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Question. 73 L48 4 speed. Restored car and NCRS Top Flight. Idles around 1,000 rpm. But throttle arm not touching solenoid plunger and idle screw not touching. Choke off cam.
Just bought and all emissions hooked up and air pump. Runs smooth as silk but around 230, which is correct in stock settings.
So I disconnected the TCS switch, plugged line and ran full manifold vacuum to distributor. Initial at 10 degrees and with vacuum hooked up adds 16 for idle timing of 26 degrees.
Runs around 220 and still high idle. See pic, plug this line an idle drops to 800. Charcoal canister vacuum leak? Other pics is current unplugged TCS and full manifold vacuum.
But the stock carb has me baffled, seems throttle plates closed. Is there something internal that keeps idle up?
The small vacuum line from carb to vapor canister must be connected to a 'ported' vacuum fitting on the carb. If it is connected to 'manifold' vacuum, that larger line would be trying to purge the contents of the vapor canister at idle. That will put extra A/F into the idle mixture and screw up idle quality. Make certain the canister 'trigger' vacuum line goes to a ported fitting.
If that line is connected correctly, the vacuum switch on the vapor canister could have failed in 'purge' mode, so that the canister is ALWAYS purging, regardless of the carb signal. If that is the case, the vapor canister and/or vacuum switch on it would need to be replaced.
But, with that purge line plugged off (as in the pic), you have removed the canister from the system and it is idling at 800 rpm. Does the curb idle adjustment screw on the carb allow you to raise/lower that idle speed? If not, you may have some other vacuum leak in the system or a carb setup problem or internal fault in the carb which is preventing proper operation.
The small vacuum line from carb to vapor canister must be connected to a 'ported' vacuum fitting on the carb. If it is connected to 'manifold' vacuum, that larger line would be trying to purge the contents of the vapor canister at idle. That will put extra A/F into the idle mixture and screw up idle quality. Make certain the canister 'trigger' vacuum line goes to a ported fitting.
If that line is connected correctly, the vacuum switch on the vapor canister could have failed in 'purge' mode, so that the canister is ALWAYS purging, regardless of the carb signal. If that is the case, the vapor canister and/or vacuum switch on it would need to be replaced.
But, with that purge line plugged off (as in the pic), you have removed the canister from the system and it is idling at 800 rpm. Does the curb idle adjustment screw on the carb allow you to raise/lower that idle speed? If not, you may have some other vacuum leak in the system or a carb setup problem or internal fault in the carb which is preventing proper operation.
I was testing all lines, the large line from base of carb, manifold vacuum, unplugged and capped off in pic brought idle down to 800. Only line to alter idle. Plugging back in to PCV T fitting brings idle back up to around 1,200. The small line from carb to canister looks like correct connection. I sprayed carb cleaner all around and no idle change. See pic, idle screw and solenoid plunger not touching throttle arm. Choke fast idle backed off. I don't know if the 1973 Qjet has some internal function, idle air bleeds, etc. that overrides what you would normally think at this point would make car stall. Idles at around 1,200 with nothing touching throttle arm. Car accelerates smooth as silk from a stop, secondaries come in like a light switch. Tested idle vacuum and reads 17", vacuum gauge does not fluctuate even a hair. Tks. Doug
I noticed that, unless the throttle plates have come loose from the cross shaft and bound up
the ability to close all the way, only other thing would be the cross shaft wore the base plate
shaft holes to the point the throttle plates are binding.
only your eyes and some history of the carb can determine which.
I noticed that, unless the throttle plates have come loose from the cross shaft and bound up
the ability to close all the way, only other thing would be the cross shaft wore the base plate
shaft holes to the point the throttle plates are binding.
only your eyes and some history of the carb can determine which.
I bought car just a few weeks ago from a NCRS judge who restored the car a few years ago. Been in storage mostly in those few years. It's a Top Flight car for whatever that is worth saying. Sitting overnight and in the morning following starting instructions per owners manual. Press accelerator, release, turn key. Starts on first click, fast idle comes on around 1,300 rpm. Warms up and drops to around 1,000. Go for a ride and throttle is smooth as silk, stop at a traffic light and it's back to around 1,200. I'm going to visit a guy who has restored my carbs over the years and ask him. I must be missing something obvious. Doug
Has the carb been rebuilt recently? If so, it is possible that incorrect primary rods were installed by mistake (or ignorance of the difference). Lars is the expert on Q-jets and the many "issues" found in rebuilt carbs. But I remember him mentioning in some post about primary rods which have a different taper than required and that it allowed too much fuel to enter the system at idle. If that is your situation, nothing short of correcting a hardware error inside the carb will resolve your problem. So, has it been recently rebuilt by someone other than yourself?
