GM TBI, Qjet or Auotlite 4100?

[Oatmeal]

I've had my '74 Bronco since 1987 and have had a couple of healthy 302s with a few different fuel systems over the years.
Started with the stock 2bbl to an Edelbrock Performer on an early Mustang intake (ran great on road, terrible off road) from there I went to a Holley Pro Jection (ran great but, would flood after a hot start) to the present Qjet on my 351W which works pretty good off road but, drains the float bowl overnight, making cold starts a real pain and mileage sucks, too.
I have a complete GM TBI conversion with custom harness and prom for my engine specs: approx 9:1 comp and Edelbrock Performer cam (my truck is plumbed with fuel return lines from the Projection system and I was planning on using the Projection pumps).....whew!
I came across a rebuilt 4100 with smaller 1.08" venturis on eBay for about $300 and am rethinking the TBI.....opinions.
Hans

 

[nvrstuk]

I can empathize with ya. I ran a stock 2bbl, a 4 bbl, Holley ProJection, Qjet and now Moates Qtrhorse driven SEFI. So I think I can understand where you are coming from.

How serious of a rock climber off camber type of driver are you? Asking for several reasons.

I am NOT a TBI guy. All the tunes I have been exposed to are all rich for a reason. The tuners do not want to run your engine too lean and error on the side of "fatness" so you won't come back at them and I don't think you are gaining anything over a properly setup Qjet. I built Qjets for years for a lot of people and they are the poor mans EFI we used to call it.

I'd KEEP the Qjet and if you can't get rid of the fuel evaporation problem then go to a 5psi electric pump and turn it on like you preheat your diesel before starting it. 2 seconds of prime time and you crank your engine and it'll fire right up. Your economy (MPG) with the Qjet should better than ANY 2bbl and here's why. When it is jetted and tuned correctly the small primaries of the Qjet give you better economy than the larger primaries of any 2 bbl. Make sense? If you stay out of the secondaries on the Qjet your mileage and throttle response will be much better than the 2bbl. IF you aren't getting better mileage then you need to work on tuning it for your engine.

You will not find a better on/off 4bbl road carb than a Qjet. You won't. The primaries are so small that your throttle response is the best out there, the secondaries can be tuned for ANY size engine. I have set them up on 501 Caddy motors and we just sold a 4 cyl, 190 hp boat engine with a 750 Qjet. Dialed in perfect. Don't let anybody tell you that it can't be done on almost any motor.

ProJection was a good start by Holley in the early '90's. Mine was one of the good ones. Flawless but I sold it and went Qjet. I ended tuning them locally but they were primitive for sure.

 

[Oatmeal]

I can empathize with ya. I ran a stock 2bbl, a 4 bbl, Holley ProJection, Qjet and now Moates Qtrhorse driven SEFI. So I think I can understand where you are coming from.

How serious of a rock climber off camber type of driver are you? Asking for several reasons.

I am NOT a TBI guy. All the tunes I have been exposed to are all rich for a reason. The tuners do not want to run your engine to lean and error on the side of "fatness".

Tow an off-road trailer, been on the Rubicon, Dusy/Ershim, Swamp Lake....like the big rocks.
Hans

 

[Broncobowsher]

I recall there is an epoxy fix for the Q-jet. Might want to look into that. Something about a pinhole leak that drains gas into the engine.

 

[73azbronco]

Second Qjet. Mine was built by the old Phoenix guy who builds quest for racers. Sat for four years, one bump and started first crank.

I did a qjet to get me going, thought of going some for of Sufi, but it runs so well I delaying that choice.

 

[Oatmeal]

I recall there is an epoxy fix for the Q-jet. Might want to look into that. Something about a pinhole leak that drains gas into the engine.

Yeah, I re epoxied(sp?) the "Welch or Welsh?" plugs and it still does it.
I like the Qjet but, with the 4 hole adapter on the Performer intake it sits pretty high so, air cleaner to hood clearance is tight.
All that aluminum under the carb base soaks up a lot of heat too.
Some say the Autolite 4100 is pretty good off road as well and so much simpler to work on....rebuilding the Qjet was a pain!
Hans

 

[Oatmeal]

Your economy (MPG) with the Qjet should better than ANY 2bbl and here's why. When it is jetted and tuned correctly the small primaries of the Qjet give you better economy than the larger primaries of any 2 bbl. Make sense? If you stay out of the secondaries on the Qjet your mileage and throttle response will be much better than the 2bbl. IF you aren't getting better mileage then you need to work on tuning it for your engine.

I know but, don't have the inclination or patience to tune it.
Moving to Utah in less than a month and doubt that anybody in Cedar City (Green Acres) has the skill or knowledge to do it for me.
That's why I was kind of leaning towards the simplicity of the 4100.
Hans

 

[jckkys]

I chose a 1.08 venturi 4100. They have the off camber abilities of the 2100. I've seen EBs nearly laying on their side and still running. We didn't have EFI or any fuel injection. Those of us that bought new Broncos, knew they were inexpensive and plentiful. So we pushed the limits in every kind of environment. The carb wasn't a problem till people started getting Holleys and Carter AFBs. Q jets have a central float bowl that is the main reason angles don't effect them much as most other carbs I hear. Since I or anyone I knew had no problems with the 2100 (CJ5 used them too) it becomes a case of "if it aint broke don't fix-it". The 2100s were calibrated for the 289-302 not some unknown GM vehicle. The annular discharge booster venturis atomize fuel droplets better than any others. The fit and linkage/fuel connections are OE. No weird manifold or spacer. It's the same with 4100s. Clean it out very thoroughly and set it up as instructed in the rebuild kit.

