Quadrajet issue
 

Have a freind with a big block, mildly cammed with a Q-jet that will not idle. Has a rebuilt carb can turn mixture screws in all the way engine still runs, says it's very rich, has completely closed throttle blades then just cracked open, still idles rich. Since the mixture screws seem to have no effect on how it idles can we assume it's bringing in fuel elsewhere? Could the pri. metering be the issue? Been a while since I've even seen a Q-jet, but doesn't it have a piston and hanger that pulls down with vacuum to seat the metering rods? Really can't come up with any other explanation. I've not personally seen the car merely going off what the owner is saying

Re: Quadrajet issue
 

If the cam has a lot of duration it might need a lighter piston spring. what you can do is remove the pri. rods and spring and put in 5 steps leaner pri. jets 67's?, then put just the piston back in.See if that don't clean it up. If it does either nip a coil,or get a lighter PP spring. Most S/SS cars run this way,(without rods).I wouldn't drive it on the street with no rods though.You can also check if the bottom well plugs aren't leaking. gsa612

Re: Quadrajet issue
 

Could just need more idle air. There are a few
Different ways to accomplish this.

Re: Quadrajet issue
 

Ok, yes he's gave it more idle air, that didn't solve it that merely made it idle faster, still rich. The wells have been epoxied, at idle the power piston should be drawn down correct? Pulling the rods into the jets? Looks like I may inherit this buggy so I'm looking for some things to try. Thanks guys.

Re: Quadrajet issue
 

Take a wooden match or small wood skewer
And stick down air vent and on top of primary
Metering rod hanger and mark height to top
Of vent tube, then fire car up and repeat this
Will tell you if the hanger is functioning while
Running.

Re: Quadrajet issue
 

After you do what Ron stated. Disconnect the accel pump, with it running. If it get crisper and idles better, you are rich and vise versa. Dean told me that one, it works. Also you might have to increase the diameter of the passages behind the fuel mixture screws in the baseplate. Example they are .079" open them up to .089". Just a thought.

Robert

Re: Quadrajet issue
 

A trick I have learned the hard way is needle and seat sometimes will leak slightly,but they won't run fuel out vent tube like holley,so it's not as obvious,will drop idle a few hundred rpm,and will bog few feet out because runs over. To check this I remove top and hold float pivot down with finger and put fuel pressure to it fuel level will come up shut off float,then watch for about a minute if leaking fuel level will slowly rise,I have got to where I just go ahead and test all of them I work on.

Another thing to look @ is primary butterflies there is idle circuits that have slotted opening the butterflies have to line up with these slots,adjust idle speed screw to line them up,if engine idles too slow then you have to start drilling holes in butterflies to increase idle speed.

You can also slighly choke w/hand if idles has vacc. leak or blocked idle circuits,too lean,etc
Qjets are more sensitive to vacc leaks,low vacc than holley.
I would also check timing could be retarded too much @ idle.
I would just go over basics first which you'll probaly do first anyway
You can find drinking straws that will fit down vent and push metering rods or watch them operate
Mike Taylor 3601

Re: Quadrajet issue
 

Things I would check:

Fuel pressure - it can't exceed 7psi. If it does, the pressure can blow the needle off of the seat and the carb will flood. Look for fuel dribbling from the booster clusters and listen for irregular "hissing" sound.

Float level - can't be too high, or the carb will dribble fuel into the venturis and the carb will flood.

Secondary hanger and rods - make sure the rods are fully seated in the orifices with the car at idle. The air door must be completely closed (not adjusted to provide additional idle air) because it can pick the rods up and allow secondary fuel.

Make sure the inability to achieve a stable idle is actually due to richness and not simply the result of a vacuum leak. Use the carb cleaner diagnosis method.

Re: Quadrajet issue
 

Is the carburetor rebuilt by a professional, or is it a remanufactured carburetor purchased from a parts store?

Re: Quadrajet issue
 

Heavy float due to absorbed fuel ---Trevor

Re: Quadrajet issue
 

Alan ,carb was off the shelf rebuild to my knowledge. Has stock fuel pump on it though that's no real indicator of correct pressure. After reading the posts I realized I've got a few old tools from back in the carb days that may help on this, thanks for all the input now I have to see when he's gonna bring it over. BTW I tried directing him on checking the PP from the air horn however it's difficult over the phone. Thanks again and I'll update after I've looked at it myself. Man it's been a loooong time since I've seen a carb wish I had a better memory.

