And keep in mind that these are common problems - I'd say at least 75% of the carbs I see have issues and problems that a "kit" is never going to fix. Most old carbs need parts, components and repairs far outside the scope of a "kit."

Lars

 

Good golly that one was a mess.

 

Way worse then I thought. Thank god I sent it off to someone who knows what they are doing.

 

I sent my original 78 L82 carb to Lars in June of this year and was stunned when he wrote with a list of what was wrong. I'm kicking myself I did not have it done sooner. What a difference driving this past summer.

 

Awesome!

 

Neil's carb is shaping up, and more problems are being corrected....

Once the carb came out of the hot tank cleaner, it was evident that the carb had been sandblasted and painted by a previous builder. Paint is some nasty stuff when applied to a carb, and I'm seeing more and more of this type of horrible hack-work on older carbs. The only "right" way to repair this is to do a complete re-plating job on the carb and all its parts, but this tends to get a little costly with the amount of labor involved in doing it. So we decided to run the carb through a de-rusting process and make it look as good as possible for a reasonable cost - the main objective is to get this thing running correctly, and running reliably.

But coming out of the cleaner I noticed that the secondary emulsion tubes looked a little funny. These are the tubes in Neil's carb. The 2 center tubes (skinny tubes) are supposed to be almost as long as the larger outer fuel supply tubes:



So I extracted the tubes out of the airhorn and put them alongside a pair of original, correct tubes. Sure as hell, somebody has cut his tubes off and destroyed them. His "shorty" tubes on the left. Correct tubes on the right:



The carb now has correct-length secondary tubes in it:



The machining and STI tapping operations were successful at the fuel inlet. Freshly tapped threads ready for cleanup and chemical conversion coating for corrosion resistance:



Chemical conversion coating (aka, "iridite" or "alodine") is applied to the threads to improve corrosion resistance prior to insert installation:


Threads being installed into the carb bowl fuel inlet:


New stainless steel threads successfully installed:


Original fuel inlet fitting installed in the carb. It can now be properly tightened with no fear of the threads pulling out:


Many parts for these carbs are no longer available from any sources, so I am fabricating some parts needed to restore the idle vent system on the carb. I use original parts as templates to fabricate the look-alike reproductions:



The broken area of the carb bowl nipple boss was machined deeper to allow a new vacuum nipple to be pressed deep into the carb bowl casting for adequate support. Although the top side of the casting stand-off is broken, the lower half is still intact, which will allow it to correctly function as a support stand for the choke pulloff bracket. Once the bracket is installed, the damage will not be evident, and everything will function correctly:



Power piston has been disassembled and re-assembled with a correct, OEM retaining collar and a correct rod retaining spring. The correct rods have been installed:


Carb is finally ready for assembly operations!


Lars

 

During final assembly and setup yet another problem was discovered. In trying to keep costs down, I was planning on re-using as many of the parts on the carb as possible, as long they were functional and operating correctly. At some point, someone had installed an incorrect choke pulloff on the carb - this pulloff is from a Rochester 2GC (2-barrel) carb and does not have adequate stroke to be used on a 4MV Q-Jet. This was preventing the secondary airvalves from opening any further than 1/2-way.

Here is the 2GC pulloff on the carb. It looks very similar to the 4MV pulloff, but it has a "squared-off" lever arm:


With the pulloff correctly adjusted for the "retracted" condition, the "extended" position will only allow the secondary airvalves to open halfway:


I had a perfectly good, used 1969 Q-Jet pulloff that I then installed, and the system is now operating as it should. Correct pulloff installed with correct "white stripe" hose:


Secondaries now open fully:


Carb is now assembled and ready for initial testing:


Idle vent valve components installed and operational, less installation of the vent valve cover. All of the airhorn hardware has been refinished to the correct black oxide coating (carb had incorrect silver hardware installed throughout):


With any luck, Neil might end up with a correctly-running carb...!

Lars

 

Looks like we got lucky: The carb is running great!

Up and running on the test engine:


Carb had a perfect cold-start at 34 degrees, and ran with no trouble with choke cracked open by the correctly-operating choke pulloff. No leaks or drips from the inlet repair. Idle vent cover has yet to be installed to cover the bowl vent components:


Running hot with choke wide open. Nice, smooth idle with excellent throttle response:


Idle mixture right on the target number at 14.7:1. Mixture screws have full range adjustability:


The carb is running exactly as it should, and all items are properly repaired. Of interest and note is that no "carb kit" was used: Of the 17 items that were wrong with the carb, not one of them could have been repaired or corrected by installing a "carb kit," and no carb kit would have included a single one of the parts needed to repair this carb. When you see carbs advertised for sale with a "fresh rebuild and carb kit" it means absolutely nothing in terms of the carb running right or being correctly set up in any way...

Lars

 

 

Lars,
This has been an interesting and educational thread.
The photographs and description documenting your work was awesome.
Thank you for sharing.
Greg

 

Glad you found it interesting, Greg! One of the most common technical assistance e-mail requests I receive is, "I rebuilt my Q-Jet and put a good quality carb kit in it, and the carb still won't run right. What's wrong with it...?" Well, as you can see, there are about 147 things that could be wrong with it, none of them can be identified or diagnosed via e-mail or Forum posts, and none of them will be fixed by installing a carb kit. For example, for the common complaint, "I don't think my secondaries are working," who would possibly think to respond, "Well, check to see if someone has installed a 2GC 2-barrel choke pulloff on the carb..." ? Any time you rebuild and work on old car parts, you have to be very careful about identifying all the crazy stuff people have done to the parts over the past half century...

Once the last few parts arrive for Neil's carb, I'll post up a couple of final "completion" photos and then get this thing sent off for him to try out. Hopefully, it will run a little better than it did before...

Lars

 

About 30+ years ago I purchased two used 660 cfm Holley’s to run on the tunnel ram on one of my boats.
I figured there was nothing to this style of carb, they would be simple to rebuild and I would save a ton of $$$.
I purchased the best quality Holley rebuild kits and a 5 gallon bucket of boiling fluid and did a good rebuild on both carbs.
That was until I installed them.
What a disaster.
Tried a second time because “I could do this simple rebuild”.
Second disaster.
I tossed both carbs and bought new.
I would never attempt to rebuild a Q-Jet.
The magic you do to these old carbs is amazing.

 

No magic - I just get lucky once in a while.

Lars

 

 

The last little detail part is finally installed, the carb is complete, and it's on its way back to Neil. Sitting in a cold workshop I had a chance to give the carb a few good cold-start tests in the mornings: Carb is firing up instantly at 25 degrees with 3 pumps of the gas pedal and going right to a perfect, stable fast idle as it should.

Let's wish Neil good luck with the installation and hope it runs equally well for him!

Carb complete with all correct parts installed just before box & ship:




Lars