TedH

Lars,

Got a q-jet question made just for you. This is related to my thread about shortening warm-up times. I have electric choke. Will switching to a hot-air style choke improve/shorten my warm-ups? Can this swap be done without major surgery on my q-jet? What's required? My intake (Edelbrock 3701) has accomodations for the hot-air style choke.

MikeC

The swap is easy as long as you have a manifold built for hot-air and all the pieces.

I originally had hot air on the vette but removed it to put on a Holley, when the Quad went back on I went electric. My hot air worked flawlessly over the time I used it.

My electric choke once tuned properly was great too although the choke stayed on too long( sound like what you are having too)

Honestly, I'd stay with the electric choke unless you have all of the parts for the hot air choke.

just my 2 cents

lars

Ted -
The style of choke you select won't affect engine warm-up times. If you have a properly functioning electric choke, swapping over to the hot air system won't do anything for you other than decrease your electrical system loading a tad.

Are you having trouble with your choke? Keep in mind that there are several adjustment variables on the choke systems, and I'll be glad to go over these with you if you need a little help in setting the choke up.

lars

Ted -
I just read your other post about your problem. I have a few thoughts. But first, would you send me, or post up, the carb number on the carb you're running, and let me know what jet/rod combination you're running? I'm sure we can get your car running right with proper jetting for the application and a good choke setting.

TedH

Lars,

Thanks, really appreciate the help. Had you rebuild the carb earlier this year. Specs from then:

Carb Number 17066563 (GM General Replacement)
Main jet size 73
Main Metering Rod Size 43
Secondary Metering Rod Code DA
Float level .410"
Idle Mixture Screws Set at (out from seated): 6

lars

Ted -
Based on your application and the symptoms you're having, I'm going to suggest we fatten up your mixture just a tad. Are you comfortable with popping the top off a Q-Jet and doing some playing, or would you like to send the carb back over to me for some fine-tuning...? I'll cover your postage. If you want to do it yourself and you know how to do it, I can send you the parts. Your symptoms, your vehicle mods, and the way I have the carb set up for you all add up to the carb being just a tad on the lean side, and this is causing poor intermediate-temperature idle characteristics. Lemme' know....

TedH

Lars,

Would be glad to try pulling the carb top off and swapping parts. Let me know what the next step is. Further, if I need to do anything/make any carb adjustments and 'report back' on final performance before you send parts, just say the word.

Stewart's74

Ted,
I popped the top off my Q-Jet per Lars' instructions and it was really easy. I had a bad accelerator pump. It actually made me more comfortable with the carb. (sounds kinda weird, but now the carb is not such a mysterious entity sitting on my engine :) )

Stew

TedH

Lars, I want to re-hook the thermal actuators on the air cleaner back onto the vacuum signal at rear base of carb to see if they help with richening (by both reducing air coming in and directing hotter air from the heat stove into carb). Once I do that, I'll take a final 'reading' and let you know how the car is behaving.

Also, if I need to do something to keep choke on longer (it settles to idle speed after about 3 minutes of sitting in the driveway) or move to a hotter thermostat to boost engine temp and speed warm-up, I can also do those things before we take it into carb surgery.

Let me know.

lars

Ted -
You can increase the duration of the choke application by loosening the 3 screws on the choke cover (the black cover) and rotating the choke cover slightly counter-clockwise. When I set the carbs up, I set them up to allow the choke to pull off pretty quickly. Start by rotating the cover about 1/2" counter-clockwise and see if that doesn't keep the car on fast idle a bit longer. Contrary to popular belief, adjusting the cover does not affect how far/lean the choke is applied: The choke pulloff determines how rich/lean the choke runs. The choke cover adjustment sets the duration of choke application. Try this in combination with your other hookups, and let me know your results. I can get you jetted a little fatter to fix the problem if that's what the car needs, but this will slightly affect your mileage.

Stewart -
Did the new accel pump fix your problem?

Jim Shea

Lars,
With respect to my Q-jet idle problem on my 75 L82 Roadster. I richened up the idle mixture by about another 1/2 turn and it seems to idle quite a bit better. This is on top of the 4 turns where you had it adjusted. Doesn't that seem awful rich?

