AJS & Matchless Owners Club

spookefoote1956 wrote:I notice that young Spriddler has suggested in other posts 7/16" btdc due to modern fuels. How do you feel about this?

I've always used 7/16" but since I adopted that figure ethanol has been added to the petrol and I continue with it because my timing stick is still marked that way.
From a purely practical point of view, bearing in mind parallax effect when sighting the stick in the plug 'ole', plus the fact that you may not be holding the stick vertical, plus the stick may slip between measurements on a domed piston, plus backlash in the timing gears and mag chain, plus it may move a tad when you tighten the mag sprocket (need I go on?) so if you can set the timing precisely within 1/8" (e.g. exactly 7/8" or exactly 1/2") you'll be a better man than I, Gunga Din Anywhere between the two figures will be O.K. Treat it as a target!
I time mine with the h/bar A/R lever not quite at full advance then if, on a test ride it seems slightly too retarded or too advanced I can always ease the h/bar A/R lever a smidge temporarily until I can be ars*d (or not) to retime th'engine at the mag. In my experience there's always more movement at the h/bar lever than is needed to move the mag plate from full advance to the starting retard position. In any case I have never needed to fully retard the h/bar lever.
Other, less slapdash opinions are available.

I'll give 7/16" a go. Hopefully the Thorspark will help when it arrives.

spookefoote1956 wrote: Hopefully the Thorspark will help when it arrives.

Gulp!

spookefoote1956 wrote:I notice that young Spriddler has suggested in other posts 7/16" btdc due to modern fuels. How do you feel about this?

Young Spriddler? Have I missed a time reversal somewhere?

ok after the insults the contribution. For many years I used a timing device that screwed into sparkplug hole and set it to 1/2 inch before tdc. It was only recently that I realised the angle meant I was actually setting it to 7/16. Could it be something like this be where the confusion about 1/2 inch versus 7/16 originated?

Don't guess... do it right, do it once!

Is that a turkey baster?

Of course, if the crown of the piston is like the one that I've got away for soda blasting but not been done yet, then there'd still be a substantial martgin for error resulting for the thickness of carbon present.

More seriously, I will probably check the timing this sort of this way before I put the head back on. But it's a Rizla Green between the points and make sure the I've used the back wheel to try and minimise backlash. I really don't think the level of precision required warrants this effort but I also applaud the intention of wanting it to be right.

It worked for Dad on his WD Matchless through the last war and been OK for the 10,000's of miles I've done on mine.

I think it is a little advanced anyhow but with the auto A/R and what's more it being sticky when cold I find wearing the trials boots with full internal steels is a good option; shortening the valve lifter cable a bit before refitting as well as it's stretched a bit.

Johnny B

spookefoote1956 wrote:Is that a turkey baster?

No

I meant air pilot screw - if it is screwed too far out the pilot jet gets too much air mixed in, so mixture is too week to start.

Looking at the photos on your other thread, the A/R cable looks to enter on the top RH corner (although hard to see and say for certain) of your mag- if this is the case this means fully advanced will be with the lever pulled back (ie your cable pulls the point actuation back plate anti-clock wise). Mine enters top R LH so the cable pulls the back plate clockwise, same direction of travel as the points. So full advanced on mine is with the level pushed forward ie "closed". If you have timed yours with the lever "closed" your timing will be way out. I got mine running with pencil in the plug hole to set the mag timing, and cigi paper in the poinis to double check it. One shouldn't need to use a timing disc etc as the tolerances are not that critical. If it can't be set up to start with "pencil and cigi paper" tools I would suggest there is something else wrong which a timing disc ain't going to fix. Good luck.