lars

Following the post and comments I did at:

http://forums.corvetteforum.com/c3-t...g-the-bad.html

Paul (”paul 74”) sent me the PPC from Canada. Paul’s carb is a “restored” carb, and it’s prettier than any Q-Jet was ever made: even the secondary airvalves and the choke plate are cad plated with yellow dichromate conversion (the originals were left plain silver cad without the dichromate conversion). These “too pretty” carbs are usually a sure-fire sign that something is amiss with the carb, and Paul has always said that this carb has never run quite right:



Upon receipt here in Denver, the carb looked OK, other than the “over-restored” cosmetic items. The carb is a 7044206, which is a 1974 Corvette Auto Trans carb with Federal emissions. It should be jetted with 75 jets, 46 primary rods, and “CH” secondary rods (I designate this jetting as 75/46/CH). A quick installation and test on the test engine showed that the carb was running lean…. Hmmmm…

Tearing the carb down showed that it was not exactly a pristine restoration, contrary to what the seller had presented. The following issues were found:

• Wrong float installed
• Non-ethanol-compatible accel pump installed – accel pump inoperative
• Jetted 68/35/DH (this is roughly 18% leaner than the correct jetting – grossly lean)
• Power piston jammed in the full rich position (to compensate for the gross lean condition)

The carb also had a significant fuel leak at the inlet fuel fitting due to severe gouging of the sealing surface cone of the inlet nut.

On the good side, it did not have the dreaded chopped-off power piston, Pontiac airhorn on a re-stamped float bowl, and the lead-plugged idle air bypass holes – the carb wasn’t completely “hacked” as I usually see.

The carb was re-assembled and set up with all the correct parts: The float was replaced, the power piston was repaired and adjusted correctly, and the carb was given the correct 75/46/CH jetting combo along with a .300 float level, a ľ turn secondary spring windup, and a .640 secondary rod height setting. The fuel inlet nut was replaced with a new reproduction part to solve the fuel leakage issue.

Back on the run engine:





The carb now runs at a perfect air/fuel mixture, and it has very snappy throttle response along with an excellent, smooth idle – both cold and hot.

The moral, once again: Just because a carb has been “rebuilt” and looks pretty doesn’t mean it’s going to run well, or that it’s even set up right. Any carb you buy “rebuilt” (and even the ones you buy new, such as a new Holley or Demon) needs to be torn down, checked, corrected, and set up right before it can be expected to run well. Paul now has a good-running carb that’s on its way back to frozen Canada…

Lars

marshal135

GREAT JOB!!!
DR. LARS
Mine is due to visit your clinic soon.
Just gotta pay my Obahma Care premium first then I can get the carb fixed.
I see they legalized weed in your neck of the woods.
Great money maker for the state for sure!!!
Have a blessed 2014!!
Marshal

rponfick

I sure thought we were going to use this as a doorstop at the Viking Lounge. I guess we will have to keep looking.

Ralph

Jeff_Keryk

Compared to others, it sounds like this carb was not too butchered. I'm sure Paul will be 100% satisfied with his Q-Jet.
Outstanding work!
I learn something with each of your posts. Thanks Lars.

Capt. Shark

it is kind of pretty

if it won't go, yellow dichromate it

lars

Actually, I had other plans for it if it had not been repairable:

It's so cold in Canada, that the carb was still at minus 14 degrees when I got it. I was planning to use the float bowl as a whiskey chiller in the Viking Lounge - it would have maintained sub-zero temps for at least a month with the Canadian cold-soak it had been through...

The Viking Lounge, open to all genuine Enthusiasts (Note open back door - it already has a "rebuild" Q-Jet for a door stop):

RATT7

Well Done !!!

Paul L

Firstly, my thanks to Lars for taking on this project!!

Shortly after I bought my 1974 in 2008 it was evident that something was wrong with the carb. In fact some choke parts had fallen off onto the manifold.



So I pulled that one and ordered the "pretty" one. It was so pretty it had to work. Wrong. I gave it a try for perhaps 2-3 hours and it simply was non-functional. (I wish to add a caveat that I do attempt any internal repairs; I do not have the knowledge to do so.) Some difficulty in starting, erratic/unstable idle, bogging on acceleration, steady speed misfires, and other bad habits I have forgotten. I played with air screws, the idle screw, timing, etc. but nothing worked. I now know why. So off it came and was stored in the basement on a spare #340261 1974 intake. It has been there 4-5 years and really impresses guests.

