Bike Wont Start!!

[egzlilgituarboy9]

ok so i just rebuilt my 2005 kx250f top end and it wont start and i dont know why. it is timed correct. all i get is backfires about every few kicks. any help would be awesome

 

[sick 96 250]

sounds like it isn't timed correctly, what makes you say it is correct? Did you rebuild it yourself or did you have a shop. Are all your valves adjusted and in spec. There are many things it could be but a newly rebuilt bike that wont fire and gives a back fire is most likely timing

 

[spark250]

Triple check the timing and the valve clearances. It should still fire if the cams are off by maybe a tooth or two... so make sure your valves are shimmed correctly.
If you are positive both are correct, start troubleshooting. Check for spark and fuel. Go from there.

 

[egzlilgituarboy9]

im 99% sure that is is timed right because i checked like 9 times. i did do it myself. i never checked the vavle clearance though. why would the valve clearance make it not start?

 

[Ol'89r]

i never checked the vavle clearance though. why would the valve clearance make it not start?

You did a top end on your bike and never checked the valve clearance???? :whoa:

If the valves are tight you won't have enough compression to start the engine. It is also very easy to get one of the shims out of place/crooked and this will cause one of the valves to hang open.

I suggest you refer to your manual or find someone with experience to help you go through the proceedure of checking your valve clearance.

 

[egzlilgituarboy9]

the intake is tight the exhaust is fine. it was my first time rebuilding a 4 stoke. so know do i just get a shim kit and go from there?

 

[Ol'89r]

Tight exhaust valves will cause it not to start. You may not need a shim kit. You can determine which shim you need and buy just one or two from your local dealer. A complete shim kit is very handy to have if you can afford it.

READ YOUR MANUAL! Sorry to shout but, you need to sit down and read your manual. Then, sit down and read it again. It will explain very clearly how to adjust your valves. Follow it step by step. Make sure you have the proper tools to torque the cam caps and follow all of the torque specs.

You can also do a search. There are several threads and videos that explain how adjust your valves.

A set of digital calipers are very handy to check shim size. Get a pair that switch from metric to inches.

When you had the head off of the engine, you should have checked the valves for proper seating. You do this by pouring gasoline into the port and watching the valve to see if any gas leaks out through the valve. If gas leaks out from the valve, you need to do a valve job.

 

[egzlilgituarboy9]

well as of right now the head is off so ill check tommrow for the valve seating. and what do i do if it needs a valve job do i need to send it out to a shop?

 

[Ol'89r]

Unless you have a valve seat grinding/cutting machine, valve guide reamers, spring testers, spring compressors and the knowledge to use all of that stuff then, yes, you should send your head to a shop.

Even if the valves seal properly, they should be replaced if they have too much time on them. If the valves have too much running time, they can come apart. This will cause major damage to your engine if not caught in time.

Replacing the stock valves with Kibblewhite stainless valves is a good idea. The stainless valves will outlast the stock valves and they don't break like the factory valves can. You will need the complete kit with valves and springs.

You should have an hour meter on your bike. This is the only accurate way to know how many hours are on your engine.

 

[Patman]

i had the same problem with mine when u ut a new top end on the compession changes and the carb needs to be tuned to the right specs..

:whoa: :whoa: :whoa:

 

[oldguy]

Unless you have a valve seat grinding/cutting machine, valve guide reamers, spring testers, spring compressors and the knowledge to use all of that stuff then, yes, you should send your head to a shop.

Even if the valves seal properly, they should be replaced if they have too much time on them. If the valves have too much running time, they can come apart. This will cause major damage to your engine if not caught in time.

Replacing the stock valves with Kibblewhite stainless valves is a good idea. The stainless valves will outlast the stock valves and they don't break like the factory valves can. You will need the complete kit with valves and springs.

You should have an hour meter on your bike. This is the only accurate way to know how many hours are on your engine.

now why would you say something like that and scare him ;)

This was an engine with less then 10 hours on it

No better reason then this to follow Ol89ers advice :cool:

 

[Ol'89r]

now why would you say something like that and scare him ;)

This was an engine with less then 10 hours on it

WOW oldguy! :yikes:

The way that Williams valve is cupped out, it looks like that engine has been rode hard and put away wet. Hard to believe it only has 10 hours on it. :whoa:

egzlilgituarboy9.

The photo that oldguy provided shows the damage that can occur when the valve loses it head. If the top of the piston looks like that, you can imagine what the head and cylinder looks like with the head of that valve bouncing around in there. They usually take out the head, cylinder and piston unless the piston breaks too. If the piston breaks you will also have bottom end damage.

Much cheaper to fix it now. :nod:

 

[oldguy]

Yep this one took out the head, cylinder, crank and main bearings. :bang: Thank god Eric Gorr is close by :nod:

 

[egzlilgituarboy9]

this actually happend to my brothers the bike had probley had less then 10 hours on but it didnt break the piston but he had to get a new head and piston

 

[egzlilgituarboy9]

this damn peice of $#!^ wont start still. i shimmed the valves it is timed correct and still all i get are backfires. what else could it be?

 

[helio lucas]

ignition timing.

 

[shaun smith]

ok so i just rebuilt my 2005 kx250f top end and it wont start and i dont know why. it is timed correct. all i get is backfires about every few kicks. any help would be awesome

 

[shaun smith]

alryte was wondering if u have had any luck yet ive rebuilt my yzf450 timed it and wnt start exact same problem it back fires thats about it stuck with it dnt know wat to try next

 

[egzlilgituarboy9]

yes it still wont start and im trying to find out whats wrong