Quadrajet problems
 

This past weekend in Ennis we acquired a stumble off the starting line that we never had before..
goes on the two step to 4600 clean no stumble but when launching it caughs a few times being a tenth and a half slow to 60' and 4 tenths down track..
we fattened it up and stumble was worse so we leaned it out some more and was faster down track but still had stumble..

Need to talk to someone that understands these well and possibly that I could send the carb to, to have it looked at...
Trying to get something going quick to make Noble and Dallas National.. thanks in Advance

Matt Diamond

Re: Quadrajet problems
 

Do you know who built this carb?

Re: Quadrajet problems
 

Matt
The best in the business (q jets) are out here on this sight. One of them should chime in fairly quick. Had a guy down here in Houston that did incredible work but he retired from work and building carbs on the side so no help there.


Quadrajets are awesome once you get them tuned up correctly, they are either on or off..LOL

Re: Quadrajet problems
 

Had a similar problem a couple of weeks ago!!
Changed the carb to a fresh one from Deano, and all was great!!!
The "removed" card is on it's way to Dean O. as well.
He does great work with great results!!!
Terry K

Re: Quadrajet problems
 

Terry is dead on ; contact Dean Oliver and you won't be sorry . He is on the net---Deano's Carburetors .

Re: Quadrajet problems
 

First thing to check is the float level and fuel pressure. Make sure you have a slosh tube on the vent and tape where the secondary metering rods go through gasket. Slow down the air door for the secondary's.

Re: Quadrajet problems
 

Thank you all for the info! I got Deans number at the track this weekend and gave him a call yesterday and voice mail and called once today, but haven't heard back.. l figure he is a very busy guy and will get back to me.

Going to check float level this evening, thanks again!

Re: Quadrajet problems
 

Several builders use a sliding piece that the secondary metering rods fit through. If your carb has one of these, make sure you did not knock it out of position when you were changing rods. Take the top off and look.

Re: Quadrajet problems
 

Matt , When you say you richened it up and then leaned it out , did you do that with secondary metering rods or did you change the primary jets ?

Re: Quadrajet problems
 

With Metering Rods, 5 thou one way and 5 thou the other.. only things i had.

Re: Quadrajet problems
 

I'm tending to support the "float too high" or "too much fuel pressure" suggestion. If the carb was fine but isn't now, your problem doesn't sound like a weather change issue. It sounds like a float that's too high (or the functional equivalent or that, too much fuel pressure) causing fuel to splash out of the bowl vent, into the primary venturis. If you leaned and richened it and the stumble wasn't affected, that would confirm that you have "uncontrolled" fuel entering the intake manifold. The car goes momentarily rich, stumbles and then gets on its way.

Re: Quadrajet problems
 

To the best of my knowledge Danny Ashley was the first Q jet builder to use the sliding piece that the rods fit through. Most builders use tape or a piece of foam. That sliding piece can move when changing rods so this is an excellent observation Mr. Hacksaw...I sure miss Danny, what a wonderful man....

Re: Quadrajet problems
 

Sometimes if the float is too high or too much fuel pressure , you can look down the primaries with the engine off , turn on the fuel pump and look to see if fuel is dribbling out the boosters . I had that problem , but could not fix it with a float level adjustment . I measured 7 psi fuel pressure . I did fix it by installing a new needle and seat . Edelbrock still sells the .145" needle and seat .

Re: Quadrajet problems
 

Interesting comment on the needle and seat, and definitely a possible contributor to the problem. I was having similar problems and called Dean Oliver, to discuss reasons why the car was so stinky, smoky rich. We confirmed the float setting and fuel pressure were right, and the next question he asked was "You're not using a .145 needle and seat, are you"? When I told him I was, his response was "Get it out of there; they flow so much fuel that they actually disrupt the fuel in the bowl". I went back to the next smaller needle and seat and the problem went away.

Re: Quadrajet problems
 

It was originally done by Pontiac in the early 70's But he was the the only guy I know of that was milling the top to accept the slider plate.

It sounds like a float level could be high and or the fuel is going past the secondary metering rods because of loose tape or something. I'd stay away from the .149 needle and seat in a qjet. They are pretty sensitive and prone to blowing over unless you run less then 5 1/2 pounds of fuel pressure. A .135 is a good choice, and you can make plenty of power with it.

Dean is also a great guy and a good choice for a carb

Re: Quadrajet problems
 

Whats your fuel system like?

Re: Quadrajet problems
 

thank you all for the info... got to Talk to Dean this morning and this evening, checked a few things ourselves and came up with nothing... so the carb is boxed up and on a ups truck heading to Dean...

Thank you all again for the help,
Matt Diamond

Re: Quadrajet problems
 

This one's on the way, via Buster Brown, but we might want to mention there is a secondary accelerator pump circuit. This was discussed in an earlier thread.
My experience is that you just can't take a Qjet that is being booted off the line, and then use it with a 2 step. If your spring is tight and your vacuum break is of the slow variety, you may be pulling fuel out of the secondary circuit.
The biggest eye opener for me was to have the driver mat it while watching with the hood open. In my mind, if the secondary flap is not WFO when releasing the brake or button, then consistency and efficiency will suffer.

Re: Quadrajet problems
 

Check the fuel pressure gauge against a known good one.

Re: Quadrajet problems
 

Danny did some beautiful work on Q jets.

Re: Quadrajet problems
 

Tighten air flap spring just a hair and see if that helps.

Re: Quadrajet problems
 

x2!

Re: Quadrajet problems
 

How much fuel pressure do you guys suggest for a Quadrajet?
I spent a few race weekends this year struggling with the hesitation issue and couldn't find out what was the problem. So now I'm wondering if too high fuel pressure could cause this issue as we raised it a little during last summer.

Re: Quadrajet problems
 

Iv'e had more than one "carb guy" tell me that 5.5 lbs of fuel pressure is max.

Re: Quadrajet problems
 

I run mine a 6 lbs. low pressure and plenty of volume is what is needed on a Q Jet. one gallon in 30 seconds is about the minimum you can get away with.

Re: Quadrajet problems
 

Thanks guys, so it looks like I'll have to lower the fuel pressure when we can get to the track the next time. Now I was running with 7 lbs pressure, so it's interesting to see if that could fix the bog when launching.

Re: Quadrajet problems
 

I build quite a few Q-jets. . For the small block I recommend .135 needle and seat. Use a Y-block off the regulator to the carb for a supply of fuel volume and use 5.5 - 7 fuel pressure. 6.5 is more than enough for the Q-jet. Rear flaps may need adjusting, but really done at the track.They should open at 1.350 for most and tension is adjusted 1/8" of a turn tighter or looser. Your Accl. pump shot can also be modified as well. There is mods that can be done to the carb for better performance. WD-40 and Marvels Mystery oil is your best friend. Keep all shafts and linkage lubricated. Hope this helps.

Re: Quadrajet problems
 

Danny Ashley I believe started the slide plate for the secondary rods. But note that the air horn needs to be milled in the area that the slide plate goes
.