 

[Oatmeal]

I chose a 1.08 venturi 4100. They have the off camber abilities of the 2100. I've seen EBs nearly laying on their side and still running. We didn't have EFI or any fuel injection. Those of us that bought new Broncos, knew they were inexpensive and plentiful. So we pushed the limits in every kind of environment. The carb wasn't a problem till people started getting Holleys and Carter AFBs. Q jets have a central float bowl that is the main reason angles don't effect them much as most other carbs I hear. Since I or anyone I knew had no problems with the 2100 (CJ5 used them too) it becomes a case of "if it aint broke don't fix-it". The 2100s were calibrated for the 289-302 not some unknown GM vehicle. The annular discharge booster venturis atomize fuel droplets better than any others. The fit and linkage/fuel connections are OE. No weird manifold or spacer. It's the same with 4100s. Clean it out very thoroughly and set it up as instructed in the rebuild kit.

Well,
Found one on eBay for a good price.
It says jetted for a 66 Mustang 289 (1.08 venturis) but, I want to run it on my 351W with a performer cam and intake.
Do you think it will run ok as is or do you think I'll have to rejet it?
On a time constraint....have a 450 mile trip to Utah coming up in less than a month and don't have time between my last few weeks of work (retiring), packing and moving.
Hans

 

[BUCKWILD]

To be honest you will continue to have carb problems no mater what with the fuel having more ethanol in it today. Go with a modern TBI (Holley) I recommend or even an explorer injection system. If you like rock crawling nothing will compete with injection and the new systems will out perform all of the old. I have a Eldelbrock pro flo4 and cant be happier, I have had mustang and explorer injection but the new systems are tunable with a tablet and easy to tune for the beginner. Just for information mine will run upside down untill I run out of oil. Just my recommendation

 

[Madgyver]

i love the Qjet. simple and dependable in my opinion.

 

[phred]

I had Jet Performance build a q-jet specific for my cam and engine profile. Pricey but well worth the money and definitely cheaper than fuel injection. Out of the box it ran great. Minor tuning to get hot start dailed in and it has been flawless for 9 years. Yep 9 years with out a rebuild or retune. I've been careful to run ethanol free gas or use a fuel stabilizer. Works well off road. Not a fan of TBI, bur I'm old school and like carbs.

 

[bmc69]

I had great luck with the older Holley Commander TBI systems...installed one on the 408 in my crawler and a couple for friends' rigs. Of course the Sniper is a great option nowadays.

But I'm an old school carb guy too. That 4100 option is a good one; I have one on the shelf now, waiting for a suitable project.

 

[Rustytruck]

I am a big fan of the Quadrajet too. go down the path you wish but don't get rid of the Quadrajet unless you go fuel injection because you will be back to it. especially in Colorado where you will be dealing with elevation changes. mine runs great from sea level to 9000 feet with no changes. I do run a fuel pressure regulator and crappy California blended gas. just make sure you have good gaskets under the carb that actually seal. Quadrajet is very sensitive to vacuum leaks around the carb. pull the gaskets and see if they are actually sealed. gaskets get thin around the big bores and some adapters are not made properly and leak. best wishes in your retirement.

 

[okie4570]

I had Jet Performance build a q-jet specific for my cam and engine profile. Pricey but well worth the money and definitely cheaper than fuel injection. Out of the box it ran great. Minor tuning to get hot start dailed in and it has been flawless for 9 years. Yep 9 years with out a rebuild or retune. I've been careful to run ethanol free gas or use a fuel stabilizer. Works well off road. Not a fan of TBI, bur I'm old school and like carbs.

I did the same, it's been great and been running it since 2013 iirc. We have real gas at every station still so that's never been an issue.

 

[SteveL]

Another fan of the q-jets from jet performance. I run em on the 351w's with an offy manifold to get rid of the adapter.

 

[jckkys]

It's interesting to hear people predict future problems and claim you're having problems now. What a load of BS. I've had no problems with OE Ford 2 and 4 barrels. I see no reason to do a GM carb and plenty of reasons not to. AFBs, AVSs, and Holley 4150/4160s work fine for a daily driver and most off pavement driving. None of them are as good as the Ford 2100, 2150, or 4100. Making a Cheby carb run on a Ford is no accomplishment in spite of what some want to think. Ford carbs work OK on a Cheby too. In both cases there's no reason to do it. The 2100s were never a problem. So again, if it's not broke why fix it?
I know the concept of a classic vehicle is hard for some to grasp.

 

[okie4570]

It's interesting to hear people predict future problems and claim you're having problems now. What a load of BS. I've had no problems with OE Ford 2 and 4 barrels. I see no reason to do a GM carb and plenty of reasons not to. AFBs, AVSs, and Holley 4150/4160s work fine for a daily driver and most off pavement driving. None of them are as good as the Ford 2100, 2150, or 4100. Making a Cheby carb run on a Ford is no accomplishment in spite of what some want to think. Ford carbs work OK on a Cheby too. In both cases there's no reason to do it. The 2100s were never a problem. So again, if it's not broke why fix it?
I know the concept of a classic vehicle is hard for some to grasp.

Sorry you can't see the reasons that some of us have clearly stated........I'd tell you what's hard for some people to grasp but you wouldn't understand.

 

[Broncobowsher]

It's not a chevy carb, it is a Rochester. When launched it was highly praised for its abilities. So much so that Ford even used them in some applications.

Rochester is just a parts supplier that sold to anyone. GM just happen to be the biggest customer.

 

[ngsd]

I have an old school GM style TBI that was built by Turbo City. it is 20 years running and still solid. That old TBI stuff may not be the best solution but is sure dependable.