I'm starting this one to get out of Rockety's thread, as what I'm dealing with has nothing to do with the rebuild, or at least I think it doesn't. So new thread....

Like some of you may have read in that thread I rebuilt my carb while a fellow member was doing his so we were trading notes. But then it got out of hand...I'll take the blame for that as I should have opened a new thread when I got that far...

Anyway, I've got a freshly rebuilt L69 carb on top of a LG4 that came out of an 87 Caprice. Motor swap was completed last summer and it runs. But while it ran the driveability was nowhere near good. Hence the carb rebuild. I'm done and it will run again, but it dies when trying to idle. Now the conflict here is, this is a computer controlled carb, that needs sensors to run right. On Naf's suggestion I checked the wires, firing order and tried starting the car without the TPS connected and then when that stalled I tried it without the MCS connected.

Without either the TPS or the MCS it warmed up, then settled at a steady 750 or right around there. Is this indicative of faulty sensors? I could swear I probably could have driven it around town easily the way it ran without the sensors. So, without the sensors, it will run and idle easily, and happily. With the sensors it runs like crap and dies. Because of the steady idle I have problems with this being a vacuum leak. If there was a leak the car wouldn't have improved when the sensors were disconnected, it would have remained the same. So again, faulty sensors or something else?

I've done some digging around on the boards here and it sounds like if the MCS is clicking then its good. I know mine clicks, I'll check when I mess around in the garage later to be sure. But that still leaves the issue of the car not running right with things hooked up and running nearly perfect with nothing hooked up. Could it be that I have a timing issue and its only showing up when the sensors are hooked up? I'll let it run as long as I can with the stuff not hooked up and see if I can get a base timing on it.

Speed...really...don't worry about it. It was all still very relevant to the forum, I think.

Have you backed your idle mixture screws out 3 3/8 turns from fully seated? Without the MCS plugged in, it is holding the rods out of the jets all the time which makes me think that you are running too lean in idle. Your O2 sensor may need changed as well as this is the only sensor that really messes with the MCS.