Ignition timing on 1.8 carb keeps slipping out

Hi
I have a 1991 1.8 carb clipper.  The cam timing is fine.  But the ignition timing is changing a few degrees every time I check it!  I have done a lot of work on the engine, and most things are new/refurbed.  The only thing I haven't changed is the distributor body (which has done 156k miles!)….could this be the issue?
Thanks
Andy

how do you mean it is slipping out?

when you check it I take it you are removing the vac pipe and blanking it off?

the only other way it can change once set is if the dizzy is twisting due to not been tight, or the internals are moving due to a worn weights (springs) or sticky diaphragm.

Hi,
Yes I am removing the vac pipe and blocking it.  I set it to 6 degrees, and then check that it advances when the vac pipe is attached and then when the revs rise.  So that all works fine, and performance on the engine is great. I tighten the clamp nice and tight, spit can't move.

Issue is it seems to slowley slips out.  I first noticed it as the engine was struggling to tick over, around 750 revs.  It happened slowly sp didn't really notice.  I checked the timing and it was back to around tdc, so had slipped 6 degrees.  I had not touched anything to do with timing.

Soi first checked the cam timing and all was still spot on.  Then readjusted ignition timing and run fine again.  I checked every day and after day 1 it has advanced a couple of degrees.  Readjusted and the next day it retarded by a couple of degrees!

The other issue is I have a long standing intermittent misfire….not enough to cause a real issue, still ticks over at 850 no issue, I can just hear a cylinder drop out every now and then.  I have checked and double checked everything like plugs, leads, caps, arms etc. and can't find the cause so kind of live with it.  The only piece in the engine that I have not not changed is the tchi unit and the dizzy, so I wonder if the 2 issue could be related?

Andy

been more of a ford person i'm not too clued up with the common isues on the VW's, but i too have the same problem with the "sounding like there is a miss fire"

I had put my problems down to the carb or the fact that i'm using unleaded and should be using super.

i would be interested to hear what others think your problem is.

with regards to the timing, if it is changing, the only thing i can thing of is work weights or sticking vac unit on the dizzy

Reddood said

when you check it I take it you are removing the vac pipe and blanking it off?

You do not blank it off, you leave it with pipe disconnected, then set ignition timing  :wink:
I am referring to a weber carb  :wink:

Not according to my hynes or BDV data catalogue. and in practice, if i leave mine disconected without blanking it, my car idles at 1800rpm and the emmisions drop from 2.7ppm to 1.9ppm

When it is disconnected the idle will drop not go higher.
Thus in turn due to engine warm/hot you then idle adjust to approx 800/900rpm, once you have set igntion timing, your car is done.
reconnect the vac pipe back to dizzy THEN it will go higher of course, in turn you now adjust via idle screw again back down to 800/900 or even lower if you wish and also adjust the emissions.
I must have been driving about for 15 years in my mk2 and mk1 out of timing lol.

you should blank the vac line when its disconnected otherwise you introduce an air leak pedders.

but! this is a later carby engine and they should be set to 18 degrees BTDC with the vacuum line to the dizzy connected!

a couple degrees is nothing really though, the factory spec is 17-19degrees

Oh I have been doing it at 6 btdc with the vacuum off and blocked.  So I need to do at 18…. Is there a mark for this?

the diamond mark on the carby flywheel should be 18degrees

6degrees with vac line off is for a GTI dizzy, and the diamond mark on gti flywheel is 6 degrees to match it

Oh, ok, I've been lining it up to the diamond, but with the vaccum off and blocked! Will adjust amd see what happens!

So I reset the timing to the diamond with the vacuum connected, and woo, engine drives better!  I can't find anywhere anything referring to setting timing like this…thanks John!

My other problem was that the timing was slipping out quite badly over time, and I still have a intermittent misfire.  Have tried everything so last thing is to get a new dizzy, my one has done 156k miles so about time for a refurb….failing that I am stumped as have done all the usual stuff

Andy

yeah you have a mk2 golf engine in there which is why most of the mk1 manuals dont cover it properly, the brown one does i think but its burried in the supplement section somewhere ?

see how things go now the timing is set properly, if its still going wrong then yeah possibly the dizzy is suspect. mk2 golf GU dizzy is the same, or if you go for a GTI cam then a mk1/2 1.8 8v k-jet dizzy will do you, but you'll have to set timing it like you were before but you'll also have to make a new mark on your flywheel for 6 deg BTDC. this should be covered in the mk1 manual, its definitly in the mk2 haynes anyway (EV or DX measurements)

Great thanks. I am not sure whether this is a bone file test, but…..

I linked my timing light to the lead from the coil to the dizzy, and get a perfect flashing light very fast. When I do the same on each of the plug leads, the the light is less perfect, and I misses every now and then, which is basically what the engine does.  Not enough to be a big issue, but is there nonetheless.  Other than the dizzy, engine and gearbox, everything else on the engine is new!

yah that is a good test to check spark actually makes it to all of the plugs, it may be as you say the hall sender in the dizzy isnt as good as it used to be. i take it the coil and the ignition unit (TCI-H) are both testing out fine as per the haynes? check the wiring is all fine too, the coil black wires and the TCI earth to the battery

Thanks john.  I did the haynes check.

My multimeterug gets 12v between terminals 2 and 4 on the tchi

When the ignition is on I get 4 v across the LT connectors on the coil, which drops to zero after 2 seconds. Haynes says it should be 2v not 4v. Is this a issue?

I have then used a length of wire to earth the centre terminal of the dizzy multi plug. The voltage does not rise at all. Haynes says this means a open circuit or a faulty switch unit. How do I test for a open circuit?

if it was an open circuit you wouldnt get any spark at all so its not that, but to test you use a multimeter on either end of the wire set to beep mode or resistance setting.

its worth trying another ignition unit, as they're easy to get hold of. all mk2s have them pretty much and compatible with mk1

Refurb dizzy arrived today.  Put it on, checked timing but was still running rough.  Checked mixture with CO meter and it was really lean at 0….so tweaked it to 2% and ticks over lovely, no sign of a misfire! I had set the co at 2 before, but I guess as it was misfiring and dumping unburnt fuel to the exhaust I had too weaken the mixture to get to 2!  Anyway all seems fine now
Thanks John for the help. Fingers crossed this fixes the initial cold start mis fires too :-)

Andy

Ha ha!  Misfire at tickover has gone, and car drives lovely.  Cold start is better, but still intermittent, and it struggles for revs for a couple of seconds after the initial fire.  Hot start is perfect.  After 4 seconds cold start it is always fine and settles nicely as it should.  I have done all the normal checks for 2e2 and everything else, and now the only things that are original in the whole engine bay are the engine, gearbox, and the tchi unit.  I checked for vacuum leaks and can't find any. The thing that puzzles me is that the fault is intermittent and very quickly sorts itself out!

:-)

So I took the waxstat off and checked it wasn't sticking.  All fine.  Choke pull down does what it should.  3PU the same.  Fairly sure the carb is doing what it should.



Then linked my timing light to 1 lead and started from cold….the timing light was not flickering as it should and was missing, and the car struggled for revs for 4 seconds….and as the revs picked up the timing flickered as it should!  So I guess somehow from cold start there is a issue with spark.

I have required the coil already as the terminals were corroded.  Earth from tchi to battery is fine.  Leads have been tested and changed.  Dizzy body, cap, arm all new.

Is there any chance my dodgy ignition barrel and immobiliser could be to blame (John you responded to my recent post about it). I also found out that my immobiliser sometimes works and sometimes doesn't!