Two Stroke Motocross

Two Stroke Motocross Forum => Technical => Topic started by: conbread on June 03, 2012, 04:10:40 AM

Title: 05 YZ250 jetting
Post by: conbread on June 03, 2012, 04:10:40 AM
hey guys im wondering what to try first.. my bike seems like it is running out of fuel sometimes, the only Power mods are procircut pipe and r302 silancer.. i just put them on and rode today, i run the bike on 100 octane and maxima 927.. The bike gets rode pretty hard and sometimes seems to get real (PEAKY) and then will come back down.. The bike was from another owner, i think the jets are stock but im going to pull it apart and look..

should i just up the main?

or up the pilot

or just drop the needle 1 clip??

i really wanted to just make 1 change... thanks for any help eric
Title: 05 YZ250 jetting
Post by: Stusmoke on June 03, 2012, 08:38:51 AM
When I was considering doing the jetting on my 2001YZ250, cos it was just dicked, I got told by crncpala to mess around with the pilot air screw and throttle stop first.
This worked really well for me and before you go tearing down the carb I'd recommend you do the same. Turn your pilot air all the way in then out around 1, 1/2 or maybe even 2 turns. Kick the bike up and turn the throttle stop screw in and out until you make the bike idle at its slowest SMOOTH speed. Then adjust the pilot air screw in and out until you bring it back up until it idles as high as possible. Then use your throttle stop screw to lower it down to its slowest smooth speed again.

This helped me ALOT with my weird power delivery and loss of fuel/oil out the arse end of my bike.

Of course if you've already tried all this just disregard lol. Good luck to you
Title: 05 YZ250 jetting
Post by: SachsGS on June 03, 2012, 02:41:18 PM
I'd first do a compression test to get some kind of an idea what kind of shape the top end is in.
Title: 05 YZ250 jetting
Post by: Stusmoke on June 04, 2012, 12:09:10 AM
Sachs raises a good point (as usual). Peaky power then dropping back down may very well be a worn out piston. You said it gets ridden pretty hard so I'd look over those sort of things before messing around with your jetting.

good luck mate
Title: 05 YZ250 jetting
Post by: cnrcpla on June 04, 2012, 12:47:19 AM
Yeah, do a compression check then check your jetting and air/fuel screw. See where your at after the compression test though, odds are if you ride it hard, depending on how many hours are on it, you may need to though some rings in it. How many hours since your last rebuild? I'm sure the guy you bought it off of said it just had a rebuild, but odds are it probably didn't.
Title: 05 YZ250 jetting
Post by: conbread on June 04, 2012, 01:44:35 AM
the bike was hardley ridden at all.. so clean and nice it was crazy.. it has tons of compression and is very crisp.. the track we was on yesterday was tight and was around 1/8 to 1/4 throttle in some spots and thats where it seemed to do it.. i have read about the 07 N3EW needle helping that out, anyone here made that switch??
Title: 05 YZ250 jetting
Post by: Stusmoke on June 04, 2012, 02:35:27 AM
Well it is possible that you'll need to do a top end but if its bad at 1/8 and 1/4 like you said odds are its an issue with jetting. If the compression test checks out I'd take the cylinder head off and just check everything out to be sure. If that all checks out mess with the pilot air and throttle stop first. If all that fails then you're probably on the money with the jetting issues. The track you rode on the weekend when you said it was having issues, was that at a different elevation? I mean a substantially different elevation?
Title: 05 YZ250 jetting
Post by: conbread on June 04, 2012, 12:13:45 PM
it was at the same elavation just right up the road from the one we rode on saturday.. sunday was the first ride with the new pipe and sliancer.. Im going over today and ill make sure the air screw is 1 1/4 to 1 1/2 out and set the idle like you told me too..
Title: 05 YZ250 jetting
Post by: Stusmoke on June 05, 2012, 07:26:43 AM
Yeah I'd try that first. It could very well be that the previous owner layered on the BS about the bike being "hardly ridden" and infact had 90 hours on the piston of hard riding you never know. So if that doesn't work or at bare minimum HELP then I would do a compression test. Maybe take a look at the piston just incase compression is fine but theres something else dicky. If that all seems fine, I'd move onto jetting.

The 1-1/2 turns out on the pilot air was suggested to me as a solution for my YZ250 Keihlin carb. It might be different on the RMs but it should let enough fuel and air in to give you a starting point.
Good luck I hope is an easy fix for you bro
Title: 05 YZ250 jetting
Post by: conbread on June 06, 2012, 03:25:50 AM
so the air screw seemed to be around 2 to 2 1/4 out.. so i set it to 1 1/2....
Title: 05 YZ250 jetting
Post by: Stusmoke on June 06, 2012, 07:37:00 AM
Like i said, its more than likely different for the RMs so don't quote me.
Quote from: Stusmoke on June 03, 2012, 03:38:51 PM
When I was considering doing the jetting on my 2001YZ250, cos it was just dicked, I got told by crncpala to mess around with the pilot air screw and throttle stop first.
This worked really well for me and before you go tearing down the carb I'd recommend you do the same. Turn your pilot air all the way in then out around 1, 1/2 or maybe even 2 turns. Kick the bike up and turn the throttle stop screw in and out until you make the bike idle at its slowest SMOOTH speed. Then adjust the pilot air screw in and out until you bring it back up until it idles as high as possible. Then use your throttle stop screw to lower it down to its slowest smooth speed again.

