MZ-B Install

[Keithuu]

For those who care, the installation of the MZ-B on my '75 250 went pretty smooth. Well, except for the fact that the puller supplied with the kit didn't quite fit the Motoplat. By a strange quirk of fate, the local Yamaha dealer had a "vintage" puller, complete with dust covered wrapping, which fit perfectly. He even sold it for the faded sticker price of $4.69. Calculate the odds!!

Anyway, after re-doing the wiring a bit, the beast started up and everything worked just fine. The bike even seems to have more power than before, but that's just a seat of the pants observation.

One concern I have is that it now takes multiple kicks to light the fire when it was a 2-3 kick starter with the Motoplat. Seems a bit incongruous to me unless the difference in timing specs accounts for it. The Motoplat was timed at "2.01 BTDC" as marked on the flywheel. I set the MZ-B at 2.2mm BTDC, as suggested in the instructions. Any thoughts on the matter?

Keithuu

[cubfan1968]

Are you sure you're BTDC not ATDC. I had the same result until I found my screw up.

Rod Whitman
1972 Six Day (Rider)
1972 Six Day (Project)

[Keithuu]

Rod;
Pretty sure I did it right - found TDC rotating the flywheel clockwise, reset the dial indicator, and backed it up (counter-clockwise) 2.2 mm. Took a "few" tries to get the rotor seated while maintaining the setting but it eventually worked out.

Unless I hear a better idea, I think I'll soften the timing to around 2.1 mm BTDC (I think that's the factory setting) and see if that has a positive effect. I left the bike at my cottage so I won't be able to conduct the experiment for a week or two. Sigh!!

Keithuu

[Knute]

Hey Keith,

I believe the instructions just give a general guideline for any 250.  We run 2.5-2.6mm on our race bike.  Also, the '74 manual says 2.55mm and the '77 manual says 2.5-2.6mm.  I'm not sure this will help with the starting issue but it should run better.

Kent

[rd400pi]

Keithuu,
  My 74 250 w/MZB literally starts on the first kick.  It has a Mikuni as well which, might skew the data a bit.  Good luck.

  Mike H.
  POG Tulsa Branch

[Keithuu]

Before I mess with the timing, I've been advised to try an Iridium or other "precious metal" plug. Apparently a standard plug has too much resistance to allow the nice fat spark it needs to light the motor at low kick over speeds with the MZ-B. The finer electrode (logically) ought to help the situation a lot. I'll report later.

Keithuu