Carburettor/Bike problems....still!

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pdee4t

hey guys. wondering if i can get some help here on where to start looking 1st.
im still having issues with the dirt bike, potentially carby related. still won't start...and when it does it just dies pretty quickly.
i had the carby cleaned twice, cleaned all the jets, put a full tank of fuel in the bike and still having problems.
when i use the electric starter, as the bike is starting, there is a slight hissing/whistling sound coming from the airbox/intake every now and then, mainly while the choke is on...wondering what would that be caused by?

the bikes had a full rebuild done. timing is spot on. new spark plug, checked for spark - all is fine and still has strong spark, checked all my electrical connections, air filter is clean and has brand new stater motor and stator in it.
not sure what else i can possibly check or what would be causing the hissing/whistling sound?

bike is a KTM 450 EXC 2004 model for those that don't know.
 
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pdee4t

im thinking could it be a valve issue of some sort?
i performed a leak down test with engine at TDC and only had 7% leak passed the rings. which was normal.
unsure what else it could be
 
2strokesteve89

2strokesteve89

Intake leak? Check the rubber boots that mount both ends of carb to air box, and the side to the engine, also check the clamps that hold it to the boot, if you hear that whistling noise when cranking I would check that first.also are you sure that fuel is making it to engine? When you crank for some time and recheck plug, is it wet? Or pull plug and crank, do you see some mist of fuel from spark plug hole?or smell it? When you had the carb out and cleaned, did you check float level and needle and seat function?
 
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pdee4t

2strokesteve89:
Intake leak? Check the rubber boots that mount both ends of carb to air box, and the side to the engine, also check the clamps that hold it to the boot, if you hear that whistling noise when cranking I would check that first.also are you sure that fuel is making it to engine? When you crank for some time and recheck plug, is it wet? Or pull plug and crank, do you see some mist of fuel or smell it? When you had the carb out and cleaned, did you check float level and needle and seat function?
Click to expand...

yeah i double checked both the rubber boots as that's what i originally thought it was. no cracks or holes or anything. clamps are very tight as well.

i'll recheck the plug tomorrow but when i originally had been cranking for some time trying to get it to start, when i took it out to check for spark, it wasn't wet.

yeah i set float height to the specs that were in the service manual and removed needle and seat and cleaned.

could it be loose exhaust valves maybe? i left em bit looser so i wouldn't have to re-adjust em as soon. usually the exhaust valves on those bikes tighten up before the intake side.
 
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2strokesteve89

2strokesteve89

So, when you had the carb off and the float bowl removed, what I do is try to blow thru fuel hose to carb with float hanging and there should be no flow, then I raise float by hand while blowing thru fuel hose until I notice flow, that doesn't tell me if float is correct height but it does tell me if the needle and seat is functioning correctly, if you did some test similar too this, then move on, if not then it needs to be rechecked.also, do you have carb cleaner spray? Or starter fluid?When cranking if you shoot some in air box and it fires (or tries to) that will tell you have a fuel problem also. Also if you have good compression and less than 10% leak down I wouldn't suspect valves.
 
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pdee4t

ok cool. i'll spray some carb cleaner in behind the air filter tomorrow and see how i go. if it does fire after that, what kind of fuel problem would it likely be? slide? jetting?, etc...
when i had the float bowl off during a test when i raised the float fuel flow stopped(didn't piss out bottom of carby) and then when i lowered it the fuel flow poured out.

i just can't understand why im getting a hissing noise or what it could be. doesn't make sense.
 
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pdee4t

bobkyle2:
Get the timing and valves within spec. Modern 4 strokes have to be damn neer spot on to run.
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timing is spot on, valves are little too loose though. could that be what's causing the hissing noise?(valves aren't opening enough to let the air in)
 
2strokesteve89

2strokesteve89

pdee4t:
timing is spot on, valves are little too loose though. could that be what's causing the hissing noise?(valves aren't opening enough to let the air in)
Click to expand...
Kyle is right bout that, that's why I only run two strokes. Those 4 strokes are quite impressive power wise, but I like the simple two stroke design, good luck with getting your ride going. Keep me informed with your progress.
 
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pdee4t

yeah perhaps that's the problem then. i'll re-adjust em tomorrow. what about the hissing noise though, any ideas about that?

cheers mate. will let you know for sure :) i had a 2 stroke but sold it. starting to think i shouldn't of now though
 
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