Carburetors in general, Holley's in particular; AKA Carb Tech

[Lindel]

In light of the large number of questions concerning carbs lately, I've been doing some searching for tech info.

Holley's website contains a lot of information and tech advice for the browsing.

http://www.holley.com/TechService/Library.asp

This page in particular give links to info on cams, carbs, fuel injection, pistons, etc.

Edelbrock also has a tech site. http://www.edelbrock.com/automotive_new/misc/tech_center/install/index.shtml

Hope this helps some folks out.

[Kristy]

Thanks for the info! Very helpful!:drivin:....Some of my parts are missing too! :p

[fulsizjeep]

http://www.ifsja.org/forums/vb/showthread.php?t=80329

[bufurd]

.Q-jet great read. florida4x4.com/tech/quadrajet/qtune.pdf

[kenny kustom]

Whats the recomended fuel pressure for a mc 4350 ?

[Lindel]

5 to 7 psi would be more than adequate.

[kenny kustom]

so my 7 psi is okay then ?

[Lindel]

It's on the high side, but if it's been running ok I wouldn't worry about it.

Where are you measuring it at, that could make a difference.

[kenny kustom]

Where are you measuring it at, that could make a difference.

At the carb. From my regulator. With the motor off.

[Lindel]

As long as you're not having flooding issues, then you're probably ok. If it starts flooding then you'll need to drop the pressure some.

[cajun_lad]

What are the gains/losses of vacuum secondaries vs. mechanical?
The reason I ask is I rebuilt my Holley TA yesterday and my dad pointed out that it would be real easy to convert from vacuum to mechanical and went on to ramble about how he hated vacuum secondaries... blah, blah, blah. Should I take his advice, or leave well enough alone?

[Lindel]

Stick with vacuum secondaries. The reasoning is that they'll only open when the engine load demands more fuel/air. With mechanical secondaries, they'll open at WOT whether they need to or not.

Mechanical secondaries are almost exclusively a high performance item, not the best application for a 4x4.

[toyjeep]

I have a Holley Truck Avenger with electric choke that seems to run pretty good.

The problem I have is it will not idle down completely after it has been running a while. I can tap the throttle and it will idle down, but it will not do it on its own when I let off the gas, like at a stop light.

Any ideas what is causing this?

[HOOT]

Guess I should look at the "Stickys" posts more often..:o

I've been beating my head for info on my Holley carb the last 2 days. No catalogs match my numbers.Today I go seek someone recommended by 3 of the 5 car parts stores I've been to in the last 2 days. I think I'll leave it with him and have him rebuild it.
I even seen one catalog that had the "specialty builds" listed by who they were for and what the did with them.ie.Driver's name/what style carb/jets/circle track racer... Still no numbers match. Did I get a carb that was heisted fom the plant piece by piece like that Johnny Cash song about the Caddy.:eek:

I'll try to remember to ask him about your idle problem.

[Lindel]

toyjeep, Most likely the return spring isn't quite stiff enough, or you've got some binding in the throttle plate shaft.

Hoot, check the links I left in the first post, one should take you to where you can call the Holley tech line. Give them the info on your carb and see if they can't help you.

[toyjeep]

toyjeep, Most likely the return spring isn't quite stiff enough, or you've got some binding in the throttle plate shaft.



Thx, I will check the linkage system and try a stiffer spring and see what happens.

[HOOT]

My carb now rests in the hands of a Holley god. He spent 1 minute scanning in his book and had the rebuild kit in his hands in under a minute. Then offered to rebuild it for me for $45. I'll let you know how it turns out.

ToyJeep,
I asked him about your idle and he suggested it may be a vacuum problem. He also said it could be the voltage on your electric choke. He was actually leaning towrds the choke voltage as the culprit.

[toyjeep]

ToyJeep,
I asked him about your idle and he suggested it may be a vacuum problem. He also said it could be the voltage on your electric choke. He was actually leaning towrds the choke voltage as the culprit.

Cool, thanks for the info. I will check that out as well.

[cajun_lad]

ToyJeep, I had a similar problem with my choke. My dad (ex-mechanic and carb genius) tried adjusting the choke and couldn't get it dialed in so he bypassed it. When we rebuilt it last weekend, we noticed during reassembly that it was not assembled right from the beginning. There was no way possible that the choke would ever allow the flapper to close the way it was assembled. We took a closer look, and changed the way we assembled the choke lever (the red plastic looking piece) and voila, problem solved. I have not yet tried it cause the tranny is currently removed, but I will let you know the results as soon as it goes back together. I will also try to take some pics to show you what I am talking about, as I really don't know carb nomenclature.

[wickedwagon767]

I'm trying to decide wether or not I need to rebuild my MC 4350. I just bought the '78 Cherokee. It had to have a liberal spraying of started fluid and several attempts over a 20 minute period to get it started when I went to pick it up. Once it cranked it ran great. Cruised between 70 and 80 all the way home, about 35 miles.

