hard to warm start...

'08 yz250f starts great cold but after riding for a while if i stall it on the trail it seems to be hard to start. The bike has been running great until the warmer weather hit. I am thinking to adjust the air screw... does that sound reasonable, and if so I'm thinking to lean it out for the warm weather? Valves are good...... thanks

Are you using the hotstart lever?

Fuel screw adjustment... 1/8 turn in, test.

thanks, this is while trying to start with or without the hot start lever

What I do is pull hot start and do three quick kicks to clear motor of excess fuel. While keeping hot start pulled I do one real kick and it always fires for me.

You're correct in your logic. Usually this issue is caused from too rich a fuel mixture. Shrub it up also suggests a good restart procedure. I have also found that if you kick too hard, it will not start.

It's the valves duh? If you pull the hot start hold throttle wide open kick through five time close throttle pull hot start and it does not go in one or two kicks on a five valve motor it's time for valves.

Not valves. Valve issues make cold starts near impossible, not hot starts. Bike is too rich on the pilot/fuel screw.

Fuel Screw/Pilot Jet

Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.

Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.

*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***

Turn the screw in until the idle becomes rough or the bike stalls.

if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.

If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.

Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.

If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.

If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.

If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.

Thaks to all, I pulled the plug, It has been burning rich. Turned the airscrew1/4 in and seems to be a bit better, I will need to get some seat time to fine tune.

Hey "gruberyz", this is the last sentence of my initial post, "Valves are good". Maybe reading the infomation in its entirety would benifit you...DUH

if none of this works...try replacing your coil. its simple to switch and try a new one. if this bike has been really hot at one time or another, this may be your problem... Two of My friends have had this same problem with the yz250fs. This fixed them both. unless they jump time, yamahas are the best on valves! A new coil is around 80 bucks. Mite try it. They did some testing at the Yamaha shop in Jasper (Obermeyer) after putting a coil in the oven, they came out testing bad...Hope this helps!

Thaks to all, I pulled the plug, It has been burning rich. Turned the airscrew1/4 in and seems to be a bit better, I will need to get some seat time to fine tune.

Hey "gruberyz", this is the last sentence of my initial post, "Valves are good". Maybe reading the infomation in its entirety would benifit you...DUH[/QU.OTE]

So you pulled the cam cover and checked the clearance? Or you know it's good because it just can't be that? Having owned an 07,09 YZ250F I'm still banking on valves. Let me know when you change them out and it starts right again. :thumbsup:

Thaks to all, I pulled the plug, It has been burning rich. Turned the airscrew1/4 in and seems to be a bit better, I will need to get some seat time to fine tune.

Hey "gruberyz", this is the last sentence of my initial post, "Valves are good". Maybe reading the infomation in its entirety would benifit you...DUH

Plug reading is a waste of time. Do not go by it. Do the test I outlined and set the fuel screw according to it. Do not make arbitrairy adjustments. Be sure the bike is completely heated up, after at least 15 minutes riding time.

"So you pulled the cam cover and checked the clearance? Or you know it's good because it just can't be that? Having owned an 07,09 YZ250F I'm still banking on valves. Let me know when you change them out and it starts right again."

-I checked the valves, there were in spec.

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