Q jet operation
Thread Starter
Race Director
Joined: Dec 2000
Posts: 10,896
Likes: 2
From: CO
Q jet operation
Since I put a 165* thermostat in my car I noticed it takes a lot longer for the secondaries to operate in the q-jet. Car has to be warm for a while.
Is there some kind of secondary lockout until something heats up in the carb?
Is there some kind of secondary lockout until something heats up in the carb?
Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
Yes, sounds like you have a hot air choke like mine was rather than an electric. There's typically a hot air tube that runs down inside the manifold that heats the air inside and delivers it to the bi-metalic spring in the choke housing on the side of the carb. As the spring gets hot it either winds up tighter or loosens depending on the design and allows the secondaries to operate through the linkages attached to it.
Do you know if you have a divorced choke? That would be a small can on top of the manifold with the spring inside it rather than hot air tubes down inside the manifold. That type might be more suseptable to engine temp than the other style and could explain the difference your seeing after the stat change.
Bill
Do you know if you have a divorced choke? That would be a small can on top of the manifold with the spring inside it rather than hot air tubes down inside the manifold. That type might be more suseptable to engine temp than the other style and could explain the difference your seeing after the stat change.
Bill
Last edited by TopGunn; Apr 19, 2006 at 12:44 PM.
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
The secondaries will stay locked out for as long as the choke is not fully open. Anything you have done to affect choke duration will affect secondary operation.
Why would you use a 165 thermostat...? Other than making your heater nearly non-functional it has no benefit to your operation. Thermostat has no effect on engine max operating temp - it only controls minimum temp. But if you don't like having a functional heater, it's a good way to go.
Why would you use a 165 thermostat...? Other than making your heater nearly non-functional it has no benefit to your operation. Thermostat has no effect on engine max operating temp - it only controls minimum temp. But if you don't like having a functional heater, it's a good way to go.
Advanced
Joined: Aug 2005
Posts: 84
Likes: 0
From: Salem WV
Originally Posted by lars
The secondaries will stay locked out for as long as the choke is not fully open. Anything you have done to affect choke duration will affect secondary operation.
Why would you use a 165 thermostat...? Other than making your heater nearly non-functional it has no benefit to your operation. Thermostat has no effect on engine max operating temp - it only controls minimum temp. But if you don't like having a functional heater, it's a good way to go.
Why would you use a 165 thermostat...? Other than making your heater nearly non-functional it has no benefit to your operation. Thermostat has no effect on engine max operating temp - it only controls minimum temp. But if you don't like having a functional heater, it's a good way to go.
When will you start working on them again Lars?
Last edited by mrrt; Apr 19, 2006 at 02:18 PM.
Thread Starter
Race Director
Joined: Dec 2000
Posts: 10,896
Likes: 2
From: CO
When I first started working on my car I ordered a 195* thermostat and was sent a 165. I wasn't sure of the difference and put it in. Well it ran about the same temp. That is until I put in a griffin alum radiator. Now it doesn't budge above 165.
So I figure I will just put a 195 back in and perhaps my secondary operation will return to normal. Another thing I noticed is that on short trips the choke will come down eventually, but then I stop the car and start it again and the choke comes back on.
I have the radiator out and a-arms off so I will jsut get a different thermostat. I just needed confirmation that I wasn't dreaming up the carb/choke issue being related to the thermostat.
Thanks all.
So I figure I will just put a 195 back in and perhaps my secondary operation will return to normal. Another thing I noticed is that on short trips the choke will come down eventually, but then I stop the car and start it again and the choke comes back on.
I have the radiator out and a-arms off so I will jsut get a different thermostat. I just needed confirmation that I wasn't dreaming up the carb/choke issue being related to the thermostat.
Thanks all.
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
If you have a 1972-73 carb on your car, the choke will set itself closed every time you shut the car down: There is a spring on the choke pulloff on those 2 years that closes the choke upon shutdown. Any other year, the choke should remain open as long as the engine is still warm. If you have a 1975+ carb on your car, the choke should not close after hot engine shutdown. If you have a hot air integral choke, the choke is heated by exhaust gas - not by water temp. Unless you have a blockage or defect on your exhaust crossover system or your hot air system, the choke should operate fine.
Thread Starter
Race Director
Joined: Dec 2000
Posts: 10,896
Likes: 2
From: CO
Originally Posted by lars
Any other year, the choke should remain open as long as the engine is still warm. If you have a 1975+ carb on your car, the choke should not close after hot engine shutdown. If you have a hot air integral choke, the choke is heated by exhaust gas - not by water temp. Unless you have a blockage or defect on your exhaust crossover system or your hot air system, the choke should operate fine.
I do have a 1975 carb with an integral choke. Stock as far as I can tell.
I wonder if I have blockage?!?!?
How long typically should the choke stay on? Mine stays for at least a mile of driving with 4 or 5 min of idle warm up time. Sometimes longer.
Its hard to know what normal on this car is. I never drove one that was new! Having to wait for water temp to come up then blipping the throttle to get the choke to open fully is "normal" for me
