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YZ250F bog and high idle

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ok i cleaned the clogged jets out twice tonight and still the same hard start even when its cold.... i guess the only thing i can do is switch the 45 jet back to the 42 stock jet, to see if it changes the problem. thats the only thing i changed so hopfully it fixes the starting problem. any ideas would help thanks

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i switched the jets back and still a really hard start when its cold. im going ridding tomorrow. we will see how it starts when its hot.....

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ok i went ridding on saturday, and it is really hard to start, i changed back to the stock jet to see if that was the reason for the hard start. it probably took 50 kicks cold or hot to start this thing. it almost seems like im not getting a spark. could the stator be going bad? what else could go wrong with this bike now... i almost think i got a lemon...lol

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Ok, so lets recap. Corre34ct me if I miss something.

Valves in spec

Hot start cable has free play and plunger moves freely.

Choke plunger is in good condition

Pilot jet is correct size, is new and the fuel screw is set correctly

Vacuum release plate on the slide is installed correctly and not cracked

Float level is correct

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valves are in spec

hot start cable has free play and the plunger moves up and down

pilot jet is the stock size (42) now thsts also called the slow jet correct?

vacuum release plate is square side down and looks fine

ok two things you said i have not checked. the choke plunger and the float level. i can figure out the choke plunger. how do i check the float level and how do i adjust it if its out of wack.

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Yes, the pilot jet is also calle dthe slow jet.

Best source for info to adjust/check the float height is your owners manual. Easy to do though you do have to remove the carb and follow the steps exactly as outlined in the Yamaha Bible. After you've read the manual a few times on this subject, if you are still confused, ask a Q then.

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"Check" the float level:

1. Place bike on level stand.

2. Hold the float bowl drain tube up to the side of the carb.

3. Open fuel tank shutoff and float bowl drain.

4. View the level fuel rises in tube. (should be at the float bowl to carb seam at the center of the carb)

If not - set it according to the manual and recheck.

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Harry, you have any idea how much of a pain it would be to terst the height, have to pull the carb, adjust the height, install the carb, check the height, pull the carb..... Let alone the fact that factory height spec has nothing to do with this method? Fuel height is below the seam on an FCR. Factory method is for the bowl off, carb on its' side, float tang barely touching the needle valve pin (no compression whatsoever) and measuring. Though if you checkedset yours right and then did the bourden tube on the side trick, you can easily see if it does need adjusting. However, I've found floats rarely do and therefore never bother to do this. Usually it is a set once and never touch again though I do spot check float height when a carb of off a bike and the bowl is removed. Sort of a 'while I am here' sort of deal.

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Turn the idle up the 45 or the 42 should work fine your high idle problem is probably not fixed and the idle is turn to low and causes the hard starting this happen to me while trying to fix the same problem still haven't found the solution. An earlier post makes sense about the oring .

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your hard starting is most likely from a high float level. Set it down a bit.

Also you did not post the valve measurement. Close might be to tight. Might want to do a little better there.

Here is a writeup on the TPS that I did a few years back - might help you out:

Many people have had a hanging idle or idle that is slow to come back down. It can be annoying to deal with and it is not a jetting issue. The problem lies in the bikes 3d ignition mapping!

In plain english your bike's CDI works on a 3D mapping. It has a preset engine mapping that adjust with the amount of throttle it senses from the TPS (throttle position sensor). The CDI can work in a 2d mode (TPS unplugged), but power and responsiveness will be degraded. The TPS is located on the carb on the opposite side as the throttle cam and is ADJUSTABLE!

Essentially the reason for the idle issues is you have the slide set to high or low and then when the ECM figures this out it adjust timing. Resulting in increasing or decreasing RPMS. This is the cause for the surging/hanging idle.

The following procedures will help you fix the problem! You will need to get the factory service manual to help you with the setting valves of the TPS ( I have a YZ250F manual, so I will take some info from that for the article. Most likely the other FCR carbs are very similar in settings and procedure)

It assumes your jetting is close, carb is clean (all jets are blown through including the leak jet, one way valves in the carb body and bowl, and all tubes in the intake bell), fuel screw is installed correctly (o-ring, washer, spring, screw), hot start and choke plunger are clean and lubed up, new or clean air cleaner, good gas, valves are in spec, and finally good compression on the motor.

You first need to set the idle screw properly and check the cable free play at the carb end. Start by disconnecting the TPS sensor.

1. Set the idle screw down until the bike will not idle. Start up the bike with about 1/8 throttle then adjust the idle screw until it holds steady RPMs.

2. You need to check the free play in the throttle pull AND push cables. Open the side cover of the carb and adjust so there is just a bit of free play. If you dont have freeplay, you will not allow the throttle cam to rest on the stop, thus the slide is up causing the fast idle.

To test if the TPS is the problem, plug it back in. If the bike does NOT idles normal, you know you have the TPS/Slide/throttle fighting each other. Now you need to plug back the TPS and get the factory manual out. Find the section on the TPS sensor. The problem you need to fix is the TPS output voltage. Basically this is telling the CDI the throttle opening. (my YZ manual has it between .58-.78V at idle). Most likely you are out of this specified range. To set this, you need a volt meter.

Tester + lead – Yellow lead on TPS plug

Tester – lead – Black lead on TPS Plug

Loosen the T25 torx screw

Start the motor and adjust the TPS until it is within the specified output voltage.

Tighten the T25 screw back down, and rev the engine a few times. Your problem should be solved now!

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Thanks guys thats alot of info and work thats gotta be done, i have not had a chance to work on it yet. it will probably be next week. i will definitly let you know...

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I adjusted the float last night. This is the first time i ever had to mess with float adjustment. i follwed the directions in the book and think its correct. on the needle seet that the float pushes up there is a little spring loaded pin, with the carb at the right angle the float should only rest on that, Right? thats how i have it. ill get back to you tonight on my valve clearance.

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ok i checked my valves and the exhaust are 0.15 left, 0.15 right. my book says .17-.22 is the spec. my intake is .12 left, .12 center, .10 right. the book says .10-.15 for the spec. my exhaust is out a little. what would that cause?

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ok i got someone to check my float that knows what they are lookin at. and the bike still does not start. he brought over a spark board and i am not getting any spark, we checked it on my wifes bike and her's sparks great (my friend got shocked pretty good. that was funny) what should i check for. Stator, CDI, ignition coil assy?

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i was just thinking about the kill switch. i will take it all apart this weekend, what is a good way to clean out the cooling system and what is a good coolant to use. while its apart i want to get all that taken care of.

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