Ignition timing with unleaded fuel

[moggymaniac]

Just about to do the timing with a gun to the specification in the manual - says 4 degrees BTDC at idol. But I've heard people say that with unleaded you need to advance or retard the timing depending on the engine. So does this apply to a 1098cc a series?
Thanks, J

[simmitc]

In principle, you "may" need to retard slightly for unleaded. No need to worry about the gun. Use the timing marks as a guide for the initial static setting, then road test. Advance until you just hear pinking under load, then back off a couple of degrees until pinking stops. That will be fine.

[bmcecosse]

Exactly as above... forget the 'gun' ! But first - check the vacuum advance is working as it should (many are not..) - suck the pipe and watch to see the base plate in the dizzy move and relax. If not - you need a new vacuum unit..Also check the mechanical advance is working - twist the rotor arm and release - it should spring back...

[Barry Brown]

I have a 'breathed on' Triumph but with the race cam, big carbs and unleaded fuel the ignition was so retarded it could have been a guest on Big Brother.
As I can't trust to what they call Lead Memory due to the hotter setup I used the Millers VSP unleaded additive but switched to the "plus" version with octane booster. (Triumph big sixes are supposed to run on 100octane. Avgas is very expensive and people get upset if you siphon their Cessna). The ignition is now back into the normal range, no pinking, no run-on and loads more power again.
Next rebuild it will go fully unleaded.

It isn't the cheapest option but the additive works for me. Other brands are available.

[bmcecosse]

the only additive that contains 'lead' is Tetra Boost. It effectively turns unleaded in to leaded fuel. Again - not inexpensive, but could be what you are after. Fortunately my TR7 engine was designed for USA use - so it is set for unleaded fuel use and needs no additives.

[bjm38]

Is this Tetra Boost stuff ethical, strictly speaking...given that the lead in petrol was wrecking childrens' brains?

Bernard

[bmcecosse]

There is considerable debate about whether the lead really did any of that - I believe the amount recommended to be added to the fuel is quite low.

[Barry Brown]

Is this Tetra Boost stuff ethical, strictly speaking...given that the lead in petrol was wrecking childrens' brains?

Bernard

Dunno Bernard but at least now they will be bright enough to know that Diesel particulates are ruining their lungs. Assuming somebody tells them via FaceTweet otherwise they will remain blissfully ignorant.

[bmcecosse]

Fortunately my diesel has a Particulate Filter - the dreaded DPF.... which needs a good full revs blow out from time to time !

[martin418]

i set my 1098 to the timing marks with a strobe light and it runs fine no pinking and pulls very well

[bmcecosse]

But which 'timing marks' - there so many variations ! It may go even better a couple of degrees further advanced - you won't know if you don't try....

[Barry Brown]

I just had the pleasure of setting the timing last night - first time on a Moggy and what a pain.
I thought it was difficult enough on a mini where you have to remove the inspection plate from the clutch housing and position a mirror so you can see the strobe flashing against the flywheel but I've never had to jack a car up before to set the timing.
On my Moggy the timing plate is on the bottom of the timing chain cover and not on the front as some other A-series lumps. The only way to see it clearly was to put it on axle stands. Anyhow tippex now painted on the 4degrees position and notch in the pulley so I can use a mirror under the car to save getting the ramps out in future.

Last jobs are fit the rear screen, insure it and then book an MoT.

[bmcecosse]

Dunno why you put yourself through all that pain - you are using a random setting determined on the 'safe side' (you can be sure) 40 or 50 years ago - with very different fuel than we buy today. The way to set is simply to move the dizzy back and forth at idle to get the smoothest/best idle. Then test run to check it's not pinking. If you wish - you can then advance slightly till it DOES start to show pinking .. and then take it back very slightly. You have then optimised the timing for YOUR engine using today's fuel... It is of course worth checking first if the vacuum advance is working - and the mechanical advance is free and working...