Hi gentlmen from across the pond.

'79 L-82 auto' std bar headers/freeflow exhaust, no smog gear, EGR manifold blanked off, 80k miles:-

Q-Jets....don't I love them

I just been playing with my Q-jets idle circuit to try and get her to idle decently when she is in gear. Plop her in 'D' and the revs drop off from 900 to 400/500 rpm so she nearly stalls....I can live with it just about, and it has taught my wife the noble art of 'two foot' driving so it's no all bad, she could in theory now perform brakestand wheelspins now

I thought I would start from scratch and I finally settled my idle screws after some 6-7 turns in!
And, I can tell that they need be 6-7 turns out, I kid you not, to keep her running, I have lots of slack in my throttle shafts, but hey 6-7 turns is a LOT of compensation for a little bit of air, isn't it? The main throttle stop isn't wound too far out either as I know this can upset the idle circuit?

The steering wheel side needs more a tad more fuel, but the given the throttle shaft wears more on this side that makes sense.
Strange thing is off-idle she runs sweet as nut and hasn't the other problems my C3 '80 gave me until I fitted a new Holley, it's just the poor idle.

If I didn't know any better I would say she has a hot cam and isn't pulley enough vacuum at idle, even sounds like it too but I'm sure as can be without looking at that cam it's the std L-82, the last owner had her since early '91 and there isn't any sign of the engine being 'got at' if you know what I'm saying.

So I checked what I could without stripping the carb down, found the upper carb half loose, and the carb base almost falling off the inlet manifold, so after securing everything I guessed she must run better.......and what do you know, made diddly squat difference

No air leaks I can find around carb, had a spray around with carb cleaner, inlet manifold all tight, ignition system fine, she runs, very very strong off idle and the way she accelerates from 50 to 100 once the secondaries open up is simply amazing, a lot quicker than my '80 ever ran even after a new carb'.... but I think this due to the super low drag strip gearing the 79 'enjoys'.

Any ideas before I go the Holley route again, just in case I haven't missed anything, strange, bizzare or even "I know this sounds wierd, but I once had this C3 that had a similar problem and you will never believe this but...."?

cheers guys for the help

 

Forgot to add:-

This C3 is not the best starter, although choke flaps are closed on cold start, still takes 5/6 or 7 pumps of the throttle to get it started then all OK on fast idle.

Gears shift fine, no delay in shifting up as maybe an auto vac' pipe leak might give.

cheers

 

5-7 pumps seems excessive, mine takes 2-3. Perhaps your fuel filter is clogged, when was the last time you changed it?

 

1. Did you set the air mixture screws with a vacuum gage at the highest vacuum level.
2. 5-7 pumps to start? Is this after setting overnight or hot start?

ED

 

thanks guys for the replies,

....she only needs 'pumping' when she has been sitting overnight, when warm/hot she starts on the button..

...I haven't checked my fuel filter and I reckon it's hasn't been cleaned for a while, thanks for the tip, what puzzles me is if she runs fine WOT, why is the idle so bad when the fuel consumption is so much lower if my filter is blocked?

Something I noticed that I didn't on my '80...this '79 hates getting stuck in traffic jams when the temp outside is real hot, say 28/30c, yes we had real hot but short summer overhere!
.....she seems to boil the fuel in the carb, vapour locks.

I know I need to pull this carb and see whats going on in there, I'm only putting it off

 

Wooooh!

I have just 2 read articles that state that smog C3 Q-Jets, which I think must be all of them, have an initial idle fuel screw build setting of around 5 turns out.....so if that is to be believed I'm not that far out.


Sorta of goes along the lines of if I understand correctly:-

....The size of the idle fuel inlet is small enough that it takes quite a large movement to get a change in fuel amount discharged, in an effort to stop someone with a little knowledge (me?) winding the fuel scews out so far as to cause real overfuelling problems....emissions protection possibly?

Can anyone clarify the initial idle screw setting from seated?
?