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Hot Starting Problems

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This is an '05 yz250f. Won't restart worth a damn if I stall during a harescramble. Hot start button dosn't help, choke doesn't help. Kicking with throtttle wide open about 10 times (or until it catches) then kicking with throttle closed sometimes helps.

Jetting is a 178Main, 40 Pilot, 1 1/2 on the screw, stock needle #4 posit, spark plug is fresh and has good spark, air cleaner fresh and valves checked and within spec, float level in carb is correct. Runs great with good throttle resp and no bog, starts fine cold.

Any suggestions on what else to check or try? I'm at a loss on what to do next.

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y would u use the choke when its already hot..it would make it richer, and the point of the hotstart lever/button is to allow air through to lean it out and cool the temps

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try a 38PJ just for giggles.

What is starting procedure cold? choke off or on? any throttle blips needed?

have you checked your valves lately?

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Cold starting procedure is turn on gas, pull choke, move starter lever to point of resistance, move back and then kick. No throttle. If its below 50F i twist throttle twice. Usually starts by 3rd kick.

Valves where checked yesterday and are in spec.

Tried the choke out of desparation. I tried the 1st 50 kicks with the hot start lever.

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One note on the valves: you are looking for them to be too _tight_. I did not clue into this right away with my 01 yz250f that was a bastard to start hot.

My valves were way out of spec and still aren't were I would like them but I had to put my bike back together for a HS. During the race I stalled a few times and either the bike fired right up with the hot start out or I tried a trick I learned here reading many, many 'won't hot start' threads: hot start out, s..l..o..w..l..y twist the throttle all the way open (so it doesn't get a shot of fuel), kick it twice, release the trottle and it started on the 2nd or 3rd kick after that.

Dunno why but man was I relieved :applause:

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try the 38PJ.

With jetting, it's never "is it right or wrong but does this jetting work on my bike."

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Wild Iquana,

did you ever find the cause of the hot start problem?

I have a 2005 YZ250F with the same problem.

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This is an '05 yz250f. Won't restart worth a damn if I stall during a harescramble. Hot start button dosn't help, choke doesn't help. Kicking with throtttle wide open about 10 times (or until it catches) then kicking with throttle closed sometimes helps.

Jetting is a 178Main, 40 Pilot, 1 1/2 on the screw, stock needle #4 posit, spark plug is fresh and has good spark, air cleaner fresh and valves checked and within spec, float level in carb is correct. Runs great with good throttle resp and no bog, starts fine cold.

Any suggestions on what else to check or try? I'm at a loss on what to do next.

I would say you're too lean on the pilot jet. What elevation are you at? I'm in California, and ride between 500 ft to 6000 ft. I'm running a 175 main, a 45 pilot, a 100 Pilot Air jet, JD jetting needle (depending on the season I use either the hot or the cold one) in the middle, and a 40 leak jet. The fuel screw should be somewhere between 1 1/2 to 2 turns out.

I know I'm on a WR, but my WR is about as close to a YZ as you can get & have the e-button.

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Join the crew, if mine gets dumped it takes 4-6 wide open throttle kicks and one half throttle kick to get it to fire up. It works every time its just annoying.

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deep joy some one else with same problem any one sort this my 450 is exactly the same and really is pain in ass

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I have two 05 YZ250Fs. One (my bike) can be a SOB to start once it's hot- it is EXACTLY like previously mentioned- crack the throttle and be ready to kick it a dozen times. Some days, it starts ok, other days it's just about horrible. When things are bad, it goes like this- stalls really easy w/ a flame-out pop, and then it's going to be a rascal to restart. However, within the very same day, it might re-start with no hassle whatsoever.

The other 05 YZ250F (kid's bike), has NO such problems. Jetting is bone stock on this bike except for a #45 pilot and 172 MJ.

Since 2003, I have also owned two 03 YZ250Fs and currently own a 05 WR250F. None of those bikes had/have such starting issues. Jetting changed things a little on these bikes, but NEVER did these bikes turn so rude as my current 05.

