[KGTO]

Carb works great, all rebuilt , everything appears to be adjusted and seems spot on ....however...

When cold and I tap the pedal it steps up to the high idle cam, but if I hold the throttle part open as I start the engine as soon as she fires and I take my foot off the pedal it drops to curb idle.

If I manually move the throttle at the carb when cold, I can see it all work as it should. So I'm confused.

I can also take my finger and with the engine off and with light pressure on the top of the cam weight I can pop it down off the fast idle screw . Should I be able to do that?

Thanks

[KGTO]

I should mention it's a divorced choke, all original

[steve25]

Is that fast idle screw just not into the notch on the cam enough maybe?

Does that cam have excess play in its pivot hole rotation wise or does it rock from side to side too much?

[65 Lamnas]

Originally Posted by KGTO

I should mention it's a divorced choke, all original

That's the 69-later cam which is an improved design over the bakelite ones. If it were me, I'd adjust the choke stove link to apply MORE "closing tension" and try it.

The fact you can move the cam easily with your finger to drop it off the high or middle step is normal.

[Kenth]

Did you set the idle mixture screws with engine running in gear (A/T)?
How many turns out from bottomed are the mixing screws at highest measured vacuum?
I have found that .400 pull-off is a tad too much, set closer to .250".
If the idle circuit is stock it is way too lean for todays fuels, i would open the idle tubes from .029" to .033" to start with.

Follow these instructions:

[steve25]

Real good point mentioned in post 4.

New divorced chokes need to be adjusted.

There rod coming up needs to be set so when cold the choke closes off all the way.
Once the engine starts and makes vacuum the pull off should open the choke no more then the distance of about 1/8”.

A drill bit is a good gauge for this setting.

This setting should keep the motor at your needed high idle setting.

If you have a good size Cam that choke opening may need to be bigger then 1/8”.

This adjustment needs to be played with because you want the choke to come off as soon as possible so you limit that rich running condition that ware’s out rings and cylinder walls .

Depending on where you live you might want a summer setting for the choke and then one for spring and fall driving.

Note that test done 5 decades ago showed that a engine experiences 60% of its ware during the time span from being cold to being fully up to normal temperature.

Start it and drive it!

Don’t let the car sit at a high idle for 5 minutes until the choke will drop out

[KGTO]

Thanks for the great info guys. I wasn't getting notified of the replies.

I do set idle with vacuum gauge, I may need to check again as I set the curb idle in gear (yes AT) but mixture screws were done in park. They are 1.75 -2 turns out. It runs, starts and drive excellent with snappy response. I built the engine, only has 500 miles on it, small cam., 068 roller

Since all seemed fine I checked the rod coming up from the stove. I opened the loop a little more giving it more tension. It seemed to do the trick. I'll have to play with it later this afternoon.

I have the choke plate set to 3/16". My understanding on the plate adjustment has the plate go full closed when engine is cold and you depress the pedal. When the engine starts it's on high idle and the plate is then at spec, in my case its at 3/16. It does go to full open when warm.

[steve25]

Sounds like you got.

[Schurkey]

If you readjust the choke pulloff, you also need to verify and perhaps readjust the linkage down to the fast idle cam.

The pulloff gets adjusted so the engine runs right--not too rich, not too lean--during the first ~30 seconds of run-time. At whatever distance the pulloff allows the engine to run right, the fast idle cam should drop so the second-highest step aligns with the fast-idle screw.

You would set the choke by pumping the gas pedal an appropriate amount based on ambient temperature. The choke blade snaps fully-closed, with the fast-idle cam on the highest step. Crank engine, engine starts, idle speed climbs. About 3--5--7 seconds of run-time, the engine has stabilized, and you tap the gas pedal. Now the fast idle cam drops ONE notch, to the second-highest step, idle speed moderates, and you drive off cautiously.

The point here, is that the fast idle cam has to be synchronized to the choke blade position as the pulloff opens the choke blade.

This--getting the fast idle cam synch'd to the choke blade--is one of the four major adjustments of the choke system.

[Cliff R]

On a cold start the divorced choke coil MUST snap the choke flap tightly closed AND at the same time lift the fast idle cam to the highest position.

As soon as the engine starts the choke pull-off opens the choke flap just far enough the engine runs on it's own without stalling out. So the choke opening angle must also be set correctly.

Do NOT hold the throttle open to assist a cold start. Set the fast idle speed instead.

IF you try to help it by applying throttle it will allow the fast idle cam to drop to the next lowest step on the cam and once the engine starts it may not stay running on it's own.

Although those early units are a bit primitive compared to later designs they work flawlessly once you set everything correctly......

