Few questions about my Electric Q-Jet Carb

[caffeineaholic]

Hi all,

I have read "Common Problems and Solutions for Q-Jet Carbs" by Lars Grimsrud -- a technical article he published.

I do not know when this was published and so I wonder if my carb is supposed to be set up a little differently. The most important question I have is if my secondary throttle plates are supposed to not turn fully vertical. The article states they should instead point to the bottom of the secondary air baffle -- I'm just wondering if this depends on the year quadrajet. As far as I know no adjustments have been made to the secondary throttle plates and they by default turn fully vertical.

My next question is if the primary booster venturies (sp?) are damaged on the top (pictures are below) will this significantly affect driveability?

Also, are there some common problems that could cause my engine to die unless I force the idle speed higher (about 1,000+ rpm even when hot)?

I have a dozen+ more questions but these are the most important ones.

I appreciate any help. Thanks!


Left venturi




Right venturi




EDIT: My Q-Jet is model #: 17084201

--

[j cAT]

I would remove the carb and with a dremel tool smooth out those slightly damaged edges...this can effect the mixing of air to the fuel ..

the secondarys under normal operation do not fully open...about 3/4 ..the adjustment is a spring that gives the delay in the opening..if too light it can backfire stumble...

you should also have a vacuum controlled linkage locking the secondarys under certain conditions...

with any carb vacuum leaks cause idle problems,,this could be the base carb gasket to vac lines to intake leaks....at idle I get 17-21 inches of vacuum high and steady no fluctuations this is good...

I have posted here on these forums vacuum engine troubleshooting ...this chart gives details on how to troubleshoot engine issues with just a vacuum guage...today it is very difficult to find tech's with the ability to do this correctly....takes too long to find the leaks...

you fix all the leaks it will run very smooth...my 84 305 cu idles at 550 rpm...

[Blt2Lst]

One very important thing to check on the q-jets is the throttle shaft for wear. With years of use, the shaft wears out the bore in the base plate of the carb causing a vaccum leak.

To check, hold the throttle shaft by where the cable attaches and try to wiggle the shaft, if the shaft moves where it goes thru the base plate, you have a worn base plate which will contribute to idle and driveability issues.

You can have bushings installed to correct this problem.

You should also have the TPS and mixture control solenoid checked while it is apart and replaced if needed.

Another thing you can do to increase WOT performance is to install larger secondary metering rods. It's about the only thing you can do to increase performance on an emissions carb that must pass local emissions.

When I recently had my q-jet carb rebuilt, they installed #CG secondary metering rods which made a noticeable difference when I floored it.
My throttle shaft was also worn and the TPS was shot also which would account for why the idle was all over the place.
Gas mileage also improved after the rebuild, that's a good thing..

[Blue Bowtie]

There is a little distortion on the secondary venturis, but the larger depressions shown in the photos are created at the factory when the fuel passages are angle-drilled through the venturi supports, just like every other 4MV/4MC/E4ME:




Blt is correct about the throttle shaft bushings. They are common wear points and are easy to repair. Remove the throttle body from the bowl. This will entail removing the bowl cover, linkages, and various assemblies and bits.

You'll need a few odd special tools like reamers:



Remove the throttle plate springs and secondary lockout pawl.

Carefully remove the throttle plate screws. They are staked, so it will take a lot of patience, a proper fit of the driver, and several applications of lubricant and reversing direction to prevent thread damage.

Note the orientation of the throttle plates and remove them. Slide the throttle shaft out of the throttle body.




Measure the length of the repair bushing and ream the body to the proper depth.




Verify the correct depth of the ream to avoid unnecessarily breaking through the throttle bore side, potentially causing throttle plate binding problems.







Drive the bushing into place.





Finish ream the bushing to the correct throttle shaft diameter.





Reassemble the throttle plates, links, and springs.

This would also be a good time to seal the Welch plugs in the metering wells on the bottom of the bowl. Both the main and secondary metering well plugs on the underside of the main carburetor body are known problem areas. Any fuel leaking there goes directly into the intake and can significantly enrich the mixture, drain the bowl after shut down, and cause flooding and hard starting. These can be cleaned off, peinned closed, and covered with a fuel-resistant epoxy to seal them against fuel leakage.



Clean the areas, make sure the Welch plugs are securely staked in place, and apply a fuel resistant epoxy to seal over the plugs:

[caffeineaholic]

j cAT:

I would remove the carb and with a dremel tool smooth out those slightly damaged edges...this can effect the mixing of air to the fuel ..

the secondarys under normal operation do not fully open...about 3/4 ..the adjustment is a spring that gives the delay in the opening..if too light it can backfire stumble...

you should also have a vacuum controlled linkage locking the secondarys under certain conditions...

I will use a dremel in the near future to carefully smooth them out. Do the secondary throttle plates only open about 3/4 of the way or did you mean the choke plates? The only reason I want to be sure is because I bought another used carb on ebay and it too has secondary throttle plates that extend completely vertical (although it's possible it is maladjusted too?)

I do have a vacuum break for the secondaries and it is adjusted correctly. Oh, and I will check to see if the engine vacuum is erratic too. Thanks for your help!


Blt2Lst:

One very important thing to check on the q-jets is the throttle shaft for wear. With years of use, the shaft wears out the bore in the base plate of the carb causing a vaccum leak.

To check, hold the throttle shaft by where the cable attaches and try to wiggle the shaft, if the shaft moves where it goes thru the base plate, you have a worn base plate which will contribute to idle and driveability issues.

You can have bushings installed to correct this problem.

You should also have the TPS and mixture control solenoid checked while it is apart and replaced if needed.

I have checked the play it has moving from side to side horizontally (the whole rod left to right, not turning) But for some reason never thought about possible gaps around the bore. I have already re-installed the carb back on the car and will check this next time I look at it.

I have checked the TPS and it seems to be almost set perfectly and the M/C solenoid is working correctly. Getting different secondary metering rods sounds like fun even if it is not a huge WOT performance increase, I'll consider it in the future -- sounds inexpensive too. Thanks for your help!

Thanks Blue Bowtie for your detailed instructions and pictures! When I check the carb, and if I find this problem, I will use what you posted to fix it.


Another question... Does anyone know if these carbs have lead in them? They seem very heavy and soft as if they are made with lead. I have been handling mine a lot and taken it apart numerous times...

Thanks.

[Blt2Lst]

[quote=caffeineaholic;6118512Does anyone know if these carbs have lead in them? They seem very heavy and soft as if they are made with lead. I have been handling mine a lot and taken it apart numerous times.
Thanks.[/quote]

I doubt very much that there is any lead in the carb.
it is probably some type of pot metal used in the casting of the body and air horn and the base plate seems to be aluminum.