dying during fast idle

[dlb]

this morning was pretty cold here so i started ron up and let him run while i was packing my lunch. when i left him, he was idling at about 1600 RPM. after a few minutes inside though, i could hear the revs slowly dropping to the point that it would sputter a little bit, and then pick back up to around 1600 again. i heard this happen several times this morning but have noticed it in recent months as well: i have done the same on other cold mornings but when i've come back out to the car, it's no longer running. if this were a new thing i would be wondering if it were connected to the dry start after the oil change i did yesterday (which i also just posted about) but since it's happened before i don't think the two are connected.

my first guess is that this is just carb icing (similar to what i get for a few minutes in the middle of the engine warming up where the weber will die on idle) but i don't really understand how the fast idle works so i'm not sure. does fast idle simply give more throttle than regular idle? if that's the case, it seems like the engine shouldn't die because even when the weber will die on idle, as long as i'm driving and giving it throttle, it's fine.

i should note that i have the weighted heater flap in the exhaust manifold permanently positioned to the 'warm engine' setting because the spring has given out on it and i don't want to be running hot all the time. i have also checked in the last few days for vacuum leaks and found none. the car drives just fine but i still appear to be getting poor mileage (25-26 mpg) even after adjusting the alignment to spec. i wonder if this can somehow be related to my poor mileage.

[Lil Beast]

I do get that little problem too on very cold days, I think it's the adapter plate that's causing like you say some sort of icing, takes about 30 sec for me. When very cold, I usually just hold the choke knob to the second position(halfway)for about that 30 second and after just leave it on fast idle. BTW mine holds on the choke if I wiggle the knob a little, it will hold until warm enough, but my spring is too tight then when it let go, it comes back all the way and dies, so got to hold it a bit.

The fast idle on the weber it's only the choke butterfly that are closed.
Maybe the carb is loose a little making a little cold stream of air goin in, another kind of icing. But most likely it's like me. Tried to get it better no success, and it's only on cold days still start right away.

[arbskynxnex]

The fast idle is a cam that sets the throttle plates open wider. Have you checked your float level at all?

Here's a little basic troubleshooting guide on weber carbs based on symptoms.
http://www.webercarbsdirect.com/v/vspfi ... 0Guide.pdf

[dlb]

thanks arb, i have used that troubleshooting guide a few times but nice to have the link on hand.

i have not checked the float level, that's a good idea. does the weber have a sight glass? how do i check it?

[arbskynxnex]

http://mcelroymotorsport.co.uk/Document ... 0guide.pdf

No sight glass. You need to take the top screws and choke linkage off and pull the top cover. Are you running a pressure regulator too? You might check it to make sure the settings haven't changed on it.

[dlb]

yes, i run an FPR. all is well there, steady at 2.7 PSI.

great link, thanks!

[Lil Beast]

As for mine goes there is no problem freshly rebuilt, float is fine (a little low but I set it like that so it doesn't overflow when driving fast in the bush) , any engine needs a little warm up time before leaving it idle or fast idling. Most don't realize how to use them, cause they usually are all automatic, electric, etc for a long time now. If it was below 0 c. I think you don't have a problem! Use your choke pull on it fully(you can pull the knob a good 2 inches out) if you need too then play with knob until steady on fast idling and/or readjust. It's my tight spring that's sets it off to hard, so got to monitored it for 10 to 30 second depending on how cold.

[Petros]

sounds like icing to me. Possible vac leak? Might check that too. Make sure the cold start linkage is all within spec too, the fast idle is tied to the choke position for either auto choke or manual. IF out of adjustment it will do weird things as it warms up.

[dlb]

i never posted the solution to this but my fast idle was simply not set high enough. this allowed the carb icing that webers are prone to to cause it to die while idling. it now fast idles till warm in sub-zero temps no problem . just checked the float level though and posted my findings in a new thread, found here:

https://tercel4wd.com/forums/viewtopic.php?f=4&t=7872