250 Monza backfiring thru carb

[machten]

What happens to the backfire above 2000-3000?

Kev

[amartina75]

Have you checked your AAU is working properly? The springs can get worn out. Also small cracks can form on the plate. Mine was cracked on my scrambler. I wouldn't have noticed it but my brother told me to check it for cracks. Timing can be difficult to get spot on, I usually have to go through it several times to get it right. I only set it static with a light, and all is well with my bikes. Good luck

[cooperplace]

on removing the points plate, the advance weights look OK: no cracks, springs intact, the weights swing out. But there is quite a lot of oil on the points, and this can't be good.

I can't find a procedure anywhere for replacing the seal that must be leaking. I can't even see the seal on the exploded diagram in the factory manual. And it's not clear how I get to the seal.

If anyone has any relevant advice, I would be very grateful.

[StewartD]

Hi Cooperplace,

I can't see that seal in the main engine exploded diagram in the Clymer manual either. It's shown in figure 82 on page 83, but the size isn't given. From memory though, it's just a standard size, so once you have the old one out, you can take it to the local engineering supply shop for replacement.

2014.07.28 Mach 1 manual fig 82.jpeg

It can be levered out of the case with a screw driver after the case is removed. This of course will wreck it further but it's the only way, as can be seen in figure 82 (attached).

The new one can be tapped into place, using a bit of pipe (or a socket and socket bar), just a bit smaller than the outside diameter of the seal. Take care to keep it from skewing though.

Cheers,

Stewart D

[Eldert]

the diamensions of the seal are 15 X 30 X 7

Eldert

[Rocla]

Hello Cooperplace,

I don't know if it is an electronic ignition but if not, don't forget that a simply worn condenser can generate such backfiring, just in disturbing the ignition timing. It happened on my Scrambler... Anyway, it is very unlikely that backfiring is not linked to the ignition timing (maybe the timing is OK but you have additionnal or residual sparks).