Question about 2008 KTM 250 SX-F

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Haven reall problems starting bike when warm espeacially valvw clearance on inlet is 0.10 and exhaust 1.2 are they to tight

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I used to have lots of trouble startin the bike when warm too, but really it is all about technique. Find T.D.C by gently pushing down on the kick start. Then pull the hot start lever in, and kick slowly and gently all the way down, rather than kicking as hard as you can. This should start the bike a lot easier.

Posted on Dec 10, 2009

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If they where to tight it would not start when cold, and get easier when warm. I would look at overheating check oil/coolant levels.

Posted on Dec 01, 2009


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Posted on Jan 02, 2017

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hi there,
this table will help you. I used to own one.. beautiful bikes easy to work on too!
Valve clearance: Inlet 0.13 0.19 mm
Exhaust 0.18 0.24 mm
Valve head thickness: Inlet 0.5mm 0.25 mm
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Valve stem bend 0.05 mm TIR
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Valve seat cutting angle 32 degrees, 45 degrees, 60 degrees

Hope it helps.. Ken

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1 Answer


Not too sure could be a couple of things or 1 simple thing, wouldnt know without looking at it but here's the clearance numbers.

Valve clearances are, Exhaust valve (imperial) 6 Thou, (metric) 0.15mm, Inlet (imperial) 4 Thou, (metric) 0.10mm.


Jul 19, 2014 | Boating

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Dear Support Manager, I have a 1972 triumph

First check the valve clearances. Check/adjust these when the engine is cold - .004' inlet and .006' for exhaust, don't be too fussy any clearance is better than no clearance! Next you should check compression for both cylinders, they should be within 10% of each other. Assuming you have the original points set-up these too can 'adjust' out of tolerance when they get warm. Keep in mind the bike is 41 years old and may need more frequent tlc, best o luck.

Mar 25, 2013 | Motorcycles

1 Answer

Rebuilding a bike which has bits from here and there. Believe motor to be 1986 GSX750. it runs, carby has fuel in it and seems to be working alrighty, plugs are sparking, but engine backfires a fair bit...

it probably isnt a firing order problem, or it probably wouldnt run

one coil fires 1 & 4 cylnder, the other coil fires 2 & 3 cylnders, as the pick up gets its signal from the crank, it sends a spark to each cylnder on the exhaust stroke as well as the compression stroke, ignition timing also doesent change as it is electronic and cant drift out like when points wear.
a short in the ingnition or kill switch can occasionally cause a backfire
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make sure everthing is clean and tight, good air filter and exhaust, check valve clearances ,and give it a compression test, check the valve timing, incase it has been assembled wrong,(they rarely jump a tooth unless the chain and tensioner are completely stuffed)

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Yes, it could (and probably is) be an air leak. Check to be sure the carb is tight in the intake manifold, and make sure the hot-start isn't loose and is sealing properly. Also make sure all of the exhaust system joints are tight, an air leak in the exhaust will make a four-stroke pop and backfire like an old work truck with no muffler...

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my mate says that if the gaps are bigger then its ok and that it's when they are smaller that u need to do something about them is this true? bit of xtra info: the manual says inlet 0.15mm and exhaust 0.25mm clearance. my bike measures inlet 0.20mm and exhaust 0.30mm i'm just a bit concerned 'cos if the worst happens i wo'nt be able to afford a top end rebuild.You should try and keep the clearance to 0.15 in and 0.25 ex. With the de-comp it is cridical to have the exhaust clearance correct. On the early 400/450 they had some cam problems so check the shim buckets and cams are not worn.,

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