'72 CB175 has mind of its own

I have a 72 CB175 with the twin carbs, and it is having a problem that
after I've warmed it up and am ready to ride it, when I give it some
throttle, the engine takes off up to 5-6000 rpm and gradually comes
down. If it doesn't sound like its gradually coming down I have to
shut it off.

It was doing this at the end of last summer, but I rebuilt the carbs
with kits, and the problem seemed to be more intermittent after that.
Now I fire it up and the problem is back big time. Strange thing I've
just realized is that it only happens after it's warmed up. I adjusted
the valves last summer too, and checked the timing..

Help!

 

Sounds like the carb boots may be leaking. Try spraying a little WD-40
or similar around the rubber carb boots while the engine is idling. If
the engine picks up speed when you do that, then the carb boots are
leaking and need to be replaced.

HTH,

JS

 

This is classic symptom of dirty pilot jets ... Have seen it a good
many times. Take them out, MAKE SURE they're clean, then synch your
carbs again and set idle speed. That should do it.

Hoyt

 

Hi;
Check the springs on the Centrifugal advance behind the points breaker
plate ,as over time they either stretch or ware grooves in either end so
that when the weights are at full advance they have trouble returning to the
closed position .Thats why it takes time for it to idle down .
How do you go getting parts for your bike as I'm trying to do up one of
these at the moment and just getting a top end gasket kit is hard enough ?
Cheers ,
neadles

 

Hi Neadles. Thanks for the tip.. I remember that I have checked this
in the past, and the springs felt very good.. but I will definately
give it another check.. as the springs are still old.

Luckily my bike doesn't/didn't need many parts (as far as I know). I
was able to buy a spare key from a guy online, and was able to buy
some carb rebuild kits at a local motorcycle wrecking yard (they were
too expensive though).

http://www.ranchomotorcycle.com/

there is the website. They are very close to my house. Maybe you can
email them.

I didnt find an online store where I could buy many parts from the
same store, I had to search for individual parts.

Good luck!