cwis said:
Hi all,
I've been doing a lot of reading about ignition, compression, etc. I think my Boyer fitted Bitza is set to 31* at 5000 RPM or thereabouts. If I have high compression pistons this is a little too advanced, isn't it? (4C cams, original type airbox and filter, Jota pipes wiv der big collector).
How can I easily tell which pistons I have fitted? Poke about down a spark plug hole? I don't really want to get the pipettes out....
Secondly, If I'm at 5000 odd rpm on a wideish open throttle and I back off the bike accelerates before slowing - too rich or lean? (128 mains).
It doesn't really want to pull through the midrange - higher revs are just fine. Ohh yes....
Best regards,
Chris
Hi Chris
it is not the rpm that is relevant, it is how much the throttle is open.
throttle closed to make 1/4 max is the slide cutaway height, idle jet, idle mixture screw, and for starting, the choke plunger
from 1/4 throttle to maybe 3/4 throttle, is the float height base setting, the needle, and the needle jet. Most of your riding is probably on the needle jet and the needle. If you are somewhere between 1/4 throttle and 3/4 throttle, and the engine speeds up as you roll OFF the throttle, the needle/needle jet combination is lean. Assuming you are using a K1 needle with an AB 265 needle jet, you want to richen your setting, by raising the needle, which means moving the needle clip down on the needle to one of the lower notches.
the main jet has some effect on mid range, but mostly is wide open throttle, 3/4 throttle and up, where the needle has cleared out of the needle jet and all that is metering the fuel is the main jet. However, float height and the float jet also have some effect on available fuel. Make sure your float height is correct, then if on full throttle, when you roll off the throttle the bike accelerates when it comes back onto the needle, you are lean on the main jet, and need to go larger. I wouldn't go much larger than 130 for starters.
but, to give accurate advice, we need to knbow what is in the carbs now - float height, float jet, idle jet, slide, needle jet and needle, main jet. Also, are your choke plunger tips in good shapoe, and seating solidly?
for ignition timing, stock on a triple is full advance of 32 degrees at roughly 2,750 rpm or so, no timing changes after that on a stock ignition. For really high compression you could pull the timing back to maybe 26 to 28 degrees at full advance, but I doubt it would make much difference. The bigger issue is at what rpm the Boyer is reaching its 32 degrees? Should be by at least 3,000 rpm, if not sooner.
also, carb setup and timing timing depend on valve clearances beiing correct, no intake vacuum leaks, etc. carb setup also depends on slide heights being equal and carbs vacuum synched......
for detailed answers, post more detailed info on your base setup.
Paul LeClair