jetting
Thread Starter
Racer
Joined: Nov 2004
Posts: 319
Likes: 0
From: Sunnyvale CA
jetting
So I figured out that my engine is running too rich, because if i pull a vacuum line off to give it air it idles higher/is more powerful. Also helps explain my terrible gas milage. Anyways, I need to rejet it then right? I think that in a week or two I'll just rebuild the whole cab.... what jet sizes should I use for a completely stock L48 with quadrajet? Is there a good website that explains how to rebuild the cab? Thanks!
Tech Contributor
Joined: Aug 1999
Posts: 14,374
Likes: 6,373
From: At my Bar drinking and wrenching in Lafayette Colorado
Use the stock jetting for the carb number. Replace the float with a NitroFill NAPA part number 2-442 and set the level to .420". Make sure the choke pulloff is functional and correctly adjusted. At the stock setup, the car will run slightly on the lean side. If you lean it further, you will get drivability problems.
More important than carb setup, be sure your timing curve is set up right and that your vacuum advance is functional and hooked up correctly. Total timing needs to be 36 degrees.
More important than carb setup, be sure your timing curve is set up right and that your vacuum advance is functional and hooked up correctly. Total timing needs to be 36 degrees.
Le Mans Master
Joined: Jan 2006
Posts: 8,319
Likes: 7
From: Wilmington DE, Drive it like you stole it, 68 327 4 speed coupe
Qjets
Q jets dont use "jets" in the same way that holleys do, they use metering rods, wich are changeble,and if bent or worn or otherwise broken will cause mixture problems. Im pretty sure that they came with the rebuild kit, but if they dont they are easy enough to get, but definately go with the stock ones, and as long as you are at it replace the power piston plunger too, but be careful, if you lose the spring, it will be a nightmare to replace (i ended up having to buy a dozen). Also check the air horn for warpness (if that is a word) these things have a tendancy to warp if overtightended and can cause all kind of performance problems you might mis-diagnose. When replacing the air horn, tighten by hand tight with a screw driver in a circular pattern and you should be fine. Q jets are easy to rebuild, and easy to tune, and once set up give miles and miles of reliable performance. The rebuild kit will also include a new float valve, and the spec on how to set it
As far as adjusting, your have two idle mixture srews on the front of the Q jet that i would play with first. to adjust simply screw in till against the seat, but be very carefull as these are easy to damage (and may be the casue of your problem to begin with) then using a vacuum gage adjust the mixture looking for the "Lean roll" point. repeat for the other side and Giddyup
Oh yeah one last thing, the Qjet needs to have the carb heat sheild to run properly. This is a thin metal plat that sits between the gasket and the intake on stock intake manifolds. If you are using an aftermarket manifold, or have a manifold that was meant to have a holley, you may have to live with out this. It's not a great big deal but one of those little things that make the Qjet really happy
tim
As far as adjusting, your have two idle mixture srews on the front of the Q jet that i would play with first. to adjust simply screw in till against the seat, but be very carefull as these are easy to damage (and may be the casue of your problem to begin with) then using a vacuum gage adjust the mixture looking for the "Lean roll" point. repeat for the other side and Giddyup
Oh yeah one last thing, the Qjet needs to have the carb heat sheild to run properly. This is a thin metal plat that sits between the gasket and the intake on stock intake manifolds. If you are using an aftermarket manifold, or have a manifold that was meant to have a holley, you may have to live with out this. It's not a great big deal but one of those little things that make the Qjet really happy
tim
Last edited by sweethence; Jan 11, 2006 at 03:21 PM.