Has the carb been rebuilt recently? If so, it is possible that incorrect primary rods were installed by mistake (or ignorance of the difference). Lars is the expert on Q-jets and the many "issues" found in rebuilt carbs. But I remember him mentioning in some post about primary rods which have a different taper than required and that it allowed too much fuel to enter the system at idle. If that is your situation, nothing short of correcting a hardware error inside the carb will resolve your problem. So, has it been recently rebuilt by someone other than yourself?
I'm not sure if rebuilt or not. When I bought it it idled at 900, factory correct. Ran hot for emissions so I unplugged TCS and ran full manifold vacuum to help cool down. That of course raises idle. I'll contact my friend Phil, owner of Custom Rebuilt Carburetors in Jersey. I'm sure he will know what is needed. Doug
Beautiful 73' vert......
Check the choke linkage and stove for complete actuation.....if it is hanging up or not pulling all the way......it can stick the throttle open.
My question is that is the throttle level on the idle screw stop? Impossible to tell from these photos......
I also urge you to get Lars tuning and timing papers......follow them. You will like the car even more afterward......
E-Mail Lars at: V8fastcars@msn.com
Beautiful 73' vert......
Check the choke linkage and stove for complete actuation.....if it is hanging up or not pulling all the way......it can stick the throttle open.
My question is that is the throttle level on the idle screw stop? Impossible to tell from these photos......
I also urge you to get Lars tuning and timing papers......follow them. You will like the car even more afterward......
E-Mail Lars at: V8fastcars@msn.com
Jebby
Thanks but I've been tining muscle cars since the mid 1960's. Drag race dual point distributors, restorations of carbs, full manifold vacuum, adjusting vacuum advance pods with my Mityvac, Carter AFB, Holleys, Qjets. I'm not versed on emissions system carbs, so that is why I'm asking questions. Choke works correct, not hanging up, can't find any vacuum leaks. In picture the idle speed screw not touching throttle, idle solenoid plunger not touching. Aside from high idle the carb function is smooth as silk. Doug
Thanks but I've been tining muscle cars since the mid 1960's. Drag race dual point distributors, restorations of carbs, full manifold vacuum, adjusting vacuum advance pods with my Mityvac, Carter AFB, Holleys, Qjets. I'm not versed on emissions system carbs, so that is why I'm asking questions. Choke works correct, not hanging up, can't find any vacuum leaks. In picture the idle speed screw not touching throttle, idle solenoid plunger not touching. Aside from high idle the carb function is smooth as silk. Doug
Then something is hanging the throttle open…..and that something is generally on the other side of the carb and has to do with the choke….the choke may work but not pulling the fast idle cam off…is the lever in the blue circle in the pic all the way down?
There is almost nothing emissions about this carb BTW…..besides the solenoid it is the same as a 66’ model Q-Jet in function…..only the choke mechanism can hold the throttle open unless there is something majorly wrong with the unit and I doubt it very highly given the condition of you car…..
There is nothing internal that bypasses or lets air through other than the plates…..and they are hung open a bit…..get them to shut and problem solved.
Good on you for the timing knowledge....where is it set at?
Then something is hanging the throttle open…..and that something is generally on the other side of the carb and has to do with the choke….the choke may work but not pulling the fast idle cam off…is the lever in the blue circle in the pic all the way down?
There is almost nothing emissions about this carb BTW…..besides the solenoid it is the same as a 66’ model Q-Jet in function…..only the choke mechanism can hold the throttle open unless there is something majorly wrong with the unit and I doubt it very highly given the condition of you car…..
There is nothing internal that bypasses or lets air through other than the plates…..and they are hung open a bit…..get them to shut and problem solved.
Good on you for the timing knowledge....where is it set at?
Jebby
It's the original 7043203 Qjet. I have bypassed the TCS and ran full manifold vacuum to the B25 pod. My understanding is this carb may have internal idle bleeds that effect idle. Stock initial timing is 12 degrees with no vacuum advance at idle first and second gear. Thus disconnect TCS. I backed initial down to 8 and with 16 from pod my idle timing is 24. Right in the sweet spot to avoid low speed over advance which can cause "towing a boat feeling". Also put lighter centrafugal weight springs to bring all in around 3,000. Your point on choke vacuum pod is a good one, I will check that to see if it's really pulling fulley.
High idle, vacuum or ?
