Holley Quadrajet EFI

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Jun 12, 2020
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SW Missouri
Wondering if anyone has any experience with Holley’s Quadrajet EFI system? I have an 86 Chevy K20 with a Quadrajet and nobody around here can get it right. I even had an old school guy I’ve known for years totally overhaul it(the guy is a genius with carburetors usually) and he can’t even get it right. Told me he couldn’t do anything else for it. I like my old stuff but I’m not terribly fond of carbs and I’m more comfortable with fuel injection as far as diagnosis and repair go. I’m thinking of going with the Holley retrofit tank and one of their distributors too. Not looking for “performance” but reliability. This is a work truck and will be getting the frame painted and a flatbed installed. It handled all of our mobile repair on the farm and was my winter/bad weather driver to work until it became unreliable.
 

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Get what right? What is it doing? Stalling? Idle too fast? Hesitation? Have you ruled out bad gas? Or timing issues. Fuel pump problems. Rebuilt the carb on an '88 454 motor home 3 times before finding out it had 2 fuel pumps and a regulator, two of which were bad.
 
watch a few episodes of WatchJRGo on youtube.

He has replaced every one of the carbs in his fleet with the holly EFI system, and they all run perfect.

It's the first thing he does when he gets a new vehicle with a carb.

He did it on a bronco of similar vintage, and a few chevys also.
 
Get what right? What is it doing? Stalling? Idle too fast? Hesitation? Have you ruled out bad gas? Or timing issues. Fuel pump problems. Rebuilt the carb on an '88 454 motor home 3 times before finding out it had 2 fuel pumps and a regulator, two of which were bad.
Problems got worse over a period of time and were unaffected by where I filled it with gas so I would say bad gas is ruled out.

New fuel pump, rest of the system is factory. Been in the family since it was 2 years old so I know most of what’s been done.

Diesels when shut off hot. Won’t restart when even slightly warm even in winter. Hesitates when trying to pull a hill, cuts out, etc. Went from 10mpg before tune-up and carb rebuild and down to 4-5 now. I’ve had 3 different places work on it in addition to what I have done tune-up wise. I would have almost bought an EFI system now if I would have started there.

Cold start is great and choke operation is fine.
 
Your guy may be great but if the throttle plate shaft(s) are worn it won’t idle and adjust properly. That’s a big issue with 35+ year old carbs. Edit: Probably cracked fuel bowl allowing raw fuel to weep in the intake. Another problem with older Qjets. Some overhaul kits used to come with epoxy to apply to that most likely crack location.
 
watch a few episodes of WatchJRGo on youtube.

He has replaced every one of the carbs in his fleet with the holly EFI system, and they all run perfect.

It's the first thing he does when he gets a new vehicle with a carb.

He did it on a bronco of similar vintage, and a few chevys also.
I believe his channel is one of the first I stumbled on. Also watched a Holley install video and was impressed.
 
Your guy may be great but if the throttle plate shaft(s) are worn it won’t idle and adjust properly. That’s a big issue with 35+ year old carbs. Edit: Probably cracked fuel bowl allowing raw fuel to weep in the intake. Another problem with older Qjets. Some overhaul kits used to come with epoxy to apply to that most likely crack location.
He specifically commented about how tight the shafts were so I don’t believe it would be that. As far as cracks are concerned, that could be a possibility because he didn’t mention it and I didn’t know to look. Not sure if it’s something we could see or not even if we had been looking with a naked eye.
 
Does it seem to be really rich at idle? Wondering if there may be something in the needle seat? One quick way to clear the needle seat: clamp the rubber fuel line at the fuel pump using vice grips, crank the engine and let it run all the fuel out of the carb. (It will die). Remove the vice grips and crank the engine and get it running with higher than idle RPMs. This will flush the needle seat with needle out of the way until the bowl is full again. If it acts right after that then you had trash in the needle seat. Hopefully your guy didn’t use Teflon tape on the flared fuel line at the carb. Big no no…
 
Does it seem to be really rich at idle? Wondering if there may be something in the needle seat? One quick way to clear the needle seat: clamp the rubber fuel line at the fuel pump using vice grips, crank the engine and let it run all the fuel out of the carb. (It will die). Remove the vice grips and crank the engine and get it running with higher than idle RPMs. This will flush the needle seat with needle out of the way until the bowl is full again. If it acts right after that then you had trash in the needle seat. Hopefully your guy didn’t use Teflon tape on the flared fuel line at the carb. Big no no…
Doesn’t seem to be. Exhaust smells normal and it idles great. No Teflon on fuel line fitting. He was the guy that taught me about different flares and hydraulic fitting types including where to use tape.
 