Stewart's74

Lars,
The Vette is Rockin and Rollin! Thanks for the help with the new pump. :cheers:

lars

Jim -
The '75 - '80 Q-Jets are in the "normal" range with the idle mixture screws anywhere from 3 to 6 turns out. The pre-'75 Q-Jets usually run 2 to 4 turns out. If you're now at 4-1/2, you're right smack in the middle of the range for that carb. Did you find the problem with the 2500 rpm idle speed..? If you're having any trouble with the carb, please let me know - I'll help you get it set up right, and I'll be glad to re-check the carb if you feel it's not right. The description of the problem you gave me with the extremely high idle speed and the engine dying makes it sound like a vacuum leak problem, and this would require the idle mixture screws to be excessively backed out in order to keep the car running. I test-run every carb I build, so the idle speed and idle mixtures should have been really close to correct - it concerns me if you had to make major changes to the speed or mixture, as this is indicative of other problems. Let me know how you're progressing...

Stew -
Glad to hear the accel pump solved your problem - good job doing the install!


[Modified by lars, 4:13 PM 11/6/2002]

TedH

Lars,

Re-connected the Thermal Actuators to vacuum and carb seems to run a tad richer now (less cold air, more warm air and less air getting in overall while the flaps are shut).

I'm going to extend the choke duration using the approach you recommended. Will likely also swap in a new thermostat with higher temp range.

With car warmed up, it idles around 900rpm in gear; 1000rpm in park. I could probably back idle screw off some to reduce to 700-800rpm in gear.

What's the recommended procedure for richening the choke setting?

lars

Ted -
To richen the choke setting, turn the adjustment screw located at the end of the choke pulloff diaphragm linkage - this screw is located on the passenger side of the carb, up high at the end of the pulloff linkage with a rear-facing phillips screw. Screw the adjustment screw IN a little to richen up the initial choke setting (this will cause the pulloff to open the choke LESS upon engine startup). If I have set your carb up for you, I have set up the pulloff to open the choke exactly 1/4" as measured from the lower forward edge of the choke to the air horn wall. Use this 1/4" measurement as a guide for your adjustments. If you need to change it significantly, I'd suggest we re-jet the carb and going back to the 1/4" adjustment where I had it set.

Your 900 rpm idle speed in drive when warmed up is a bit high - you might want to back this off a tad. I test-run and set up the carbs on a 455 with a bit of a cam, so my idle speed settings tend to be just a touch on the high side for a small block near sea level.

If you keep having trouble, let me know, and I'll send you out a different pair of jets to get you dialed in a little better.

TedH

Lars,

I think I'll take those replacement metering rods/jets. Just tell me where to send the check and for how much. Will need some instructions on replacement procedure. If you need mine in exchange to offset part of the price, just say the word.

I'm going to extend the duration of choke for time being and reduce that idle about 100rpms (down to about 800rpm in gear) but will not be adjusting the choke rich/lean setting as I think you have it right where it needs to be.

lars

There's no charge - you'll be getting donor parts from the Forum Donor Program. I'll send the parts with complete installation instructions. Once you get the parts installed, and the carb runs okay, send me back the unused/surplus parts so I can keep the Forum Donor parts supply furnished. I'll also include my ph# with the parts so you can call me with any questions or if you need any assistance with the swap.

On your electric choke cover adjustment for duration: If you look at the black choke cover from the passenger side of the car, note that the cover clip at the 2-o'clock position has a little tang on it that engages in a notch in the cover. This engagement clocks the cover to the "correct" position. In order to rotate the cover to a longer-duration setting (counter-clockwise), you're best off removing the clip with the tang and grinding the tang off the clip. This will make the clocking clip look just like the other two clips on the cover. Once you get the new jets from me, you might want to rotate the cover back to the original position as a starting point with the new jetting.

TedH

Lars,

Can't thank you enough for taking the time to offer this Q-jet repair service. Will gladly return the parts that I remove for 'recycling'.

I can't imagine the grief that I would go through with local 'repair shops' if I had to deal with them to resolve this problem. Probably would get more of what I had at the time when I sent the carb to you (the metering rods had been hit with a grinder and ruined by a speed shop).

My wife thanks you too (saving me $$$). :eek: