[conner21]

I just put a new cylander, piston and rings, cylander head and valves in my 05 rf 250r and it wont start any ideas?

[crfsonly]

welcome to CRF's Only! there are many reasons why it may not be starting. check the timing. check for spark. check the carb, make sure the AP is giving good squirt. check the jets and make sure neither is clogged. when in doubt replace them. check for air boot leaks. check hot start cable is seated and functioning correctly. report back.

again, welcome.

ken

[conner21]

I checked the timing and it has spark. It backfires evry once in a while and it srems like its tryn to start. Ill check the carb and let u kno.

[crfsonly]

make sure you are checking the timing with the cam chain tensioner active. it's very easy to be off one tooth. if you went into the carb, make sure you have the floating valve plate and seal installed correctly.

[conner21]

The carb looked really clean and the jets werent cloged. When i kick it over it sounds like airs comin out of my airbox. my intake valves are at .005 and .006 and my exaust us at .010

[crfsonly]

even partially clogged jets, especially the pilot jet, will have a significant affect and you can't just do a "light test" to verify. i would also check the slide and make sure the plate is installed correctly.

[conner21]

Im gonna tear the carb down and clean the whole thing just to make sure. Does the air comn out of the airbox mean anything?

[crfsonly]

don't use carb cleaner to clean the carb as it will break down any rubber seals. check our how-to's for some carb restoration tips. if you are talking about the vent tube you will need to either restor the oem vent equipment or use this blocked off with one of these kits:

http://www.crfsonly.com/catalog/product ... ts_id/1048

ken

[conner21]

Thanks alot ill let ya kno if it works

[Fugm-all]

Who rebuilt the head. Air coming out of the air box is usually a sign that the valves are leaking air back through the valves. And make sure u are timed correctly.

Hope u get it running.

[conner21]

I got a new head from another site and they said it was ready to be put on. My valves are set but if i go down. 005 t doesnt have air comn out of the airbox but all it does is backfire. I cleaned the carb and it does the same

[Fugm-all]

Sorry what do u mean by if I go down .005. U talking about no valve lash?

[conner21]

Im talkn about a smaller shim but it still wont start. Im outta ideas

[crfsonly]

are the valves you installed new? what valves? are the springs, retainers, seals and cotters new? have you had experience installing valves? make sure the cotters(keepers) are set correctly. retainers are directional so you have to install them in the correct orientation. same with the base washers and springs.

new valves in a new head will work. they come from the factory like this. when we build a head with new valves we put it through our CNC process to eliminate the "production" variances and shortcomings and to increase port bowl to seat performance. this CNC work not only increases performance but also increases valve durability. however, if the valves and head are both new and installed correctly you should not have any head/valve issues.

[Fugm-all]

ok,first off make sure the plug is new and not flooded, but i think your timing is off.Just make sure the punchmarks all line up.If this is all correct and the plug is new i would either do a compression test or pull the head and make sure the valves are not leaking past.compression test will tell you if the head is good or not.