Ignition Advance

[pacomotorstuff]

Hi all,
Posted something similar on the VRRA website but seeing as a lot of you don't go there, well, here ya go...
Was ****ing around with one of my 175 Honda twins today, checking the ignition and the advance, blah blah blah.
Anyway, my understanding of the ignition advance on the bike is that it is retarded to help starting and then goes to full advance as the revs go up.
The bike pulls better through the gears than any 175 I remember from the '60's, but I'm always looking for that little bit more and wondered if I should try to get full ignition advance in as soon as I can - maybe pull off one of the advance springs or something? BTW, the advance unit is working per Honda - not sticking at all.
No indication of the engine backfiring or anything like that - when the bike is warm, it starts halfway through the first kick.
I'm also running a high output coil with the plug gap at .035, still using points, don't know if either have any bearing or not.
This topic is probably applicable to a lot of the early bikes we work on and maybe some newer ones as well.
Thoughts please?
Pat

 

[teazer]

We run ours at full advance all the way up the revs by pinning the "cam" and throwing away springs and weights. And we use more advance than stock at higher compression ratio to boot.

You probably won't need the full 45 degrees of advance that a CR72 needs let alone the 60 or so that an RC164 reportedly used, but somewhere around 40 degrees or maybe a touch more - or less might be in your future.

Depends on the shape of the combustion chamber, squish effect and fuel you use. I like high compression and fast burning fuel and whatever the dyno says I need in terms of total advance. Compression on those motors is typically low, combustion chamber shape terrible, and squish non existent. But a race motor is all sorts of different.

 

[pacomotorstuff]

Richard,
You are the bomb like always, sharing your info with the less intelligent.
There is a lot - and I mean "a lot" of info in your response, which folks should read, re-read and ruminate on.
I'm running a little more compression than stock, cam pretty much stock, will try to pin the advance and see what happens.
Your comment on "fast burning fuel" is a good one.
I was running 94 pump gas, just so I could get ethanol-free fuel. I've dumped a load of 91 octane in today, seems to run fine.
Just by way of historical info, the uber-high revving Honda GP bikes of the '60's (5 cylinder 125 cc. that revved 22 grand through the gears) ran low octane fuel - probably 89 RON - because the "ignition event" was so short.
Maybe the next time, I'll try 89 octane.
I'll let you know what happens re: advance.
Thanks again,
Pat

 

[teazer]

BTW,
Our CL175 motor made a poofteenth more power on 89 than it did on C12 or even 93 octane street gas, but the difference was so small that I just played safe and used more octane than it needed just to play safe.

 

[Sonreir]

I'm running higher initial advance on my 360 due to the domed pistons and high duration cam, but my total advance remains the same. I bent the tabs that stop the weights in order to shorten the advance, and then dialed in my static timing to 22° BTDC. She occasionally kicks back on start, but the revs come on quickly when you give her a bit of throttle.