Idle drops at stop lights and other fun stuff.

[ozmington]

My recently purchased 1981 Spider (Bella) is up and running well enough that I am no longer “white knuckled” running across town. This forum has been a large part of my success so far. I am now at the point of smoothing things out so that I can enjoy a more predictable ride. The car's original fuel injection was removed (not my doing so help me keep my chin up by holding commentary on this), and replaced with Weber 40IDF's. There is no choke but it's warm here and I'm content to baby her on start until she's happy. At that point, she'll stay running fine at about 850rpm but when completely warmed up, it creeps up to about 1200 at stays there. OK, so we head out on the road and at stop lights, the idle drops excessively and would stall if I didn't feather the gas. Also, restarts after a quick stop at the store require 3 to 4 attempts for turnover. Long and short, sounds great in the driveway but she's not happy when hot in city driving and the result seems to be an idle that is low when at lights and can't take the additional load of the fan. First couple of miles are the most enjoyable part of the ride.

Fuel tank is new, lines were cleaned, I reset the idle speed and air mix per tech specs, I think I've resolved any vacuum issues, I can hear the fuel pump even during difficult starts so we know it's functioning. Also, linkage checked, seems to work smoothly. Never completely fails to start and runs steadily when given gas. Thoughts ??

You guys have gotten me through other problems, I know you can get me through this one. Bella thanks you.

[So Cal Mark]

you have to make sure the engine is completely warmed up to make adjustments. If you just start it up and let it idle, you're adjusting mixture and speed before the engine and intake are up to temp.

[ozmington]

I will look at the temp/adjust subject again although I think I did that by setting the screws (idle & mix) to the tech manual settings and then fine tuned after warm. Again I'll re-look.

Fan's running alot in this hot weather and it's doing it's job but that seems to be when the idle drops. If I stop at a light after a long cruise and the engines on the cooler side, it doesn't happen but when I'm going stop light to stop light and the fan is on most of the time, I think that's when it happens. Do you think the load of the fan could be enough to affect this? Could it be electrical problem???

[So Cal Mark]

the fan puts a pretty heavy load on the alternator

[JConnerly]

Just a thought. My 81 was running rough when warm at idle, still have FI, just got my valves adjusted and the problem was a exhaust valve that was out of adjustment. Now it idles smooth cold and hot..

[GeorgeT]

One other thought: while stopped does the idle speed increase if you take your foot off the brake? I had a similar issue and the problem was a combination of a weak battery and an alternator with a bad diode. The alternator would not put out enough power at idle speed to power both the brake lights and the injectors. By reving the engine, enought volts were made. It always restarted with no problems but would not idle with the brake lights on - lights off no problem.

[AZ79]

Or it could be a leaking brake booster.

[ozmington]

Brakes on or off is the same but I do think I'm going to take a look at the electric side of things. I've done some regrounding, etc. but haven't really checked to see that the alternator is correct, size, etc. I'll report back soon (away on vacation at the moment). Stand by for further announcements..........

and thanks, as always, for the help.