A forum for owners of Yamaha TTR250 trail and enduro bikes!

sounds annoying .

so 

Good spark , plugs OK ? 

plugs dry , no fuel getting through .

carby drain confirms fuel is getting through to carby bowl 

a bit of cam chain wear shouldn't affect it 

compression OK ? (check with kick start or roll in gear to check for compression ). extreme loss of compression could result in loss of Vacuum and not drawing fuel/air in 

back to dry plug , the carbys are notorious for although appearing clean have still got a bit of crud in the jets ( only bit between the bowl and the inlet tract that could stop the fuel  ) 

 

A check 

a little squirt of fuel through the carby , or a little down the plug hole re assemble and see if it fires a bit . (  the accelerator pump may provide enough fuel with a few quick openings of the throttle then crank ) , if it fires with added fuel again falls back to Jets and or float height .

 

something to consider if the sparks ok 

 

 

 

 

-- Edited by ttboof on Wednesday 17th of April 2019 05:23:40 AM

I can feel the compression but not sure if its as good as it should be

Yeah i might pull it apart again and try a rebuild kit maybe hopefully that will do something

Whenever I need to quickly diagnose a no-start condition (like the one you now have) and the history and condition are unknown, I use a fuel substitution method. Essentially, you separate the engine from the carburetor and air box and leak a combustible gas into the intake boot while cranking. I typically use propane. This is how it works:

1. Remove carburetor from the intake boot and set aside (you don't need to completely remove it, just expose the intake)
2. Using a propane bottle torch (or similar), open the gas valve just enough to leak gas into the intake boot - not much gas
3. Attempt to start the engine 

A few things may happen at this point:

1. Nothing at all (try again or pursue engine diagnostics)
2. Spitting backfires and trying to run (problem likely from intake boot back to air box)
3. Starts up and idles (problem definitely from intake boot back to air box - pursue carburetor and air intake diagnostics)

I hope you find a resolution to this no-start quickly and relieve the frustration that goes with it. Please don't incinerate yourself in the process - seek help if you are uncomfortable with any repair suggestion.

You could always try a squirt of Start Ya Bastard in the airbox 

We don't have that in the UK - our equivalent is EasyStart which smells lovely - some sort of ether-based spray I guess.

It's the carb! It's always the carb!! (Well, almost always, assuming the carb boot has not completely failed - but I think you'd have noticed this when pulling the carb off)

If it was full of hardened fuel when you got it it's guaranteed. Full stripdown, ream out the main and pilot jets with copper wire strand, remove and check fuel screw circuit. Ultrasonic clean if you have access to one. Check the pumper diaphragm - this should pump a jet of fuel that you can see from the air filter side when you twist the throttle even if the other jets are blocked.

Then do it all again just to be sure!!

If it was timing I think you'd still be getting a wet plug.

Good luck, and welcome to the forum! Glad your first post gave us something to chew on

I am pretty sure the TTR operates on a "lost spark" system such that it fires every revolution and the spark on the exhaust stroke is "lost".

What might have happened is that the valve timing is out. Check the photos on here to make sure that the cam lobes were facing outwards when you timed the sprockets up.

Agree with the carb comments. I'm not convinced you got the carb done (because I've had the same experience). My 2 cents, worth exactly 2 cents, is buy the All Balls rebuilt kit with OEM jets.

Ok i tried the fuel straight in the intake with no carby and nothing definitely has spark and definitely firing on the comp cycle also checked valves specs in pic and also checked cams at TDC and i think the chain is well worn looking at it level would that make much difference