Not firing on left cylinder CB72

Sooty521 · Post by **Sooty521** » Mon Jul 04, 2016 10:47 am

I have finally finished the restoration of my CB72 Cafe Racer, and bought I had sorted the problem I was having with misfiring by replacing the condenser.

However, I am now having a problem when trying to start her as the left side just will not fire!

The plug gets flooded with petrol, even to the point where unburnt fuel drips to the floor.

No problems on the right cylinder, and when I clean and swap the plugs, both cylinders fire but the left still misfires at low revs. All is fine over 6000 rpm, but it makes slower riding very difficult!

Tickover is fine when both cylinders are firing, but the left exhaust and header do not seem to heat up quickly or to the temp of the right?

I have spoken to several "experts" who say it is just a high revving bike and I need to keep the revs up, as well as they were temperamental bikes and always difficult to start and run.

I cannot work out if it is a fueling or ignition problem, but it is only on the left cylinder and is driving me mad!

Any advice would be much appreciated. Should I be using different plugs from those recommended?

Thanks in advance

Chris

SMBH · Post by **SMBH** » Mon Jul 04, 2016 2:25 pm

Sorry Sooy521 I have to disagree with your so called experts you write -

I have spoken to several "experts" who say it is just a high revving bike and I need to keep the revs up, as well as they were temperamental bikes and always difficult to start and run.

My 1964 CB77 is so easy to start and is not temperamental runs just lovely at all revs, I do have electronic ignition fitted but im sure the CB72 will run just as well on the STD setup if SETUP right.

Not running right on one cylinder can be a lot of things just few - PLUGS/HT LEAD/PLUG CAP/COIL/WIRING TO COILS/POINTS/ and lots more im sure you will get a lot of replys as to what it may be but they are not and never were temperamental bikes I had a CB72 and CB77 back in the early 60s and they were great.

Sooty521 · Post by **Sooty521** » Mon Jul 04, 2016 2:41 pm

Thanks SMBH. I thought that might be the case!

Have got new coils, plugs, points and leads, as has been a 3 year ground up rebuild.

Will keep trying different things, as may be a fueling or carb balance issue as well.

I am tempted by electronic ignition, what set up have you got?

Thanks again

mike in idaho · Post by **mike in idaho** » Mon Jul 04, 2016 3:04 pm

The stock ignition system, in good condition, is more than adequate for clean running. Did you properly clean the preservative grease from the new points when installing them? It would be a good idea to go through the carbs first, before throwing money at a different ignition setup.

Sooty521 · Post by **Sooty521** » Mon Jul 04, 2016 3:14 pm

Cheers Mike.

Points are all clean and got good spark at cap. Just seems to be the plug getting fouled/wet, so will look at carbs again.

I'm not the best at setting them up though!

SMBH · Post by **SMBH** » Mon Jul 04, 2016 6:25 pm

Sooty521 wrote:Thanks SMBH. I thought that might be the case!

Have got new coils, plugs, points and leads, as has been a 3 year ground up rebuild.

Will keep trying different things, as may be a fueling or carb balance issue as well.

I am tempted by electronic ignition, what set up have you got?

Thanks again

This is the one I have and very happy with it http://www.charlies-place.com/product-c ... ignitions/

ramwing7 · Post by **ramwing7** » Wed Mar 08, 2017 12:30 pm

So, how did you resolve this?
I'm having the same problem and having little success resolving it.
Thanks.