08 450 jetting help.

I have searched through the jetting sticky, and didn't see too much on 08's.

Looking for some suggestions. I am having troubles with the bike stalling in slow speed corners and trails, seems like flame out stalls. Its not an rpm issue, I don't think. It is also hard to start. I.E. When cold, I have to use the hot start and choke 10 kicks or so makes no difference if I prime or not. If it stalls it takes a good 10 kicks to start it, and I still haven't perfected that routine. If I stop the engine on my own, and restart it 2 minutes later, it will fire right up with the hot start. The bike is well broken in, and has done this since I put the fmf Q4 muffler on it, stock head pipe. When I put the pipe on it, I had to re jet as it would not run hardly at all. Elevation is 1500 ft. Temps are 70-80 right now. The bike ran well in stock trim, no decel pop, started good. The bike runs well in current trim, no decel pop, strong power from top to bottom, aside from the hard starting and stalling, I am happy with it.

Jetting in it now:

pilot: 50

Main: 165

Needle: NFLR clip in 3rd slot from top

Leak: Stock 55

Starter: stock 72

Air screw: MSR 2.75 turns out

Stock Jetting

pilot: 45

main: 160

Needle: NFLR 3

Air screw: 1.5

I just put in a 48 p.j. and am going to give that a try tomorrow.

Thank you for any suggestions in advance

Stalling on throttle chops and idle down situations are normally due to an excessively rich idle circuit, and your pilot is way big. The fact that it has no decel popping is another indication that it's too rich at idle.

A friend of mine is running this on an '08 with a race exhuast:

43 pilot

160 main

NFLP needle in the 5th groove

50 leak

2.5 turns on the screw

The concept is to keep the pilot small to clean up the idle and prevent stalling, while using a smaller diameter needle to richen the off-idle transition through 1/4 throttle instead of a fatter pilot, along with a smaller leak jet to beef up the pump shot a little bit.

Stalling on throttle chops and idle down situations are normally due to an excessively rich idle circuit, and your pilot is way big. The fact that it has no decel popping is another indication that it's too rich at idle.

A friend of mine is running this on an '08 with a race exhuast:

43 pilot

160 main

NFLP needle in the 5th groove

50 leak

2.5 turns on the screw

The concept is to keep the pilot small to clean up the idle and prevent stalling, while using a smaller diameter needle to richen the off-idle transition through 1/4 throttle instead of a fatter pilot, along with a smaller leak jet to beef up the pump shot a little bit.

Hey there Gray! I have an excellent suggestion for this gentleman and i believe his bike will run excellent with his FMF. First of all that 50 pilot is WAAAAY to big. He needs to keep the stock jetting...everything except the leak jet. He should swap the 55 for a 50. So...45 pilot,nflr needle,160 or maybe a 162 main,50 leak and 2-2.5 turns on the screw. After messing with mine a bunch, I actually put the stock needle back in and feel it performs better than the NFLP. I raced it last weekend at Milestone and it ran perfect. The temperatures were nice outside...on the warm side...It seems to run much better when the outside temperatures are high.

well, I put a 48 pilot in it, and lowered the clip one groove. As far as stock jetting, the bike would not run at all with the stock jetting. It would barely start and idle, and any throttle at all, it would bog and die. The 50 pilot was my first shot at it. and I haven't messed with it since then. However, have a few hare scrambles coming up, and want an easy starting no stalling machine.

I will test my changes tomorrow. As far as starting, on the stand, I already see an improvement.

I would like to be able to cure this problem with fuel screw, pilot and main jet, and needle clip position.

However I guess, if it is required to change leak jet, I will do it, as a last resort.

Thank you for the replies.

Can you get leak jets from a part unlimited catalog? Anyone know a part # for 50 and 55 leak jets? I cant find that anywhere....

im at about 2800 ft and mine was hard to start so i went ahead and put the 48 pilot in.i also put a different pipe on it and bumped the main to 168.the bike runs great and starts a little better,not like it should but it will probably get better once it breaks in.i thought about dropping the main to maybe a 165 but i will be doing some gp's and dont want to be lean at wot.also at a steady 1/4 throttle this bike hesitates,not bad but it is really strange,others have reported the same hesitation on here.i may try moving the needle to see what that might do.

Listen to what gray said, if the bike hesitates at 1/4 throttle you prob need the richer need like they mentioned to richen the off idle transition. I just put an akropovic on an 08 and noticed that it hesitates at very low throttle position also. I have stock needle stock clip, 165 main, 48 pilot. Its very cold here right now, and raining in texas, so Im gonna wait a few days for some 75 degree weather. Boy the exhaust wakes up that 08. Its got gobs of low end power now, Im barely twisting the throttle and going decievingly fast in record time. Lots of low end to shoot you over jumps too.

