Several years ago carb specialist Lars told me my carb was from a heavy duty truck and would always run rich. Details: Rochester Q Jet, 17084288, 1994 HKF. Can I rebuild it to work in my 73 with an 82 crate 350. No smog, slightly upgraded cam, street use. NAPA says they can still get the kits if I know the part number. Happy Holidays, Thanks

 

I am not well versed in the differences between truck carbs and car carbs, but the nice thing about the Quadrajet is with a bit of tweeking they can be made to work well on almost anything.
There are plenty out there and it may be a better idea to find a clean auto carb core to start with.
If you do a bit of searching here, you will find plenty of help from Lars and others on this same subject.
One thing I would recommend is to get a kit and tuning parts from Cliffshighperformance.com.
Pretty much the best kits available and some of the best back up tech from Cliff.
Might as well pic up a copy of Cliffs Quadrajet book as well so some if the tweeks and mods are understood. Lots of good info from this book.
If I am not mistaken I believe Lars uses his kits and parts for the work he does.

 

 

My 2cents..............Lars is the only name for QJets.................period!!!!

JJ78

 

Trying to rebuild a carb will be a fun project. Unfortunately most of the time the rebuild/ restoration turns out with way too many carb problems. One of my car show buddies has been a copier repairman for over 35 years. He rebuilt is 1978 OEM Quadrajet 5 years ago, and still has starting problems when the engine gets hot. With all his repair experience, you would think the carb would work perfectly. Wrong, he has tried every aftermarket remedy to solve the problems, but none has worked. The last thing he tried was installing an electric choke ( more wasted time and money). One of the problems is that these carbs are old, and some of the parts are worn from many years of use, sure the rebuild parts are fine, if the carbs were only two years old. Adding new shafts / parts to old worn carbs does make the problems disappear. I believe that in some cases Lars repairs the carb bodies, because the tolerances from wear are too great. My friend could have had Lars repair 5 carbs with the amount of money he has spent trying to fix his problems. Who knows how much time he has wasted?

 

I don't believe I would have said that the '84 truck carb would unconditionally and unilaterally run rich. I probably indicated that the truck carbs are set up with boosters and air bleeds that provide a much stronger fuel metering signal at low rpm and under low-rpm load, which is not a well-suited match for a Corvette application. I probably indicated that it would require a level of modification and tuning that would not be worth the effort, and I probably advised you to find a good, rebuildable Chevy passenger car core to work with your '82 crate engine. I probably gave you a "pass" on doing the work, since a carb like that would have to be extensively tuned and set up using a wideband on the actual vehicle in order to get the fuel curve anywhere close to the ballpark. I still suggest that you find a good, rebuildable, unmolested 1976 - 1979 Chevy passenger car core and convert it to electric choke to operate on the 1982 intake manifold. With minor setup and tuning, a carb like this would be an easy setup and a good match for your engine. Good cores are still available for under $200, and you can frequently find them under $100.

Unfortunately, the Echlin/NAPA kits have lost all and any level of product quality they once had. The accelerator pumps are junk (they swell up and seize in modern pump gas); they have the wrong needle/seat assemblies in them; kits are frequently missing parts or have incorrect parts in them; and they have increased prices to the point that it is obvious that they don't want to sell carb kits or parts anymore. If you're going to buy a "kit" for the truck carb, get your parts from Cliff Ruggles - he is the only remaining source for good quality Q-Jet parts.

Just my opinions and suggestions...

Lars

 

Carburetors unlimited in AZ. owner Bruce is well educated and has tremendous skill with qjets as well

 

...not to be confused with Steve at Carbs Unlimited in Washington, who is no longer building Q-Jets...

Lars

 

[QUOTE=Eliredandblack;1609321570
[b]He rebuilt is 1978 OEM Quadrajet 5 years ago, and still has starting problems when the engine gets hot. [/QUOTE]

I'm beginning to believe that a Quadrajet equipped motor that is a bit reluctant to start when hot MAY be due to today's ethanol contaminated fuel.

My '76 L82 with stock Q-jet carburetor gets stage-fright when attempting to start when the motor is hot. Not a problem to start immediately after shut-down, but if allowed to sit hot for 10 minutes or so it requires more starter time than when the motor is cold.

