Fuel screw washer

What would be the impact if the washer on the fuel screw is missing but the oring and spring are present?  Bike is 2007 KTM 250 SXF.  I am assuming this has been this way for quite some time and the bike is extremely difficult to start.  Troubleshooting other parts of the carb but discovered this on the fuel screw.  

You need it.

Without it you will leak air.

Replace your pilot jet with a new on while you are at it.

Thanks.  I hope that is the case and part of the cause for the problem.  10-4 on the pilot jet replacement.  Just put a new one in as part of the troubleshooting effort.  Much appreciated.

To add, not only does it add pressure and help sealing, it prevents the sharp edge of the spring from digging into the oring and tearing it.

Thank you.  So you think then that a missing washer could be a contributing factor to a hard starting condition?

Well... maybe.


If it is only hard starting when cold, that could be too tight valves.


Usually, choke adds enough fuel to compensate of any 'imperfections', even the size of the starter jet is not that big a deal.


If when the bike is running, it idles normally, then the pilot/fuel screw is not a significant issue. If the fuel is old, that can contribute to hard starting. Some bikes the carb passages drain out and if the bike has been siting for any length of time, take a few kicks to refil them. My DRZ is like that, the WR, is not. Both have a FCR carb. The DRZ has a vacuum petcock and it takes a few vacuum pulses to refl the bowl, contributing to it.


Starting is the one time when everything must be right. RPM is only between 500 to 1,000, that is 1/4 to 1/3 of idle speed. So all the ducks must be in a row.

All 4 valves are right in middle of spec.  Cam timing is spot on.  Choke is new.  JD jet kit (installed many years ago) which has a different needle, 185 main (stock was 170 or 175), the addition of the leak jet (60) from a plug, and the oring mod.  Otherwise bike is totally stock.  Carb is clean and installed a new 42 pilot jet (previous was the original 40).  Just extremely difficult to start with the kick starter.  Pretty easy to get her going with a bump start and once running runs very strong.  Also, it was not great at restarting once warm but alot better than when cold.  


I have not remounted the carb yet with new pilot jet as I found this issue with the fuel screw so I will get that today and then put her back together and give it a try.  Accel pump diaphram is fairly new as well (which is a JD jet part that has a longer rivet/rod than stock I believe).


Any other recommendations while I have the carb off the bike?

Nope. You sound like you are on top of it.


This might help

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 1,850 rpm, but go by the spec in your manual.

Put everything back together and same deal.  No start using kickstarter.  Got her started by bumping and set the fuel screw setting.  She idles perfect and does seem to start better when ho and runs like a champ through the entire rpm range.  Let her sit overnight and same deal, no start with kickstart.  Seems like she wants to catch but just doesn't.  Still think its fuel/air related.  Started messing with the start procedure and found that she is more likely to catch when cold if I hold the throttle at about 1/4 open.  


The choke does not help when cold but pretty sure the choke circuit is working as when she is warmed up and idling and i pull choke she dies.  


What does holding the throttle at 1/4 open do in respect to fuel and air and is there a logical reason why this would help the cold starting?  

Have you checked the valve clearances? Hard cold starts is also signs of too tight valves.

Yep.  All 4 are right in the middle of the spec.  Have not tested compression or done a leak down but she sure seems to have good compression.

how old is the spark plug in it?

Brand new.  Replaced it when I reassembled this time.  The old one was not that old either and looked in good condition.  No signs of anything bad based on the brownish color.  

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