calum wrote: Now that I can finally ride my bike, I've noticed a pretty bad flat spot at about 5500-7500 rpm (very little power and not running smoothly). I started the diagnosis here: kzrider.com/forum/3-carburetor/613898-81...arb-tuning-questions
Since then I've done a few more tests and am pretty sure I need some new secondary main jets. I'll order some 130's and see if it gets better or worse (have the stock 125's in now). It should be an improvement as it is probably running a bit leaner due to the exhaust.
Getting back to this now. I was reading this thread as it seemed like a similar problem: kzrider.com/forum/4-electrical/614135-82...td-upper-rpm-breakup
I realised that I had just got the plugs specified in the manual and not even thought about resistance (only just learnt that the R in BR8ES means resistance ). I had put new NGK caps on (5kOhm) and made sure that I used non-resistor wiring, but as I said, didn't give the plugs a second thought. Today I put in some B8ES plugs and goodbye stuttering
There is still a very slight stutter at about 6500rpm but it pulls out of it almost straight away. It gets a bit worse under more load (uphill) but it is nothing compared to before. The bike is more than rideable now
I set all the idle screws back to 2 1/4 turns out and it's idling well if running a bit lean (slight popping on deceleration). When I get bored I'll have a look at the idle screws and put in some larger secondary mains (just to see if that sorts out the slight stutter at 6500rpm).
Tried to sort out the flat spot yesterday. Had a talk to the neighbour and we figured if it was pulling fine above 7000rpm then the jetting must be OK and I just needed to shim the needle to make it a bit richer in the mid-range. I took the tank off and started pulling out the vacuum pistons. Number two was sticking quite badly so I cleaned it up, stuck them back in without changing the needles and went for a ride. Problem solved!
She's running pretty close to perfect now. It's still a bit lean but I only notice it under high load (uphill). If I open the choke up a bit it gets better so I either need to put in the 130 secondary mains I have lying around or put a shim under the needle. Not sure which, but I'm thinking the jets as it doesn't seem to get much better above 7000rpm.
Anyway, I won't be changing anything until the trip meter ticks over again (about 850km). I'm just going to put in a new set of plugs and ride. In a month or so I'll have a stock 750L exhaust and then I'll decide if I put in the jets or swap the exhausts. Until then I'll just chuck in some earplugs and enjoy the newfound power
So I made it about 300km before I started messing around again
I have shimmed the needles, that made a bit of difference, but it was still a bit rough until it got proper warmed up. Today I stuck the 130 secondary mains in and that seemed to sort things out a bit more. I tweeked the float height as well as it was a bit low. I did a dry adjustment (made sure the floats were all the same height when the needle valve was just closed) and I'll double check with the clear tube method tomorrow.
I have two questions for the experts out there
- When I open up the throttle it now pulls strongly through the previous flat spot. However, when it gets to about 7000rpm it noticeably smooths out and pulls away. I know this is about peak torque (7500rpm) but am wondering if it is normal that it gets a lot smoother? As I said, it still pulls decently under 7000, it just gets a lot smoother above that. Wondering if I need to raise the needles a bit more?
- Whenever I pull the plugs, number 3 is black. I figure it must be the idle circuit or the float level as everything else is the same as the other carbs. The idle screw is three turns out, half a turn more than the others. I tried turning it back in but it idles a lot worse. Number three is also the only one that I can properly set up using the idle drop method. The other idle screws don't seem to make a difference unless it's really lean (1 turn out) or really rich (4 turns out).
No Vacuum leaks and idle is steady at about 1000-1100rpm. Basically it's running fine but I'd like to know why the idle screws don't really make a difference and why number 3 is too rich.