I thought it would be a pretty simple process to get this jetted right. I thought wrong. The machine ran perfectly before I tried the mods. Bone stock engine, air filter, and exhaust setup. I tried so many jetting combinations and it seems like once I get one part right the rest gets fouled up. The original idle screw settings were 2.5/2.75, but I turned them out with the filter since the machine wouldn't idle once it warmed up. 3/3.25 fixed that problem nicely.

Here's an interesting note: I checked the fuel level in both carbs, and the level is 3mm ABOVE the float bowl mating surface. The owner's manual (page 7-8) says this level should be 3-4mm BELOW the mating surface. The float height (page 7-7 in manual) was correct at around 13mm the last time I checked it, though. Anyone else checked the fuel level before?

Here are the specifics:
Altitude: about 50-100 ft.
Exhaust: stock
Engine Mods: None
Idle screw settings: 3/3.25
Filter setup: Pro Design Pro Flow FOAM with no airbox lid


Jet/needle setting combos tried: (in all cases, smaller jet on left side carb, the one with the throttle and choke attachments)
155/160, clip 3rd groove from top
160/165, clip 3rd groove from top
165/170, clip 3rd groove from top
- For all of these, the power is fine everywhere but at the highest 1/4 to 1/8th throttle where it kind of makes a hollow almost bogging sound and doesn't rev like it did at 3/4 throttle. No sputtering or hesistation or backfiring or anything, just bogs at full throttle. Power seems less at 1/4/-3/4 than other combos I later tried but slightly better than stock.

185/190, clip 3rd groove from top
- Awesome pull at full throttle. Pulls harder than I've ever felt that thing pull. Decelerating to 1/2 throttle from full gives short hesistation. Acceleration once it's revved a little or in lower gears (less load) is awesome. Acceleration in a high gear from low rev sputters bad, and once it gets started sputtering it won't stop until I lay off and let it rev up a little. No backfiring. Sputtering is very regular cadence and sustainable if I stay on the throttle. Once revs pick up, all is well.

185/190, clip 4th groove from top
-Same as 3rd clip, but sputtering at 1/4-3/4 under hard acceleration seems worse.

185/190, clip 2nd groove from top
-Sputters like crazy now. Runs poorly at full throttle now as well. I didn't think the needle position was supposed to affect full throttle operation?

180/185, clip 3rd groove from top
-Doesn't pull as hard at full throttle as 185/190 3rd groove. Also doesn't pull nearly as hard off the line in lower gears as the 185/190 3rd clip setup. Sputtering not as bad, though.


What the hell is up with these carbs? It's like I'm not allowed to have good full throttle power and good 1/4-3/4 throttle power at the same time. Going lower on the jets gets everything fine but full throttle, and going higher gets me my full throttle power and kills the rest. And moving the needles when I've got the full throttle power dialed in screws everything up. Man, I thought it was a simple "needles for 1/4-3/4 throttle adjustments, main jet for full throttle adjustments."

It does seem like my jetting needs to be much higher than what everyone else seems to be using, but the lower main jets kill the full throttle power. I haven't done a plug check since I wanted to get everything feeling right before I did the check. No sense in checking the accuracy of what I know is bad. I figured once everything felt right I'd do a check to be sure I was correct in my findings.

 

Hmmm. You should allways start by adjusting your float level, that effects everything but mostly 1/8 to 1/3 throttle and the tube method is the only way to do it IMO. I would also say to get a GYT-R jet kit but if not at least get some 25 pilot jets. The mains your using are huge for stock, I don't know what the heck to think about that. I'm at 170/175 and I think I'm a tad rich but that's with the GYT-R needles.

 

Airraptor,
Thanks for the ideas. I'll check the boots when I get back to the machine. I assumed they were fine since everything ran right before I tried the new setup, but it's worth a check. The very first combo I tried acted similar to the next few, so if they tore, it happened early on in my experimenting.
As far as the WOT test, the machine definitely accelerated when I went from full throttle to 7/8th for all combos but the 185/190. That's why I kept going up from 155/160 to 160/165 to 165/170. In all of those cases it felt better at 7/8 throttle than at full throttle. I checked to be sure the carbs opened fully with the throttle with every run. I didn't try making sure the slides moved up all the way. There's another area to check.

sixsixT,
I was confused when I checked the float level with the tube method since the level was 3mm above the bowl mating surface rather than 3mm below like the manual said it should be. When you checked yours, what did you find? The last time I checked the float height from the inside by comparing the float surface with the carb bowl mating surface, the measurement was correct. That's why I didn't understand how the tube measurement could be so far off. I assumed there was a misprint in the manual (something similar happened with my Prairie650 and it took many, many hours of time and a call to Kawi to find out the manual was wrong).
And by the way, is the GYTR jet kit just Dynojets or are they Mikuni parts?

