MG
The Classic Marque

Mark, Willy, Bob

Thank you for your comments and advice. You have been very helpful.

I haven't started dismantling the box yet so I don't know the state of the teeth in the sliding ring. I am assuming that I will be replacing it so that I don't have to go through it all again in a couple of years time.

Bob, I won't be going for straight cut gears this time round mainly o...

We have found 90++% of timing scatter is down to wear in the gear on the camshaft.
Fit a new camshaft and it goes away completely.

Yes third gear needs replacing the teeth are quite worn. You may get away with the synchro hub. I have rebuilt quite a few boxes without renewing the hub and they have been fine.
As you are stripping the box, are you allowed to use straight cut gears? They are stronger and have closer ratios albeit noisy but a complete set is pricy

Trevor, have you checked the timing with the vacuum to the dizzy disconnected while you increase and decrease the RPMs?

Jud

If it's retarding as the revs rise then something is wrong somewhere. I would suggest getting someone else to look over what is happening.

The timing at any revs should be short of pinking. When the plug fires the mixture doesn't explode but burns, and that takes a finite time. This starts as the piston approached TDC, which increases cylinder pressure above the increase that is coming...

Yes it is a 41288, I suppose the jitter could be from the timing chain but they were changed about 5/6 years ago when I rebuilt the engine and probably done less than 10,000 miles since.
Tightening the plate and pickup collar certainly improved things a lot as before it was retardening past tdc. Now it’s retardening to about 5/6 btdc. So it is an improvement.
Using the strobe I set it at...

Jeremy, that frogeye is on Gary's excelent frogeye site

https://frogeye.smugmug.com/Mk1SpritesFrogeye/Mk1-Sprites-Reg-400-499/i-H6rJrNs/A

Is it Gary's?
I dont know what plate is on his "new" frogeye after he sold gaps?

Timing jitter can come from timing chain/gear wear. Also cam and drive dog gear but less likely. Usually a minor issue that can be ignored for typical usage.

What is the reference number of your distributor? Should be 41288 for high compression.

Retarding instead of advancing with revs was covered at the beginning of the month under Ignition Timing, you said you found the trig...

With your help think I have the carbs set up well now but is still not running as I expected. I think the problem is coming from the dizzy, it doesn’t seem to be increasing the timing as the revs increase, according to to the strobe light it is decreasing the advance when the revs are increased. I know the dizzy is quite old as I believe it is original to the car and has been stripped down recen...

Colin, you're getting some decent input here- and Mark's pic shows it all. Although his pics are showing a syncro surface failure, they also show the fault you have.
If you have a good look at the pic with the blue circle, just above the circle are the teeth the syncro slider dogs onto. The surface on these teeth on the right hand side of the teeth in this pic is the side/surface that is dri...