jetting

[Ruckass]

I have a quick question. I have put a few mods on my Ruckus and am about to jet the carb. If I can get some response from others who have jetted, I could save myself some time trying out various jet sizes.
I have installed a Kitaco CDI, a K$N Filter kit, and a new Battlecooter Variator kit with the 5.5 weights is about to go on tomorrow. What size jet would be recomended. I'm thinking a 90. Feedback?

Ruckass

[chanito]

I would recommend to shim the needle first, get confortable and then try jetting, so you can really feel any difference

[Ruckass]

You have to shim the needle as well as jet? Or can I just jet the carb? Also, any ideas what size jet?

Ruckass

[milw]

putting the shim in is lots easier than the jet; a 100 was definitely too rich for mine with mod level similar to yours. I decided to back down to 90 and try with and without shim... riding to work tomorrow (Thurs), can post results then.

[Dandy Dan]

I would definately shim and jet the carb. Just jetting it won't likely run that great. I opened my airbox up all the way and added a high flow filter and all i did was change the jet to a 95. Mine runs great up to 25mph but then its too rich. The result is a slower top speed. It depends whether your mods change the airflow evenly across all rpms or have a bigger effect at a high/low rpm.

I scratched my airbox cover up in a crash so i ordered a new one. I'm not going to open it up again until i have the time to do it right.

I've never shimmed a needle before but i'm guessing the best way to do it would be to find what size jet runs the best at higher speeds. (Its ok if it runs crappy to 30mph if it sings above that). That'll tell you what size jet you need. Then raise or lower the needle (can one lower it? I doubt you'll need to) so that it runs nice at lower speeds. I'm guessin you'll need an 80 or 85 with a decent amount of shimming. I don't know how much difference your filter kit makes but i don't think you'll need to go 90 if you shim it right.

Does everyone understand how shimming works???
For those that don't here's a quick explanation. (No garentees that i'm right, this is just how i think it works)

Think of your main jet as a funnel. The jet size would be the size of the hole at the bottom of the funnel. Carbs have a needle that sticks into the funnel/hole to block some of the flow. It would run way too rich if it was wide open off the line.

As your rpms increase the needle slowly draws out of the hole leaving it more and more wide open until at top speed the needle isn't interfering and the only restriction on gas flow is the size of the jet hole.

If you open up the airbox you increase the airflow unproportionally so that it makes a bigger difference at lower rpms. If you try to get it running nicely you may mistakenly (as i did) just keep increasing the jet size until it runs nice off the line. But then as the rpms climb and the needle stops blocking part of the hole you get too much gas and now your running rich. The solution is to 'shim' the needle. This means you add a washer of some sort around the neck of the needle (i think, remember i haven't done it) with the goal of raising the needle so it blocks less of the fuel. The result is more fuel flow at lower rpms but the same flow at higher rpms.

With all that said battlescooter.com has a much more detailed explaination including pictures of how everything works. If you're confused go check it out. (battlescooter.com -> ' tech' -> 'intake/ignition')

Happy Jetting,
Dan

[Ruckass]

Thanks for all the input on the carb jetting, this has definitely enlightened me. There was some specs on the shim dimensions somewhere on the site with the diameter of the hole the diameter of the washer and thickness. Does anyone know where this info is hiding?

Ruckass

[Dandy Dan]

look under 'stock modifications' and then click on 'rejetted, now it feels like i'm running hot'. Should be what you're looking for. Also there's some shim sizing info on battlescooter.com

[chanito]

I like shimming to start with, just becouse by shimming you affect the whole range of rpm, however just going to a bigger jet will mostly afect the top rpm range.
Then when you are satisfied, try going to a bigger jet if you feel you need it, the best shims are some small washers that are supose to be use with pop rivets, i found them at some places where they do body work or you can make your own out of sheet metal, just cut asmall piece, drill a 1/8 hole and grind it till it fits in the hole at the end of the diaphragm, the best tool to turn the needle holder is one of those screwdriver that you can change the tips, if you remove the tip it turns into a nice 1/4 socket
thin enoght to fit in the hole and have the six sides need to turn the holder ;D ;D

[Ruckass]

Thanks Mil, Chanito, Dan. I'm all done the jetting.
I finally finished my mods and took her for a test drive.She PUUUURRRRRS!!

I searched in a few hardware stores for the right sized washer but finally had to go into electronics shops to find a washer small enuff and even it needed to be sanded down. I got a 5mm washer and its actually a .5mm in width. It seated quite nicely in the indent and the needle went in nicely too. I used a 90 jet. Took it for a spin and although the sound of the air being sucked in by the new filter was disturbing, it ran really well. I got it up to 60km and no problems. I am going to put the seat and floor tray on and take it down to a flat road and do some 0-30mph speed tests.

Thanks again everyone. I wouldnt have been able to do it with out ya'll.

(Smilin') Ruckass

[Ruckass]

Well having run it around for a few days, I'm finding I'm not getting the extra speed I thought I would. I've got to 60 but I was getting to 60 (kmh) before the mods. I have a CDI, a new variator with a few different roller weights and a K&N air filter kit. I've tried swapping around with various weights, no go. I've oiled the filters, nadda. I'm gonna tape the intake hose next. Any other ideas?

I have more take off speed and uphill power, just no top end extra speed.

Ruckass

[Dandy Dan]

shorten the spacer

[chanito]

Hopefully, tomorrow i will post some pictures showing how to shorten the variator spacer and grind the nose of the outer face of the variator.
I did not like the idea of bypassing the rev limiter becouse 8k is high enough so i make shure the variator shoot the belt far out enough to use the whole range, by the way to mail the windscreen to Vancouver via UPS will be about ten dollar and shoul be there in less than 10 days, email me if you are interested, mi email is in my profile.

[Ruckass]

Success! Finally getting higher speeds. I taped up my filter and the ride got worse. So I untaped it and Gavin and I stepped down the jetting to an 85. I took it for a spin with the seat and floor plate off and got to about 44+mph no probs! I went back and put the gear back on and it still went well over 40mph. But not quite as high. I realize how much wind resistance plays in this equation. When I was sitting low (no seat) it really flew. I'm contemplating lowering my seat now.

Gavin and I went out for a spin tonight and although I am slightly faster with my mods, we are close. However the tuck position makes a big difference.

I have to say every dollar we have spent on our scoots has been money well spent. Thanks Battlescooter (store and site). And thanks to all you guys and girls who have helped with the advise!

Ruckass

[Dandy Dan]

Great to hear you're getting it figured out. I'm running a 95 and it's definately too rich. I do have a higher flowing filter and the temperature here in Canada is about 0 degrees C. (32 Far?). The plug is totally black and its running crappy. About 34mph. Once i have a bit of time i'm hoping to get things sorted out.

Anyways...what i was wondering is if you've shortened the variator spacer at all yet? If not you could probably see 42mph with one if you getting 40 without. That's getting pretty respectable (for a 50cc 4 stroke).

[Vishnuk]

I'm running a shimmed 95 jet and my plug is chocolate brown. Temps 80F / 27C. A 90 jet doesn't run worth a damn in my scoot neither. Anyone know what could be going on?

[abe]

You could be too rich also.

You can do the tape test to see if you are rich or lean.
Remember to apply the tape so it only restricts the volume of air
not the flow.