The next step was to contact an old friend at NAPA who found me a #7044206 in their Montreal warehouse. It worked much better although "something" was not
quite right but it did get me through the summer. A colleague eventually did a re-build that has served me well through to the summer of 2013. My thanks to RonR.

But the pretty one nagged away at me. So when Lars posted recently about the quality of rebuilds I said why not send it to the master? He had done excellent work for me in the past (my 1979 and 1967). So I did and here we are. When I take the 1974 out of storage in April I have no doubt that I have a completely functional AND pretty Q-Jet.

So my thanks again to Lars! He did not mention that the primary rods were off by 11 sizes and the jets were seven sizes too lean. In one of my e-mail replies to him I stated, "It's almost as if someone worked very hard to get things all wrong."

cardo0

Wow, another happy ending thanks to lars. Both Paul and lars are a great encouraging force on this forum im glad to read that carb was returned to useful service. And in short order.
Paul is the complete enthusiast and lars the selfless master makes this one of or the best forums on the internet.

cardo0

Paul L

Thanks for the kind words. I just change points/condensor, spark plugs, etc. and drive. Lars is the mechanical magician.

Avette4me

Paul L

Lars was being facetious although the windchill was -40*F when I took that carb down to the UPS store.

*Edit* - Just an afterthought about that week. I shipped on January 2 and the ETA was January 9 according to UPS. That was a week of terrible USA mid-west snow storms and icy conditions. But the carb arrived in Denver only one day late. You have to give credit to people in the commercial world who drive hundreds of miles in such conditions. I admire them as I sit home inside, let the snow and freezing rain fall, have a few beers, and track the shipment. A big thumbs-up to professional drivers! Not an easy way to make a living.

CA-Legal-Vette

This pic reminded me of a question. We're the heat shields below the carb specific to any years? Also, would he stock gasket go above the plate and a plain one below?

Very pretty carb Paul!

Now it'll workas nicely as it looks.

Paul L

You ask a very interesting question. The heatshield was one of my experiments that I like to try but usually do not follow through with. I have such bad habits. I never had carb fuel bowl boiling problems as I have a fuel return line on my pump. But I tend to fix things until they go wrong. So I imagined the carb needed heat protection.

The shield was sourced as Dr Rebuild #3726140 for 1970 300, 350, 390 HP. It was the only one I found for a spread-bore Q-Jet. I have no idea if it is still available. I had visions of adapting it to my 1974 with the original TCS (transmission controlled spark) solenoid also seen in my pic of today. Yes, I have all those components! But with time I just gave up on the originality kinky stuff and decided to drive. As to your question, I would think the gasket glued to the shield would be roughly equivalent to a stock base gasket. But Lars can help me with this.

Paul L

If you look in the upper left hand corner you will see a 5-liter Molson Canadian keg that I gifted to Lars many years ago (empty I regret). They are no longer sold here so that is a rare item .

lars

It's rightfully called the "Bubba Keg," and it's displayed with pride in the Corvette Viking Lounge... quite the topic of conversation amongst those astute and sober enough to notice it...


Yeah... brilliant idea. We just had a stoner so whacked out that he rear-ended and sideswiped 2 State Trooper cars. First of a bunch of mayhem to come, I predict. If one of those weed-smokin' morons hits me, I'm takin' his head off... "Gee, Officer, I don't know how that could have happened... he must have smashed his face on the steering wheel.."

Lars

maverickmk

When I lived in Michigan, my cop friends always said he "slipped and bumped his head" when they had some unruly sorts going to jail.

On a note to the carbs not being "bolt 'n go" I recently purchased a new-in-the-box Holley from a member here. When I installed it the accelerator pump did not work. I took it all apart, checked all the passage ways, put it all together and it now works like a champ. Not really sure what the problem was, but it works and that's all that matters.

I have an old Holley DP that needs a rebuild, do you happen to work on those as well Lars?

CA-Legal-Vette

Interesting! Im embarrassed to say that I haven't looked on the bottom of the shield that I picked up from a Forum member. It's at lockup now so I can't check. I'll find a pick of my q-jet base gasket which will better show what I'm concerned about.

I had a real problem with vapor lock last summer. I attributed it to the side pipe running too close to the fuel and return line but really have no evidence one way or another. I picked up the heat shield as an easy "just in case" measure. As you said, the scientist in me requires that I do the fix in separate stages so that I know what the problem actually was. The driver in me doesn't care, as long as the problem goes away.

CA-Legal-Vette

This didn't end up being a big problem in CA. Turns out that stoners (I'm sorry, glaucoma sufferers) don't often have cars.

TedH

Beautiful ride!