Stalling on throttle chops and idle down situations are normally due to an excessively rich idle circuit, and your pilot is way big. The fact that it has no decel popping is another indication that it's too rich at idle.

A friend of mine is running this on an '08 with a race exhuast:

43 pilot

160 main

NFLP needle in the 5th groove

50 leak

2.5 turns on the screw

The concept is to keep the pilot small to clean up the idle and prevent stalling, while using a smaller diameter needle to richen the off-idle transition through 1/4 throttle instead of a fatter pilot, along with a smaller leak jet to beef up the pump shot a little bit.

I have to thank you for that info. I put the 45 pilot in, and changed the leak jet to a 50. What a world of difference. I still have like a 1/8-3/16 throttle stumble, however I am going to try raising the needle a bit more.

Thank you again.

I just put an akropovic on an 08

Can you post a pic of the exhaust on the bike?

I have to thank you for that info. I put the 45 pilot in, and changed the leak jet to a 50. What a world of difference. I still have like a 1/8-3/16 throttle stumble, however I am going to try raising the needle a bit more.

Thank you again.

If raising it the needle doesn't seem to make a difference, try the NFLP (the part number should be in your manual, look in the Tuning section). That needle has the same taper at the same height as your stock NFLR, but the straight section is smaller, making the mixture richer at small throttle openings before the taper starts to be exposed.

Another thing worth trying is a jet kit from JD.

Well, I figured if I was going to spend money on the carb, I would send it to zip ty for their mod.

I did get out and test it today, on the normal rocky trails we ride, it was much better, It didn't seem to stall like it did before. However, I now have a mid throttle bog/stumble. It only happens if I am riding it a gear high, like in a sand wash, coming out of a turn, transitioning from the exit of the turn, to the straight and getting on the gas. Or going up a whoopy rocky trail, and being in the middle of the rpm range, and go to blip it to loft the front end over a trail obstacle. Seemed to happen at very pecuilar times. Any suggestions?

Current jetting.

Pilot 45

Main 165

Needle Stock NFLR in the 5th clip pos

Leak 50

Fuel screw 2 1/4 turns

Zip-Ty doesn't re-jet when the mod is done. What they do is to modify the main air circuit and change the emulsion tube (needle jet, discharge nozzle). This improves sharpness and throttle response throughout the range, but doesn't guaranty that your current jetting is right. I know of very few people who had this done who aren't happy with it, and I haven't heard anyone say it made the carb worse.

At this point, it's important to start changing one thing at a time and testing the results. If your only change this last time was to raise the needle, and the results were that you moved your stumble from 1/8-1/4 to around half throttle, you need to separate how it behaves AT half throttle from how it behaves when transitioning to half throttle.

Also, the engine can stumble from too much fuel just as from too little. Here, you had and engine that had a 1/4 throttle weakness and raising the needle moved that to 1/2. So it looks like the extra fuel was good for the 1/4 issue, but the bike doesn't like it at wider openings. I would return the needle to where it was, then open the fuel screw some to see if that improves the 1/4 throttle response (even though it may cause stalling or idle problems). If it does, and your half throttle behavior returns to normal, then I'd have to once again suggest the alternate needle as a cure.

Zip-Ty doesn't re-jet when the mod is done. What they do is to modify the main air circuit and change the emulsion tube (needle jet, discharge nozzle). This improves sharpness and throttle response throughout the range, but doesn't guaranty that your current jetting is right. I know of very few people who had this done who aren't happy with it, and I haven't heard anyone say it made the carb worse.

At this point, it's important to start changing one thing at a time and testing the results. If your only change this last time was to raise the needle, and the results were that you moved your stumble from 1/8-1/4 to around half throttle, you need to separate how it behaves AT half throttle from how it behaves when transitioning to half throttle.

Also, the engine can stumble from too much fuel just as from too little. Here, you had and engine that had a 1/4 throttle weakness and raising the needle moved that to 1/2. So it looks like the extra fuel was good for the 1/4 issue, but the bike doesn't like it at wider openings. I would return the needle to where it was, then open the fuel screw some to see if that improves the 1/4 throttle response (even though it may cause stalling or idle problems). If it does, and your half throttle behavior returns to normal, then I'd have to once again suggest the alternate needle as a cure.

