vac line off #2 carb going to vac advance blocked with a bearing inside the line.

**DiverRay** · 10-11-2025, 03:44 PM

It could be the advance unit had the diaphragm fail and that was "the fix". I would test the advance with a vacuum pump before going much farther. If it's bad, you will need to try and locate a good used one, as they are NLA as far as I know. If it checks out good, it may have been "rattling" because of being connected to the carb holder port and not the carb port.

**LoftCol** · 10-12-2025, 10:01 AM

I found similar on mine. I believe the carbs had been changed at some time for a set that didn't have a vacuum advance connection. My work around , with the help of a mate of mine, was to connect the vacuum advance to the balancing port on number two. I also fitted a small airline regulator that I adjusted gradually until I got it to run reasonably smoothly. There seems to be a dead spot up to 3000 revs, once past it no problems. I have managed to get a set of the correct carbs, which I will fit over winter.

**Eastcoaster** · 10-12-2025, 10:46 AM

Thanks Guys for pointing me in the right direction i have not worked on a bike in years and was helping this young gent out with his new find.
i did put the vacuum Gague on no vacuum opened up the cover I guess the PO never did the line was off the diaphragm I guess his solution was the bearing in the line reconnected held and worked fine. I cleaned and synced the carbs and a few other things. I think this lad was completely shocked at what these bikes can do he is thrilled with his find and I was probably more thrilled to help. Thanks guys for the sanity check

**LenB** · 10-12-2025, 11:53 AM

Does sound like a pooched vacuum advance. However I would also recommend checking the continuity of the pickup leads, a very common problem. Mine failed when the bike had warmed up enough to cause the insulation on the wires to stretch, pulling the fatigued wires apart. The ball bearing "fix" would probably give you power to a certain RPM past which that crazy advance curve wasn't there anymore and it would run like crap, but it wouldn't die.

**speedlimit85** · 10-13-2025, 06:15 AM

I did this as a roadside repair. Pinch the vacuum line with a zip tie can make the bike run right. Then repair the wires at home instead of the side of the road.