Re: Quadrajet issue
 

Joe, if it came off a shelf at a parts house, I'd almost bet they've thrown away most or all of the Rochester metering parts, and they've used lead slugs to block the air bleeds in the main metering body.

I used to work for Mayo and Shrum in Nashville, we were the top carburetor shop in this area. It was company policy to refuse to work on remanufactured carburetors unless the work was on a per hour plus parts basis. I don't think I ever fooled with a remanufactured Q-Jet from any remanufacturer that had the original Rochester metering parts, or that did not have the air bleeds plugged. As a result, they all ran at about 8% CO on a 4 gas analyzer, otherwise known as pig rich.

You have to know what metering parts belong in the carburetor to fix it right, but if you have the gaskets, you can at least take it apart and knock the plugs out of the air bleeds in the main metering body, and that should at least make it somewhat useable.

If I can help, or answer any questions, send me an email or a PM, I'll do what I can.

Re: Quadrajet issue
 

It's also quite possible it's idling on the secondaries. Improperly adjusted linkage, air valve or sec metering rods set or sticking high will cause it to idle incredibly rich with no fuel at all from the primaries or idle circuit.

Re: Quadrajet issue
 

OK so I've got the car now, yeah it'll burn your eyes at idle, checked for PP operation piston is pulled down with engine running. So I start looking around and looking down the carb I see liquid fuel dropping on the throttle blades, little on the left, lots on the right, so I'm thinking floats sunk or too high. Pulled carb removed top and level looks normal to me, however I don't have any height chart to work off of. It's been prolly 20 years since I've even seen a Qjet but this looks like it has a cavity for an Mixture control solenoid which has been covered with an alum. plate siliconed in place. carb number is gone (ground off) any general deminsion for the float height? Since it doesn't LOOK high and the throttle blades had minimum opening, any ideas why it's pulling fuel over? Acts just like a holley with a high float level. Thanks Joe

Re: Quadrajet issue
 

Set just about any Q-Jet float to 5/16" from the top of the main metering body, without the gasket.

Joe, can you post, email, or PM a picture or two?

Re: Quadrajet issue
 

Heavy float,
Float arms (bent) rubbing on power piston housing,
Needle & seat lift clip is not on correct and binding ( IT DOES NOT! Go through the small holes on the float arm)
??

Re: Quadrajet issue
 

I never use the clip...

Re: Quadrajet issue
 

Alan ,yeah I'll try to get some pics found needle lift clip in well for Mix controll solenoid. I'll measure but float looks pretty close to that measurement.Float not rubbing any where. Looks to me like they took alot of mismatched qjet parts and tried to make a carb out of it. There is some sort of valve in the bottom of the well where I'd say an MC solenoid once sat, seem to recall way back they made a qjet with some sort of secondary enrichment needle or valve in that area. Any way I'll try this weekend to post some pics and hopefully can resolve this. BTW this is a 1971 429 SCJ mustang, I'm lead to believe this is the only year they put a Qjet on this engine.

Re: Quadrajet issue
 

After speaking with the owner of the car today We've decided to ***** can this carb.Going to try and find a source for a street Qjet for this engine, where's the best place? Needs to have eletric choke and pull offs ect. Thanks Joe

Re: Quadrajet issue
 

You could try Sean Murphy. He did the Q jet on my 454 Suburban.It took a couple attempts, but it runs really well.

http://www.smicarburetor.com/

Re: Quadrajet issue
 

Joe, if that's the original carb the owner should hang onto it in case he ever decides to restore the car in the future. Just sayin'.....

Re: Quadrajet issue
 

Good choice. I have seen the Edelbrock Q-Jets show up on ebay new every so often. I've also seen some NOS Rochester carbs show up.

Look at newagemetal.com, and get a manual, try this page: http://www.carbkitsource.com/manuals...als/CM355.html

Use that to find carburetor numbers, then look for a good unmolested core to either build yourself or have built.

Re: Quadrajet issue
 

Alan,
Looked @ link you posted,could'nt tell does it list what specs are on carbs for jets,metering rods etc.?

Joe,
From what info you gave us I'd say canning that carb is good ideal.
Mike Taylor 3601

Re: Quadrajet issue
 

Yup ! Just bagged a mint, looks-to-be never used Edelbrock Q Jet on Ebay for $197 !!!