jetting and needle

[tbrooks]

I didn't get much response on my rebuild thread about jetting (thanks tho tfaith), and wanted a little more input and knowledge. I've got lid removed, uni filter with outerwears cover, full fmf, premix 32:1, and Ken just bored it to 66.5, no porting or mods, just didn't have the cash My break-in period will mostly be around 3200 feet, but there maybe a trip or 2 to a nearby park at 2000 feet and a friends property (actually close to the park) which varies from 4000 to 5000. Elevations change pretty rapidly around here so I know I'll have to be careful with my jetting. I can drive (in a car) 15 min south and be at 1000 or ten minutes north and be at 5000. Oh and I didn't mention temps in summer time normally run in the 80's.

I'm still learning a lot of this stuff, what I have learned comes from u guys. Most of what I've seen on here and fmf site shows pipe should be 260, filter and lid off +3, and should add 1 more for the premix, so that's sitting at 300. But because of my elevation I thought I should drop back to 290 and go 300 (maybe?) at the park. Tfaith and myusername (who I got parts from) suggested 300, which a little rich on the main won't hurt since I'm gonna be in break-in period anyway.

I was wondering more about the needle as well, I poked around a little and couldn't find much on how to come up with its setting. I think usually with my set-up you guys call for middle clip, but wasn't sure if the elevation would make a difference. Of course it would only be too rich so I guess that's not a big deal. Just thirsty for knowledge and want to make sure I do it right

 

[Wifesblaster]

You will probably be at 260-270. We run a 270 main in the summer time in one of our bikes with the same mods.

Not sure how much elevation will change it because I have never ridden anywhere above sea level. You can either tune the needle by feel (what I do) or you can do 1/4 and 1/2 throttle plug chops.

This is all assuming you are running a stock carb.

 

[blasterkid1998]

here in missouri im running at about 1000 feet with a 280 main jet with full fmf ,light porting (just cleaned up casting flaws) ,filter and no air box lid. running a tad on the rich side.

 

[Wifesblaster]

here in missouri im running at about 1000 feet with a 280 main jet with full fmf ,light porting (just cleaned up casting flaws) ,filter and no air box lid. running a tad on the rich side.

That's exactly how one of our bikes is. Some people will say 310-320 main for those mods. I don't understand how some people can run those jets with those mods.

 

[jus_me]

If you are willing and capable which I am sure you are, start from the back door and work in.. Start 300 and go from there.. Bring some plugs and do some chops.. I would say 280- (290 maybe) but only a plug chop can tell.. As far as the needle , stock needle middle clip??? Like Wifesblaster said I do mine by feel.. But you can plug chop at any throttle position/fuel circuit..

Best to start bigger and work in from there..

 

[Blaaster]

With your mods here at sea level and temps around freezing I would use #320 main.

But in your case you need much smaller jets.

I have not been able to remember the ratios for altitude and temp, but I do remember Awk08 posting something a while age, it may pay to PM him.

 

[tbrooks]

Thanks guys. It is a stock carb. I won't be tuning the needle by feel, because I don't have the experience as you do. So when I'm ready I'll plug chop it as well. I read an article on here about elevation affects on jetting. There was a formula and some charts, and basically what I took from it was about every 2000 feet needs down one. You guys have given me a much wider range than I expected, looks like I'll need a lot of plugs lol

 

[MercMenace]

I live at 5200 feet I run 28:1, lid off, Uni filter. I am at a 270 at home here which is just a touch rich. I go up to 7200 feet to ride and only drop to a 260. That keep me at just a touch to the rich as well. I do plan on +4 advance and a DMC/FMF pipe/silencer. I am speculating a 290/280 home/mountain Jet. won't know till i add parts. avg. temps i ride in are 80 degrees.


EDIT! Stock Needle Middle clip.

 

[MercMenace]

There was a formula and some charts, and basically what I took from it was about every 2000 feet needs down one. You guys have given me a much wider range than I expected, looks like I'll need a lot of plugs lol

That i pretty much spot on for what I have tested. -1 Jet size per 2000ft in elevation.

I get a lot of elevation changes too, while I am riding in the mountains. Mostly mine are anywhere from 500 - 1000 ft. Not sure how your elevation changes are while you are riding but Jet to the rich side and you should be good to go.

It was a lot of fun finding a suitable spot to chop at the camp site.

 

[Blaaster]

Although not a common practice one can emulate jet sizes by changing the pre mix oil ratio.

I prefer not to go into detail as it can cause confusion as all jetting recommended settings on BF are based on the common 32:1 ratio.

If you need to investigate more, I am happy for you to PM.

 

[tbrooks]

Thanks guys. Merc its good to here from someone at elevation. Did you plug chop your needle? Of course if you don't have a aftermarket pipe yet, that may change things. I was thinking I can do that about halfway through my break-in without hurting anything. Its gonna be hard for me to plug chop as well, but luckily there's a good straight on the highway right by me and we don't see the cops around here much. Even if I did they prob wouldn't say much.

Blaaster I appreciate the offer, but I think its best for me to keep it simple. I would rather change jets than mix!

 

[tbrooks]

Oh another thing, the straight I'm gonna chop on is inclined, I assume I should go uphill for my run to work the engine harder?

 

[MercMenace]

Only reason I changed oil mix was peace of mind. keep us posted on your findings.

 

[Blaaster]

Plug chop runs can be done in the lower gears, but the engine must be made to pull hard, inclines and applying the brakes can help.

 

[tbrooks]

I'm think I can get through all the gears. If it was a car it wouldn't be a problem, I can hit 100 and slow down for the curve at the top of the hill, but quads I'm not too used to. I haven't rode a dirt bike in, oh about 20 years and this is my first 2 stroke quad, so I have to find the limits and get a comfort zone lol

 

[MercMenace]

Good bike to recut you teeth with. Quick but not insane. Hopefully you have hydros.