Fuel Mixture Question - Shim or Jet for this set-up?

[folky15]

This site has a ton of info about jetting/shimming and it's all been very helpful! I just bought my bike a few weeks ago and here are some plans I have for it:

-Competition Werkes GP slip-on exhaust
-Removing the Snorkel
-K&N air filter

I was planning on shimming the needles (with 2 or 3 washers) but I need to know:
With the 3 mods above, would I need to jet? or would I be alright just w/ the shimming adjustment?

[EthioKnight]

Rejetting the carbs (preferably by a professional with access to a dyno) is always going to provide the best, all round performance gain, but since you're only putting a slip-on on and making reasonably minor intake mods, I'd recommend shimming. It's hella cheap and very effective. As to the amount of washers, that you're going to determine for yourself through trial and error, though the generic 2 washers worked perfectly for me. If you are indeed going to go ahead and shim, save yourself the headache of stripped screws and get yourself JIS screw bits and an offset screwdriver. Much luck

[xSean13]

Originally Posted by EthioKnight

Rejetting the carbs (preferably by a professional with access to a dyno) is always going to provide the best, all round performance gain, but since you're only putting a slip-on on and making reasonably minor intake mods, I'd recommend shimming. It's hella cheap and very effective. As to the amount of washers, that you're going to determine for yourself through trial and error, though the generic 2 washers worked perfectly for me. If you are indeed going to go ahead and shim, save yourself the headache of stripped screws and get yourself JIS screw bits and an offset screwdriver. Much luck

What he said about stripping screws :P

I stripped the top right screw on the right carb (a pain to get to)...so I then took a dremel and made a shallow slice down the middle, allowing a flat head to get it out.

[choneofakind]

The oem main jets are Keihin size 98. You'll want to pick up a set of Keihin size 100 mains.

First, make all the desired changes to your intake/exhaust that you want. Here's what you'll have to do to get the jetting right:

• Test ride it as it is. Take note of only how the bike pulls at WOT and high rpm's
• Install size 100 mains. Do same testing you just did. Stick with the main jets that pulled the hardest. Pull the caps off your idle mix screws while the carbs are off the bike.
• 1 washer on each needle. Test ride, paying attention to mid-range and gradual roll-on's/roll-off everywhere from 3k-10kish, not WOT
• 2 washers on each needle. Same test.
• 3 washers on each needle. Same test.
• 4 washers on each needle. Same test.
• 5 washers on each needle. Same test. Stick with the number of washers that was the smoothest throughout the entire throttle/rpm range.
• Adjust mix screws by blipping the throttle lightly. If the rpm's hang above idle and then go to idle, turn the mix screws out 1/4 turn. If the rpm's drop below idle and come back up to idle, turn the mix screws in 1/4 turn.
• sync the carbs and put it all back together

That should get it running nicely.

notes for jetting:
Factory Pro tuning guidelines
faq.ninja250.org guidlines
DIY how to shim the needles
Carburetor photos for reference
If you strip screws on either the bowls or the caps, they can be replaced with M4x16 hex key screws. Those make carb work les stressful.

[folky15]

Originally Posted by choneofakind

That should get it running nicely.

Chris, you are the man! Thanks for your post

If possible, I'd like to avoid the jetting / carb syncing process (due to finances and lack of access to a proper garage).

Is shimming likely to get me a properly running bike? (maybe not quite optimized, but close to it?)

Maybe I'll wait awhile before I go with a K&N, and that would hopefully lessen my need for changing out the jets.

(btw - I've already picked up some JIC bits here: RJR Tools and a racheting offset screwdriver from Amazon

[choneofakind]

You might be able to get by on just the 98 mains and shimmed needles. It will likely be okay, but from my experience, it pulls better with 1 size larger main jet. As long as it's not giving lean symptoms at WOT and high rpm's, you should be close enough to ride it.

Every bike is different, and it's going to take test riding to be sure that it is right. You might be just fine on the 98 mains.

[edxmon]

Originally Posted by EthioKnight

Rejetting the carbs (preferably by a professional with access to a dyno) is always going to provide the best, all round performance gain, but since you're only putting a slip-on on and making reasonably minor intake mods, I'd recommend shimming. It's hella cheap and very effective. As to the amount of washers, that you're going to determine for yourself through trial and error, though the generic 2 washers worked perfectly for me. If you are indeed going to go ahead and shim, save yourself the headache of stripped screws and get yourself JIS screw bits and an offset screwdriver. Much luck

get the offset screwdriver for sure. I replaced my carb cap screws with socket head cap screws, so I could take them off with an allen wrench/bit (M4 x .7 x16) from home depot, got 8 of them for like 3 bucks

[Racer x]

Regarding the screws. Cutting a slot to use a flat blade screwdriver is a great way to get the screws out. But if you reuse the screw it has a risk of breaking. I was doing a Lot of tuning when I had stock carbs and wore out the screws .

I went to Home Depo and bought Allen bolts that replace the screws. It cost about ten bucks.

