Q-Jet Fast Idle Issues

[geezer#99]

It’s working as designed.
When first started the choke coil heats up just enough in a short period of time to kick off the high idle. Heat comes from the exhaust crossover initially on the underside of the intake. The ambient air around the coil and cover also heats up. Once moving down the road that warm ambient air around the stove is cooled back down due to air movement in the engine bay. The coil cools just enough to kick the high idle back on. With prolonged driving the heat in the engine naturally rises and keeps the choke coil warm enough to keep the choke off and high idle dropped off.
Yours is likely set just right. If it kicks down and you can drive off without it quitting or stumbling then the cure would be turning down the high idle to an acceptable rpm.
The linkage rod from the coil to the carb controls the richness or leanness of your choke.
You can fine tune it by adjusting the length of the rod.
A strategic bend can change the length.
It can be tricky finding the length that acts just right.
I suspect yours is set right at it’s leanest length. Likely about perfect for your driving.
Be happy you’re living in a warm climate. In 40 below country setting chokes is way more fun.
I used to have a couple different linkage rods that I would change out depending on time of the year. Made them from wire coat hangers.

[dz1087]

Originally Posted by geezer#99

It’s working as designed.
When first started the choke coil heats up just enough in a short period of time to kick off the high idle. Heat comes from the exhaust crossover initially on the underside of the intake. The ambient air around the coil and cover also heats up. Once moving down the road that warm ambient air around the stove is cooled back down due to air movement in the engine bay. The coil cools just enough to kick the high idle back on. With prolonged driving the heat in the engine naturally rises and keeps the choke coil warm enough to keep the choke off and high idle dropped off.
Yours is likely set just right. If it kicks down and you can drive off without it quitting or stumbling then the cure would be turning down the high idle to an acceptable rpm.
The linkage rod from the coil to the carb controls the richness or leanness of your choke.
You can fine tune it by adjusting the length of the rod.
A strategic bend can change the length.
It can be tricky finding the length that acts just right.
I suspect yours is set right at it’s leanest length. Likely about perfect for your driving.
Be happy you’re living in a warm climate. In 40 below country setting chokes is way more fun.
I used to have a couple different linkage rods that I would change out depending on time of the year. Made them from wire coat hangers.

Sounds fun having to swap those out in the frozen tundra....

Thanks for the info. I was playing around with the carb last night and saw where the coil could cool and pull the fast idle circuit arm back up, so I suspect you're completely right - it's behaving this way based on the choke rod length.

Next step is to slow the fast idle circuit a little.