[Che]

I'm wondering what a healthy idle should sound like in an older Sierra... Seeing i've owned EFI cars for the last 10 years, i'm used to an idle that'll sit on 1000 RPM and budge for nothing.

In my 1990 Sierra theres a fluctuation of idle speed, and I can't work it out.


For example - i'll start it up first thing in the morning and idle will sit on 850RPM, i'll drive an hour to the coast and then idle will be 1100RPM. I'll drive home later that day and idle will be 1000RPM, and once i've driven home, idle will be 800 RPM.... I can't work it out.


And when you listen to any given idle speed there seems to be a natural variation of +/- 50 RPM... not the clinical idle of an EFI car, that's for sure, but to be expected on a carby car? I can't remember.


Engine is as healthy as can be, and doesn't have any knocks, taps, whirrs, squeaks, vacuum leaks, or other things that'd suggest a problem. Oil, sparkplugs, leads, dist cap are all new, timing is spot on.... I just dunno what it is.


The only constant is that on a cold startup, idle speed is panel rattling, rich, and just above the point of stalling, but if you give it a minute to warm up it goes away.


The cold start thing to me it sounds like a bodgy choke, but I can't explain why idle speed jumps around between 800 - 1200 RPM.... maybe choke related also?

I've recently converted from petrol to running straight LPG, but it also had this problem on petrol - so i'm suspecting the Aisin carby at this stage. Everything else in the fuel line is new, afterall. Choke is still connected too, but i'm unsure how to adjust it.



Can anyone suggest anything?

[BUZOOKA]

on a cold start my zook idles at about 6 hundred tehn after a min or 2 ibles up to about 950 1k kind of annoying really but mine is only pertol

[Scrawny]

Disregard my babbling

[alien]

check the choke as mentioned above, and check your leads.

[shep]

i didnt think that you still had a carby that works like a carby, maybe the
problem is with your gas stuff.

[want33s]

If you are running the carby solely as a throttle body then you should plug all the venturi holes in the barrells except for vacuum advance. Also plug the float chamber vent pipe.
Check the base gasket isn't leaking too.

[ball]

alien wrote:

check the choke as mentioned above, and check your leads.

The choke will only help if it is still running on fuel, it won't make a difference when running on straight gas.

[oozuk]

make sure you have slack on your accelerator cable and then readjust you idle speed screw

If your still having problems then it could be wear in the base plate of the carby

[Che]

Choke is still connected to the system - the heater hoses from the LPG regulator now supply the temperature to the choke.

I'm not sure exactly why the LPG installer didn't just get rid of it, or what purpose it serves with my Aisin now being a throttle body. To my understanding, LPG delivers optimum fuel/air mixture automatically, so to my thoughts a choke will just get in the way of this... I think that's my current problem.

I probably will rip it all off/out, just wanna make double and triple sure i'm not gonna waste my time and end up putting it back on.


How to block the venturi holes? I wanna smooth out the barrels like you say, but not sure how to do this without putting my car off the road for a couple of days.