Hi Lars,

I have an old Q-Jet that I'd like to temporarily install on my '68 L-36 (stock 427/390). I plan to remove my current 3x2 setup (to have it rebuilt), so the Q-Jet will be a temporary measure to keep the car on the road. The carb is part #7028212. What metering rods, jets, etc. do you think I should start with?

I've already installed one of your distributor kits (currently 36 total, 0 init.)

Thanks!

-Joe

 

Joe -
Hi! Good hearing from you!

First, I see you got the curve kit on the car and that you're running 36 total with a 0 initial..... This does not sound right, and is indicative of the advance curve being too long - there is something wrong. If you e-mail me your phone number, I'll give you a call and discuss your setup. The 0-degree initial is going to give you terrible off-idle throttle response, so we need to get you set up right.... I'll be more than glad to chat with you about it to make sure you get the car running up to its potential.

Now, on the carb:
The 7028212 is a great carb to start with for your 427. In '68, the small block and the big block carbs were all jetted pretty much the same, so you can probably run the 212 carb in its stock configuration with great results. Here s a listing of the '68 Q-Jet carbs of interest with their jetting specs:

Carb# Application Main Jet Main Rod Secondary Rod

7028208 Chev 68 327/350 AT VETTE 71 46 AN
7028209 Chev 68 427 HIGH PERF MT VETTE 71 45 AX
7028212 Chev 68 327/350 AT 71 46 AN
7028216 Chev 68 427 HIGH PERF AT VETTE 71 47 AX
7028217 Chev 68 396 HIGH PERF MT VETTE 71 45 AX
7028218 Chev 68 396 HIGH PERF AT VETTE 71 47 AX
7028219 Chev 68 HIGH PERF MT VETTE 66 36 BG
7028229 Chev 68 HIGH PERF MT CHEVY II 66 36 BG

As you see, the 71 main jet is a good selection, and slight variations to cruise mixture was done my using rods between 45 and 47 with the 71 jets. If you have a free-flowing exhaust on your car, or have made other changes which will improve volumetric efficiency, you can bump the main jet size up to a 72 or a 73 for a little edge on performance. Run your float level at 3/8" with any of these jet combinations, set your secondary airvalve spring windup to 7/8 turn and back it off to 3/4 if you get no stumble, and set your secondary rod hanger height with the airvalve wide open to 41/64". If you're jetted right, your idle mixture screws should work well when backed out 1-1/2 to 3 turns from fully seated.

Let me know if you need any other setup assistance.

 

Hi Lars,

Thanks for the thorough (and quick!) explanation.

In regard to timing, here's what I did (after reading your paper): With the advance springs removed and vacuum advance hose disconnected, I revved the engine to around 2000 rpm (advance came in very quickly with no springs), then set my adjustable light to 36 degrees, then rotated the distributer until the 0 mark lined up with the TDC mark on the balancer. Correct so far? Next, I reinstalled the springs and vacuum line, tightened the distributor hold-down, set the light back to 0, then rechecked my timing at idle. It now reads 0 degrees at 750 rpm. Sound wrong? Do I need to limit the mechanical advance so that I can dial in more initial? (I did install the advance limiting bronze bushing from your kit, and it's on there very tight).

As far as I can tell by the numbers, this is the original distributer that came with the car. I'll send you my number via email, but you have to let me pay for the call, since I'm on the east coast.

Thanks!

Joe

 

Joe -
Your timing technique sounds good - you did it right for setting up the total timing to 36, and this technique usually works very well.

Occasionally, I come across a distributor that does not behave right when the springs are pulled off: for some reason, it will go to an over-advanced condition that is not obtainable with the springs in place, and this results in the timing being retarded. So do this first:

You have the light springs from the kit on your distributor. These springs will give you your full advance below 3000 rpm. With the springs in place, and with the vac advance disconnected, set your light up to 36 degrees, start the engine, and briefly rev it up past 2500 rpm. Observe the timing marks with the light and see if the full centrifugal timing is coming in and pegging out. Make sure you're really set up at 36 degrees advanced with the springs in place once the timing pegs out. You may find that you're running a little retarded (no pun intended). If this is the case, advance the timing to get the 36 total, and then re-check where your initial ends up with the vac disconnected.

If you find that you are, in fact, getting the 36 degree total with the springs in place and that you are NOT running retarded, and you're still getting 0 degrees initial timing, you have a problem with the advance limit slot in the distributor. In the past, it was a common "performance" mod to lengthen the advance slot (the slot that the brass bushing rides in) to get more total timing for more "power." I frequently have to weld up the advance slots in the distributors I rebuild to bring the slots back to their design length. If the slot is correct, it should measure .400" - .415" in total length. You have to disassemble the distributor to be able to measure it. If it is longer than .420", the slot must be shortened in order for the distributor to provide good timing.

I'll call you and chat with you about this once I get your number. And the call is on me: you buy my parts, you actually get tech service as required at no charge.