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Hoping someone can chime in with some help here. I've had my '69 427 390 car for a few months now. Let me preface this by saying the car does not have the correct Qjet on it, but it is a 7040502. It's always started and acted like the choke was working fine. Recently, I changed the timing which got it running better than ever. Only changes I made to the carb were the idle mixture screws and idle speed screw. Soon after though, it was idling high, acting like the high idle was sticking...once in a while when really warm, it would kick down, but occasionally get stuck up again. I started messing with it, and it seems like the choke spring is not releasing fast enough. It's at the point where the choke will not open fully, even though the engine is warm. I tested the spring with a heat gun, and it does respond to heat. Just puzzled as it worked fine before...started at about 1200 rpms on the high idle, then dropped to about 800 when I tapped the throttle. Maybe I knocked something out of whack when putting the air cleaner on and off while
I'm hoping someone can take a picture or video of their carburetor when the engine is started cold, and then show how the choke comes off. Things I have checked so far:
Vacuum pulloff is functioning and not leaking..checked with vacuum pump
Not sure if car has correct choke spring, or rod, but it worked fine before
Car runs excellent when warmed up with choke disconnected choke rod is disconnected in this photo
From: At my Bar drinking and wrenching in Lafayette Colorado
One thing I can see right off the bat is that the choke pulloff spring is not hooked up/correctly attached for your 1970 carb's choke system. You might want to start by assembling it correctly.
Correct 1970 choke - note the spring attach point in the pulloff lever:
Lars! I was hoping you might chime in...I wasn't sure if you were still around this forum or not. If you're referring to the small spring attached to the vacuum pulloff, yes I disconnected that as it seemed to allow the choke to pull off a little more. Thank you for posting the pictures of the correct orientation for it. When I first started working on this car, I think this may have been disconnected from the beginning, but I can't be 100% sure. I've actually been in touch with you via email and you've sent me a lot of papers...I also did some internet research and came across your choke setup paper which I checked as well, and everything seems to be set up well...maybe I can take a video from when it's cold to when it warms up and post it. Thanks in advance!
From: At my Bar drinking and wrenching in Lafayette Colorado
The purpose of the spring is to slightly close the choke upon hot engine shutdown so the car will re-start without touching the gas pedal - like an injected car. The drawback is that if you do depress the gas prior to hot start, the choke will snap fully closed on the hot engine, and you will flood it upon hot start. Disconnecting the spring can cause the fast idle cam to be a little sticky, and this can contribute to inconsistent idle speeds.
Well I did a little more research, and with some help from others on Facebook, I think I figured it out. I have verified that the choke is now coming completely off (aftter a good amount of time and well after the motor is warmed up). I am attributing the fact that it is taking so long to a couple of reasons:
There is no heat riser coming off the exhaust manifold, therefore the manifold is not getting hot enough quick enough to heat the coil and release the choke faster
I was testing this outside where the temperature has been in the low to mid 30's, with the hood, and air cleaner off...probably making it even harder for the choke coil to warm up as well.
By advancing the timing (per Lars' timing paper), I've helped the engine to run better, therefore I am now seeing a noticeable hesitation when I rev the engine a little, and the choke has not opened up fully as it should. Since I've bought the car, I've changed the plugs and wires, and advanced the timing, and I notice now how much better it runs than when I got it. Maybe the choke always came off like this, and I just never noticed it since the engine was not running optimally anyway.
It seems to be running great when it's completely warmed up, so I'm not going to mess with it...if I have to put up with a little hesitation in the beginning, so be it. I'm not going to install a heat riser as I've read mixed reviews on those anyway. Boy I love this car though!!
The purpose of the spring is to slightly close the choke upon hot engine shutdown so the car will re-start without touching the gas pedal - like an injected car. The drawback is that if you do depress the gas prior to hot start, the choke will snap fully closed on the hot engine, and you will flood it upon hot start. Disconnecting the spring can cause the fast idle cam to be a little sticky, and this can contribute to inconsistent idle speeds.
Lars
Thanks Lars...I will reconnect the spring as well.
I was just looking at your engine pic again and don't see any vacuum advance line to your distributor from the carb. Do you have it blocked or is it tee'd off the line from the single manifold fitting behind the carb?
They heat riser passage across the center of the intake could be getting plugged up too. drag cars and boats don't need vacuum advance. drag cars that drive to the track need it. your car needs it.
Buy a stock unit and put a electronic conversion kit in it. Make sure it has the correct advance can in it per Lars papers. You could run it with point too but with electronic no dwell to set and you can leave the key in the forward position without fear of burning points......install a curve kit in it.
Looks like A1 Cardone rebuilds them but you may find a nice unit on here from a member.....
Buy a stock unit and put a electronic conversion kit in it. Make sure it has the correct advance can in it per Lars papers. You could run it with point too but with electronic no dwell to set and you can leave the key in the forward position without fear of burning points......install a curve kit in it.
Looks like A1 Cardone rebuilds them but you may find a nice unit on here from a member.....
thanks for the replies guys...I think at this point I'm leaning towards a rebuilt original and doing the electronic conversion as I want to maintain the stock ignition shielding. Also, I don't think the choke pull off is contacting the part of the carb that it is supposed to in order to get the initial pull off...not sure what's up with it, but i ordered another carb (in rough shape) so I'm going to compare it to mine and see what's up. I also ordered a new pull off unit just in case that is bent or something.
I found when I hooked up that little spring, it was putting the choke on partially when it was warm, causing a hesitation and higher idle. It ran better when disconnected...so the troubleshooting continues!
Lars do you have any more pictures of the correct 1970 carb? I would like to compare to mine to see what I'm working with. I can already see that my choke pull off rod looks different from this one you've posted.
69 427 390 choke issues
