Been out on the NSR over the last two days and can't help but feel the mid range should be a little crisper. Top end (8000 - 11500) feels great, but there's very little midrange.

This was the plug colour yesterday - the bike was used by BIKE magazine for their 500 mile ride to the Spanish GP, hence the quite large build up of deposits (oil pump was set WAY too rich for one thing):


I properly adjusted the pump, and dropped the needles to the bottom clip. Top end felt the same, mid range improved but the bottom was terrible - kept stalling as I tried to pull away!

Plug looked like this after today's ride:


Not much difference really. My question is, should I go down another size on the main jet, or is that colour about perfect?
_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball



Last edited by Dave Ett on Sun Apr 11, 2010 11:13 am; edited 1 time in total

What would going down a size on sj do? I just figure raising the needle may have richened up the slow running circuit. And as you said you are happy with the mid-hi range.

Just wondering, you are normally answering these types of questions for people like me. Why don't you trust your own judgment? I don't think I have ever read a post where you have given anything but excellent advise.

Andy

Bandit7

bandit_7 wrote:What would going down a size on sj do? I just figure raising the needle may have richened up the slow running circuit. And as you said you are happy with the mid-hi range.

I think the problem was a goof up by me: I forgot to reconnect the TPS! Doh! Proof, were it needed, that we all make mistakes. Also proof the TPS really does make a difference!

bandit_7 wrote:
Just wondering, you are normally answering these types of questions for people like me. Why don't you trust your own judgment? I don't think I have ever read a post where you have given anything but excellent advise.

Wow, cheers! I do trust my judgement, but thought this post might serve two purposes: Firstly to verify what others thought of the plug colour and secondly for those who have no idea what colour it ought to look like, to see for themselves and perhaps learn a little.

I have chosen to drop a size, raise the needles to second notch from top and reconnected the TPS! We'll see if I was right or not later...

(Just for refernce, I am running the standard SJ - a 38 - and don't have anything smaller, just 40 and 42 as per the HRC kit. Also have the PJ's installed and not blanked.)
_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

i thought jetting altered the engine's response to throttle openings, regardless of revs? Altering the slow jet will only change the engine's response at throttle openings from closed to about 1/3 open for example, whether your at 2000 or 12000 revs.

I find my bike's mid throttle shove feels weaker than 1/4 throttle - like there's a drop in torque as i roll on whilst exiting a corner. I crack it open and there's a strong push, then as i roll on further it seems to get a touch weaker (though its still picking up speed quickly) and as i get above 2/3rds open it starts shoving much harder again. This happens regardless of revs too as i said before.

Dunno why yours would feel weak below 8000rpm but i dont think its jetting's fault because you can be at 8k whilst using 1/4 throttle or WOT - do all throttle openings feel noticeably guttless below 8k?
_________________
After years of moaning about immigrants now i am one...

Revs are not directly linked to jetting of course, but there is a general correlation since you can't achieve high RPM in a higher gear without the throttle being opened all the way.

Being flat slides also muddies the mix, as you can open the throttle all the way and thus the air intake aperture, but if the air velocity is too low because the engine isn't spinning fast enough, the fuel will not be sucked from the float bowl and you'll bog down.

Once you get the MJ setting right, you have to fine tune to make the rest of the rev range / throttle openings as good as they can be with the best top end.
_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

Well it didn't go pop!

Top end (8-11500) is really good, mid range much better and bottom end restored.

Phew!

Now, dare I go another size down...
_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

Dave I find myself answering some of my own questions by typing them out sometimes. I'll get half a post started here and suddenly the answer pops into my head. So sometimes I type it out, think about it for a while, then read my post before submitting it. I'll discover that I work it out by reading my own threads a good portion of the time.

At least that way I sometimes save myself from getting a smart *** response from you, so it's always worth a shot. LOL

Heh heh, always happy to help!

Today I'm gonna drop the needles again, see if I can improve the midrange to match the nice top end.

How disappointed am I that I can't get to the dyno day and show my once 8hp motor off?










(I'm going to the Spanish MotoGP, so there is a good reason! )
_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

Well, much better again. Just a patch that is still not as good as I want it. Maybe time to go for a C needle...
_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball