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need jetting help


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ok...i searched, but there were so many pages, i figured it would be easier to just ask.

as you may now, i had been having problems with my 95 yz250. it didnt like running at all to say it simply.

i found out the problem was the timing. now it starts, and after it starts, it runs like a raped ape. the problem is getting it to start. it is still a bear to start. i have found that if i open the throttle somewhat whle kicking it over, it will start easier. i know it has to be a jetting issue now. can anyone shed some light on what i need to adjust to make it easier to start?

the only things it has done are a new wiseco top end, and then the boyesen power reeds. i ride in the trails a lot, so i left the stock exhaust on there to keep some bottom end.

carb settings:

168 main jet

48 pilot jet

air screw is 1.25 turns out

stock needle in the third clip position i believe

i know the carb is not dirty, as i literally cleaned it right before i put it on the bike. so please, any help would be appreciated.

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clean air filter? new, properly gapped plug? fresh fuel? choke? once started, how does it idle?

brand new air filter, brand new freshly gapped plug, fuel was just mixed 5 minutes before pouring it in. what do you mean on the choke, and after about 30 seconds at idle, it dies

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turn your idle screw in (higher idle) see if that helps, 48 pilot seems big but I've never had a 95 yz250, so I dont know

i dont really care if it idles. i can keep it running once its fired and started. what im getting mad at is how hard it is to start. or are you saying you think opening the idle screw up a bit more would make it easier to start?

and the 48 is stock iirc

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yes the higher idle makes it easier to start, thats why you have to open the throttle right now to make it start easier becuase your idle is too low. increasing your idle is basically like holding the throttle open a little while kickin it over, except you dont have to touch the throttle.

My 125 will idle all day long (ofcourse I dont let it do that)

Edited by Luigic81
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yes the higher idle makes it easier to start, thats why you have to open the throttle right now to make it start easier becuase your idle is too low. increasing your idle is basically like holding the throttle open a little while kickin it over, except you dont have to touch the throttle.

My 125 will idle all day long (ofcourse I dont let it do that)

makes sense. right after i posted that, i was like "wait...the idle just holds it open a bit more...kinda like when im twisting the throttle........."

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stock jetting for your bike is as follows

Main: 175

pilot:48

needle/clip pos.:r1367k-3

neddle jet:2.9

air screw:1 1/4 turns out

starter jet: 85

float arm height: 15-17mm 0.59+/-0.69 inch

do you use the choke when you start it? if so keep your hand off the throttle. maybe turn up your idle. if the bike surges at idle turn your air screw in in 1/8 turns untill it idles smoothly.

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update. in addition to what i said in my first post, i need to add that when trying to start it today, it backfired like three times. i dont know what to do at this point, but i know going to a shop isnt the right choice

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did you try raising the idle?

I dont think I've ever heard a 2 stroke backfire

i did raise the idle. i guess i shouldnt have said backfire. i really dont know what the hell to call it though. it sounds a lot like a huge burst of compressed air being released. Im not sure if its coming from the airbox or tailpipe though. i would assume the tailpipe, as the airbox is basically closed off from backpressure due to the reeds. maybe you have heard something similar happen? worst case scenario, i can make a video of me trying to start it and hope that sound happens again

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another addition. i just realized that i am a fkn moron. i had forgotten that the CYLINDER is from a 96, but the bottom end is from a 95. in the manual, it says to set the timing at tdc for the 96, and .031" BTDC for the 95. Is it possible that the porting on the 06 cylinder is causing all this and giving me this massive starting headache? if nothing else, should i just go for broke and set the timing for that and at least try it out?

throw me suggestions please.

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another update. the bike starts reliably(first or second kick cold) as long as i have the throttle wide open. after that, it runs fine. what would be the proper jetting modifications to fix this? i have a 168 main, 48 pilot, 85 starter, and the air screw is 1 and 1/4 turns out

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Air screw sounds right, as long as it is at least 1 turn out. Your now saying that it idles fine AFTER you hold the throttle wide open when you start the bike?

From your kick starting video I heard it pop twice, sounds like it's not getting enough fuel upon startup. Your choke passageway could be clogged, and/or the pilot jet is clogged.

