? for the jetting guy's?

Here is the problem:

When I'm behind traffic in 4th gear (coasting along) at about 1/4 throttle, just above lugging it and before the bike takes off, there is a spot where the bike won't run smoothly. If I hold the trottle as steady as possible the rev's won't hold steady and the bike is very jerky.

I live in the city and I have to ride through a lot of traffic before I get to where I need to be. I would like to smooth out that lower rpm dead spot. I know there is a direction I should be going on the jetting, but have no idea which.

Any ideas would help. I moved the blue needle clip up 1 to #3 and it seemed to help a bit, but the problem is still there. :)

You accelerator pump causes this surge of power. Yamaha intended for this so that you would have good power response above idle in the dirt. Try and turn it down (lean out the fuel delivery)to a mimimum squirt and then go to a smaller pilot jet to soften the bottom end.

I would just learn to ride with the sudden aggressive response and give yourself some space in traffic.

You accelerator pump causes this surge of power.

If he is really holding the throttle steady the accelerator pump won't be operating.

I doubt it is the needle clip, I would say that doesn't matter until almost 1/3 throttle. It sounds like you may want to change needles to a richer straight diameter and/or try a richer pilot. You don't list your pilot jet size in your sig.

After reading your post again I can't decide if you are rich or lean. A lean bike will surge at constant throttle settings like you describe, too rich and it will stumble. Not a big distinction I know...

...but it sounds more like you are lean.

Also, the Pilot Air Jet can affect low throttle settings, especially at higher rpms.

I tried to hold the throttle as steady as possible to eliminate the acc. pump. The electrode and the tip of the ground electrode were white, but the perimeter of the plug was black, so I figured the engine is not getting hot enough to clear the whole plug and that is why I raised a clip to lean it out and get some more heat on the plug. I haven’t pulled the new plug to see if there was a difference, nor am I sure if it was the right thing to do.

I’m running the stock #45 pilot jet. The bike runs great and when I get to where I can ride freely, I hammer the hell out of it. I wish I could just smooth out this small area in the throttle range. I just hate it when the bike is jerking on and off. I could either lug her in 5th or run her in 3rd at higher rpm. The only problem in the higher rpm is that she wants to take off like a bat out of hell and in heavy traffic that creates a lot of acc. and deceleration. I want to be able to cruise at ~40mph in fourth without jerking the bike around. I know there is an adjustment to smooth this out and maybe it’s the pilot jet, of which I have no experience and wouldn’t know which way to go.

Another question… and I must first thank Indy for giving me specific settings for my red and blue needles in different temps… but I would like to know what the difference between the 2 are and which I should use when trying to achieve a particular setting.

Another question… and I must first thank Indy for giving me specific settings for my red and blue needles in different temps… but I would like to know what the difference between the 2 are and which I should use when trying to achieve a particular setting.

You could measure them.

Or you could ask JD. :)

I'm thinking that what you need to do is adjust your jetting before you come on to the needle's taper. This means pilot, pilot air, idle, and needle straight diameter. The straight diameter is the portion of needle that fills the main before the throttle lifts it up to the tapered portion. A smaller straight diameter is richer because it allows more fuel to pass, bigger is leaner. This governs jetting at slightly off idle to that point where the taper portion of the needle begins to come out.

If you want to learn to jet each carb circuit it helps to mark the throttle positions with a sharpie or something. Figure out where, exactly, the glitch is. If you listen, the seat of your pants will tell you when you get to the needle taper, I'm thinking your glitch is before this point.

Back to the measuring, if you have a micrometer you can compare the needles straight diameters directly.

One sure fire way to see which carb circuit it is is to change something. Try leaning your idle mix up a whole bunch, like 3/4 of a turn, and see what happens in 4th gear, low throttle as you try to duplicate this glitch. I doubt you can fix the problem with the idle mix, but this may "spill over" enough to higher throttle settings to generate some feedback.

If possible you may also try feathering your hot start while experiencing this glitch to see what that does...

Hope this helps.

Blue has a richer taper then the red needle. You can ask JD over on the jetting forum particular questions. The tip diameter and main needle diameter are different from red to blue. I think Blue "2 is close to Red #5. But JD can answer this better. You are most likely at 1/8 to 1/4 open steady throttle when you have the surging issue. It is very hard to get that part of the jetting to be perfect. This is a Yamaha trait. 42 pilot and lowering the needle will help soften the bottom end. Dont over do it or you will not get it to idle right amd may be more stall prone.

Thanks hick. I think I just learned something and it does make sense. I'm sure the glitch is just at that point at the end of the straight beginning of the taper as it is just before the bike wants to take off.

What should I be looking for by leaning out the idle and how will it effect the trottle at about 1/4?

Also what should I be looking for with regards to the pilot jets etc.

I like the idea of feathering the hot start. I'll give it a go first thing tomorrow. :)

Feathering the hot start will simulate leaner jetting and will give you a clue as to the effect of softening the bottom. In my experience the lowering of the right needle is the key. I never use blue 1 or 2 because of this effect. I always prefer to run my bike at clip 3,4,5 positions on the right needle. Give blue 1 or 2 a try. :) Then try a 42 pilot if that is not enough.

