Last year I rejetted for a delkevic slipon and k&n lunchbox. Made the bike alot more fun but lately have been feeling it could be better.
Getting popping on decel and while im pretty sure its a rich pop, I'm not certain. Also a slight hesitation on throttle roll on with a sensation of losing some pull at the higher end rpm.
This could all be in my head :cookoo: I don't really have anything to compare it to.
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ANYWAY! While the jetting matrix was helpful I'd like to hear what others are running.
Post your exhaust, air filter, jet sizes, needle shims, and air screw turns if you've changed those.
I've got 40/150 jets, 1 shim, 2 turns of the air screw. Delkevic shorty and KN lunchbox. Hope to hear from ya'll :thumb:
Stock exhaust [for now... there's plans for something in the future.]
Slip-in K@N lunch box air filter, no restrictor
#20 pilots, #60 mids, #140 mains.
2 turns out.
1 shim.
currently with this new model set-up it isn't set in stone. I couldn't find the 62.5 mid jets I wanted to use anywhere online I was buying from. and feared 65's where gonna be too large, probably just gonna turn down some drill rod to the #62.5 equivalent and ream a new hole. if I need more after that, ill just ream it off to #65
but that's what it currently is as it sits in the garage. final adjustments will be made after it goes VROOOM again.
jetting is always a funny one, so many variables. i've tuned a couple and it's crazy how much a hot or cold day can through out the tune or swapping one aftermarket can for another will do.
to summarise:
couple of things you really need to get done before playing with jetting is valve clearances, float height, clean air filter, carbs balanced, compression test doesn't hurt and make sure you're getting good spark. otherwise you're P***ing into the wind with it. learned that lesson.
my go to base tune on the gs for full system and K&N lunchbox is
pilot 40
main 150
needle raised one clip (or shimmed 1mm)
and 2.5 to 3 turns out on the air/mix screw
but thats a base tune, might even be the one from the jetting matrix. on one can i ran 150 with remus innovation (reflective core), another 152.5 with 8'' shorty viper (absorptive core) and on danmoto extreme gp (absorptive core) on 147.5 and all were tweaked each to suit, should have most of it documented in my build thread but i think the 152 was standard needle clip height, 2.5 turns out, 150 and 142 tunes were one clip raised and 2.5 to 3 turns out. all were with a k&n lunchbox and open and not additionally baffled exhausts
no two bikes are going to be exactly the same but it can help to get you in the right ballpark.
at the moment i'm on a dynojet kit with aggressively tapered needles so it's completely different tuning parameters, used mikuni jets though, runs brilliant once warm and it transformed my fuel economy vs just doing a basic rejet. need to tweak it for winter running in low and minus C temps unfortunately.
best thing you can do is set a day aside to tweak it little by little, taking notes, until you've got it dialled in, this method also allows you to jump back to completely different tunes for comparison. then swear at it the following day when it's not running quite as well :icon_lol: lots of trial and error unless you want to pay for dyno time. 150 main is a good place to start, take it out for full throttle thrash, pull the plugs and see how they are reading, drop a main size if it's fouling. remember it's all to do with throttle position and its relation to the active fuel circuit and overlap.
when it comes to finer tuning lean = crisp feeling, rich = bogging. you'll also make more power at top end with a slightly leaner main jet. a good technique is smell the exhaust fumes to see if it's smelling fuelly at idle.
based on what you've said, i'd get it warm and try turning out your air/mix screws by a 1/4 and see how it is, turn out more and repeat until it starts getting bad and turn it back in till it's optimal. a good reference point is that it should be right when the engine idles highest when adjusting the screws. see how it rides and if you have to go any further than 3 turns out it'll likely warrant lifting the needle and readjusting the screw to suit, if it then has problems higher up in the throttle range you'll have to drop or increase main jet size and start all over again. you'll probably need to change your main jet though, popping on decel can be lean or rich, if you've got a removable baffle you can fit/remove to change conditions slightly.
excuse the rambling but that's my general experiences with rejetting :icon_lol: but yeah cover the groundwork, research how the circuits overlap so you're not working blind and banging in random settings from the internet expecting a perfect tune or it'll never be right. thats my advice for anyone playing with jetting... but seriously cover the groundwork :icon_lol: :thumb: :cheers:
I think your jetting is probably very close if not a hair rich which is probably still good.
Popping on decel is not due to being rich, it's due to being lean. But that's not a problem. It's actually an indication that you have it tuned pretty close to right.
That hesitation may be a problem, who knows. Could be a tuning point. I can find a way to ride my bike where it will hesitate just a touch going from pilot to main, but I have to do it on purpose. Point is, there is a potential for a problem there. Most likely it's your lunchbox filter, turbulence, the lack of a velocity stack, etc. Go back to 125 main jet and the stock airbox and it will probably be fixed.
you could always buy a colour tune :), will tell you if its running lean or rich and they are pretty handy things :)
Quote from: ChironTL34 on October 19, 2017, 06:48:25 PM
Last year I rejetted for a delkevic slipon and k&n lunchbox. Made the bike alot more fun but lately have been feeling it could be better.
Getting popping on decel and while im pretty sure its a rich pop, I'm not certain. Also a slight hesitation on throttle roll on with a sensation of losing some pull at the higher end rpm.
This could all be in my head :cookoo: I don't really have anything to compare it to.
----------------------------------------------------------------------------------------------------------------------------------------------
ANYWAY! While the jetting matrix was helpful I'd like to hear what others are running.
Post your exhaust, air filter, jet sizes, needle shims, and air screw turns if you've changed those.
I've got 40/150 jets, 1 shim, 2 turns of the air screw. Delkevic shorty and KN lunchbox. Hope to hear from ya'll :thumb:
2 Turns = you're probably rich on something else. Like where is your float ? I'll bet its high.
I have 20/132.5/1 washer/3 turns on a 02 carb fitted onto a 95,
Cool.
Buddha.
Quote from: iamhiding on October 25, 2017, 05:01:35 AM
couple of things you really need to get done before playing with jetting is valve clearances, float height, clean air filter, carbs balanced, compression test doesn't hurt and make sure you're getting good spark. otherwise you're P***ing into the wind with it. learned that lesson.
:bowdown: :bowdown:
Man this was really good advice! Thank god I read it in time!
I suppose that here is a good place B!t!ch about the jets, right?
I am struggling for months to get my gs pilot right... and I am still being bullied by these carbs.
So... if anybody has an idea I will be grateful.
I am running a stock pilot jet ( #20 )
My bike idles ok... HOWEVER my issue is when I starts to move (1k-2k rpm)! The bike feels weak (hesitating).
I believe that my pilot is to thin... I put 3 and a half turns on the mixture screw ... and I still get backfiring on the carb.
I already cleaned everything... 3 times or so.... (valve clearances and timing are checked)
My line of thinking makes sense to you?... the problem is the pilot?
Strange thing is.. why with the stock needle (second hand bike.. so I am not 100% sure) I cannot get proper adjusting?