Ignition timing and fuel mixture help
Discussion
When I picked up my 1982 W123 Mercedes, it would lose power on the motorway periodically and then leap back to being OK. I tracked the problem down to an old clogged up fuel filter. Changing this fixed that problem.
There was also a strong petrol smell on idling which was almost completely resolved by adjusting the mixture on the carb.
I changed the spark plugs and also the leads which were crumbling with corrosion. Distributor cap and rotor have also been changed.
Today, I checked the ignition timing. A sticker under the bonnet says it should be 13 at 850rpm. It was set at 10 so I advanced it to 13. I also further weakened the mixture to see if I could get rid of the petrol smell completely. Stupidly, I did both these things before checking their individual effects on a test drive.
The car fine and smooth at idle, but when trying to pull away, bogged down and spluttered. As revs rose, the car pulled away but with reduced power and struggling under load. I initially put this down to weakening the mixture too much, so I adjusted it to make it richer again. The same symptoms happened on another test drive so I adjusted the mixture further. Same symptoms again and now the mixture is richer than it was before I started.
Question is, does advancing ignition timing result in the need for a richer mixture or does ignition need advancing further? Car runs on regular unleaded and starts immediately hot or cold and before, during and after the changes I've made.
There was also a strong petrol smell on idling which was almost completely resolved by adjusting the mixture on the carb.
I changed the spark plugs and also the leads which were crumbling with corrosion. Distributor cap and rotor have also been changed.
Today, I checked the ignition timing. A sticker under the bonnet says it should be 13 at 850rpm. It was set at 10 so I advanced it to 13. I also further weakened the mixture to see if I could get rid of the petrol smell completely. Stupidly, I did both these things before checking their individual effects on a test drive.
The car fine and smooth at idle, but when trying to pull away, bogged down and spluttered. As revs rose, the car pulled away but with reduced power and struggling under load. I initially put this down to weakening the mixture too much, so I adjusted it to make it richer again. The same symptoms happened on another test drive so I adjusted the mixture further. Same symptoms again and now the mixture is richer than it was before I started.
Question is, does advancing ignition timing result in the need for a richer mixture or does ignition need advancing further? Car runs on regular unleaded and starts immediately hot or cold and before, during and after the changes I've made.
Edited by Rollin on Friday 24th May 17:46
Do you know the procedure for adjusting the ignition timing? That 12 degrees is in the right ballpark for a car with vacuum advance disabled and at low rpm so there is no mechanical advance. Assuming you do have a vac advance, you'd need to disable that during the adjustment unless you have ported vacuum (and the throttle is adjusted correctly to close the port). Have you also checked that the vac and mechanical advance are working correctly? I don't know that engine but I guess you'd expect to have somewhere around 10-15 deg vac advance and a further 15-20 mechanical.
If you're using a timing strobe against reference marks on the front pulley to measure the timing, don't assume that the timing marks are accurate unless you have checked them.
It would have to be very rich indeed to have any noticeable petrol smell under the bonnet, so consider the possibility that you have a fuel leak, or a carb that is overflowing, or something like that.
If you're using a timing strobe against reference marks on the front pulley to measure the timing, don't assume that the timing marks are accurate unless you have checked them.
It would have to be very rich indeed to have any noticeable petrol smell under the bonnet, so consider the possibility that you have a fuel leak, or a carb that is overflowing, or something like that.
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