Jason

 

I do hot-soak re-start testing on every carb I build and never have a problem running pump-gas in the test engine. If the carb has a hot-soak re-start problem, it's usually due to an issue with fuel getting into the intake manifold after shutdown, which is usually caused by loss of fuel level control in the float bowl.

 

I hear you.

I disassembled my carburetor and discovered the two aluminum plugs that seal the cross-drilled holes in the bowl were leaking. Ah ha, that's the problem I thought. So, I carefully drilled out the plugs, tapped the holes and installed set screws with fuel-resistant epoxy on the threads.

Reassembled the carburetor, installed it on the intake manifold, started up the motor and the hot-start problem still persists.

Jason

 

I'm all ears if you have suggestions on how to eliminate the hot-start problem. Perhaps the float level is a smidgen too high?

Jason

 

Here's an easy test to see if you have a fuel level control problem after shutdown: Immediately after shutdown, put a rag under the fuel inlet fitting and loosen your fuel line to relieve all pressure in the line. Leave it disconnected/loose for the 10 minutes that usually causes the problem. Tighten the line back up and then re-start.

 

I like it!

Except I'm confused. Leaving the fuel line disconnected/loose for 10 minutes usually causes what problem?

My interpretation of your test is that if the motor starts after the 10-minute period without having to crank on it like the Hurdy Gurdy man, then the float level is too high and that by relieving the upstream pressure, overflow from the bowl to the intake manifold was mitigated.

Or, have I misinterpreted your test?

Jason

 

Disconnecting the line won't cause any problem as long as you don't try to start the engine with the line disconnected.
Eliminating the residual fuel pressure after shutdown means that that the bowl won't continue to fill with fuel if you have a fuel level control problem. A fuel level control problem can be caused by several different issues, and will cause fuel to "dribble" into the intake after shutdown. If the problem goes away after you've immediately disconnected the fuel line after shutdown (and then re-attached it before starting), it means you have an issue with fuel control. A high float will not generally cause the problem unless your float level is so high that the fuel level is above the level of the main discharge nozzles.

 

Ok, I'll do the test tomorrow and report my findings.

The float needle and seat are less than a year old, purchased from Cliff Ruggles, so I don't suspect them as the problem. Moreover, I've replaced the aluminum cross-drill plugs with set screws and epoxy, so no more leakage from those areas. The only thing remaining is perhaps a misadjusted float. But I'm getting ahead of myself. Let's see what tomorrow's testing tells us.

Jason

 

After rebuilding a good quadrajet core and replacing HEI distributor installed by previous owner with a aftermarket small cap distributor with tach drive. I had a hot start issue that got worse as time passed. After pulling the air horn twice to check float level I put the HEI distributor back in. Hot start problems were gone. I would have to hold the pedal on the floor to get it to start hot. With HEI don't have to touch the pedal when hot. When cold depress pedal once to set choke and it fires off.

The main thing I learned from this was to only make one change at a time. Had I replaced carb and got that tuned then replaced distributor I want to believe I would have known it was a junk aftermarket distributor.

 

"90% of all carb problems are ignitions problems."
Lars' opening statement from the "Tuning for Beer World Tour" events...

Lars

 

And I thought that only applied to old British motorcycles with Lucas electrical systems!

I would like to apologize to Capt Ken for jumping into his topic; I hope I'm not inconveniencing you too much.

Yesterday it was 83* F in Katy, Texas and today it was 51* F at the time of my carburetor test. I ran the car for about 12-15 miles at mixed speeds, disconnected the fuel line from the carburetor and let it heat-soak for 10 minutes. I reconnected the fuel line and started the car and did not experience a hard-start problem. So what does that mean?

I'm concerned that it simply was not hot enough to cause hard starting. I'll wait for an 80* F-plus day and perform the test again.

But in the meantime, observing the same test results at higher temperatures suggests a float needle/valve leak. So, I'll install a new needle and seat, notwithstanding I replaced them less than a year ago from a parts kit purchased from Ruggles.

My ignition system is stock, except for new wires, dizzy cap, rotor and spark plugs.

So what else could the problem be?

​​​​​​​Jason

 

Do you have the correct 1/4" spacer gasket installed? What is your timing set at? Heat riser system still on the car? Crossover blocked?

​​​​​​​Jebby