How many turns is your idle screw from fully in? should only be about 2-3 turns out for a decent idle, any more than that and you'll have to keep your idle going by blipping the throttle.

Take the carb off, remove the bowl, remove the choke plunger and take out the main and pilot jets along with the float.

Use carb cleaner and blow out all passageways, use q-tips to clean out the choke passageway and main jet passageway. The main jet passageway is pretty thin, but if you pull off most of the cotton on the q-tip and leave just a little on, you can swab it good ­čśĆ

Check your float, the tang on the float should appear to be straight and not bent, either way check the float hieght and make sure that it is in spec.

After all is said and done the bike should start in the first two-three kicks at the most with the choke on and engine cold.

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Air screw sounds right, as long as it is at least 1 turn out. Your now saying that it idles fine AFTER you hold the throttle wide open when you start the bike?

From your kick starting video I heard it pop twice, sounds like it's not getting enough fuel upon startup. Your choke passageway could be clogged, and/or the pilot jet is clogged.

How many turns is your idle screw from fully in? should only be about 2-3 turns out for a decent idle, any more than that and you'll have to keep your idle going by blipping the throttle.

Take the carb off, remove the bowl, remove the choke plunger and take out the main and pilot jets along with the float.

Use carb cleaner and blow out all passageways, use q-tips to clean out the choke passageway and main jet passageway. The main jet passageway is pretty thin, but if you pull off most of the cotton on the q-tip and leave just a little on, you can swab it good ­čśĆ

Check your float, the tang on the float should appear to be straight and not bent, either way check the float hieght and make sure that it is in spec.

After all is said and done the bike should start in the first two-three kicks at the most with the choke on and engine cold.

well...its REALLY hard to tell on the idle screw. this model came with the keihin carb that has the idle adjuster on the choke knob. it feels like it just spins for days. also, it doesnt idle good as of right now. i have to blip the throttle to keep it running(not a big deal to me...used to doing this on my rc cars). i was trying to adjust the idle today while blipping the throttle, but was a dumbass and turned the knob the wrong way.

as far as the carb being clean...it is cleaner than a brand new ferrari. the only thing i didnt check was the choke plunger, but I will do that tomorrow.

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If the idle adjustment is on the choke plunger and it will not seem to come to any sort of setting, maybe something is stripped internally.

A new choke lever is around 50$ and might be worth the money if you want to stop blipping the damn throttle every 5 seconds to keep the bike alive.

I suppose if you do MX or SX or hare scrambles, your not really ever going to come to an idle when your riding the bike. But when your trail riding, waiting for your friends, or taking a quick break, or getting something from your pack, it's nice to not have to touch the throttle to keep the bike going.

For me this would be worth the 50$

Or you could find one used for 5-10$

Again though, does the bike idle fine after you start it? You said it ran fine after you started it in post 14 but I don't know if you mean it runs fine but doesn't idle, or idles and runs fine???

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what model is your carb? do you have a pic of it?

DSC01948.jpg

DSC01950.jpg

If the idle adjustment is on the choke plunger and it will not seem to come to any sort of setting, maybe something is stripped internally.

A new choke lever is around 50$ and might be worth the money if you want to stop blipping the damn throttle every 5 seconds to keep the bike alive.

I suppose if you do MX or SX or hare scrambles, your not really ever going to come to an idle when your riding the bike. But when your trail riding, waiting for your friends, or taking a quick break, or getting something from your pack, it's nice to not have to touch the throttle to keep the bike going.

For me this would be worth the 50$

Or you could find one used for 5-10$

Again though, does the bike idle fine after you start it? You said it ran fine after you started it in post 14 but I don't know if you mean it runs fine but doesn't idle, or idles and runs fine???

the bike runs fine, aside from idling. and i am pretty sure the idle can be taken care of via the adjustment knob. when i turn it, it makes a definite difference. i can crank the idle way up or have it where it is now and not let it idle. im hoping if i can work out the idle tomorrow(technically today), it will start fine. if i can get it to start fine and not fix the idle, i really dont care. money is tight here, and i still have work i need to do on my streetbike, so im trying to keep any costs at a minimum. as i said earlier, i am used to having to blip the throttle all the time with weed eaters, chainsaws, and all my rc cars, so it kind of comes natural

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