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Just wanted to run something past you guys. Maybe I have a problem? I'm not sure what's normal. On my 66' Toronado with the 425 and original Quadrajet, when the engine is cold but still in a warm environment (let's say, 75-80 degrees) and I go to start it up I always hit the pedal once to set the choke and the high idle. Once it starts up, if I immediately bump the throttle after the start it comes completely off the high idle and goes right to the slow idle and tends to stall out. Once it's off the high idle, obviously there's no way for me to get it back on the high idle and it's a pain in the butt trying to get it going.
Just wanted to run something past you guys. Maybe I have a problem? I'm not sure what's normal. On my 66' Toronado with the 425 and original Quadrajet, when the engine is cold but still in a warm environment (let's say, 75-80 degrees) and I go to start it up I always hit the pedal once to set the choke and the high idle. Once it starts up, if I immediately bump the throttle after the start it comes completely off the high idle and goes right to the slow idle and tends to stall out. Once it's off the high idle, obviously there's no way for me to get it back on the high idle and it's a pain in the butt trying to get it going.
Is this normal operation?
No, it is not normal operation. It sounds like your choke isn't adjusted properly or the coil has lost tension. There are several intermediate steps on the fast idle cam that are supposed to lower the fast idle speed incrementally as the choke opens. If it is immediately opening all the way, that's not working properly.
No, it is not normal operation. It sounds like your choke isn't adjusted properly or the coil has lost tension. There are several intermediate steps on the fast idle cam that are supposed to lower the fast idle speed incrementally as the choke opens. If it is immediately opening all the way, that's not working properly.
Ok good info.
This is how it goes.....Before I start it, I hit the pedal and the choke closes completely. When the car starts up the choke is pulled open ever so slightly and it's running on the fast idle pretty good. That's correct operation so far right? Then I bump the throttle and the engine immediately goes right to slow idle and the engine tries to die.
Couple of options that just _might_ be worth considering:
1) Nudge your ordinary idle up to 750 or 800 rpm after the choke has kicked down. Use a vacuum gauge or other tools to confirm idle mixture. I find 700 - 750 idle rpm (in gear) just about right, but it’s somewhat of a personal taste thing.
2) If you don’t care too much about originality, swap in a 170 series (74 & up) qjet with an electric choke. I’ve found they work great and the center fuel inlet is safer. GM made an enormous number of choke kick down levers in the 70’s (probably 60’s too…) so lots of choices for choke drop down rates if you’re willing to mix & match experiment. Find replacements in your local boneyard or check out quadrjet.com.
3) Clean the living h*ll out of your bimetallic spring. 50 years on, it may have lost its ability to slowly open the choke as we’d hope for. Maybe there are replacement ‘66 Olds bimetallic choke springs, but they are probably hard to find now.
Good luck from here. Suggest lots of patience and changing 1 thing at a time from here.
Say what? You’re gonna have to explain how that works.
I'm not going to suggest or even hint I am an expert on the history of manifold vs. ported vacuum for engines with or without emissions (standards) equipment. I haven't written a compendium on the subject and I don't claim to be an expert. There are what appears to be entire treatises written on the subject since I first began to work on my own vehicles in the mid-60s. I really don't want to get into an explanation which I already know is going to develop into a battle of minds. I only made the suggestion based upon "some" past experience with "some" of my vehicles with a "certain" amount of emission control and "some" with no emission control on various Oldsmobile engines and non-Oldsmobile engines with varying degrees of manifold vacuum, distributors, carburetors & vacuum advance canisters. Just the entire notion of beginning a discussion of ported vs. manifold vacuum makes me blue-in-the-face to be perfectly honest.
I was making a suggestion. That's all it was - a suggestion.
I'm not going to suggest or even hint I am an expert on the history of manifold vs. ported vacuum for engines with or without emissions (standards) equipment. I haven't written a compendium on the subject and I don't claim to be an expert. There are what appears to be entire treatises written on the subject since I first began to work on my own vehicles in the mid-60s. I really don't want to get into an explanation which I already know is going to develop into a battle of minds. I only made the suggestion based upon "some" past experience with "some" of my vehicles with a "certain" amount of emission control and "some" with no emission control on various Oldsmobile engines and non-Oldsmobile engines with varying degrees of manifold vacuum, distributors, carburetors & vacuum advance canisters. Just the entire notion of beginning a discussion of ported vs. manifold vacuum makes me blue-in-the-face to be perfectly honest.
