1964 CB72

toastyhamster · Post by **toastyhamster** » Wed Mar 03, 2010 1:20 pm

It runs!

New floats sorted the overflow problem, and swapping bowls cured the leaky gasket problem.

Struggles to start as the right hand side only fires after the left hand side has been running for a while, so need to check float height etc on that carb. Not had it running long enough to start messing about with idle speed (screws fully out at the moment) - what is the recommended idle speed? Didn't seem happy under 2k but that will improve I hope as it heats up.

Not happy with the throttle cable, one side of the pair is a bit sticky, no matter which carb it goes to. New cable as well :-(

toastyhamster · Post by **toastyhamster** » Fri Mar 12, 2010 9:54 am

Started it up again today and it ran a lot better:

http://www.flickr.com/photos/39665805@N ... 501687588/

Right hand side doesn't like running under 1500rpm but hopefully one of my keyster pilot jets will sort that.

A few bolts to tighten and split pins to attach and it's good to go.

teazer · Post by **teazer** » Fri Mar 12, 2010 11:36 am

That is one fine looking motorcycle. Nicely done.

High revs on one side can be from a number of things, so start with the basics. Pop the air filters and intake tubes off and see/feel if the two choke plates are working properly and are both fully opening and fully closing.

Next, check to see if both throttle slides are rising together and to see that they are both closing together. That sticky cable could be a routing issue . Try rerouting the forked ends to the carbs slightly and see if that improves things.

Then try to see if both slides are as closed or if one is hanging higher than the other. It may be that the slide is hanging up on the throttle stop screw or on a burr in the carb.

If that was not teh issue, I would suspect the jetting and/or the flanges. Those carbs are easily distorted and bowed by overtightening the two nuts. I would prefer to use Honda jets. Keysters are typically not good.

Have you made sure the mounting flanges are dead flat and so are the tufnol/phenolic resin insulators? it is not uncommon for them to be bowed. The fix is easy. Rub them on a piece of wet and dry on a dead flat surface with wd40 as a lube.

You are on the home stretch now and it always takes longer to finish that last 5%. Bikes are like most projects. The last 5% takes 50% of the time to finish things off and take care of the details.

That's what the term "fettling" comes in. When castings are cast, the flash has to be removed nd the casting fettled or finished off. That clean up can take almost as long as it took to pour the casting but it is useless without it.

toastyhamster · Post by **toastyhamster** » Fri Mar 12, 2010 12:54 pm

It's low running that's the problem, it revs fine but when idling at about 1500 the right hand side cuts out and the bike stalls. Have checked pilot jet already and it's clear, so it can't hurt to try the keyster bits.

teazer · Post by **teazer** » Fri Mar 12, 2010 2:50 pm

Er.. That's why I listed the things I had there - they all apply to poor idle conditions and erratic running at the bottom end. Open the taps and the issues I mention have less impact.

The right side cutting out could be ignition related but it sure sounds like a fuel issue on the pilot circuit.

When you had the carbs apart did you check ach circuit on both crabs and compare them? I use a can of carb cleaner and spray it through one passageway and then repeat on the other carb for comparison. I would try all the pilot passageways for air, fuel and mix on both.

Carb synch, air leaks and slides hanging all have more effect on the bottom end that higher up. IMHO it is important to be 100% sure about the fundamentals first. LM has a good checklist too.

If it's not the carbs, it might be a low compression on that side. Have you checked that?

Spargett · Post by **Spargett** » Fri Mar 12, 2010 2:55 pm

Teazer has good input. If there's one hard lesson I learned with my carbs, it's "give 'em a fraction of a millimeter and they'll take a mile".

As un-fun as it sounds, it might be a good idea to pull em off and go through them again making sure everything is PERFECT. Especially for piece of mind. No sense in troubleshooting step "R" through "Z" if there's issues remaining in steps "B" or "D".

toastyhamster · Post by **toastyhamster** » Sat Mar 13, 2010 4:07 am

Both cars have been ultrasonically cleaned so I was hoping to avoid carb problems with this restoration. I've got both 2 spare original sets of jets and 2 sets of keyster kits, so hopefully swapping the pilots will fix it.

edit: Needed a neutral switch and saw that David Silver has genuine pilot jets in stock, so hopefully that will sort it.