I'm sure the glitch is just at that point at the end of the straight beginning of the taper as it is just before the bike wants to take off.

Bingo. That is exactly what I was talking about.

What should I be looking for by leaning out the idle and how will it effect the trottle at about 1/4?

At steady speeds, say 4th gear 1/4 throttle or less, if too lean you would feel the motor surging and hesitating. Too rich and it will stutter and stumble. The idle mix should affect 1/4 throttle jetting enough to be felt, although not nearly as much as an outright change in pilot jet size. But it should be enough to steer you in the right direction; try going 1/2 turn richer and then leaner (1 full turn in from before) and see how this affects your 1/4 throttle cruising.

If your biike consistently prefers richer idle mix settings then that would be a good time to try a richer pilot jet. And vice versa.

Hope this helps.

Keep us posted.

Took a 40mile ride this evening to try and figure this out.

I found the blue needle at #4 seems to give the best pull up to full throttle. The temp was 50deg this evening. I pulled the plug, and at this setting I get the best spark plug color.

I was messing with the idle and fuel screw and found 1 turn out was alot better than the 1 3/4 I was running before. Going to 2 to 2 1/2 turns felt the same to a little worse. I should of turned it down more to see what it would happen, but it was getting dark and I couldn't see &%$#@! I was doing.

I have a extra 40 pilot jet (it came with the bike from the dealer, I'm not sure if this is normal, but I have it) and was thinking of trying it. What do you guys think? Will it be way off and will a 42 be a better first try?

Btw I checked the oil and it was cool at the dipstick. Is this normal? The motor felt quite cool as well. I thought it would be cooking as I was punching it most the time. I changed oil and filter yesterday. :)

Try the 40 first and if it is too lean then buy a 42. You wont hurt the bike by running a 40.

I went and looked at the FMF web site tonight and on the WR450 they recommend a 42 pilot, 178 main 4th clip needle. That's a long ways off of what I'm running on my stock needle. This weekend at 2000' I ran 45 pilot and 155 main, 4th clip needle, 40 degrees, and had good performance.

Hey Indy

What about the cool engine/oil temp? What do you think? :)

I think a hotter engine would perform better.

True that a hotter combustion temp engine will generate more power. But within the design of the Yamaha WR450 motor your best choice for power is good jetting (not lean), high flow exhaust, modify air box to allow a good volume of air to get in, and a YZ450 exhaust cam or aftermarket Hot Cams for even more power. :) Then if you want more, higher compression, porting the engine, ignition system mods will take you to the next level. :D

I was wondering if I anyone covers some of the radiator in cold weather?

What effect sould I expect going with the red needle instead of blue, but 2 clips lower on the red ie #6. Should this keep the top end similar and leaning out the lower end? Does the straight portion of the needle have any effect on the pilot circuit? Where does the pilot circuit end and the needle come in?

I was wondering if I anyone covers some of the radiator in cold weather?

Yes, I run a strip of duct tape down the center of each rad. to get the temp. up, works great.

The Blue clip 3 and Red 5 are similar, with the red5 leaner on the bottom. Colder temps require richer jetting. You can lean it out to get the temp up but it won't run well. Cover part of the rads but don't lean it out to get it hot.

You should read the JD jetting guide to understanding how the main, needle, pilot, main air, pilot air , leak , starter and other jets work with throttle position and general engine carburation tuning. You can buy the jetting guide on this forum store. JD will email it to you. Low cost. Great insight. :)

Well I went for another ride tonight. Installed the red needle #6 before I left. The bike runs great. Came back and moved it up to #5 (fuel screw out 2). Now if I only listened to Indy in the first place, I wouldn't of wasted so much time. Actually, I learned a lot experimenting and thanks for all your input. How can I tell if I'm to lean on the needle?

The bottom 1/4 throttle is smoothed out now. The bike started easier than it ever has. I've never been able to start it on the first kick, with the kick starter, when cold. Now its like butter. Now I hardly touch the e-starter and she fires up.

It seems to pull as hard as with the blue, but it's difficult to tell. Will there be differnce in acceleration with the red? :)

Good jetting will give you a snapier throttle response and it will accelerate better. You are jetted fine with a red # 5 for 60 to 70 degree temps at lower altitudes uncorked. If you think you are off slightly just pull in your hot start to various levels and see if it pulls harder. I think you will see if you are to rich if it runs better with partial hot start engagement. Normal needle jetting lean condition will result in backfires when you are running 1/4 to 1/2 throttle steady and back off the gas. If it backfires you are lean. If it sputters and soft gurgles you are rich. Otherwise dont mess with it unless you are a perfectionist like me. I rejet 20 plus times a year. :)

It's smooth right now so I'll leave it alone.

Thanks again Indy. I'm sure I'll start messing with something else soon and need some more advise.

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