I was making a suggestion. That's all it was - a suggestion.
Changing from ported to manifold vacuum and back, without changing the initial timing, will change the idle speed all the time, not just when the throttle is on the fast idle cam.
To the OP: if the car stays on fast idle all the time, either the choke coil is not working properly, or it's misadjusted, or the fast idle speed is misadjusted, or the fast idle cam or linkage is sticking. There aren't a lot of other potential causes.
Changing from ported to manifold vacuum and back, without changing the initial timing, will change the idle speed all the time, not just when the throttle is on the fast idle cam.
Agreed, you'd have to change initial - no doubt. I think your suggestion is a better suggestion than mine and honestly makes better logic for troubleshooting. I'm going to let my suggestion die a slow, painful death. I do have some reasoning, but talking ported vs. manifold is a heated discussion (generally).
Norm, I was nowhere near wanting to have a ported vs. manifold vacuum debate.
What I was wanting was for you to explain how connecting the vacuum advance to a different source would have anything to do with how long the carburetor stayed on the high idle step of the choke.
Originally Posted by Greg Rogers
Mine tends to stay on high idle too long- I think it's just a balancing point.
Originally Posted by Vintage Chief
Greg - If your distributor vacuum advance is connected to manifold vacuum, try ported vacuum.
Originally Posted by Fun71
Say what? You’re gonna have to explain how that works.
Changing from ported to manifold vacuum and back, without changing the initial timing, will change the idle speed all the time, not just when the throttle is on the fast idle cam.
To the OP: if the car stays on fast idle all the time, either the choke coil is not working properly, or it's misadjusted, or the fast idle speed is misadjusted, or the fast idle cam or linkage is sticking. There aren't a lot of other potential causes.
Hmm, I wonder if I didn't explain this problem correctly.
The issue isn't that it stays on fast idle all the time......the issue is fast idle sets perfectly but when I kick the throttle, just a tickle after it starts up the fast idle goes straight to the slow idle. The choke butterfly is still partially closed but the fast idle cam is completely off and the car struggles to stay going at the slow idle speed.
Hmm, I wonder if I didn't explain this problem correctly.
The issue isn't that it stays on fast idle all the time......the issue is fast idle sets perfectly but when I kick the throttle, just a tickle after it starts up the fast idle goes straight to the slow idle. The choke butterfly is still partially closed but the fast idle cam is completely off and the car struggles to stay going at the slow idle speed.
Either way, the fast idle cam is linked directly to the choke coil. There are a number of steps on the cam that are intended to gradually lower the fast idle speed as the choke (and thus the engine) warms up. If it goes directly from fast idle to slow, it isn't adjusted properly or the coil has lost tension. It's also possible that the plastic fast idle cam is damaged. Adjustment is spelled out in the Chassis Service Manual.
My '71 350 4 bbl did this when I bought it. Texas car. Never needed choke. Fast idle cam was sticking. Was adjusted w/ no fast idle. I loosened up the cam so it moved freely. Then adjusted the choke coil counterclockwise until it stayed on for a while til warm. CORRECTION. Wrong picture for a '66 carburetor. Can't read.
Last edited by Falkon; December 3rd, 2022 at 10:40 AM.
I went through all the adjustments and I'm so close. Currently, the fast idle will set and when I kick the throttle it only drops down a single notch on the cam........perfect! The only problem I have right now, I think, is that the choke isn't getting pulled off quite enough by the vacuum break when it first starts. I have to open the choke ever so slightly with my finger to keep it from loading up. I tested the vaccum break and it's leaking so it's not pulling on the choke enough.
From what I understand, the original vacuum break on my car is a one year only item (66') and reproductions are not made so they are pretty much un-obtainium without shelling out big cash for old stock. My cars original vacuum break was destroyed in a small fire so I cobbled one together from an old one (it looks identical but doesn't have the long slot - just a single hole for the linkage). I just measured the slot in the old one and copied it to the new one by drilling a bunch of holes and then using a dremel to make the slot roughly the same size. Anyway, I guess the break I used was leaking internally so I guess I'll have to try making another one and trying again.
My original, fire damaged, choke with destroyed break
My "cobbled together" solution. Unfortunately, it leaks.
As currently installed on the car. The choke is the one from the fire damaged picture.....it cleaned up decently.
Last edited by ourkid2000; December 4th, 2022 at 04:22 PM.
October 25th, 2022, 07:44 AM
