run my vacuum advance off of manifold vacuum so it idles with close to 30 and I allow 18 in my MSD distributor.

best vacuum readings I can get at idle are just shy of 12"
 
I've made it no secret that i'm a fan of manifold vac for the adv. But this may? be a case where ported could work better. I want to see how "cracked" feels about it. I have a thought about the carb, but if any timing changes are gonna take place i'll wait until that's squared away.
 
Its really hard to get it to idle with that little initial only. damn msd dizzy will only let me limit my mechanical to 18..

Also, I used to run much more initial and vacuum adv. to ported with way to much total timing and it still acted this way...
 
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