timing conundrum

[IanA]

Hi Chaps,

Cracked fibre timing gear replaced with a nice brand new metal one, checked timing marks on the old one and the haynes manual, 7 teeth between the 2 markers, and yet the only way the bike becomes a first kick starter is to remove one timing backing plate screw and advance beyond what is normally within range, then it fires up a treat and runs beautifully. Within normal range i cant get it to start at all!
I', tempted to advance the timing gear another tooth to move the trigger point into the normal range. the motoplat rotor is in perfect shape no damage, and all timing marks in the valve train are correct, triple checked those.

Has anyone else had this issue, it's a late 1975 350 with motoplat ignition. I haven't used a timing disc on the crank yet but will borrow one tomorrow to check with that.

[IanA]

Having asked the right words in the search function, i now see this isnt a unique situation and that quite a few have muted, if not done, moving the timing gear one tooth. As this engine is most likely to have been made in spain due to its age, motoplat ignition and fibre timing gear despite being a Uk/ Walker supplied bike, and that mototrans engines often had 2 timing marks on the crank bevel gear. Sure i didnt see 2 but think moving the timing gear one tooth is the right solution. Now to work out which way?

[Duccout]

Hi Ian,

Hopefully Jon will see your post and offer some advice. AFAIK the two timing marks are on the crank bevel gear, so obviously moving it one tooth will affect the valve timing, not the ignition timing, so it will be prudent to leave all alone until you can put a degree disc on the crank and check the valve timing. If that checks out OK, then maybe it is just the points gear that needs changing one tooth, which is what you have done!

[IanA]

pulled it apart again, and only one timing mark on the bevel gear on the end of the crank, so valve timing should be at risk, plus when i do advance the timing having removed the backplate screw it sounds lovely and smooth, no clatter from the valves.

[IanA]

Just to conclude this one, i put all the timing gears back as they should be aligned to timing marks, using dial gauge i could see the backplate needed to be further advanced, so i took off backplate and extended the slot so that i could comfortably move the backplate to the correct 36-38 degrees of advance. Bike is now a first or second kick starter and ticks over sweetly.

[Duccout]

That seems to be a common problem, my Spanish 250 was the same, I had to move the points plate right to the end of the slots to get it to time. Anyway, sounds like you have it sorted.

Colin