Cliff's Quadrajet Parts and Rebuild Kits

Quadrajet Problem Solving => Diagnose a Quadrajet carburetor problem => Topic started by: jxu109 on March 30, 2009, 09:24:19 PM

Title: Runs great, unless it's less than 50 deg. outside.
Post by: jxu109 on March 30, 2009, 09:24:19 PM

When the outside temp is below 50-55 degrees, I have an off-idle stumble, and a lazy spot on light-medium acceleration, no matter what the engine temp.

As soon as it's warmer than 55 or so, it's a completely different experience.  It runs perfect all across the board.  No more stumble, and no more lazy spot on acceleration.

It sound like I'm running a bit lean?  But where, and how do I correct it? 

Thanks

Title: Re: Runs great, unless it's less than 50 deg. outside.
Post by: Cliff Ruggles on April 03, 2009, 06:05:29 AM

What is the carburetor part number, application, and have any modifications been done to the engine and/or carburetor?.....Cliff

Title: Re: Runs great, unless it's less than 50 deg. outside.
Post by: jxu109 on April 06, 2009, 06:08:36 AM

17057204AYN
1367

68 C10 2wd
Super T-10 4 speed
3:73 rear, 275/60/15
350 ci bored .030,
 ~10:1 compression,
Comp Cams 270H 
Performer RPM Heads,
Performer intake
MSD digital E-curve Distributor
Thorley Tri-Y's,
 Magnaflow x-pipe and mufflers.

The carb has been modified and re-built.  I'm not sure what modifications were done.

Thanks

Title: Re: Runs great, unless it's less than 50 deg. outside.
Post by: Cliff Ruggles on April 09, 2009, 05:16:57 AM

Difficult to help out unless the specific modifications to the carb are known.

My guess, it still uses the HUGE main airbleed set-up.  It is difficult if not near impossible to get those to work no matter how much jet you install in them.

My advice, recalibrate it according to the correct "recipe" in our book, exactly, in all areas......Cliff

Title: Re: Runs great, unless it's less than 50 deg. outside.
Post by: jxu109 on April 09, 2009, 06:27:05 AM

Can you suggest one?  As far as I remember, there was a pretty mild build, and then something with a pretty wild cam.  I thought when reading that my build fell somewhere in the middle of those 2.

Thanks.

Title: Re: Runs great, unless it's less than 50 deg. outside.
Post by: Cliff Ruggles on April 10, 2009, 03:23:36 AM

I would use recipe #3 from the book, but would reduce the bypass air to around .100", and the idle down channel to .055"......Cliff

Title: Re: Runs great, unless it's less than 50 deg. outside.
Post by: jxu109 on April 10, 2009, 05:11:23 AM

I took the top off last night, it has either 76 or 78 jets in it, with 41 (or maybe a K???) rods in it.

Should I really mess with this one, or is there a much better carb out there for me to deal with?

Thanks for all your help.

Title: Re: Runs great, unless it's less than 50 deg. outside.
Post by: jxu109 on April 10, 2009, 05:28:08 AM

I think I'm going to get a different model. . . if this one isn't ideal, I would rather start with something better. 

Is it best for me to find one, and send it to you?  Or do you have a bunch that you could sell?



Thanks for all your help.

Title: Re: Runs great, unless it's less than 50 deg. outside.
Post by: Cliff Ruggles on April 11, 2009, 02:42:16 AM

Those carbs are fine, they just need some help.  I would recomend installing 4 of our screw in main airbleeds into the main body and airhorn, then new jets and metering rods.  I've never been happy with any of those large main airbleed models.  They just have way too much emulsion air and it's difficult to get enough jet in them, and small enough metering rods for a good fuel curve clear across the engine speed/load range.....Cliff

Title: Re: Runs great, unless it's less than 50 deg. outside.
Post by: jxu109 on April 11, 2009, 04:38:05 AM

Last night after re-reading the page on big main air bleeds, I started filling with aluminum...  the main bleeds are filled, and it looks pretty good.

Then I moved on to fill in the ones in the air horn, and ended up massaging things a little too hard.  I need to go get a new air horn today ....

Wish I would have known about the screw in style earlier :D

Title: Re: Runs great, unless it's less than 50 deg. outside.
Post by: jxu109 on April 12, 2009, 06:46:28 AM

I used everything from the new carb, except the throttle plate.  This new one has the single bleed in the air horn.

The primary side feels much stronger than with the old carb...

I lost the 'holy crap' effect my secondaries used to have though, but I did use the same secondary rods and hanger.

Also, the old carb had some passages  plugged on the outboard side in the main body -- does this sound familiar, and should I do it to the new one too?

I'm thinking the best thing to do to get the secondaries back to the way they were would be to start measuring the holes in the old one, but I wasn't clear on which passages were for the secondaries.

Thanks again!

Title: Re: Runs great, unless it's less than 50 deg. outside.
Post by: jxu109 on April 12, 2009, 08:10:30 PM

I'm starting to wonder if the secondaries feel weaker to me because the primary side is working so much better.

I took some tension off the air flap, and it made a difference, but overall, it still seems like the secondaries aren't coming in as strong as they did with the previous carb.

The only other thing I can think of doing is modifying the pull-off.... it's about 2.5 seconds as of now.

Title: Re: Runs great, unless it's less than 50 deg. outside.
Post by: jxu109 on April 13, 2009, 05:19:02 AM

Here's a pic of the hole that was plugged on the old one -- why was this done?

(http://www.personal.psu.edu/jxu109/truck/carb/carb.jpg)

Title: Re: Runs great, unless it's less than 50 deg. outside.
Post by: Cliff Ruggles on April 14, 2009, 04:38:58 AM

Those are the idle air bypass passages in the main body.  These were plugged by companies who intalled "generic" calibrations into q-jets during commercial remanufacturing.....Cliff

Title: Re: Runs great, unless it's less than 50 deg. outside.
Post by: jxu109 on April 14, 2009, 05:25:23 AM

That would make sense.  It came from JET, but I know better now.