'05 YZ250 jetting help

jim7411 · Jul 24, 2005

05 YZ250 jetting

I was hoping that somebody could give me their guesses and comments about my jetting. I am at 670' ASL and the temps have been in the 90's with high humidity. today it's supposed to be 101. :yikes:
My cuurent jetting is -
main jet - 172
needle is stock and at the 1st clip position
pilot - 48
air screw - 1 1/2 out

bike mods are - twin air filter, Pro Curcuit silencer (304 factory sound), stock pipe, V Force 3 reeds.
I run premium standard pump fuel now but I will probably be changing to 1/2 pump gas and 1/2 VP fuel.

I just changed to this jetting last night and I have not ridden it yet. before that I was at 175 main, clip position 2, 50 pilot and 1 1/4 out on airscrew. The bike just seems like it smokes to much. This is my first two stroke and I am not really sure how much smoke I should be seeing one the bike is warmed up and I give it a quick twist of the throttle off idle. I have been using Yamalube 2R since the bike was new.
With this jetting I looked at the plug and the isulator is dark brown. not tan kie it sould be but dark brown. I only rode it around the back yard before checking the plug however so I haven't given it the best test yet. It just seems like it shouldn't smoke that much.
Since this is my first two stroke I just worry about being to lean and frying the bike. So if anyone that has knowledge about this bike and what jetting would be good I would appreciate some starting points.

jim7411 · Jul 24, 2005

I was hoping that somebody could give me their guesses and comments about my jetting. I am at 670' ASL and the temps have been in the 90's with high humidity. today it's supposed to be 101. :yikes:
My cuurent jetting is -
main jet - 172
needle is stock and at the 1st clip position
pilot - 48
air screw - 1 1/2 out

bike mods are - twin air filter, Pro Curcuit silencer (304 factory sound), stock pipe, V Force 3 reeds.
I run premium standard pump fuel now but I will probably be changing to 1/2 pump gas and 1/2 VP fuel.

I just changed to this jetting last night and I have not ridden it yet. before that I was at 175 main, clip position 2, 50 pilot and 1 1/4 out on airscrew. The bike just seems like it smokes to much. This is my first two stroke and I am not really sure how much smoke I should be seeing one the bike is warmed up and I give it a quick twist of the throttle off idle. I have been using Yamalube 2R since the bike was new.
With this jetting I looked at the plug and the isulator is dark brown. not tan kie it sould be but dark brown. I only rode it around the back yard before checking the plug however so I haven't given it the best test yet. It just seems like it shouldn't smoke that much.
Since this is my first two stroke I just worry about being to lean and frying the bike. So if anyone that has knowledge about this bike and what jetting would be good I would appreciate some starting points.

ellandoh · Jul 24, 2005

i dont know about this particular bike but ........when messing with the jetting on anything ive owned i like to make 1 adjustment at a time , when i do anything else i end up having to go back to all original settings or set 1 of 2 back and start fresh.

biglou · Jul 24, 2005

That pilot soiunds pretty fat to me. I'm at 42, needle and clip position stock, main is stock. PC Pipe and the Factory Sound 304 shorty silencer. In these temps, I'm still a little fat. I could probably go to a 40 pilot. I'm running straight TT111 (B32).

jim7411 · Jul 24, 2005

biglou said:
That pilot soiunds pretty fat to me. I'm at 42, needle and clip position stock, main is stock. PC Pipe and the Factory Sound 304 shorty silencer. In these temps, I'm still a little fat. I could probably go to a 40 pilot. I'm running straight TT111 (B32).

Thanks for the reply. The 52 pilot is stock and I just changed it to 50. Did you lower your pilot all the way to 42? Was it that rich from the factory? From your settings, even with your mods, it looks like it is pretty much just the pilot that is rich from the factory and everything else looks to be okay. Is that your feelings?

biglou · Jul 24, 2005

I think mine had a 45 stock. It might have been a 48, but I can't remember for sure. And, FWIW, the B32 and CP12 will tend to require a leaner jetting than pump premium. Bclapham seems to think I can go leaner, especially at the 90-100 temps I've been riding in lately. To tell the truth, I got it right where I'm used to it, and it feels great to me, and predictable, so I figure I'll just be doing the "40/42 pilot in the summer, 45/48 in the winter" jetting changes along with tweaking the air screw each day after warmup. I can live with a little spatter on the inside of the right side plate. I might play with the needle clip position and see what that gets me, but like I said, I'm pretty happy with it as is. :cool:

steve125 · Jul 24, 2005

My jetting

168 main
stock needle 2nd clip from the top
48 pilot
air screw 1 3/4 to 2 out... no idle set

don't run the main that lean without using a race fuel with a low end point temp. VP C-12 would be a good fairly low cost example to follow.

bedell99 · Jul 24, 2005

I find it so odd that you guys are running so lean. I run 172, 48 pilot, stock clip at 6000ft. Not one drip of goop. no smoke. It will load up if I'm not hammering moto's, but the bike sings as long as your twisting the throttle.

Erik

bclapham · Jul 24, 2005

bedell99 said:
I find it so odd that you guys are running so lean. I run 172, 48 pilot, stock clip at 6000ft. Not one drip of goop. no smoke. It will load up if I'm not hammering moto's, but the bike sings as long as your twisting the throttle.