Appreciate the response. This is my first 4t, so learning the jetting aspect of it, will most likely come from individuals who have already done the research.

The stumble now is more from a transition of 1/2 throttle to larger throttle openings, and like I said, it seems to happen more, when the load is greater on the motor, almost as if it is loading up just a bit, then opening the throttle more, it stumbles a bit, then picks up and revs out. At a steady 1/2 throttle it is fine, a smooth roll on from bottom to top is fine, a gear high, and a quick dab of the clutch and it is fine.

I will try the needle movement as suggested, and in the mean time see if I might be able to locate that needle tomorrow. Might try a 43 pilot as well, however I will only change one thing at a time.

Would the 165 main be feeding it too much fuel possibly? It seems to me, it is a rich fuel bog, when it happens.

The 1/4 throttle hesitation was, more of a steady throttle, stumble, the rpms fluxuating when the throttle was held steady.

Can you get leak jets from a part unlimited catalog? Anyone know a part # for 50 and 55 leak jets? I cant find that anywhere....

Any dealer can tell you the part numbers for the different size leak jets....Honda/Yamaha/Kawasaki...they are all the same jets

Appreciate the response. This is my first 4t, so learning the jetting aspect of it, will most likely come from individuals who have already done the research.

The stumble now is more from a transition of 1/2 throttle to larger throttle openings, and like I said, it seems to happen more, when the load is greater on the motor, almost as if it is loading up just a bit, then opening the throttle more, it stumbles a bit, then picks up and revs out. At a steady 1/2 throttle it is fine, a smooth roll on from bottom to top is fine, a gear high, and a quick dab of the clutch and it is fine.

I will try the needle movement as suggested, and in the mean time see if I might be able to locate that needle tomorrow. Might try a 43 pilot as well, however I will only change one thing at a time.

Would the 165 main be feeding it too much fuel possibly? It seems to me, it is a rich fuel bog, when it happens.

The 1/4 throttle hesitation was, more of a steady throttle, stumble, the rpms fluxuating when the throttle was held steady.

You will need to try a 42 pilot.....That 43 was a miss-post from earlier......my fingers got a little carried away....there is no such thing as a 43 pilot jet...at least i've never seen one...unless a 42 was drilled.

You will need to try a 42 pilot.....That 43 was a miss-post from earlier......my fingers got a little carried away....there is no such thing as a 43 pilot jet...at least i've never seen one...unless a 42 was drilled.

I figured that out, once I looked thru the manual for the part number for the needle.

The two main influences are the main jet and the pilot. The main circuit doesn't do anything at an idle because there's no air flow to activate it. At full throttle, the pilot jet will still be flowing fuel, and add to the total, but it is such a small amount compared to the main that it effectively has little influence. The main jet, however, will influence everything from full throttle down to an eighth or so, so you have to get the main and the pilot right before you start trimming the needle for part throttle.

Study the tuning section of your manual. You will see how the different jetting elements overlap each other in their influences on different stages of throttle opening, and the stage at which each element has the most influence. The way it sounds to me, you had a 1/4 throttle surge that cleared up when you made it richer, either by raising the needle, or by using a larger pilot. This is because each of those elements has an overlapping influence on that stage of the throttle. But when you did either of those things, you found yourself too rich in the area of primary influence. With the larger pilot, it started to stall, and now with the needle, it acts as if it's rich at part throttle. That suggests, once again, that the thing that needs changing is the needle diameter, which has primary influence over the 1/8-1/4 throttle range.

As to whether an oversized main could cause the problem you have now, yes it certainly could. The closer you get to WOT, the more you are running purely on the main jet. Since it's easier, you might give that a try first.

Well, I found 1 shop in town that had the NFLP in stock. Stuck that in, with the clip in the fourth position. Also dropped the main to a 160. On a quick test ride on the asphalt in my 'hood, it definately seemed more responsive or crisp, I couldn't get it to do the stumble like I had yesterday, however I didn't notice that until I was on some pretty technical single track.

I am going to head out wednesday after work and give it a try.

Appreciate your help Gray.

Still need to get mine out for a ride to see how it runs (well, actually still need to break it in). Not to confuse or undermine things in anyway, the MXA Crew recommended the following on their test bike (in fact claim that Yamaha adopted their 07 settings for the 08):

Main: 160

Pilot: 45

Needle: NFLR

Clip Position: Third from top

Fuel Screw: 2-3/8 turns

Leak Jet: 55

They also ran the bike with an FMF, DR.D & Pro Circuit pipe - don't mention what jetting changes they made with the aftermarket pipes)

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