timing/idle/mixture - what to set first

Hi chaps, bear with me on this one, it could be a bit long…

For those that haven't read my build thread (shame on you) - I have an 83 Gti, engine fully rebuilt - static timing is bang on, WUR fully rebuilt, Metering head fully rebuilt, new injectors,fuel pump, filter. Tank is completely clean. I've tested the injector flow and all are equal, cold and warm pressures on wur are in spec - tripple checked as I know that has a big bearing on things.
Spent some time last night with a mate adjusting timing, idle, mixture when the engine was fully warm.
Got the timing set at 6 deg BTDC which I beleive to be standard, and got the idle at roughly 1k. Tweaked the mixture and measured the CO at 1.5% with a Gunson gas analyser. Picks up nicely when revved and the idle settles back to where it should be.
Tried a cold start this morning and whilst it starts, it will only run for 1 to 2 mins before the idle starts dropping and it stalls. Giving it some revs and lifting off causes it to stall more quickly.
When we set the timing, we had the vac advance connected - there was some debate on this - Haynes says it should be disconnected but my mate was adamant that he'd never done his with it disconnected. Which should it be? Would this even impact cold running?
The mixture was low according to the Gunson, so I adjusted it up a little (clockwise) this improved the idle, but weirdly didn't register much on the guage. Is it worth adjusting it up more to nearer 2% - would this improve the cold idle?
Idle screw doesn't seem as sensitive as I thought it would be, but I did a smoke test of the vac system after rebuild and it is fully airtight. Throttle stop has been wound back so I know it's not running part open.
Is it possible/sensible to try and set the timing/mixture on a cold, not stone cold, but not fully warm, engine?
I'm struggling to find a baseline to start from really as adjusting the timing and miixture then impacts idle, and when you adjust the idle down, you need to check the timing again.
Any thoughts/suggestions you helpful bunch?

Cheers,

J

Oh, I and I know I'm getting a good spark as got a right belt when I got a bit near the timing light pick up when moving the dizzy. I think I've done quite well as in 30+ years of tinkering with motors I've never shocked myself (mains electrics are a different story!)
 

I would not try and adjust things on a cold engine, adjust the mixture when it's warm.
I believe it's best to unplug the vac advance and block it off when adjusting the timing using a light.
The Gunson gas analyser is not accurate enough to get the mixture spot on, I've got one and plugged mine in straight after having an MOT done with the mixture reading from there machine and the Gunson was 1% out so best find a local friendly mot garage and see if they can plug your car in to get it set up.

When the engine is warm have you tried increasing the idle speed on the idle screw up to 1500 rpm, rev the car a few times and lower the idle speed to 1000rpm to see if that helps with the idle dropping?

Thanks Mark. I made sure the engine was hot before adjusting. From further reading I reckon the most important to set first is idle and timing and then come back to mixture and idle. I'll have another go on the merry go round one evening this week.

J

Cars and Sex have a lot in common, but great running cars and great sex is always Timing. Who new that they had so much in common.



First thing always is timing.  Everything else is a placebo.