Weird idling problem

[bcbennett]

Hello all,

OK, when I start my TR6 in the garage and let it warm up, it idles great--right at 1200 rpm. As it gets really warm, it adjusts down to 1000.

However, when I take it for a 20-minute drive and bring it back to my garage, it will idle for about a minute at 1000, then start to dip down to 800, 700, and sputter down to die--even though the temp gauge is fine.

Could this be a fault in the temp regulator in my carbs?

 

[DougF]

Are you running the car on choke when it idles well at first or is 1200 a warm idle? Is your car stock with all the vaccuum lines etc. in place?

 

[bcbennett]

Hi Doug,

I pull the choke out, start her up, wait about 30 seconds, then choke it down fully. It runs at 1000/1200 when warm, fully choked.

Vacuum lines in place, but not emission equipment.

 

[poolboy]

I can think of a couple of things, but the first thing that comes to my mind is a Throttle Bypass Valve that is not closing when you come to an idle.
You'll see a small adjustment screw sticking out of the TBV assembly on the right side of the carbs. The next time the idle hangs up, press the screws with your fingers and see if that brings the idle down. It won't move much, less tha a 16th of an inch, but if you can manually close the valve by doing this then, either the diaphram surrounding the brass valve is shot or it needs more tension. You can increase the spring tension on the valve with a CounterClockwise turn or two of the screw.
Another thing to check, particularly since the emission stuff has been modified, is to be sure that the float chamber vent has not been capped off.
It is a brass nipple on the left side of the carbs, very close to the air filter housing.
If it has been capped off, the idle will definitly be affected whereas higher speeds will not be affected.
If that doesn't solve the problem please repost; we'll get to the bottom of it.
To answer your question about the Temperature Compensator, I really doubt it.
When the carbs are cold, the Temperature Compensator port is closed and all the air entering the carbs comes in from the "mouth" of the carbs. When the carb gets to about 100 degrees, the port in the Temp Comp is supposed to be fully open and a small amount of air will be allowed to flow thru a 1/4" diameter hole in the air box mounting flange into the carb's mixing chamber, leaning out the initial warm-up fuel/ air mixture, just that little bit. Not enough of an effect to cause what you describe.