Motorcycle Repair: cold start, engine vacuum, peak battery

Question
I have a Yamaha 750 three cly special l only have a problem on cold starts like at 50 f or so is there something l can do about that or is that just the way they are.

Answer
Hi Rick,

These bikes were a bit cranky even when new
but it may be because of the lean
fuel mixtures they came fitted for.

If you pop the limiter cap off the
pilot screws and give them all a half turn
out or counterclockwise it might help.
The pilot screws should be near the
engine side of the carbs on the side
of the carbs.

When starting, the plunger style chokes
need the throttle closed to work
efficiently. They need the engine vacuum
to pull the fuel in.
If you open the throttles it looses this
vacuum and defeats the choke's operation.

Also, your valve clearance needs
to be correct to aid starting
so cylinder pressures are right.

Yamaha ignitions of this era require
peak battery power or they do not
perform well.

A worn or partly discharged battery
or just dirty or loose
battery cables can hinder the power
to the ignition and starter.

It may require a small battery tender
or charger on it if you do only short
trips.

Getting the carbs in sync with vacuum sticks
may also help a bit.

Good bikes though, I use to setup new ones
back in the seventies/eighties.

Good luck!
Wayne S.
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