I have a Quadrajet on a 350 (w/a mild cam) that is acting up in a manner I have never experienced or heard of. From a cold start, I sometimes have to pat the gas several times (nothing really odd there). Here's where it gets weird; it idles great for about 3 to 5 minutes then dies (seemingly when the temp gauge just begins to move). At this point, I have to spin it and pat the gas (not too much or it floods) until it fires up and hold it at about 2k until it gets past this "sticking point." After this, it will run fine for the remainder of the day (that's the weird part). I have tolerated it because it runs great afterwards. I am at a loss to diagnose the issue. I have purchased a rebuild kit but I wanted to see what you guys say before I break it down. Anybody else heard of and/or dealt with this? P.S. Already changed the fuel pump.
Forgot about that. It's electric and when I first discovered this issue, that is what I focused on. I adjusted it and it appears to be working properly but it had zero impact. I wish I could put a mechanical/manual choke on a Quadrajet.
I am no carburetor expert, frankly it sounds like it works perfectly and you have a built in theft prevention system (except for the fact that everyone on the internet just read this) so forget that part. I but your rebuild will cure the issue. A lot of guys use Teflon tape on their fuel line fittings. That is a no-no, It will clog idle circuits and cause all sorts of mayhem. I have an OT 396 that I'd be pleased as hell if it ran as good as what you are dealing with. Good luck on the rebuild.
Also......when you mention heat gauge just starting to come up......sounds like thermostat just opening up.....do you have any kind of thermo controlled vacuum valve in the thermostat housing or other coolant passage ? Is that sending a vacuum signal to carb or distributor or another vacuum operated device that is creating a vacuum leak ?
I'd bet you lunch it's choke related. Now, an electric choke goes from closed to open based solely on time, clicks of the clock. Once it sees power the clock starts. It don't give a flying fuck thru a rolling doughnut what temp the engine is at. The engine needs its choke until operating temp and that won't be hurried by time. Your choke is opening too fast or the fast idle cam is a bit slippery. The cam should hold engine at fast idle until you tap the gas and release it. If the fast idle cam is falling out early the issues could be the mousetrap type mechanics at the fast idle cam.
Yes, I believe it does and you may be on to something there. I'll check it out as well as give the choke a once over.
Not sure about pat the gas , you should be able to press it down a couple times release slowly to set the choke and it should idle on it's own until warm. Sent from my LG-TP450 using The H.A.M.B. mobile app
The way the system is designed to work is , before turning the key, push the accelerator pedal all the way to the floor. The choke should close and the throttle screw will be sitting on the step of the fast idle cam. Take your foot off the accelerator AND LEAVE IT OFF. Turn the key to start cranking the engine without touching the accelerator. The engine should start and run at fast idle. The fast idle cam is held in position by the throttle spring so as long as you don't touch the accelerator, it will run at fast idle. Playing with the throttle lets the fast idle cam move with the choke. The linkage has a slot to allow the choke to open without moving the fast idle cam. As the choke heater heats the choke spring, the choke gradually opens. With age, the choke spring gets weaker and might need to be set a little richer to stay on long enough. Having to pump the accelerator after the engine has been running for a few minutes is a sure sign that the choke is opening too soon. If you rebuild the carb, the kit should have detailed instructions on how to adjust the linkages. These adjustments are the most important part of a carburetor rebuild but they are often ignored.
many q-jets have vacuum choke pull-offs or unloaders , w/ more cam than stock , your engine needs more fuel when cold , you might be able to just richen the choke , or readjust the pull-off to not open the flap as far..
If it is when there is moisture in the air it can possibly be icing up, requiring more throttle to get air past the throttle plates.
Don't know if it could be related or not but the only real problem I had was the throttle shaft bushings being worn . I have had to re-bush a few. Usually ran weird when warm though. Or part throttle. Lippy
I don't know if it was working or not. It rattled like a bastard headed cat (opening and closing extremely fast) so I disconnected it and plugged the vacuum line. It was sweet relief. We don't need one down here anyway. It doesn't get that cold. I'll have to get back with you tomorrow on that choke crossover. I doubt it's plugged, it's a stock set-up but you never know who has laid hands on it
That's what's weird about this. For 3 minutes after startup and once past the "sticking point", it runs like a champ.
Re-read 31Vicky's reply, post 6. I think he nailed your problem! VERY common issue with electric chokes, especially if the engine happens to be attached to a dogmatic transmission. I hear there are now electric chokes with a rheostat to control the time, but have not personally seen one. Jon.
For anyone who cares to know about the outcome, Several of you were right and I thank you all for your input. There were 2 known, major vacuum leaks associated with old dry rotted vacuum line (all replaced). I had to readjust the choke (electric) also because it was opening to soon. I had to take it to the farthest extreme of rich for it to operate correctly. I guess it's as 2OLD2FAST said "w/ more cam than stock , your engine needs more fuel when cold" as it does have a "mild cam". As an aside (and just FYI), this carburetor caused me a little trouble due to the fact that it has a front choke pull off installed but it was "missing" the wire linkage. I robbed one off a parts carb but there was no place to tie it in . It's a R4-M4ME (17082224) and apparently (though there IS a part number listed) it's not supposed to have one. New one on me. Bottom line, she runs great now. CASE CLOSED
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