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To rejet or not to rejet?

  • Thread starter Thread starter zblip2
  • Start date Start date
It sucks!
I went to a 4-1 and pods and it was an ordeal, but now it's all good. Thanks to the help of the forum here.
 
I wouldn't buy that. If you want to "rejet" a stock engine I'd start by raising the needles a tad. If you want a jet kit, buy from dynajet.
 
If Factory Pro makes a kit for your bike, I'd suggest going with it over the Dynojet kits. I've had much better luck and experiences with FP kits over the DJ kits.

With that said, jetting isn't fun. It's time consuming and a lot of it is just hoping you guess correctly. It's not like most other mods where you can ask someone else what they've done and then just mirror that and have good luck. For example, if you know someone else has put different sprockets on their bike and liked the acceleration gain, you can just ask what they have and do the same thing.

However, I heard something once and to me, it is 100% correct. Jetting is one part science, one part skill, and one part wizardry.

Like I said, you can't ask someone what they have done and automatically think that you can do the same and have it work. What jetting settings work for one person might not work for you at all. Jetting is BIKE SPECIFIC. That's not model specific, it's BIKE specific. Meaning that each individual bike will jet slightly differently than another bike.

Now, of course, asking what someone else has done can get you to a good starting point for your bike, but it will still require some work on your own part.

I have my Ninja 250 jetted. It's got a FP Stage III kit, UNI Pods, and a Kerker straight through race pipe. I can honestly tell you that I spent probably about 50 hours of my own time jetting the bike. Granted, I was going for perfection, not just "close enough." I got it correct after about 15 hours...then the weather changed and the jetting was off again.

So, if you're up to the task, jetting can and will generally make your bike run a bit better...but if you're not up to spending a good amount of time tearing the carbs out of the bike, tearing the carbs apart, putting the carbs back together, putting them back in the bike, then doing it all over again and again until you've got it right, then I would suggest you pass on it.
 
You seem to talk of wisdom. Ok, unless some one comes uo with really good arguments in favor of jetting, I'll just follow your nadvice!
:)Thanks!
 
look at your spark pugs. the engine has distinct signs when it need something
.

white and blistered give it more gas. black and slick take gas away from it.
 
On an 850 with the stock exhaust and airbox, rejetting is not necessary.

Make sure the airbox is sealed properly, all eight of the carb boots are new, and the o-rings on the carb/engine boots are new, and the valve clearances are correct. The carbs must be clean with fresh o-rings, and the air filter must be very lightly oiled and sealed where it mounts to the airbox.

Then, set the idle mixture screws to about 2.5 to 3 turns out.

Next, set float height precisely -- there's a range in the manual, and set it at the lower end of the range or 0.5mm lower.


If you do not have the stock intake system or exhaust, then I'm sorry -- you missed out on one of the sweetest-running engines ever.

If you have made or are contemplating modifications to the intake and/or exhaust, then perhaps you might share the nature of those modifications so the GSR Hive Mind can offer relevant advice.
 
bwringer said:
On an 850 with the stock exhaust and airbox, rejetting is not necessary.
Click to expand...

I am sorry but it is not as cut and dry as that.

jetting that works in Indiana won't necessarily work as well in Florida or Colorado. gains all around can be found in slight tweaks one way or the other.
I switched the carbs on my 1100E to a set from the exact same year and model bike but they came from Canada and the jets and needles and air bleeds are different on Canadian bikes (no emission restrictions) and it made a very noticeable difference. much better running and starting.

on my 1000G going up 1 size on the pilot jets made a great improvement in cold starting and idle quality.

heck installing a power commander usb on my SV (fuel injected) and doing a little tweaking to the fuel mapping at idle and low speed got rid of a very annoying surge and its tendency to cough and die when pulling away from a stop.
 
If the bike is stock, maintained and tuned well, the bike should run fine.
You would rarely need to change the jet needle position. If mostly used in higher elevations, maybe 2.5 leaner mains? The mixture screw should be able to fine tune most pilot circuit issues if needed.
 
focus frenzy said:
I am sorry but it is not as cut and dry as that.

jetting that works in Indiana won't necessarily work as well in Florida or Colorado. gains all around can be found in slight tweaks one way or the other.
Click to expand...

Agreed. You'll note that I mentioned setting the float height a bit lower to slightly richen the idle/mid transition, and setting the idle mixture screw a bit richer as well. With this particular motorcycle with stock intake and exhaust, adjustments are needed, not new brass.

Indiana has more temperature variation, but it's just as humid as Florida and only slightly higher. Our highest point is a nondescript hill only 1,257 feet high, and most of the state is between 300 and 600 feet.

The highest I've been on my GS850 is Mt. Mitchell, 6,684 feet (highest point east of the Mississippi), and it ran just fine.

Might need to twiddle some more if I ever get out west to higher elevations. A while back I had the idea of using the high-elevation expansion of a bag of Fritos to open a door in the airbox... :D
 
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