So back to my 05..... I've checked and double-checked everything possible. I was wondering if maybe clutch drag is the problem; sorta seemed so, maybe(??). Just a couple of days ago, I swapped to a new CDI box. I have not yet taken the bike for a good heat-soaked ride, but I can say that the starting SEEMS substantially better and the closed throttle back popping is ALL different than before. Rule out the clutch drag- with the new CDI, I can release the clutch until it drags and the engine will still start reliably. Here's to hoping the old CDI was the issue.

Stay tuned, I'll post more as I learn more.

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yep went out last night still bastard to start really annoying me know ,noticed winding pilot all way in doesnt make one bit of difference so going to try 40 pilot,see if that helps,noticed if stalls only way to get going is 10 kicks throttle wide open then kick as normall usually works but got hare scramble sunday so some help before would be appreciated ,come to stage where thinking getting bike with electric start:cry:

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Pmayo,

Sorry to hear your bike is being a jerk. I shared/feel your pain. It truely sucks when the bike doesn't start, I've tossed away two of three races this year while booting away this year. Needless to say, it REALLY tests your faith in the bike when it coughs out and leaves you kicking. What also REALLY sucked about my YZF's starting, is that my girl-button WR kick-starts soooo reliably that it really doesn't need a button. My other YZFs were also very reliable starters, ALWAYS starting within 1/2 dozen kicks even after a hot-engine cartwheel, flopped off the side of a hill, etc.

My advice would be to not get an e-start based off of owning a bike with a personal problem, btw. The E-start bikes are heavier and are different animals if you are used to a YZF. Not trying to say the E-button bikes are bad, but just different and you might not like the difference.

I'll get some testing in this weekend and report back.

The fuel screw (is that what you meant) should be something in the range of 1.62-2.25 turns out.

Also, give the carb a really good cleaning.

-As a salvage plan for the weekend, try starting with the bike in neutral when restarting. That seemed to help a bunch when my bike was in a bad mood.

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yep went out last night still bastard to start really annoying me know ,noticed winding pilot all way in doesnt make one bit of difference so going to try 40 pilot,see if that helps,noticed if stalls only way to get going is 10 kicks throttle wide open then kick as normall usually works but got hare scramble sunday so some help before would be appreciated ,come to stage where thinking getting bike with electric start:cry:

I'll guess that when you said "winding pilot all way in" means you turned the fuel screw (bottom of carb, accessable through a hole in the float bowl).

The purpose of the fuel screw is to fine tune the pilot jet so it has the perfect air fuel ratio. It can adjust the pilot jet from one size lower to one size bigger than what you have in there. Now the problem is getting within one jet of having the right jet in there. What I'd do is look at the jetting sticky on this forum, and try to find a good number of bikes that are equipped like your is. See what they are running. Get an average of that, and your'e probably going to be pretty close to finding the right pilot jet.

In order for this procedure to work, the bike needs to be idling somewhere around 2000 rpm's.

Put the one you decide on in the carb. If you don't have a lengthened fuel screw it might be a good time to get one. It makes adjusting it easier than the stock one. It's hidden up in there pretty good, and you'll need a tool to adjust it. The lengthened ones you can do it with your hand (no tool needed).

Set the fuel screw to 1 3/4 turns out from all the way in.

Start the bike (hopefully it will behave itself). Get it good & warm (ride it for 5 minutes or so). Now start turning the fuel screw 1/4 turn at a time, and listen. What you are listening for is a change in idle. You're trying to find the highest idle you can get, with the fuel screw out somewhere around 2 turns.

So turn it out 1/4 turn then listen for 5 seconds or so (it takes a second or 2 for the change to take effect). You just richened the mixture a little. If it didn't change anything turn it another 1/4 turn out & listen. If you have it more than 3 turns out & it hasn't made a change start turning it in. This will start leaning it out. Keep turning it in until you either hear the idle change, or the screw is all the way in.

If you have the right pilot in there, you'll find the spot where the idle goes to it's highest somewhere around 2 turns out. If you have to go up to 3 turns out to make a change you have too lean a pilot, and need to go to the next number higher. If you can turn it all the way in (shutting it off completely) and the bike doesn't die, then you have too rich a pilot in there & need to go one size leaner.

Of course an exhaust gas analyzer makes this much easier, but not everyone has one of those (but I do). I tuned many bikes by ear without one but having it makes that job go quicker & when you're doing it for a living, it's all about being quicker.

good Luck!!!!

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