Erik

i think a lot of it comes down to fuel, also, the Keihin carbs are notorious for having float levels out of adjustment from the factory.

my ten peneth, i think Lou needs to drop his needle 1 or maybe 2 slots, and definately go leaner on the main. The bike has the pull and grunt that it should, but i think there is some pazzazz still to be had.

also, steve first tuned me into this, but sometimes you can overdo it with fuel- straight C12 IMO is too much for regular compression motor and tends to make the bike run a bit lazy- i had better results mixing C12 and Pump 1:1. I know Rich will be tearing his hair out, but its his own fault for not showing up to ride this week. :)

steve125 · Jul 25, 2005

bclapham said:
i

also, steve first tuned me into this, but sometimes you can overdo it with fuel- straight C12 IMO is too much for regular compression motor and tends to make the bike run a bit lazy- i had better results mixing C12 and Pump 1:1. I know Rich will be tearing his hair out, but its his own fault for not showing up to ride this week. :)

This can be so true, but there is a way around this that will keep Rich's hair in place. :nod: :)

Run the VP U4 or U2 depending on the engines octane requirements straight up, no mix with pump. :coocoo: Both fuels hit like pump and make more power on top and extend over rev.

The C-12 provides excellent detonation protection, and improved throttle response, but has a tendency to smooth the power delivery. Bad for some, but good for others that want to lessen that hit.

biglou · Jul 25, 2005

I'm liking the power delivery of mine at the moment. Plus, there's a shop (regardless of how much I hate it...) right off the hiway on the way home where I can pick up the TT111. I'd like to try the U4, but haven't searched it out around here.

It's interesting the perception of power delivery. Nikki thinks my bike has a "80-like powerband" in that it's like a light switch: on or off. I think it's a rather smooth transition onto the pipe, and this coming off 3+ years on the big four strokes. Like RR also says, as long as I'm happy, that is the ultimate justification! :)

I still love reading all this info from you smart fuel guys, too! :cool:

bedell99 · Jul 25, 2005

Hey lou TT111 is what i run. I feel safe with the fuel, because I generally tend to run at high RPM's out here in colorado. The track are more of the wide open type.

Erik

jim7411 · Jul 25, 2005

steve125 said:
My jetting

168 main
stock needle 2nd clip from the top
48 pilot
air screw 1 3/4 to 2 out... no idle set

don't run the main that lean without using a race fuel with a low end point temp. VP C-12 would be a good fairly low cost example to follow.

Thanks for the reply. I have a few questions for you if you don't mind.
1) When you say "no idle set", tell me about that a little bit. I have heard about not having an idle on a two stroke but I don't really understand what is involved.
2) I rode around the oval in my backyard a bit yesterday and then checked the plug and the new jetting that I listed above did clean the plug up some and it was around 100 degrees yesterday. I notice that on the inside edge of the silencer it is wet with what seams to be gas. But it is thin not spooge. Also the hose coming from the left side of the jug seems to be doing the same type of draining. Does this all seem normal?
3) Once you get the jetting were you want it how much do you generally have to change as the temps change. Is it all in the airscrew or do you need to change clip position and main jet? How much of a temperature change warrants a change of the main or the clip?
4) Lastly, I don't know what temps you are riding in or the elevation at which you ride but comparing my jetting to yours it's seems pretty close. But I may move the clip down one just because I was kind of thinking that it was maybe going to far to go to the 1st position.

The main thing that I am trying to do is get pretty close with the mods that I have without blowing up the bike by being to lean. Then I can take it out to the track and run a few laps and pull the plug to see how it looks. Does that seem like the right approach or should I be attacking it differently?

Thanks for everybody’s help. I had a 2002 YZ250F and I worked with the jetting and made notes until I got that where it needed to be. Then I knew how to adjust as temperatures changed. But I am more timid about the two stroke because I have this thing in my mind that it can more easily be blown up if you have the jetting to lean. Now that may be my own misconception but this is why I am asking all these questions. So any help is appreciated.

biglou · Jul 25, 2005

I'll let Bruce and Steve answer these questions, but I wanted to add something Rich told me at DW2001: "No one ever seized a motor by having too lean a pilot jet". I've kept that kernel of info stashed in my mem banks ever since. :cool:

ellandoh · Jul 25, 2005

biglou said:
I'll let Bruce and Steve answer these questions, but I wanted to add something Rich told me at DW2001: "No one ever seized a motor by having too lean a pilot jet". I've kept that kernel of info stashed in my mem banks ever since. :cool:

is that hold true even if you were riding the side of the road for miles with 1/16 to 1/8 throttle??

bedell99 · Jul 25, 2005

Remember jetting is a very selective thing. A novice and pro can ride the same bike and have different jetting requirments.

Erik

bclapham · Jul 25, 2005

you'd be hard pressed to blow a yz250 up with bad jetting- really bad and a fast rider, maybe.

pilot- too lean, it will just bog at lower throttle.

needle- too lean, you should be able to hear the detonation long before it blows up.

main, too lean, again listen for detonation as long as you can hold a 250 all the way to the stops. ;)

dont forget, detonation is your friend- thats when you know its tuned right up to the edge.

as for different bikes and conditions, ive run mine with just about the same jetting for the last year. rain or shine, night or day, high or low altitude and all over the country. But some bikes need major adjustments when the wind changes direction.

biglou · Jul 25, 2005

I've been real lucky with mine, too, Bruce. I dropped from a 45-42 pilot when the temps got above 65f. Other than that, I haven't touched it, and I'm real happy with it. Still running the stock plug (knock on wood).

oldfrt613 · Jul 26, 2005

We dropped the pilot on our '05 1 size. We are at about 500' and it was 102 deg Sunday with High humidity. All other settings are stock. Motor runs great. You may want to consider something other than Yammagoo.

bedell99 · Jul 28, 2005

I have to agree I jsut can't see running that lean unless, you run in the woods or don't really twist the throttle. The bike runs real strong wiht my setting and that is at 6000 feet.

Erik

'05 YZ250 jetting help

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