Acts like governed

When I run the 77 KZ750 twin hard....about 5K at 90 the it quits pulling and backfires a bit....sounds like its backfiring out the front? I'm mechanically inclined, but have now knowledge of bikes other thatn the little fooling I've done since becoming a new owner. If I let off and get back on it it tops out at 5 grand again. Does it sound like the carbs need synced???? If not does anything else come to mind?

Thanks in advance,

It's probably running out of fuel, take the petcock off the tank and clean the junk from around the screen.

Thanks for the reminder Steel. I was so excited about finally getting it on the road I forgot the screen was missing when I reassembled it. :whistle: :silly: :blush:

If the screen is missing then you may need to disassemble the petcock to clean it.

In your original post are you saying that your bike does 90 mph at 5k rpm?

Yes. I'm in top gear and its really revving. Should the tach not read that low.....I have no idea. I never had a bike or ridden one other than an old Enduro 100 as a teen. Might be a little closer to 6K.....Do you think I may have a problem..I did install an aftermarket tach cable..The old one was leaking.... When you talk about the screen are you referring to the small tube next to the brass/copper tube or is there supposed to physically be a screen for filtering rouoghly the size of a nickel in the base....I'll check the diagram. Sorry if revisiting old issues or asking dumb questions...Newbie trying to learn from some experts

Thanks again steel:)

Post edited by: got12narow, at: 2006/06/30 09:17

The 750 twin petcock has a little sediment bowl at the bottom of the petcock that catches the water and with no screen it also catches all the trash. When it fills up it blocks the fuel flow.
You can unscrew it from the bottom to clean it out.

KZ750 twin with stock 16/38 gearing turns ~4400 rpm at 65 mph, ~6000 rpm at at 90 mph, and a top speed (on a good day and tuned) of ~110 mph.

Free advice
There is a grease fitting on the top right side of the swingarm, it's behind the right side frame tube and below the battery box, grease it. It's often neglected and the swingarm pivot bushing goes bad and has to be replaced.

You also might remove the points cover (little round cover towards the front of right side engine cover) and make sure the timing advancer (points cam that openes and closes the points) turns freely, rotate it clockwise and it should return to it's original position when you let go.
If it don't, then you need to remove the points plate and the small bolt in the end of the crank, pull the advancer off, and disassemble to clean and lube it.

Those numbers look a little closer. Thanks for the advice. I replaced the point and condenser. I'll check the advancer too. Thanks...Tried timing it by the shop manual, but it still isn't quite right. The petcock has no screen. I'll pick one up, and thought a handfull of in-line filters might be a good idea also???? I'll get to greasing this evening.

Thanks for the help!