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Discussion Starter · #1 ·
The front cylinder on this bike was dropping outand sometimes it wouldn't start at all. I had the carburetors rebuilt and the plugs and plug caps replaced. (There never has been a spark problem here that we can see).
I had the carburetors rebuilt. Wow! I never knew this bike was so fast. Apparently it has never been running at full power all the time I've owned it. When the carburetors were rebuilt it was discovered that the front cylinder carburetor diaphragm was torn and apparently that cylinder was running rich for a long time.
That's the history. Now for the mystery. The machine runs smooth and great at all speeds and idles perfectly when the engine is warm. The problem is on a cold start. The front cylinder is "lazy". Usually the back cylinder will fire right off but the front cylinder won't start firing for 30 seconds or more. Once the front cylinder kicks in everything is great.

The current theory is that there are carbon deposits in the front cylinder or on its valves that are creating a problem until the cylinder is warm. These deposits having been created from the bad carb running rich for a long time.
Since the machine runs so well when it's warm we are assuming there is no fuel pump problem or fuel delivery problem. I replaced the fuel filter just in case. I've run fuel system cleaner through a couple of tanks of gas (chemtool) hoping it would help but it hasn't.

Does anybody have any idea why the front cylinder won't fire right away when the bike is cold. By the way I've also got the hotter plugs in this bike which made a big difference in how it started years ago.

I was about to give up on the old girl but it's in mint shape; and now it runs really fast. However I can't reliably ride it anywhere and let it cool off lest it be difficult to start and get back home. The problem does seem to be getting a little worse and now it's hard to get rear cylinder to fire easily all the time. Again once the machine is warm all is well.
Thanks for your consideration!
Just an old guy with an old motorcycle. AKA Old John
 

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Discussion Starter · #3 ·
Lazy cylinder/ replace wires

Dave thanks so much for your reply. I'll give that a try as soon as I can find some new wires. So I didn't reply sooner I've been away. All the best!
 
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