I was trying to connect the rattle with the surging idle as they seem to come together after a few minutes of running. But it definitely might not be a problem; just looking for any clue to continue diagnosis on this beast. I did the valve adjustment and pretty much every valve was .001 UNDER spec, except the IN valve on 4. DIdn't see any noticeable problems but it is hard to see the chain and the valve springs. Compression went up 20PSI on all cylinders except 4 (170, 160, 170, 175) I will ride it tomorrow and see if the acceleration is smoother or still lurching.

 

I’m not sure if anyone mentioned this about your idle problem but generally when idle is not steady and takes a bit to settle down after throttled, there is a vacuum leak somewhere. Most common is carbs not completely seated in the boots. There also are sometimes nipples in the sync connectors that need to be capped off. Spray some WD40 around the boots when running. If the idle goes up you have a leak.

just re-read your first post. If the idle is way higher when choked, then it is most definitely a vacuum leak. Leaks cause the engine to run lean. Choke adds fuel so the fuel air ratio is compensated resulting in higher idle.

Check that your carbs are seated fully in the boots. This can be tricky. I use a block of wood across the carb throats and a mallet to make sure they are fully home. Make sure all the clamps are loose when you do this.

BTW, these engines run like a watch when set up properly. I’ve owned Harley’s and a number of British long stroke singles and twins. There is no comparison. Once you get there you will be surprised in a good way.

 

The boots are new. The carb rack from the bike has been completely gone though, cleaned, blown out, rejetted. I bought a used carb rack from e-bay from an '89 hurricane and repaired a fuel leak in fuel rails to help me diagnose. The current state of the bike is that it is running pretty well with that second carb rack. I think the vacuum leak theory is probably correct but it must be from a strange place in the original carbs that I am unable to find. The only problem I see with the bike now is some flutter when off the gas and back on the gas at mid engine speed (3-4k). It definitely seems usable now. By the way, I also adjusted the valves and got a 20PSI bump in compression. I am still not convinced the charging system or battery is where it needs to be; seems to me that the battery should hold a charge longer than it does, even though the local auto parts store checked the battery and gave it a thumbs up.
Everyone on this forum have been awesome with providing help.

 

not suggesting crack boots...the carbs may not be seated in the boots all the way. It’s a coomon problem when the carbs are taken off and put back. Check for nipples on the sync ports. One of them may be open.

Vacuum leak will act act exactly as you have explained your problem. Spray some WD40 and see if it changes.

 

Thanks. That is good to know. At some point I will probably have to try my re-built carb again to see if remounting it makes it work fine. The other one seems to be fine at the moment. It might also explain the intermittent behavior if it was 'marginally' loose in the boot and hence could shift.