DJet Hiccups

[HMeeder]

Car starts great cold and after about 2 minutes of driving instantly begins to run very poorly, bucking, having no guts and "brraaapp"-ing out of the exhaust. After 10 minutes of driving, all problems go away and and car accelerates and drives completely normally. Culprit? I suspect one of the thermo switches or the Aux Air Regulator. Nelin describes the functions of the individual components but doesn't really describe the symptoms of failure of the parts. Thought I would skip a step instead of going through the entire procedure he has outlined (though I will get ambitious someday and do it.)
Herb

[Pritchard]

Hi there-

I have had the same symptoms you are experiencing. I haven't yet found the remedy to make my engine run as good as new, but the engine runs pretty good.

It sounds like the problem goes away when the engine is up to temp. So my guess would be to check the valves (cold) for correct clearences, and to verify that the CHT is providing at least 2000 ohms when cold. Check the CHT again when engine is warmed up to verify that the ohms are around 100 or below.
If the problem starts after a couple of minutes, the Aux. Air Regulator is probably functioning as it should. The AAR will allow extra air into the mix until it heats up. At which time it closes off the extra air flow. I had a leak in my retard diaphram (sp?) in the advance unit which caused me some of the symptoms. Check to see if the retard side (hose/nipple closest to the distributor) will hold a vacuum. It should if working properly.

There are so many things that could cause these symptoms. If you have access to an exhaust gas analizer, check to see if you are running rich or lean. This will help to narrow down what is causing the problems. You can also do this by revving the engine and suddenly (don't let engine come back to idle) turning it off and check the plugs. This method is less acurate but will give some idea of what's going on as far as mixture. Black sooty plug tips indicate a rich mixture. Tan plugs are good.

If the mixture is rich, check the cold start valve. You can clamp off the fuel line going to this 5th injector to prevent fuel from being dumped into the mix if your CSV is leaking.

Good luck, I know how frustrating this can be.

Pritchard

[HMeeder]

Pritchard-
Thanks for the reply. I kind of guessed the Aux Air Regulator was doing the right thing. I just got smog checked about 3 weeks ago and all the levels were just fine. Car neither rich nor too lean. I was examining DDarling's vacuum hose diagram and I do not seem to have the second vacuum nipple on the throttle body that he indicates may be missing on '74 and later models. (This caused my car to fail smog the first time around. "tampering". I attached a hose to the vacuum advance and just snaked it into a dark part of the engine bay. Passed!) Any way, I'll give your suggestions a shot and failing that, I'll take a day and go through Nelin's procedure. It would probably be in my best interest to do so any way.
Herb