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Refuses to idle when hot!

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neilh

neilh

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My 79 CA emissions Midget rebuild refuses to idle! It runs great on the auto choke until the choke backs off when hot, then it will run above about 2000 rpm, but coughs and splutters to a halt if i back off the throttle. The Cd-150 carb is completely rebuilt, the timing is set static at 10BTDC, and I can't get it to idle long enough to put the strobe on it and check advance at 800rpm as it won't idle at that speed.
I suspected a big vacuum leak, but can't find one, when cold a vac gauge is right on in the green zone, but it drops to zero ( atmospheric) when hot!
Any one have any ideas? EGR stuck open maybe?

Neil
 
Bump ... no one has any ideas?
 
I'm terrible at trouble shooting problems involving emission equipment. I usually start pulling vacuum hoses and capping them until I find one that makes a difference... then figure out from there if there is an abnormal issue.

How do you know the mixture on the ZS is correct?
 
I had the same problem with my ZS. I always suspected the decel circuit but eventually gave up and got a Weber. Now the idle is way more stable than with the ZS but I think I gave a little away in fuel economy. Could have been the fast road cam, header, and 1 7/8" free flow exhaust...lol
JC
 
There are two idle set screws on the auto-choke ZS. One controls high or choke idle, the other controls low or normal idle. Perhaps you need to adjust your low idle. Or perhaps it has something to do with the hot air flapper.

Other than that, I would run the low idle screw up to a point that the car will stay running. At that point you can attempt to diagnos the problem. Carb cleaner sprayed around all gaskets and vaccum connections will help you find leaks. If the idle changes while you are spraying a particular gasket or hose, you have found your leak.

Other than that you can remove and plug all of your various emissions gadgets one at a time and see if that fixes the problem. Before removing the EGR plumbing, you might try pulling and plugging the vaccum line that operates the valve, putting one end of a small hose against the EGR pipe and the other in your ear. If you hear air hissing through there while the enginge is running then Bob's your uncle.
 
budk1953 is removing a weber that is working good to replace it with a set of duals. You might contact him. Otherwise you might check on the Triumph site and see if anybody has had this problem on a spitfire. Definitely sounds like a leak. I'm thinking it would not be the egr stuck because it should do it cold as well, but could be some other problem related to vaccum. My money is on the vacuum being it. It could be a bad hose or leak going to one of those thermovalves that open when it gets hot and you might not be able to find it when cold.
 
He probably can't put a Weber on it since he is in CA. I thought it might be the EGR valve leaking as well but even after I disconnected it and plugged the manifold it did the same thing. I had a manual choke so I was pretty sure it wasn't tied to the choke circuit somehow. I also noticed that if I stopped hard or stopped on a steep slope it would stumble pretty bad as well. I went through the ZS with a fine tooth comb but in the end...Well I like the weber but would have loved a set of duals.
JC
 
I have no experience with 1500's (much less Cailf 1500's) but if they have an idle shut-off solenoid (to stop desieling upon shutoff) it may be the culprit. I have fixed a few Toyotas and VWs where the wire activating the shut-off had broken by just reconnecting the solenoid to the hot lead on the coil.
Bill
--Just a thought--??
 
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