Timing and tuning

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Brenjacques
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Timing and tuning

Post by Brenjacques » Fri Dec 03, 2021 7:08 pm

Hi all

I was adjusting the timing on my scirocco last weekend after having it back from a garage. I noticed advancing the ignition timing from the flywheel mark increased the idle and the engine seemed to run a lot smoother. I backed it off a bit and then reset the idle speed and it seems mostly okay although I think it's running a little rich.

Just to query the above, should the idle speed peak when advancing the ignition? I'd have presumed it would peak when it's close to the timing mark on the flywheel. Whether this is a combination of a rich mixture and advancing causing the idle to rise I don't know. Then theres always the chance of a leaky vacuum advance but if I unplug the vac hose it does drop quite a bit so I presume the advance unit is okay.

As some may remember I did have some rough start trouble a while back and this has got a lot better with some ignition advance. I want to get it spot on as I'll be driving to the peak district during Christmas and I'd like it at its best for the trip. Should I set the ignition closer to where the idle peaks and back off if any pinking occurs then re-adjust mixture as necessary?

I know these engines like some advance but it feels as though I'm turning the dizzy a lot more than I'd have thought. I don't have an adjustable gun so I can't actually measure at what degree it peaks at. I used to have a great local tuning centre ran by a few older chaps who could really get carb engines tuned and timed up to a tee but unfortualtey they've been gone for the best part of a year now.

Any thoughts as to the above?



GT_II
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Location: Warwickshire

Re: Timing and tuning

Post by GT_II » Sat Dec 04, 2021 3:46 am

The correct timing angle for the EX engine is 16-20 deg BTDC if using 98 RON petrol (Super Plus) or 12-14 deg BTDC if using 95 RON (Premium). Vaccum hoses should all be connected, engine warm, idle speed 700 - 800 rpm.

TDC is a small mark to the right of that near a bolt head, vaguely like an "0". According to the VW workshop manual, there should be a line marking at 18 deg BTDC. What I'm less sure about is what the mark looks like, or if there is also another mark.


1992 VW Scirocco GT II 1.8 90PS Brilliant Black 30k
2011 VW Caddy Van C20 Startline 1.6 TDI 102PS 65k
2015 Skoda Yeti SE Outdoor 1.2 TSI DSG 105PS 35k
2013 Fiat 500 Pop 1.2 69PS 40k
2009 VW Fox 1.2 54PS 60k
2009 Smart Fortwo Passion 1.0 mhd 71PS 25k

Brenjacques
Posts: 120
Joined: Sat Jan 19, 2019 3:07 pm
fill in the right answer: 15

Re: Timing and tuning

Post by Brenjacques » Sat Dec 04, 2021 10:30 am

Thanks for that, this is how I've previously set it up. The 18° mark looks like a diamond stamping and involves removing the green cap to see it. I suppose another question is if the flywheel has been replaced with a non-standard part such as one from a DX, are they interchangeable? In that case I'd be timing it closer to tdc. I think I'll invest in an adjustable gun so that way I can be sure by timing it up with the TDC marking instead.



GT_II
Posts: 374
Joined: Fri Feb 24, 2017 12:18 am
fill in the right answer: 15
Location: Warwickshire

Re: Timing and tuning

Post by GT_II » Sat Dec 04, 2021 11:16 am

Applying some GCSE maths, for a 210 mm diameter flywheel (figure I found for the 1.8 mk2 engine flywheel on the net), the circumference (360 deg) would be 660 mm. So 18 deg would measure 33 mm along the circumference before TDC. Is your diamond mark around this distance to the left of the TDC mark? 13 deg would be 24 mm to left of TDC.

I think the DX timing is 6 deg before TDC, which would be 11 mm to the left of the TDC mark.

It's a few years since I checked my '92 EX, but from memory it was set part way round towards the diamond mark, I'm guessing 13 deg. I didn't change it as the locking screw on the distributor still had its factory anti-tamper cap fitted, so likely set up for 95 RON from new. From memory, it became a legal requirement for new cars to be compatible with unleaded 95 around that time.


1992 VW Scirocco GT II 1.8 90PS Brilliant Black 30k
2011 VW Caddy Van C20 Startline 1.6 TDI 102PS 65k
2015 Skoda Yeti SE Outdoor 1.2 TSI DSG 105PS 35k
2013 Fiat 500 Pop 1.2 69PS 40k
2009 VW Fox 1.2 54PS 60k
2009 Smart Fortwo Passion 1.0 mhd 71PS 25k

Brenjacques
Posts: 120
Joined: Sat Jan 19, 2019 3:07 pm
fill in the right answer: 15

Re: Timing and tuning

Post by Brenjacques » Fri Dec 10, 2021 2:58 pm

That all sounds about right, I'm sure my flywheel has the mark at 18° judging from your workings out. I'll have a play around this weekend, I now have an adjustable timing gun so I'll measure where it's currently sat and adjust as necessary if it's too far advanced.