Ignition timing issues

[Daurie]

I'm having minor ignition timing issues that are more baffling than problematic. I have a Turner 8:1, 2.25 Petrol engine in my S3. Lucas 45d dizzy with Pertronix unit. The reccommended timing per Turner is 3 to 6 deg advanced static (obviously)

I know timing has been discussed to death nearly on here and I have gone through all the methods explained but always seem to fall back on stroboscopic timing method as it's never failed me in the past.

Whats happening is if I set it at 3 deg adv and plug in the vac adv unit everything seems fine then once everything evens out I get a little poop / pop out of the exhaust which is also percieved as a slight miss if you were at the front and couldn't hear the exhaust. It's very random but happens regularly at idle. I've pulled plug wires to try and isolate it to a particular cyl. but as the idle and vaccuum (timing) decrease the miss dissapears (except, obviously, the miss of the cylinder I pulled the wire off). If I advance any more than 3 deg it gets worse. I rechecked all the valve clearances and everything is spec. My vaccuum advance, advances 25 degrees at 750 rpm. Does this sound right? I haven't gone as far as checking the advance curve but I believe the unit to be good as it was new in 2006. I get no pinging or valve rattling under running conditions and frequently have full throttle accelerations in 3rd and 4th up to 3500 rpm that are very smooth.

The PO stated that he found the timing to be best set at a little higher than 6 deg adv! Which is also confusing me because I have no doubt that it was set at that and don't remember the popping when I bought the truck.

Any ideas?? :confused:

[Daurie]

wanted to bump this up as I'm hoping to work on it tonight. Any thoughts on this issue?

[friar mike]

Ok let me see if I can help poping out the ex can be a lean run problem try riching up the carb. one qwick way is to pull the choke out a little. 25 degrees sounds about right for max advance you can run up to 30 degrees I hate to go more. The way I tune older cars is max advance Iam not too worryed about base timing my timing light has a advance knob to do this. Base timing between 3 to 6 is good. also check for a vac leak where the manifold meets the head that can also make it pop.

[Tim Smith]

The petronics is an electronic ignition, right? My first thought was that the points were dirty or out of adjustment but if you're running electronic, then I'm at a loss. Maybe the plugs or wires?

Edit: A new thought... run it in the dark with the hood up and see if there is any arking coming off your wires?

[Daurie]

Got new plugs and new Magnacore wires. I've checked for vac leaks with ether. Another very experienced rover fellow told me the pop could be coming from a RICH running condition. It's very random. It may run 2 minutes without a pop then there it is appearing out of the blue, then it may not happen for another minute or it may do it with in seconds. I'm just going to have to do some tweaking and playing around to figure it out. The truck runs great and it's really nothing more than a nuisance.

[singingcamel]

last time your valves were adjusted?
you may want to do a compression check? looking for a valve or valve seat problem
you may have a valve that not seating right do to carbon , this can cause a miss fire but one would think that it would be a constant miss.
I've also seen a burnt valve cause a miss but again its a constant miss and heard the best at the tail pipe .
I'm saying this is your problem but if timing does'nt clear it and all the vaccum line are without leaks something to think about.
any play in the dizzy or wobble to the dizzy itself while running?
also the timing may vary from the norm due to timing chain placement.
these things you can't always go by the text, but a good place to start..

[Daurie]

I too was suspesting the valvetrain and checked valve adjustment to make sure. I can make the problem worse with timing advance. I think, however it may be a lean idle issue like a previous poster suspected. I leaned it waaaay out at idle and it became more frequent. I've backet out to my previousl setting and then a bit to see how that helps.

On a side note, strangely, my timing changes on it's own it appears. I set the timing at around 4.5 deg (between 3 and 6 on the indicator) a few days ago and today it was slightly above 6. I'm beginning to suspect my dizzy or vac advance unit is troubling me.

Either way I richened my idle mix a bit and brought the timing back to around 4 and shes acting a little more civilized.

I do time by ear to a degree but I still like to know where I was and where I ended up. I do somewhat use my light but don't rely on it as the end all to setting my timing.

Thanks for your replys!

[friar mike]

It real eazy to check for a burt or not seating valve just hook up a vac gauge.

[Momo]

Daurie, I've been having the very same issue, but worse. Like you I have a good distributor, new ignition components, etc. My carb was rebuilt a year ago. Lately I've played with timing and mixture with inconsistent results.

The other day I adjusted the valves, and none were overly loose or tight.
On no. 3 cylinder the plug was fouled and one valve spring & stem are varnished while the others are clean (the head is only a year 1/2 old). So there is obviously some excessive heat buildup on that valve.

Then I found that one of the nuts on my exhaust downpipe has worked its way off- so I've had an exhaust leak right at the manifold outlet. Not a big gap in the joint, too subtle to be obvious... but now it makes sense because I could swear my motor had gotten slightly throatier.

Anyway I did a compression test:

#1: 150 psi
#2: 148 psi
#3: 80 psi (aha!)
#4: 150 psi

Next week I'll pull the head and inspect things. But in any event you should do a compression test. If you have a valve issue it's easy to fix. You should also check your exhaust connections, especially at the downpipe!

[Daurie]

I too had an exhaust leak at my downpipe exactly as you. My 2 and 3 plugs were slightly more blackened than my 1 and 4 which look right on the money. My engine is a little over a year old. Looks like I need to do a compression check. :rolleyes: As easy as it is I don't know why I haven't yet anyway.

[Momo]

Cool, let us know what the results are. By the way, how do you like your NRP exhaust? Where did you buy it?

[Daurie]

It came with the truck. I like it. Has a good sound and is well built. :thumb-up:

[singingcamel]

What kind of carb are you using? weber ???

[Daurie]

Affirmative on the Weber. Ideas???

[singingcamel]

You may have a warped base , zeniths are noted for this causing problems.
make sure your gaskets are good below the carb , tighten the bolts to the carb (snug only) see if this helps...
If not you may have to glass the base of the card to correct the warp.
you could spray some wd 40 near the base to see if it alter the idle, if it does you may have a leak ..

[Daurie]

Will check that. I caught myself checking for vac leaks around there but I could have missed a spot as the carb base "looked" pretty good.

Thanks!