On a side note, the first place I took it to told me it had a broken wrist pin and that’s why it idled rough. Put it on an old school Sun machine and it turned out to be a spark plug with a crack in the ceramic. That’s when I did the tuneup. The idle drastically improved with the tuneup and carb rebuild but other drive ability issues remained or got worse. No broken wrist pin….🙃
 
It’s a shame. A Qjet is about as close to fuel injection as a carb can be when they are right… in my opinion. There is one other adjustment (APT) that if tampered with can be really critical to get back right. We called it the “DFW” valve. Don’t Fu@# With.
 
Diesels when shut off hot.
Carbon buildup in the cylinder. Italian tune up or GM Top Engine Cleaner
Hesitates when trying to pull a hill, cuts out, etc.
Seems like a lean condition. How do the plugs look?
Won’t restart when even slightly warm even in winter. Went from 10mpg before tune-up and carb rebuild and down to 4-5 now.
And that could indicate a rich condition. Again, how do the plugs look?
 
Carbon buildup in the cylinder. Italian tune up or GM Top Engine Cleaner

Seems like a lean condition. How do the plugs look?

And that could indicate a rich condition. Again, how do the plugs look?
I haven’t had them out in over a year now so I couldn’t tell you. Hoping to have time to mess with it soon. I bought my 16 F250 in November last year because I couldn’t keep limping by with this truck. It’s been used a few times on the farm since but that’s it.
 
Not a spreadbore, but I did install a Holley Sniper EFI and the electronic ignition on a 427 in a 66 Chevelle for a friend last year. Aside from one ignition trigger issue inside the throttle body, it has been stellar. Starts and idles beautifully, stinks WAY less than when the car had the double pumper on it. It had a Proform HEI distributor on it when he first got it. Timing was everywhere. I messed with it, shimming the gear so it didn't move up and down too much, tried different weights and springs, finally did the Holley and now the timing is rock solid.

I haven't messed with a Q jet in years but I used to have one built by Brad Urban in my Chevy powered 80 Firebird. Carb was awesome.
 
It’s a shame. A Qjet is about as close to fuel injection as a carb can be when they are right… in my opinion. There is one other adjustment (APT) that if tampered with can be really critical to get back right. We called it the “DFW” valve. Don’t Fu@# With.
Yep, the Q-Jet stood the test of time with GM and eventually saw it’s grave in the 1990s. It was, alongside the Aisin and Keihin carbs on Toyota and Honda an electronically-controlled carb in the 1980s.

Never fussed around with one, finding someone familiar with them these days is rare. I can see the appeal with a EFI conversion.
 
I put gm tbi on my 78 k20 that had a quadrajet. If i had to do it over again i would have kept it stock. While the fuel injection is fine and im sure the holley system is great i really like the simplicity of the carburetor. Have you considered buying a remanufactured carburetor? Also make sure the camshaft is ok if its original along with the timing chain. Worn lobes can do weird things with it running and a loose chain can cause timing to jump around causing bogging.
 
I remember back in the day when a carb would act like this, folks would say "yeah, it's vapor locked". I don't know where that vapor was supposed to be, and the carb was always full of fuel... :LOL: but that's what they'd say.
 
On a side note, the first place I took it to told me it had a broken wrist pin and that’s why it idled rough. Put it on an old school Sun machine and it turned out to be a spark plug with a crack in the ceramic. That’s when I did the tuneup. The idle drastically improved with the tuneup and carb rebuild but other drive ability issues remained or got worse. No broken wrist pin….🙃

Many “carburetor” problems turn out to be ignition problems. The Holley system looks like a great option, but please make sure you don’t have a simple problem with your existing ignition system.
 
I've used the Holley system (their TBI system) on an S-10 with a 355 in it that was warmed over and run on nitrous (this was my buddy's dad's truck, we installed it). It works fantastically well, the kit we had used a wide-band and was self-tuning. It was extremely reliable and provided a big improvement in gas mileage and behaviour, I'd highly recommend it.
 
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