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Author Topic: Holley 5200 idle jet size...curious.  (Read 16496 times)

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Offline jeremysdad

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Re: Holley 5200 idle jet size...curious.
« Reply #30 on: August 29, 2013, 10:32:28 PM »
It is a Weber. Define 'top', Good Sir. The two you can't see without removing the air cleaner are your 'air correctors'. The one you can see without removing your air cleaner is your Primary Idle jet. The one you have to crook your head around your valve cleaner...well ...that's your secondary idle jet, and that doesn't come into play until over 2200 rpm.

The two under your 'air correctors' are your 'emulsion tubes', which everything I have read says should not be touched unless you are an air/fuel ratio meter. :D lol

If it doesn't fit this: Speed screw less than 1 & 1/2 turns from not touching, and mixture between 1 & 1/4 to 1 & 3/4 turns from bottomed, then your Weber isn't jetted correctly.

Offline amc49

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Re: Holley 5200 idle jet size...curious.
« Reply #31 on: August 29, 2013, 11:01:45 PM »
Believe me, unless you have STRONG reason to and are a tuning guru, you do not want to change any AIR jet on a carb. Not as simple as fuel changes, and much harder to understand the effect. Changing a fuel jet pretty much richens everywhere, change an airjet or emulsion tube and you change the entire CURVE of fuel, say low fuel at low rpm to high fuel at same rpm but the same fuel amount further up the range. The change is NOT equilateral across the whole spectrum of the jet use at all. Think of a steep ramp as versus a shallower one, but with same fuel at the top, or same fuel at the bottom. Now take that steep ramp and grab it in the middle and yank it one way or the other, what airjets and emulsion tubes can do. You can get lost there so fast it's not funny.

When you have a carb pretty much dialed in like stock ones are you are dollars to donuts miles ahead by changing fuel jets only.

Say I have car that runs too lean at less rpm and too rich at higher, all at WOT so mainjet only, how would you correct it? Think about it. Oh, and I took the power valve away from you too........... .............. .....

Offline 74 PintoWagon

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Re: Holley 5200 idle jet size...curious.
« Reply #32 on: August 30, 2013, 08:44:45 AM »
Oh OK, so if I install the smaller pair that came with the carb combined with the larger fuel jets I installed from the stock carb it should richen it up. I swapped all 4 assuming they were all fuel related. I forget the sizes but all 4 stock jets were larger than the jets in the NOS carb.

Probably time to go back to square one and start over, and only "one" change at a time, shouldn't really have to change the air bleeds unless you did extensive mods on the motor?. . Don't know if you seen this before but this explains how the different circuits work, it is pretty simple.
http://www.thesamba.com/vw/archives/manuals/holley_carburetor/Holley_5200_Carburetor.pdf

Art
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Offline jeremysdad

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Re: Holley 5200 idle jet size...curious.
« Reply #33 on: August 31, 2013, 07:40:50 PM »
So, I remembered why my brain said 'It needs more fuel.' All the gas around here that you can find anymore is E10. Now, as we all (should know), adding ethanol to your gas sounds good (in theory, but not really), but it decreases fuel mileage. Why? Less potential energy. Modern vehicles can compensate for it on the fly, but we have to adjust through tuning. Have you ever read the jetting specs for an alcohol powered drag car? They're HUGE!!!

That's all I wanted to say. Hope everybody's having a great Labor Day weekend!!! :D

Keep it between the ditches. :)

Offline Pinto5.0

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Re: Holley 5200 idle jet size...curious.
« Reply #34 on: September 03, 2013, 11:15:18 PM »
I'm not too bad at chasing jetting. I swapped all 4 jets because the NOS carb was running lean & all 4 jets were smaller than my stock carb. It's not AS lean now but it's still lean. Putting the smaller air corrector jets that came with the NOS carb back in & leaving the larger 36 year old fuel jets in place should richen the mixture. My plugs are white & ashy.
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Offline 74 PintoWagon

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Re: Holley 5200 idle jet size...curious.
« Reply #35 on: September 03, 2013, 11:33:51 PM »
Is the idle circuit lean also?, changing the idle jets only affect the idle mixture at idle, you only need to change those if you can't get an adjustment on the mixture screw, once the butterfly is past the transfer slot you're on the main and the idle jets have no effect.
Art
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Offline jeremysdad

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Re: Holley 5200 idle jet size...curious.
« Reply #36 on: September 04, 2013, 03:18:08 PM »
Is the idle circuit lean also?, changing the idle jets only affect the idle mixture at idle, you only need to change those if you can't get an adjustment on the mixture screw, once the butterfly is past the transfer slot you're on the main and the idle jets have no effect.

My brain is too tired to process the thought it is trying to get out, but in a Weber-designed carb, the progression holes (first ones uncovered if you flip it over and look just above the mixture screw) is also fed by the idle jet. I had a page with an illustration, but forgot to bookmark it. Thus the "speed screw open no more than 1 to 1&1/2 turns, mixture screw no more than 2 turns out" rule. The speed screw too far in is fudging a too lean idle jet by uncovering the progression circuit (and causes a flat spot when you tip in because you are idling on your enrichment circuit).

Does that make sense?

Eta: What you said is spot on for a standard Holley-design carb (your typical Motorcraft/Autolite carb, etc).

Eta 2: Not exactly what I was looking for, but shows the circuit pretty well. Notice how the hole right above the throttle plates are fed from the channel that feeds the idle mixture screw. https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&docid=VFqNCfVDaDhFKM&tbnid=W3T5fTYa4xV2BM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.webercarburatori.com%2F%3Fp%3Dhandbook%26s%3D2&ei=25gnUrORB8rC4AO1kIDYDQ&bvm=bv.51495398,d.dmg&psig=AFQjCNFnNmr0FiMJQYyPBuuIo-XrNUgIWA&ust=1378413057600345

Offline 74 PintoWagon

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Re: Holley 5200 idle jet size...curious.
« Reply #37 on: September 04, 2013, 03:48:34 PM »
Yep it makes sense and I know how it works just didn't word it right I guess, but basics are the same though just more adjustability with the Weber which makes them superior over most carbs.
Art
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