[edxmon]

Originally Posted by Racer x

Regarding the screws. Cutting a slot to use a flat blade screwdriver is a great way to get the screws out. But if you reuse the screw it has a risk of breaking. I was doing a Lot of tuning when I had stock carbs and wore out the screws .

I went to Home Depo and bought Allen bolts that replace the screws. It cost about ten bucks.

holy nuts, $10? What were they made of?
Also, OP: home depot had the offset screwdriver cheaper than amazon, check it out

[choneofakind]

Stainless Steel. Don't want them to rust.

That sounds about right. For me, (16) Stainless Steel M4x16 hex key screws were about $10 total.

[Felipe the Ant]

Put 2 washers and see how it feels around town, it should make an improvement. If you don't get any surging or bogging around the midrange you're good there. To determine if you need to rejet get on a road where you can do roughly a 50-70mph pull at WOT. If you can't make it to 70 you definitely need new jets, otherwise you're in the ok range. If it surges forward after you start closing the throttle I recommend a step larger on the main jets.

Also you might want to richen up your idle mix a little bit, it's usually pretty lean from the factory and you'll get rid of the jerk when you open the throttle at low rpm. You have to take the carbs out to do this though, so it's up to you. If you want to do everything at once I recommend Area P's special jet kit, it's a Dynojet kit with larger jets in case you take the airbox out and comes with 8 hex screws and a drill bit for drilling the caps over the idle mix screws.

[Racer x]

When you drill off the aluminum caps that cover the idle screws. BE CAREFUL. Put something on the drill bit so it does not hit the screws. I have see drill bits hit the screw and drive the idle screw down so tight it damaged the carb.

[Felipe the Ant]

Originally Posted by Racer x

When you drill off the aluminum caps that cover the idle screws. BE CAREFUL. Put something on the drill bit so it does not hit the screws. I have see drill bits hit the screw and drive the idle screw down so tight it damaged the carb.

This or stop and check frequently. When I did it I didn't drill all the way through, just enough where it broke through in the center and then I stuck a small screwdriver in and pried the cap out

[Racer x]

That is the way it should done.

[folky15]

Originally Posted by choneofakind

The oem main jets are Keihin size 98. You'll want to pick up a set of Keihin size 100 mains.

First, make all the desired changes to your intake/exhaust that you want. Here's what you'll have to do to get the jetting right:

• Test ride it as it is. Take note of only how the bike pulls at WOT and high rpm's
• Install size 100 mains. Do same testing you just did. Stick with the main jets that pulled the hardest. Pull the caps off your idle mix screws while the carbs are off the bike.
• 1 washer on each needle. Test ride, paying attention to mid-range and gradual roll-on's/roll-off everywhere from 3k-10kish, not WOT
• 2 washers on each needle. Same test.
• 3 washers on each needle. Same test.
• 4 washers on each needle. Same test.
• 5 washers on each needle. Same test. Stick with the number of washers that was the smoothest throughout the entire throttle/rpm range.
• Adjust mix screws by blipping the throttle lightly. If the rpm's hang above idle and then go to idle, turn the mix screws out 1/4 turn. If the rpm's drop below idle and come back up to idle, turn the mix screws in 1/4 turn.
• sync the carbs and put it all back together

notes for jetting:
Factory Pro tuning guidelines
faq.ninja250.org guidlines
DIY how to shim the needles
Carburetor photos for reference
If you strip screws on either the bowls or the caps, they can be replaced with M4x16 hex key screws. Those make carb work les stressful.

This post is so complete and well-organized that it should prob be added to the wiki or some kind of sticky, eh?

[choneofakind]

nah. That topic is covered enough in the faq.ninja250.org and a few other places here. Just link those instead.

[Felipe the Ant]

lol 5 washers?

[choneofakind]

yepp. that's what faq.ninja250 suggests. they suggest testing up to 5 washers and sticking with the one that worked best. I'm on 3 and that's still surging if I just cruise at high rpms, so I'm moving up to 4 eventually.

[Felipe the Ant]

Just get a real jet kit. 5 washers is ridiculous

[folky15]

I would think reasonably it goes.....:

Start w/ 2 washers and go up to 3 if 2 wasn't enough.
And if 3 wasn't enough, you'd go up to 4 washers.
And in the rare case that 4 wasn't enough, then you'd either go to 5 or get a jet kit.

[choneofakind]

Originally Posted by Felipe the Ant

Just get a real jet kit. 5 washers is ridiculous

I never had to use 5. It was ridiculously rich when I tested it. But I can tell you that for my setup, 3 is not quuiiiiiiiite enough. I just haven't gotten around to going back to 4 because my break ended before I was able to go back to 4 for comparison. I thought 3 was right initially, so I wanted to do some more lengthy testing and then ran out of time.

Jet kits also cost $60+. I spend $12 on a pair of jets. There's not that much improvement in the needles that come in a jet kit except when I'm in a really really gradual roll-on at 3k and there's a weird overlap between the idle mix and the needle height.