Runs well, plugs foul....

Many Mikuni carbs have that spring seat or a disc which holds the needle in place. I cannot remember what is there in my Mk2 Amals, but I have never had a problem with a needle moving independently of the slide. If the needle rises as much as one notch, it is the difference between sluggish and good. You have probably had the jetting miles too rich

The effect of the balance pipe probably changes according to how restrictive the mufflers are. Personally, I would not have it because the exhaust system functions on resonance. To me it looks like something designed to make the bike a better commuter, rather than to gain a performance advantage. - Probably a noise thing ?

acotrel said:

Probably a noise thing ?

Click to expand...

https://www.accessnorton.com/NortonCommando/doug-hele-and-the-balance-pipe.24927/

More than 30 year ago , I made a balance pipe with a valve for testing purposes ,
open or closed with a choke lever on the handlebar .
But at that time , I had only my senses to rely on .
Now I have better tools : decibel meter , gas analiser , AF meter .. but no balanced pipes ..

The 750 SFC Laverda has a cross in the exhaust system under the motor. It means the back pressure is probably less because both mufflers work at all times. My feeling is that the exhaust system resonates and the cross-over makes little difference. With a 2 into 1 pipe, the tail pipe probably resonates at twice the frequency of one header pipe, so it's length should probably be a multiple of that of a header pipe, or the same length. The diameter of the tail pipe is critical. Any increase in back pressure takes power off the top of the rev range. But with a 2 into 1 pipe, noise can become a problem. I've seen photos of the commonly used 2 into 1 pipes - most appear to use the same diameter for the header pipes and the tail pipe. With my 2 into 1 pipe, the I tail pipe gives twice the cross-sectional area of a header pipe.

ludwig said:

More than 30 year ago , I made a balance pipe with a valve for testing purposes ,
open or closed with a choke lever on the handlebar .
But at that time , I had only my senses to rely on .
Now I have better tools : decibel meter , gas analiser , AF meter .. but no balanced pipes ..

Click to expand...

What was your conclusion at the time? I’m guessing it was not positive, otherwise you’d now have a balance pipe ?