Holley Jet numbering

[cribbs74]

Does anybody have an idea how the jet numbering system works on Holley carbs?

I run a 2 barrel 2245 on my 318 and while it runs a heck of a lot better than my BBD it still is not right. I had a lean condition that I corrected by drilling out the jets one drill size larger. Now the problem is when it's choked up in the morning it runs crazy rich to the point that there is a big black spot on the driveway.

My jets are both stamped with the number 642 on them I assume one jet is for the choke and one is for the pump? That's what the parts listing says anyway. So I thought I would go ahead and fill the choke jet back in and re drill to the original size. Sounded good in theory but yet again I am a rich on choke and now a little lean off choke. Makes me wonder if both jets interact with the choke.

So I decided to get a jet assortment and start playing. The problem is holley advertises replacement jets numbering 40-100 not anything 3 digit like 642. I am thinking the "2" is something generic and the 64 number is what I should be concerned with. Anybody have any info they could provide? Thanks

[volaredon]

if you don't know what size the jets are, how do you know that you only went "1 size" bigger? Also the jets are 1 for each barrel. Once warm adjust mixture screws with a vac gauge to the highest (steady) reading and highest RPM without touching idle speed screw; I'd be looking at the choke pull off, linkage adjustment (vacuum "kick", etc) and elec choke coil. Did you put a 360 intake on there as the 2245 is larger than a BBD. The choke works by cutting off air so the vacuum produced by the engine pulls more fuel out of the various passages. Sure you dont have a vac leak that shows up warm (the choke being on could be masking it when cold)

[cribbs74]

I didn't say 1 size larger I said 1 drill size larger. I've done all the choke adjustments per Chiltons manual instruction to include the pulloff, vaccum kick and choke linkage. The 2245 has a mechanical choke not electric. If you know of a modification to convert it to electric I'm all ears. The intake is from a 360 and I'm aware the CFM's are more from the Holley than the BBD. Im am almost positive that I don't have any vaccum leak, but I will keep my eye on it just in case.

I am thinking of going the 4 barrel route, but gifts for the kids take priority right now. If I can figure out the numbering for the jets I can try and fine tune it as it sits for now. Thanks for the rundown on the carb operation the rebuild manual lists one jet for choke and one for the pump that was why I was a little confused. Like you I thought they were one jet per barrel and now that they are mismatched the engine operation changed when warmed(went a touch lean) so that confirms it. Thanks for the reply

[Speed Dragon]

I don't think there is a separate jet for the choke, there's one jet for each venturi. The choke just improves airflow or turbulence or something when it's cold. If you are running rich on the choke, then you need to adjust the choke rod, not jet size.

[cribbs74]

I have adjusted the choke rod from stock specs to almost fully open at idle when cold and it still runs rich. It ran fine on choke before I modified the jets but ran real lean once the choke came off. Now it runs great off choke but super rich when the choke is on.

[B-300]

The example of a 642 is a 64 jet and the third digit "2" indicates that it's a close limit jet which has a better tolerance.
Holley uses flow, not size to determine jet size. Some jets are drilled with the same drill size and have different length restrictions.
If I recall correctly close limit jets are +/- 1.5% and standard jets are +/- 3% from the specified flow.

[cribbs74]

B300,

That's a good bit of info and will help immensely. Thanks for the education.

[volaredon]

By "Mechanical" choke; you mean manual choke? Because if you have the choke rod going to the intake, it most likely has a wire going to a resistor too; making it an electric choke. Just because it does not have a "black dial" on it like a GM or Furd, does not mean it is not "electric"; they also have a bi metallic spring in the choke well that relaxes as it heats up, opening the choke. The electric part just speeds things along.
There were A FEW that did not have the electric "assist" on the choke unit, but not alot.

[cribbs74]

I guess mine is one of the few. It has no electric assist to the plate that holds the coil spring. As far as I can tell it never had one either. The coil spring that moves the choke rod is heated by the manifold only. So it appears to be entirely mechanical to me. I guess it is one of those things where terms have different meaning, manual to me means you have a choke cable with a knob in the cab that you operate by hand. Kind of wish I had one of those at times.

[DODGEN1]

if you have 642 there #62 jets the larger the no the larger the jet. 1 drill size is a big jump. like a 32nd. holleys are in thousands and they dont track an increase order because there done by flow. you will be allitle rich at choke idle but cleaner at nornal temp. get a book there is the a chart with the jet size and drill size and then you could work back to find the best jetting.

[B-300]

Addition: According to a book on Holley carburetors a 642 is a #64 close limit jet in the middle of the range. Close limit jets are supposed to be within 1.5% of each other (+/- 0.75%) for the same size jets.
Each jet size is a change in flow of about 4.5% according to what I read.
Standard jets (2 digit) flow within 3% (+/- 1.5%) of each other for the same size #.

