Topic: CB 400f Advancer Springs

[Traviscsd]

Ive been working on my CB400f for about 6 months now and she has come a long way from being in non-running "barn find" condition to now.  The bike actually runs pretty well, pulls through the gears nicely but I have been having a little trouble dialing in the ignition. The bike definitely loses power on the top end and through my timing light I can see its not really advancing as far as it should. I figured out I wasn't tuning for full advance because it was advancing slightly at idle due to loose advancer springs.

I tried to tighten them up by cutting and re-bending like some have had success with but the darn thing slipped out of my pliers and shot across the garage.  It maybe shot into an alternate dimension or something, because I cannot for the life of me find it.  Seems no one state side makes a comparable spring for these bikes?  I did some research and bought some springs from Mcmastercarr.  I put these (https://www.mcmaster.com/94135K239/)  on the bike and they work OK.  No advance at idle but basically full advance at 2k.  I will probably try to get the next step up in wire size, but does anyone have experience with this?  Any recommendations?

The bike runs like a bat out of hell at full advance now...

[scottly]

As long as the advance is returning to the F mark at idle, reaching full advance at 2000 RPM instead of 2400 RPM shouldn't be a problem; after all, a 400 doesn't make any real power until much higher revs.

[Traviscsd]

I took it for a short ride again today and it seems to stumble for a bit around 2k rpm coming out of 1st.  Maybe its not as happy now for casual riding /coming off low rpm? Would that be pinging? It seemed to get better as the bike warmed up more.

I got slightly heavier springs in the mail so i will try those when they come in and see if I can get a more gradual advance.  Anyone tried mixing and matching springs?  I read a thread about using two different weight springs to give you a more dynamic advance, since each spring has a linear rate of resistance.  Makes sense in my head.  Probably not going to make a difference to my nearly 45 year old bike, but I want to pretend like its a finely tuned piece of machinery.  Also learning something new is most of the fun.

[scottly]

Mixing/matching springs to tailor the advance curve was common practice, back when cars had distributors.