[KGTO]

Mine does snap closed, just as both of you outlined. Then the pull off brings the choke blade to the open spec.

Are you saying that once you give the carb a squirt or two that you should start the car as you would if it were EFI (no throttle) ? All my carbed engines have always been sans choke, so I'm used to starting the engine with the throttle open a little.

When the engine is slightly warm, or up to temp all I usually have to do is bump the key and she fires right up. I'm no expert with the Q-jet, but having played with this for a while I will say it's truly a great carb.

Oh, a little off topic...I notice if the car sits a while I see the top gasket is "moist" which makes me think the float is a tad high and fuel is wicking into the gasket.

[steve25]

Yes that it does.
Remember that once the motor is shut off the .carb will heat soak and expand the fuel volume in the bowl and with todays ethanol cut fuel it will boil off also .

I would go with setting the float at .030” lower and see what that gets you.

Also double check that your air horn gasket is not somewhat blocking the fuel bowl vent.

[Cliff R]

Yoiu do not need to help the engine start with additional throttle.

Set the fast idle speed to do that for you.

Usually one or two pushes on the throttle is enough to set the choke flap, raise the cam to the highest position and put enough fuel into the engine so it fires up just like fuel injection.

The choke pull-offs job is to open the choke flap to the ideal angle so it's neither rich or lean while on the highest step of the fast idle cam. I'll add here that IF you have replaced your plastic choke pull-off in the last 15 years or so with one of those cheap POS while ones it is NOT going to work well. When they suppliers went off-shore for those parts the Chinaman put a spring inside them that requires over 14" vacuum to apply the unit. Factory specs are 5-6". Those pull-offs also open INSTANTLY so you get screwed twice and they do NOT dampen the secondaries going quickly to full thorttle. I've been modifying those pull-offs with the correct spring and adding a tiny restriction to the inlet for many years now so they work like they are supposed to:

https://cliffshighperformance.com/pr...pull-off-67-70

The fast idle speed screw must also be adjusted for optimum RPM on initial starts. After about 10-15 seconds tap the throttle once and the fast idle cam will drop to the next step and the engine RPM's will slow down, but it should continue to run just fine.

Some fast idle cams have more steps than others so there may be one or two more drops in engine RPM's if the push lightly on the throttle during the warm up process. Once the choke coil is hot enough it allows the fast idle cam to drop out of the way and the throttle speed is then controlled by the idle speed screw.

Early divorced chokes are somewhat of a PITA to get set up right as you have to bend a few things in the mix. Pontiac Q-jets 73-74 have an adjustable hot-air choke but you still have to bend parts to acheive the ideal open angle of the choke flap at start-up.

1975 and later hot air and electric choke carbs are adjusted by turning the choke dial for how long the choke stays on and a phillips head screw on the pull-off for the angle of the choke flap.

Factory choke coils, both divorced and hot-air were very well made and unless they get exposed to the elements and rusty will usually last just about forever.

The biggest problem I see here with factory chokes are folks blocking off heat crossovers or going to heads that don't have them. At that point an electric choke upgrade is going to be required, unless you want to put a hole thru the firewall for a cable and mount it under the dash.......

[59safaricat]

Originally Posted by KGTO

Are you saying that once you give the carb a squirt or two that you should start the car as you would if it were EFI (no throttle) ?

Yes

https://www.youtube.com/watch?v=_BTEdWt2V3s

[grivera]

Originally Posted by 59safaricat

Yes

https://www.youtube.com/watch?v=_BTEdWt2V3s

Love that video!

[Cliff R]

Good video, haven't seen it in a while.

It doesn't appear much has changed in the past 50 years or so and this applies to most things in life.

Right t the two minute markk they hit the nail on the head saying that their research showed that "many if not most" hard starting issues were a direct result of operator error.

Hard starting issues are further compounded today because of how fast this new fuel evaporates in a vented system and in a carburetor sitting on a hot engine after shut-down. So it's not uncommon to find the fuel bowl low or even empty after a few days or sitting.

Even so, fuel should quickly return to a bone dry carburetor within one or two short cranking cycles so the correct starting procedured should still be followed, not the typically pumping the piss out of the accellerator the entire time you are cranking the engine to get fuel back up to the carb.......FWIW......

[KGTO]

Awesome video! That's how I've been starting it and it's now like clockwork, fires right up!

[Cliff R]

Awesome, another story with a happy ending!....

[KGTO]

Yessir, thanks to everyone's help!

BTW Cliff, that converter I bought from you really works well. Fun car to drive

[Cliff R]

Good news! I love good news in a World where we get up every morning and see WAY too much doom and gloom when we log onto our home-page......