This helped me ALOT with my weird power delivery and loss of fuel/oil out the arse end of my bike.

Of course if you've already tried all this just disregard lol. Good luck to you

Remember to follow those steps after you've put the pilot air 1-1/2 turns out. I hope this works for you bro I can remember dreading having to screw with my jetting.
Title: 05 YZ250 jetting
Post by: conbread on June 10, 2012, 01:32:42 AM
ok so i went out to Wide open MX today, this is a fast sandy killer track.. I added the N3EW needle and the Bike loves it, she has tons of low to mid responce and wants to wheelie out of all the turns.. It never seemed to rev like it was running outta gas today.. i checked the plug a few times and it was always a pretty Tan color...

was running 100 octane and Maxima K2 high rpm mix... also while i had the carb off i seen the bike has carbon reeds in it..
Title: 05 YZ250 jetting
Post by: conbread on June 10, 2012, 01:50:53 AM
heres a few pics with the new back grounds.




Title: 05 YZ250 jetting
Post by: Stusmoke on June 10, 2012, 02:16:59 AM
Pretty tan color eh? If you google: Spark plug conditions you should be able to get a good reading of where your machine and plug are at just by taking the plug out. From what you've described its worn
Title: 05 YZ250 jetting
Post by: conbread on June 10, 2012, 02:46:04 AM
Quote from: Stusmoke on June 10, 2012, 09:16:59 AM
Pretty tan color eh? If you google: Spark plug conditions you should be able to get a good reading of where your machine and plug are at just by taking the plug out. From what you've described its worn

lol, thats funny.. yea it has a pretty good look to it.. way diff from my buddys Grey/black 2004 cr250... man i love this 2 stroke, dont know why i started out on a yz250f..
Title: 05 YZ250 jetting
Post by: Stusmoke on June 10, 2012, 03:06:11 AM
I made the same mistake friend... I bought a CRF250R, it grenaded within 10 hours of riding. I'm still parting the POS out. Anyway as soon as I drove out the gate on my YZ250 I was sold on 2 strokes for life
Title: 05 YZ250 jetting
Post by: scotty dog on June 10, 2012, 11:14:27 PM
a nice tan/brown colour is spot on, Grey/White is lean and black & oily is rich. Glad ya got it goin good, a well jetted bike is great to ride  :D
Title: 05 YZ250 jetting
Post by: Stusmoke on June 11, 2012, 07:44:28 AM
Clarify something for me cos I've heard six thousand mixed opinions.

If I say a mixture is rich does that mean its got alot of oil in it? or its rich in fuel?

I was always under the impression that a rich mixture had alot of oil in it
Title: 05 YZ250 jetting
Post by: TMKIWI on June 11, 2012, 09:24:37 AM
Rich mixture is rich in fuel.
Title: 05 YZ250 jetting
Post by: Stusmoke on June 11, 2012, 11:08:08 AM
I couldn't decide hey, peopel saying the opposite things left right and centre
Title: 05 YZ250 jetting
Post by: riffraff on June 11, 2012, 02:45:03 PM
Quote from: TMKIWI on June 11, 2012, 04:24:37 PM
Rich mixture is rich in fuel.

x2
Title: 05 YZ250 jetting
Post by: teampryor on June 11, 2012, 11:00:44 PM
Yes a high fuel to air ratio is rich
Not a high fuel to oil ratio that should be constant, at 32:1 or appropriate ratio.
Title: 05 YZ250 jetting
Post by: Recovered on June 11, 2012, 11:12:18 PM
Pro Circuit does suggest to go 1 leaner on the main jet useing there exhausts
Title: 05 YZ250 jetting
Post by: arnego2 on June 14, 2012, 09:45:48 PM
I would not rely just on the spark plug color, the head give you the idea where your jetting is.
And if the jetting is correct you would have a pool in the crank ca. 1 to 2mm of premix oil.

Advance timing makes the spark plug gray. I get a dark gray plug color but the head plus the pool in the crank tells me thet the jetting is correct. When ride harder and harder most people forget that they run the engine higher and need to put the jetting in the area of racing jetting.   
Title: 05 YZ250 jetting
Post by: Stusmoke on June 15, 2012, 12:48:37 AM
I hate to steal someones thread but my bike has ALOT of unburnt fuel/oil coming out the pipe and the exhaust port, I really need reseat the springs and seals on the exhaust port I'm hoping that will fix that part. But theres still ALOT of it coming out. Theres pools on the floor of my garage. Its so much it drips onto the swing arm then flows down to the back wheel from there. Thoughts? I was thinking fuel/air mixture but When I try to thin it out the smoke goes white.
Title: 05 YZ250 jetting
Post by: arnego2 on June 15, 2012, 11:09:09 PM
Ok but how do ride they bike hard or not hard, fast meaning th e 3 rd gear at less the half wot?