[Speed Dragon]

How do you know it was running lean before? There's no way a 360 Holley carb doesn't have enough fuel flow for a 318, maybe you had a different problem, like a vacuum or intake leak.

[cribbs74]

Speed, Backfiring through the carb, stumble when accelerating, surging at a steady speed and when It was cold in the morning and on choke it ran fine. Once the choke came off it was back to the backfire, stumble, surge thing. Now after my backyard mod it runs great when the choke is off and poor with the choke on.

You are correct and I would have thought with a 360 carb if anything it would have been rich, keep in mind my BBD was also less CFM than my Holley so I am also sucking more air in as well.

[cribbs74]

if you have 642 there #62 jets the larger the no the larger the jet. 1 drill size is a big jump. like a 32nd. holleys are in thousands and they dont track an increase order because there done by flow. you will be allitle rich at choke idle but cleaner at nornal temp. get a book there is the a chart with the jet size and drill size and then you could work back to find the best jetting.

Yeah it was pretty dumb to start drilling, found that out the hard way, however it did confirm I did in fact have a lean condition. I found a chart online for replacement jets but the 642 number did not show so that's why I posted originally. I'll have to get some new jets now and go from there. Thanks for the info

[Speed Dragon]

Speed, Backfiring through the carb, stumble when accelerating, surging at a steady speed and when It was cold in the morning and on choke it ran fine. Once the choke came off it was back to the backfire, stumble, surge thing. Now after my backyard mod it runs great when the choke is off and poor with the choke on.

You are correct and I would have thought with a 360 carb if anything it would have been rich, keep in mind my BBD was also less CFM than my Holley so I am also sucking more air in as well.

Sounds like a bad vacuum leak to me. And while you may have the capability to suck more air, it doesn't mean the engine actually is. It would really only be noticeable at 3/4-more throttle I think. I have turned a 360 w/ a cam up to 6200 rpm on a BBD w/o much problem.

[cribbs74]

Hmm, well it's definitely something to look into although I have sprayed that intake with ether as well as the carb and vaccum port and nothing happened. It idles as smooth as can be so if it's sucking air it must be internal.

[Speed Dragon]

It is pretty odd. Have you tried just running w/o the choke? Mine generally start w/o it, although they are a bit cold-natured at first.

[cribbs74]

Yeah I have run it without choke before I drilled the jets. It wouldn't stay running for crap until it was fully warm. It made stop and go traffic interesting. It may run ok now off choke seeing as I'm richer.

[cribbs74]

Thought I would update on this. I replaced the jets with new #66 from Summit. Runs better but still a tad on the lean side. If I romp on the gas I still get the backfire through the carb and a slight stumble when I start accelerating from a standstill. I am a little puzzed on this one. I went ahead and bought another can of starting fluid and sprayed all around the intake, brake booster, vacumn port and carb base. Nothing happened at all. I can live with it right now, but I want it to run right. Any suggestions?

[B-300]

The float level is crucial on the Carter BBD for good progression... The same is probably true for the holley 2bbl. (Don't have experience with them.)
If it was "sucking" (leaking) internally it would be sucking oil and would show on a sparkplug... Doubt the manifold is cracked into the crossover as it would be hard to get a smooth idle.. It would be like an EGR valve stuck open.

[cribbs74]

Thanks for the reply B-300, Good point. I initially set the float level when I rebuilt the carb, I thought I got it right, but it wouldn't hurt to check it again.

The bad thing is if I have oil an a few plugs it could be a number of things that could cause that and hard to narrow down. Right now I have ash deposits on a couple plugs that I attributed to worn valve seals, I think if I had ring issues the plugs would be wet with oil. So I could do a compression test and eliminate the rings.

That being said I have had a vaccum gauge on the engine and the needle fluctuated rapidly. This was a while back when I had carb issues so I wasn't sure about a vaccum leak at that time. I really should check it again. Thanks for your help and direction.

[volaredon]

how bout timing, (both chain related and ignition related) vac advance hooked up right? (to correct port) Advance weights sticking? Where's your basic timing? the underhood sticker is not necessarily correct; parts and/or motor changes, differences in your local fuel supply, etc means tat you gotta play around a bit. How bout tinkering with the adjustment in the vac advance pod? A lot of people do not know about that one.

