BIKE NOT STAYING RUNNING

IM LOOKING AT A 1985 XJ700 MAXIM UT STARTS UP BUT BATTERIES ARE DEAD NOW BUT IT WOULD ONLY STAY STARTED UP FOR 10 TO 15 MINS THEN DIE WOULD THIS BE A ALTERNATOR OR CARB PROBLEM?

 

Sure. Or a "seriously needs valve adjustment" problem.

DO A COMPRESSION TEST.

If you don't really know what that means or entails, please say so.

 

YEA IM A LITTLE LOST ON THAT ONE HOW WOULD I GO ABOUT THAT?

 

You need a compression tester ($25 or less at virtually any auto parts or Sears) with a 14mm* "end" on it, a spark plug socket and a fully charged battery (I usually bring my own.)

Locate and disconnect (unplug) the TCI (Ignition "black box") unit;

Remove all 4 spark plugs;

Hold or tape the throttles wide open (if carbs installed.)

Then hook up the compression gauge to a cylinder, and spin the motor over until the gauge stops climbing. (Usually about 6~8 "cranks.")

Record reading.

Repeat for the other 3 cylinders. You want to see readings within about 10% (14psi) of each other, and between about 120psi and 150psi for the 650/750.

*NOTE: ***The 550s and I believe, the "X" models use a 12mm plug; all of the "big bikes" 650/750/900 use a 14mm plug. I'm not sure what size the 700's use.***

 

ok thanks this will be very usefull in my near future, i just hope i can use both these bikes to make one finding a 750 or a good 650 engine is bad here this 700 is the closet i found.

 

be patient and keep looking

 

CRAZY qUESTION I KNOW BUT WILL A 650 BOTTOM END FIT A 750 HEAD JUST A QUESTION IF IT IS DO ABLE SOMEONE BROUGHT IT UP TO ME AND I HAVE NO CLUE

 

Only the right ones and there's really no advantage, the castings (when applicable) are the same.

There are YICS motors, and earlier, non-YICS motors. The heads are not interchangeable, the YICS cross-passage is cast into the cylinder bank.

All of the 750s sold here had YICS motors.

The 650 Maxim had a non-YICS motor for two model years, then it got a YICS motor too. The USA-market 650 Seca was a one-year bike and it had a non-YICS motor.

 

ok thanks for the great info:

btw i found a 82 seca xj750 complete bike no title running great compression engine with only 4700 mile been stored for most its life but will start up im going to look at it tomorrow so i can finally have my bike back.