Two Stroke Motocross
Two Stroke Motocross Forum => Technical => Topic started by: scotty dog on September 07, 2011, 02:46:32 AM
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Im not happy with the way my 05CR 250 is running at the moment.
It fouls up easily if im just riding slow even for a short distance and it never has been very crisp.
On the weekend even just sitting on the start gate for 2 minutes it would choke up even though i had just cleared it out. Although i have issues with it pinging. I dropped the needle one clip position but then it pinged worse so i lifted the needle 2 positions and it stopped it pinging and seemed to run ok on the track.
Its doing my head in not really knowing what to do and i know it will perform a whole lot better once its sorted.
I checked out the FMF jetting guide and they reccomended,
Pilot-35
Main-410
Needle-12-82 second clip position
Air screw- 1.5
At the moment it has
Pilot-40
Main-430
Needle-26-65.......(im guessing you go by the last four numbers on it)
Clip- 4th position....(down from the top)
Air screw- 1.5
I dont know what the standard jets are but have been told that it is one bigger than stock on the main and they go up in tens.
I think its stock apart from the FMF Pipe and shorty and i run 98 octane.
Any help or suggestions would be greatly appreciated if i haven't confused you all
Cheers Scotty :D
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I'm not familiar with the CR jetting specs, but, in my experience, the correct needle can really make a big difference. I have a KTM for which jetting can be difficult, but after some trail and error, I got her where I want it.
How worn is the top end? I ask as many times I've seen a worn top end wreck havoc on jetting. What worked before now doesn't, why... the top end is over due for a rebuild...Sorry I can't help you with the specs, but I'm sure someone will post something that will get you headed in the right direction. One piece of advice, change one thing at a time Keep notes as to the changes made and how the bike runs. It helps knowing what changed when trying to evaluate how the bike is performing.
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Oh yeah the top end is 2 rides old and the cylinder is near perfect.
Pipe is not much older with zero dings or anything.
Thanks Eric :-)
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Could you post a picture of the plug?
Silencer/filter o.k?
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The the silencer is new and have only ridden the bike about 4/5 times with it on there.
Filter is clean everytime i ride the bike, i checked it yesterday after the weekend and it was spotless because it was so muddy.
Pplug is black n wet.
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Check your needle and seat. It may be flooding.
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I thought about that kiwi and the float level seemed a bit high, the needle n seat looked good though so i set that.
Goin out again sunday so will see how it goes then.
Thanks for the input :D
And can anyone tell me what a JD jetting kit is? Is it just a box full of jets n needles n stuff?
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Scotty
What spark plug are you useing in your CR? If you are useing a #9 plug try dropping to a # 8 plug that will be a little hotter plug and that will help burn off the excess pre-mix that is put into the engine on start up. You could also drop 1 number on your pilot jet that will cut back on the pre-mix that is put into the engine on start up also. Find out what the stock jetting should be first and go from there but dropping 1 number on the pilot and going to a # 8 plug would be the first two things I would do then adjust the air screw according to get the correct reading on the spark plug. You say you are useing a FMF exhaust so FMF is probably saying to go 1 to 2 main jets leaner I'm just guessing though if thats the case then start with the next leaner main from stock main jet and try adjusting the air screw 1/8 turn in from what your manual says for that leaner main jet and do the WOT test and see what your plug looks like. I have a 2002 Honda CR125 I'm useing a pro circuit works exhaust with mine and I did the things to my bike that I suggested to you and my 125 is running great I'm going to go 1 more main jet leaner #380 to get rid of a little more spooge nothing is running out the end of the exhaust but you can see just a little yet just around the inside edge of the silencer.
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Scotty
The stock jetting spec for your 2005 CR 250 are main jet #420
pilot jet #40
neddle 6DGy26-65 clip 3rd position from top
air screw 2 turns out
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Scotty
One thing a motocross bike shouldn't have is a idle couple of reason's for that 1 being if your racing or just play riding and you go down your bike will shut itself off and not lay there running wide open and possibly blow the engine. Reason 2 is fairly simple when you start the engine your putting pre-mix into the engine and if your bike is sitting there idleing your engine is actually loading itself up.Because the engine isn't running at high enough RPM to keep the eccess pre-mix burnt off. If you get rid of the idle you have to keep blipping the throttle to keep it running and your keeping it cleared out. But I would still try going 1 size smaller on the pilot jet and 1 number hotter on the spark plug both of these will help also.
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Hey Oldermxr
Im pretty sure im runnung an 8, and obviously my jetting is stock apart from the richer main jet,
i think i'll take your advice and go one leaner on the pilot coz thats were i thought
the problem was.
I know what ya mean bout the idling thing, ive never really liked my bike to idle for those reasons you stated. When im sittin on the line just givin it small blips to keep it goin while puttin me goggles on she got choked up bigtime.
Will try the smaller pilot and check the plug heat range and see how it goes.
Thanks for the info, appreciate it
Scotty :D
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What type of mix are you running?
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Im running 32:1 bel ray SL-2
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Scotty
No problem hope I was some help I'm useing a NGK iridium plug in my CR125 and I think they are much better than the regular NGK plugs they take less spark to fire and throttle responce is some better also.
