1200 JOTA said:
Timing is standard (as recommended) with a base angle set at 10 degrees (have tried 8 degrees) and a gradual curve from 12@2000 to 25@3000 and then up to 32 or 35 max.
Base advance isn't something that you fiddle around with to tune the engine. It isn't the idle advance setting as some people think. What it does is tell the ignition unit where the pickups are set relative to TDC. The ignition unit needs to know that bit of information as a reference point to apply the correct advance settings that are programmed into the map. It can vary between bikes, but once set for a particular installation, it never changes.
To find out what your base advance should be set to, use the following procedure.:
1. Download and save your ignition map.
2. Set all advance settings in the Ignitech map to zero, including base advance. You'll then have a flat advance curve of zero across all revs.
3. Fit a degree wheel and pointer, and zero to TDC using a piston stop in the spark plug hole. Re-fit the spark plug when done.
4. Connect a strobe light, start the engine and rev it a bit above idle to get a stable reading with the strobe. The reading on the degree wheel will usually be somewhere between 0? and 10? BTDC. That's where your pickups are relative to TDC, and it's the base advance figure you need to set in your Ignitech program.
5. Re-load your advance map and then set the base advance to the figure you determined above. That's it, you're done.
Once set, base advance never changes (unless you move the pickup base plate, in which case you'll have to do it all again). You can play around all you like with the advance settings in the map, but don't mess with the base advance or it'll throw the whole advance map out of phase with the crank position.
I like a base advance as close to TDC as I can get without going after TDC (Ignitech won't accept a negative base advance). Between 0? and 4? is my preference. If it strobes at anything higher, then I'll move the pickup plate closer to TDC and re-strobe. The reason for that is because the engine cranks on the starter at low revs (before the advance map comes into effect) so it actually starts on whatever the base advance is. A small advance setting makes starting easier and gives the starter gear (starter motor, sprag clutch, etc.) a much easier time. The starter cranks the engine at around 200-400 rpm, depending on compression and the state of your battery. So set your first advance point on the map to 10? at around 500 revs. Once the engine fires, and revs pick up, the programmed advance map comes into effect and it'll settle into an idle at 10? advance.
PS: I've attached the advance map from my Jota below. It has Jota spec engine with HC pistons, 4C cams, big bore exhaust, Mikuni carbs, so may be similar to your engine. Max advance of 30? was determined on a dyno for max power at WOT. As you can see, my base advance is 3?. Yours will be whatever you measure it at.
