I have been working on a ground up restoration on a 1969 350/350 vette for a couple years now. I have the car put together but I seem to have run into a problem. I have had the Rochester Quadrajet carb (# 17058229BJN) rebuilt TWICE, but the car still runs very rich. It just keeps fouling out plugs?

I can adjust the idle screws down, but all that does is decrease the RPM. It still runs rich.

Does anyone have any suggestions for me?

Any help would be most appreciated.

Thanks.

 

i don't think it is the correct carb.(numbers)

 

Look at your combination of primary jets and rods. Maybe a different combination of the two will solve your problem.

 

Get a copy of Lars QJet tuning paper at www.corvettefaq.com

 

Carb 17058229 is not the right carb number or carb model for your car, but that's not to say it cannot be made to run right. That carb is a carb off of a big block 400-454 1978 GMC Heavy Duty Truck & Suburban, 1/2-ton, 3/4-ton and 1-ton models. In its stock form, it is jetted with #64 main jets, #39 primary rods, and "DG" secondary rods. This is extremely lean for a Vette on the primary side, and extremely rich on the secondary side. So lean, in fact, that it may not idle on the idle circuit, forcing the idle speed screw to be cranked up into the main metering circuit. This will reduce manifold vacuum, and can unseat the power piston, resulting on an over-rich condition due to the lean condition, if that makes sense....

Just because a carb has been "rebuilt" does not make it correct. Here are a few things I would check and do:

1. How is your choke set up? The carb you have is unique in that it's a 1978 carb set up for a divorced choke (used only on Heavy Duty trucks in '78 - all other Q-Jets used a hot air choke that year), but the big block chokes were often reversed from the passenger car chokes used in '69. In other words, the choke on your carb may be set up to go "closed" as yor engine warms up. Check and make sure that your choke is actually working in the correct direction - if not, you may need to drill a choke rod attachment hole on the opposite side of the choke rod lever on the carb... this would be my first guess for a problem....

2. Next, pop the top off that carb. A carb that has been jetted that lean in its stock format has most likely been messed around with. It could have some very "unique" jetting. I'd bump those primary jets up to at least a pair of 69's if you have the stock #39 rods in it. If it has a different combo than this, let me know what you have and I can recommend a setup for you.

3. Make sure you have a NitroFill float and not a brass float. The brass floats do not float correctly. Take any brass float and throw it over the fence into your neighbor's yard and get a correct NitroFill float from Napa. Set it to a height of .420".

4. Make sure your power piston stop has been correctly set. If this adjustment has been moved up or down, it will adversely affect mixtures at idle and cruise. If you need info on this, drop me an e-mail for my setup paper.

5. Check your manifold vacuum at idle. If you're below (numerically lower) than 14 inches, your power piston will not seat at idle, causing rich run problems.

Tag me back if you need further info.