[cribbs74]

The timing is currently set to maximum advance without knock. I set it that way because if I set it to stock specs it runs like garbage. Believe me I have played with timing for a while. I have not checked the timing chain. The engine has 154,000 miles on it and as far as I know it is the original chain. The vaccum advance is connected to the right port at least the right port as shown in my Chiltons manual. I have not adjusted the vac advance unit. The vaccum advance unit shouldn't be the problem with the stumble off idle. The distributor is a new reman Chrysler unit with about 400 miles on it. I hope the weights aren't sticking on it yet. Thanks for the reply

[DODGEN1]

how many degrees of ad vance? where are you at now?if you slow down the advance curve you can go for more advance timing. youve got to et ahead of the chain slop.

[volaredon]

Yea the advance could be something to do wit the stumble; remember you have both vacuum and mechanical advance; in my 83 factory shop manual they show at least 3-4 different distributors that could have been in an 83 Dodge truck with a 318, all with different mechanical and vacuum advance specs. Reman places typically toss all the various pieces that fit a given engine in the same bin and what you get as a reman product is anyone's guess; especially when you consider part number consolidation, etc. Chrysler's reman distributors are sourced from the exact sme company as Car Quest Napa and Autozone; A-1 Cardone. and all the way from 73-89 they only show a couple of numbers for a distributor in a Mopar smallblock, car or truck, with ECU (non Lean burn) ignition; I have other year service manuals, each one shows all the possible distributors possible in a given year with the specs that go with that dist; so if it has ever been swapped out, those factory specs are out the window; then the old "advance til it pings, then back it off a little" comes into play.

[AMP762]

I had a problem like this,turned out to be the coil wire breaking down under load.

[Speed Dragon]

I had to swap dizzys in mine to get rid of the same problem, it had a LB dizzy in it and it advanced too quick. It really sounds like timing to me.

[volaredon]

I had to swap dizzys in mine to get rid of the same problem, it had a LB dizzy in it and it advanced too quick. It really sounds like timing to me.

Uhhh.... LB Dist; as in LEAN BURN??? They don't have ANY advance built in what so ever. No weights, no vacuum can.

[cribbs74]

Well sounds good in theory, however it did that with my original(to the engine)distributor as well. Would the timing chain being slack cause that problem as well? And what about the WOT backfire through the carb? Not that I drive WOT all the time, but I would like to have it when it's needed. Thanks for all the good replies

[Speed Dragon]

Uhhh.... LB Dist; as in LEAN BURN??? They don't have ANY advance built in what so ever. No weights, no vacuum can.

Sorry, an ESC dizzy :o It was a factory '85 van dizzy, it had ESC w/ the vacuum advance on the dizzy instead of the ESC computer. Odd piece I guess.

[volaredon]

Sorry, an ESC dizzy :o It was a factory '85 van dizzy, it had ESC w/ the vacuum advance on the dizzy instead of the ESC computer. Odd piece I guess.

Oh. on the other forums I visit most guys lump "ESC", EFC". and whatever other names they had for the computerized system that still used a carb as "Lean Burn".

and on the 85 van with such a system and a vac advance pod; you did not have both; (from the factory anyways) someone converted that over to a regular elec advance somewhere along the way; and unless it was a Cali van originally OR a /6, (which it could not be or its dizzy would not fit a V8); I guess someone could have previously swapped that out too; 49-stste V8 trucks still had standard Mopar elec ignition; they didnt start using the computer setup that 'regularly" on trucks til '86. You should have seen the cobble job conversion done on the pickup I pulled the Edelbrock intake and carb off of last week in the junk yard! OOOOH BOY:banghead::YUK:

i've seen LOTS of conversions where people would leave the computer box hanging with most of its wiring; people do things rather crudely sometimes;

[Speed Dragon]

Hmm, well I could be wrong, maybe it had elec ignition. It was several years ago :) Anyhow, it was a stock '85 dizzy, and whatever the problem was it had, it was advancing way too quickly I guess, I swapped in another, older dizzy and it fixed it.

[volaredon]

could have been sticky weights like on my 83 or the vac advance pod needed adjustment; I ran into this on the new Summit dizzy I put into the 83 went from a tire shredding ping machine, to something that would not get out of its own way, depending on where had the Allen screw in the end of the vac can (where the hose attatches at) with the same base timing setting.

[Speed Dragon]

Yeah that's possible too. I think my S6 truck is having the same issue, it's sitting at the base setting until around 1800 then goes all in.

[B-300]

2 items.
The 2 and 4 bbl vaccum advance have different advance: Most 2 bbl start at 5" end, full advance with 8 degrees at 15". 4bbl start latter ~7" and end sooner at ~12" with more advance ~12 degrees.... they use the inner hole on the advance plate, the 2bbl units that have less advance use the outer hole.
2nd item: with changing fuel a different timing curve is needed. Gas has changed in 30 years to less octane and has a different evaporation rate which needs different timing than stock for best efficiency/power.