I've been told the floats "get stuck" when older carbs sit for a while without being run. This one was a daily driver for a year, then was started periodically over six months until I bought it.

Any leads?

[Keman]

I'm trying to decide wether or not I need to rebuild my MC 4350. I just bought the '78 Cherokee. It had to have a liberal spraying of started fluid and several attempts over a 20 minute period to get it started when I went to pick it up. Once it cranked it ran great. Cruised between 70 and 80 all the way home, about 35 miles.

I've been told the floats "get stuck" when older carbs sit for a while without being run. This one was a daily driver for a year, then was started periodically over six months until I bought it.

Any leads?

Is it one with a float level view hole? Should be a bolt or screw on the side of the bowls. If it is, open the view hole and spray carb cleaner into the float bowl. That may clean enough gunk to release it.. Otherwise, get gaskets and pop off the float bowls and clean them manually. way less that a full rebuild, and should take less than a half hour.

My 2300 had just the opposite issue, the float stuck in the open position and poured gas out the top vent. I did a complete rebuild due to the 41 year age and unknown maintanence history.

[wickedwagon767]

Is it one with a float level view hole? Should be a bolt or screw on the side of the bowls. If it is, open the view hole and spray carb cleaner into the float bowl. That may clean enough gunk to release it.. Otherwise, get gaskets and pop off the float bowls and clean them manually. way less that a full rebuild, and should take less than a half hour.

My 2300 had just the opposite issue, the float stuck in the open position and poured gas out the top vent. I did a complete rebuild due to the 41 year age and unknown maintanence history.


I'll take a closer look for a view hole:thumbsup:

[AMC4ME]

2100 Series
6RHA2 Model

Seems to be leaking from the accelerator pump, possibly the diaphram. Would the diaphram be an easy fix:confused: ? Is this a good carb? Jeep runs good but takes a lot of pumps to get initial start.

[Lindel]

You'll probably have to buy a complete kit to get the diaphram, but it's an easy fix on the 2150. It's on the front of the carb, and at worst it's messy. Don't do with the engine hot.

2150 is an excellent carb, especially for off-road. It's down side is that it's not very big (only around 350 cfm), and the top can warp fairly easily.

[AMC4ME]

You'll probably have to buy a complete kit to get the diaphram, but it's an easy fix on the 2150. It's on the front of the carb, and at worst it's messy. Don't do with the engine hot.

2150 is an excellent carb, especially for off-road. It's down side is that it's not very big (only around 350 cfm), and the top can warp fairly easily.

My carb is a 2100 series. I replaced the diaphram but I broke one of the bolts from over tightning!!!! GRRRRRR! Its not leaking now but just knowing that it is only being held by the three bolts is driving me crazy:banghead: ! I tried needle nose pliers but it can't get a grip to remove it. What should I do?

[Lindel]

You could try vise grips, or if there's a carb rebuilder near you then give them a try.

Is there enough to get a pair of vise grips on them?

[AMC4ME]

You could try vise grips, or if there's a carb rebuilder near you then give them a try.

Is there enough to get a pair of vise grips on them?

Negative. It is super cold up here and I should have done this job in a warm garage. SNAP! GRRR! I have a punch list of things that need to be accomplished before she is road worthy. The carb rebuild is one of them and I'm sure that they could pull it out, hopefully. I don't even know is this carb is functioning correctly and if all parts are even there to begin with. The Jeep does start though so thats good.

A drive around the block and I can only top her out at about 25mph. I'm missing the driver side exhaust manifold down pipe. Could no back pressure do this?

[chrisnsarah]

I am curious to know when the accelerator pump arm is supposed to start moving on this carb. Is it supposed to be at the same time the throttle starts to open.

When you start out in gear or jab the accelerator quickly, it will spit or miss, then idle fine or run fine once you get moving.

I noticed the pump arm doesn't move until the throttle is partially opened. I have a spare Holley and the arm moves immediately when the throttle is moved.

There is no mention of an adjustment in the manual. Is it ust trial and error until I find a good spot? I overhauled this carb during the summer.

[Lindel]

Chris, I've always adjusted the accel pump (on a Holley) so that I can blip the throttle (in park) and it doesn't stumble or hesitate. It's always worked for me.

If you go to Holley's website, you should be able to find the initial tune up for installing it. That has all the adjustments you need to do out of the box.

AMC, on yours I don't think that back pressure (or lack of) would be your problem. It's most likely carb related, and probably a choke adjustment. It may very well be a vacuum leak, these monsters are prone to that. Look to see if the PCV hose has come off the back of the carb. If it's not vacuum, look at the choke.

[AMC4ME]

Chris, I've always adjusted the accel pump (on a Holley) so that I can blip the throttle (in park) and it doesn't stumble or hesitate. It's always worked for me.

If you go to Holley's website, you should be able to find the initial tune up for installing it. That has all the adjustments you need to do out of the box.