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What type (octane) of gas are you using? ;D
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Im running 98 octane
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Has your CR run better in the past? What's running through the back of my mind is that I recall Motocross Action doing a test on your bike and having problems similar to what you described.I also remember them becoming quite frustrated in their attempts to rectify these "driveability"
issues.I'm trying to figure out if your jetting problems are just that, jetting problems,or if you are up against something more that is a result of Honda releasing a motorcycle that was (maybe) not quite right.The CRF450 was brought out just after this model (if my memory is correct) and your case reed,electronic power valved CR suffered as a result.
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Could it be very sensitive to temperature/weather conditions etc?
The reason i ask is yesterday the thing ran perfect!
It didnt reslly choke up at all, only a slight sputter when i would go back on the track.
Last week was wet n miserable and about 19 degrees C
Yesterday was perfect about 25 C. The best day for riding.
Now that you mention it Sachs it has its moments.
I might still get a leaner pilot just to clean up the bottom.
Thanks for the input :-)
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i think the best way to get a proper jetting to a cr is to forget about the mikuni tmx and go for a keihin carb.
i'm about to do that on my cr 125..
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I thought getting a new carb too........maybe one thats attached to a new bike :-)
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Scotty I see you are still having some problems with your CR250 I would still try going 1 number smaller on the pilot jet there not that expensive. And something else I was wondering how old or how many times have you rode your bike with the spark plug you have in it now? Plugs for a 2t don't actually last a real long time maybe your plug is in need of being replaced. And how fresh is your pre-mix your useing?
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Could it be very sensitive to temperature/weather conditions etc?
The reason i ask is yesterday the thing ran perfect!
It didnt reslly choke up at all, only a slight sputter when i would go back on the track.
Last week was wet n miserable and about 19 degrees C
Yesterday was perfect about 25 C. The best day for riding.
Now that you mention it Sachs it has its moments.
I might still get a leaner pilot just to clean up the bottom.
Thanks for the input :-)
I can't answer about your CR, but my KTm is very sensitive to weather conditions. Currently I've jetted it for summer conditions, but I will be adjusting as it gets colder. Sometimes its just an air screw adj, but when it gets colder, I'll be adjusting the clip position, and then the needle too.
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Scotty how many races/rides do you have on the present spark plug in your CR250? your bike isn't going to be tempermental to only a 6 degree tempurature change.#1 It could very well be that your spark plug needs to be replaced #2 did you mix up a new batch of pre-mix and you got new gas? You could have got ahold of some bad gas too that does occationally happen.
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Oldermxr, im not too sure how old the plug is, i know its not too old but i think it might have been fouled and cleaned so im gunna get a new one and a smaller pilot, i didnt get a chance last week due to work, my premix is always new, i put what i dont use in the car.
Thanks fellas :-)
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Scotty your plug could very well be part of your problem that I last read about specially if it's been fouled before and cleaned. If you are doing alot of racing and play rideing I would replace your plug every 8 races/rides. And glad to see your going to go with 1 number smaller on your pilot jet. A new plug and smaller pilot jet you should be good to go.
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Will let ya know how it goes,
thanks Scotty :D
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Im not happy with the way my 05CR 250 is running at the moment.
It fouls up easily if im just riding slow even for a short distance and it never has been very crisp.
On the weekend even just sitting on the start gate for 2 minutes it would choke up even though i had just cleared it out. Although i have issues with it pinging. I dropped the needle one clip position but then it pinged worse so i lifted the needle 2 positions and it stopped it pinging and seemed to run ok on the track.
Its doing my head in not really knowing what to do and i know it will perform a whole lot better once its sorted.
I checked out the FMF jetting guide and they reccomended,
Pilot-35
Main-410
Needle-12-82 second clip position
Air screw- 1.5
At the moment it has
Pilot-40
Main-430
Needle-26-65.......(im guessing you go by the last four numbers on it)
Clip- 4th position....(down from the top)
Air screw- 1.5
I dont know what the standard jets are but have been told that it is one bigger than stock on the main and they go up in tens.
I think its stock apart from the FMF Pipe and shorty and i run 98 octane.
Any help or suggestions would be greatly appreciated if i haven't confused you all
Cheers Scotty :D
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maybe get rid of the mikuni carb and put a keihin
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Scotty I looked at the test that Motocross Action Magazine did on your 05 Honda CR250 and they said going up one on the main jet made it burble on going down one made it ping so they left the stock 420 main in. Your clip possition on your needle should be 3rd from the top. Your air screw should be 2 turns out from all the way in with useing the stock pilot jet wich is a #40. Also try your pre-mix ratio at 40:1 instead of 32:1 that will make a big differance also. Your running too rich so you need to lean it out put the stock 420 main jet in try 1 smaller on the pilot and mix up your pre-mix at 40:1 Turn air screw all the way in and back it out 1/4 turn and start the engine start blipping the throttle and turn the air screw out 1/4 turn at a time till you get clean crisp throttle responce also put a number #8 spark plug in it.