I have always been a 2 stroke guy and have decided to retire my LT250r. I have just bought an 03 Z400 that already has a Yoshi setup. I would like to help it some more with some mods and was just wondering what mods will help the best. Also what jetting do the Yoshi guys have on theirs?

Thanks
Cp

 

Well like the 2 strokes a bigger carb is one thing.......aftermarket cams...cams have the effect on a 4 stroke like reeds do a 2 stroke if ya ask me.... polished ports, higher rev-limiter...bigger bore, longer stroke for more displacement.....those are all options

later
Superstar

 

It depends on where you live (the elevation where you live is going to be different than other peoples elevations where they live) so you usually need to just need to go trial and error mode, if you know what I mean, to find out which jet size is going to be best FOR YOU.

 

Drop in a K&N and a pro flow adaptor, lose the lid, rejet it accordingly.
Add one or both cams. Hot Cams are nice, other options as well. FCR carb is a great addition. DRZ base gasket, will up compression to 12:1, for $10.00.
Thats what I would do.....

 

An inexpensive alternative to the FCR carb is the 42mm BSR carb used on the Predator or DS650. this is the route I went (for experimentation) and it far exceeded my expectations. The power throughout the powerband is incredible. I was able to go to a 15t front with no problem. Beating Rappys and Preds now in drags (stock of course). With all other mods before the carb, I could just keep up with a stock rappy, but got beat by the Pred. Now, it's all over. [img]i/expressions/face-icon-small-smile.gif[/img]

Total cost for the 42mm BSR was about $250. Basically swapped all parts from the stocker to the BSR. Choke, Jets, bowl, needle, needle valve, etc. Had to fasion the carb to engine boot, but that was simple and .50 worth of parts. For airbox to carb boot I used a 400ex boot. Could have used stock but I wanted to use something else because it did need a little stretching, and now I can put it back to stock when I sell it if I like the new Z450 when it comes out. [img]i/expressions/face-icon-small-smile.gif[/img]

 

Thats a good suggestion. I tried a DS 650 carb, its works great. It has a little less throttle response, and like all vacuum operated carbs, it can slam the slide shut from hard landings. Just depends on what you are doing.
Good bang for the buck.

 

Just trim the slide spring and that solves a lot of those problems. I noticed no degredation anywhere after the mods (including chopping about 5 lengths of the spring).

The CV carbs are nice because they provide smooth even power compared to CR slide carbs which hit hard. Sometimes you don't want that for hooking up. But it sure feels cool. I think I read somewhere that CV carbs are the closes you'll get to FI with a carb as far as smoothness. So, either instant response or smooth response... either way a CV isn't as bad as some writers make you think. [img]i/expressions/face-icon-small-wink.gif[/img]

 

I cut at least that much off the spring on my stocker and off the DS carb. Big jumps, hard through the woops, g-outs, it cuts out. When my woman rides it, no problems.
I didn't say they were bad. I said good bang for the buck, and it depends on what you are doing. They use it for emissions. It can be ran very lean.

 

I'm so proud of my KFX!Took it out last weekend (LaDunes) for the first time with all my mods and was pulling madd hole shots on Rappys that had rejet extended swingarm paddle tires and hmf exhaust and 400ex's with paddle tires pipe and rejet filter etc.
We draged 100 yard strip, I would pull the hole shot and pull on them up to about 65 yards then they would pass me most of the times.
Got spanked by the Banshee's on alcohol though lol...

 

KGB,

Sorry, I didn't mean to imply you said it was a bad mod. I guess I drive more like your GF... more XC than MX. Frozen rivers, ditches, trails, gravel pits. Haven't had the cutout problem you describe. But, I could see how that might happen.

I know on mine I pretty much swapped all parts from my stock BSR36 including the needle valve (for better fuel flow since the stock BSR42 is tiny, and needs a fuel pump), bowl, needle jet, etc.. pretty much everything that would swap, I swapped. Don't know if that makes a difference with anything.

I was running into problems draining the bowl on WOT runs so I first swapped the bowls (36 is a lot bigger). Helped some. Then the needle jet and splash guard (36mm was longer and got deeper into the bigger bowl).

Helped, but still had problems on long WOT runs, especially on Ice. That's when I checked out the needle valve and the 42mm was tiny, almost as small as a 155 main jet. The 36's valve was huge (and had a micro-filter on it, extra protection and another place to look for clogs). After swapping that out, no problems at all.