 

mine needles are set where they were factory, with a 160/155 jets. mine is running great, but i'm going to adjust on the needles again to see if anything runs better then what it is right now. but mine also has the alba pipe.

 

do you have the spark arestor in?? airbox lid on???

put on a GYTR slip-on exhaust $200 and take the airbox lid off. 160/165 mains, needle in 3rd clip. worked great for me at your altitude.

 

FuorStroke the level is usually high from the factory I set them level to a mm above the mating surface.
The GYT-R kit is Mikuni with a more agressive tapper on the needle.

 

BlueLeader,
I've got a pipe on my other Raptor (which has been in pieces for months now). I never got that quad running right with the Pro Design filter and CT pipe/header, so I figured I'd just take the filter from that machine and throw it in my other one for some simple gains in HP without the ear shattering noise. Turns out I'm having the same type of problem with this quad with the stock exhaust as I had with the other quad and the CT exhaust. That one with 185/190s acted similar to this one with 160/165s. Runs fine everywhere and in every way (no stuttering or backfiring) but kind of goes "blaaaa" when going from 7/8 to full throttle and revs way better at 7/8.

sixsixT,
Did you read the numbers off the GYTR needles before you put them in? I don't need a whole kit since I already have all of the main jets. I should be able to get just the needles from someplace like Chaparral or something. Are the #25 pilot jets really necessary?

 

my opinion is that you are rich in both cases. 160/165 mains with a stock exhuast with spark arestor is too rich. Jet down or pull the sparky out.

 

OK, an update. I'm starting to get a little frustrated with this.

Checked the intake boots, and they're fine. All four rubber boots are, as a matter of fact.

After looking into the inside of the air filter, I saw that there were two metal mesh tubes tucked in there which led to the two outer tubes that the hose clamps sit on. My buddy thought that maybe there was some strange vacuum or some sort of air flow interaction between the two mesh tubes within the air filter at full throttle which was causing the strange behavior I was seeing and which might explain why jetting up really made no difference at full throttle. So I taped the neighboring sides of the mesh shut with duct tape so that no air could be swapped from one tube to another once it got in there from the outside of the filter.

That definitely changed things quite a bit. I jetted up to 170/175, took it for a spin, and it ran really good at full throttle, half throttle, and everything in between. Quick jabs from idle to half or full throttle got the same sputtering problem I had before, but it revved higher when I went from 7/8 throttle to full throttle rather than falling flat like it had previously.

So I bought a couple of new spark plugs for under $2 a piece at Pep Boys (thanks airraptor) and did a bunch of fifth gear full throttle chops for plug reading. That's a damn scary process, let me tell you. Letting go with one hand to turn off the motor is not a safe thing at 75 or so miles per hour. Anyway, I did three readings, all after the engine reached full operating temperature and all after about 60 seconds of full throttle in fifth using 170/175 jets, needles 3rd clip from the top. For all three, the plug porcelain was totally white from the electrode all the way up into the plug. It looked like it had just come out of the box. The ground strap was only slightly discolored, and definitely not black. The bottom of the threaded part of the plug (that the ground strap is welded to) was almost like new. Slightly white, actually. This all scared me since I thought it was probably way too lean, but the machine ran really well with the exception of transitions between throttle positions.

So I figured I was lean and jetted up to 180/185, needles 3rd clip. Almost identical behavior as 170/175. And exact same plug reading.

So for grins I went down to 160/165, which is what some people seem to be using with similar mods (including dirt wheels when they jetted up and hacked their Raptor's air box lid to be just large enough to hold the stock filter on - but they kept their stock filter). Anyway, the machine ran awful. It fell flat at anything past half throttle. Sputtering and really running awful. So jetting down wasn't the trick.

Now I'm still at the point where I'm almost jetted higher than anyone who owns a Raptor and still appear to be lean even at 180/185 with the stock pipe! The fuel flows out of the fuel petcock damn fast, so there's nothing clogged that affects the fuel flow going into the carbs. And the float level if anything is a little high (3mm above the float boal mating surface - I haven't touched that from the stock settings). The machine ran perfectly before I put that Pro-Design filter on and got rid of the air box lid, and I'd bet dollars to doughnuts it would run fine again if I went back to the stock filter and 140/145s. But I don't want to give up on this.

What the hell am I missing here?

 

Mine runs great like this at a similar elevation. I have the front half of the lid on though back to the 2nd clips. Alot of the problems with these carbs is velocity. letting the air in at the front of the filter slows things down. I like my air coming from the back and underneith as well as the top. 185/190 is insanely large

there is a good link around here somewhere on how to jet CV carbs from the top down, and what affects the float level has. But its still a pain in the *** and very time consuming - ever thought of tuning on a dyno?