AMC, on yours I don't think that back pressure (or lack of) would be your problem. It's most likely carb related, and probably a choke adjustment. It may very well be a vacuum leak, these monsters are prone to that. Look to see if the PCV hose has come off the back of the carb. If it's not vacuum, look at the choke.

Thanks Lindel ---

I'll check around the carb.

I've ordered a Haines manual and hopefully it will help me. Other people I spoke too also concluded that the down pipe should not make a difference. My carb is probably way out of wack. Should the butterfly valve flap open/closed when throttling? If so mine does not.......

Again I would like to get it rebuilt but I'm just trying to get the Jeep to run as best as possible with little $ down. Just to see what I have and go from there.

[Lindel]

If you're talking about the flat metal at the top of the carb, that's the choke. This time of year it should be nearly closed when you start the engine, and slowly open as the engine warms up. If it's not opening up, then that could be part of your problem, not enough air available to the engine.

[AMC4ME]

Choke valve is open and I believe that a part of my problem might be a bad fuel pump. I have to give a few shots of gas to the carb before initial start. I'm going to change out the fuel pump and see what happends. I called a local carb guy and thinks this would be my problem. Keeping my fingers crossed!:banghead:

[AMC4ME]

Maybe my fuel filter needs to be replaced.... I'll try that first.

[jeepbob]

I just bought a Generic bolt on holley with no external float adjustment tossed it on and just adjusted the idle jets and speeds (high and low speed Idle) and it was good to go. I do run a pressure regulator at 3.5 lbs.

[AMC4ME]

I replaced both fuel pump and filter. Better initial starts but still only moves to 25mph with a high rpm. I checked around the carb and all hoses seem to be intact. The manifold (vent?) hose behind the carb has been plugged. Replace carb? Bad timing? Bah...........

[AMC4ME]

What are your guys thought on maybe a bad transmission modulator? When the Jeep wants to switch to second gear it hesitates (briefly) as if it does not know what to do. Engine idle is good. I'm still wondering if maybe the missing down pipe from exhaust manifold is still in play.

[Lindel]

I was thinking along those lines, not modulator specifically, but tranny related.

I don't thing your exhaust is an engine issue at this point.

[AMC4ME]

I've been glancing thru the Haines manual lately and I'm trying to come up with different solutions to the problem. This not the original engine ( I believe) and it was not quite honed in. Now I'm guessing on throttle control linkage with the tranny. Perhaps the linkage has too much slack?.

Sorry all ----- I really don't mean to clutter up this forum with my particular Jeep issue. I don't have any one to physicaly help me on my Jeep and I'm learning as I go.

[Lindel]

Don't sweat it, that's what we're here for.

[Peter Matusov]

Thanks for the link to the article on the Quadrajet.

I've swapped the QJet that came with the 72 Buick 350 (that was definitely leaning out close to WOT) with a known-good Chevy QJet. It idles well, runs well, and I should be all over it - but starting the truck became a matter of probability and full battery charge! One tap of the foot in the inopportune moment, and it'll flood the engine.

I wish I could make one good carb out of these two...

[Lindel]

Welcome back Peter! Good to see you're still around!

[Peter Matusov]

Thanks Lindel,

I never went away - been lurking every now and then.
My son took the long Rangie away, and I never quite got used to driving a Volvo to work; the Disco on 32s takes just as much gas to drive to work as the Wagoneer, but the Wag rides much nicer. So...
... 'soon as I get back from the sandbox, I'll devote some time to get back from a FSJ owner to an FSJ daily driver again.

[OutdoorNM]

Hi Folks,

I just acquired a 1986 Cherokee 160K with auto trans. When I couldn't get the vehicle started I took it to the local jeep(dealer) shop. They wanted $1000- for a rebuilt carb(no labor, just the carb).....:( I eventually got a local garage to slap on a carb from the junk yard and do a bunch of other stuff for $600- It is now slow to start up, but once warmed up runs like a champ. I'm new to Jeeps, but have heard the carburetors can give you a lot of problems. I saw an add for 'remanufactured' Holly Carbs for my vehicle for about $525- which can be ordered thru' Auto Zone in 2 days.

I was wondering if I should consider the Reman' Holly should I have trouble with my existing unit? Your advice would be appreciated! :)

Lincoln

[Lindel]

Take a look at www.summitracing.com or www.jegs.com for Holley carbs, and you should be able to get a remanufactured carb for $300 at the most. I'd start looking elsewhere to get your parts.

You'd be money ahead to pick up a shop manual of some kind and do the work yourself.

[OutdoorNM]

I will check out those sites. I plan on doing a lot of my own rebuilding, but I was desperate to get the jeep functional.

Lincoln

[TheJeeper]

Hey speaking of Holleys, I need a rebuild kit for a model 1920 on my '65 with a 230. Any of you guys know where I might get one?

[jaber]

I think Ristows thread on his Holley should be linked over to this one.

http://www.ifsja.org/forums/vb/showthread.php?t=100852