Question about KTM SX 525 Racing Motorcycles

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How do I set the Fuel/air mix on my 2003 525sx. I recently stripped and cleaned carby and tampered with mix scew and since then it has been very hard to start does not idle to good but runs great when you get the revs up???

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Set the mix screw back to standard and if you dont know the standard setting do it 2 turns out from fully in (dont tighten it, just feel for the stop) then finely adjust from there.

Posted on Mar 18, 2011

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Sthil ts410 fitted new barrel &piston runs ok till air filter housing is on ok with just filter till plastic housing is on all air ways to housing have been stripped and cleaned

check that the gasket to the barrel is installed correctly and not upside down blocking of an air hole to the carby
the problem is that the fuel level is excessive causing flooding when the filter is fitted
that is normally from lack of control to the carby diaphragm from blockage or vacuum hole problem
if you have reconditioned the carby , check the way the diaphragm has been fitted in relation to the gasket

Jun 23, 2016 | Garden

1 Answer


check for spark plug
check for correct oil/fuel mixture and correct oil in use ( not engine oil)
check the quality of fuel as most small engines do not like e-fuel mix
clean air filter
overhaul the carby

Aug 10, 2015 | Garden

1 Answer

Only runs with full choke, I bought the bike last week and the float needle was stuck and I think it had bad gas. so I changed the gas, cleaned the carb, reset the float needle. I also set the main slide...

Hi mate reverse the needle clip position back to factory setting this issue is pilot circuit for sure - If you have cleaned carbi you need to replace or clean the pilot jet and compress air clean the hole where the pilot jet came out of to clear the circuit. Running only with choke on is classic symptom of block pilot circuit...
Also check you fuel air mix screw this may have been altered trying to correct this issue it should be 1.5 - 2.5 turns out from fully closed..
all the change of needle position clip is doing is allowing your bike to run off the main jet (not good)
and reason for running with choke on is it is changes air fuel mix with choke on compensating for lack of fuel from the pilot jet blockage
regards Jamie

Aug 07, 2011 | 2004 Honda CRF 150 F

1 Answer

Tanaka TBC 160- very hard to start, any suggestions for possible reasons? Replaced the gas mix but it starts up & then stops running. tried new gas mix, checked throttle- seems to operate, Any...

hi there

paul 46 here.

all being well and compression and spark and timming , muffler is clear , carby is clean , and diaphrams are all ok , fresh mix , and fuel filter and lines are good

does the unit run with 2 stroke mix in the plug hole - ?
if yes assume compression and spark are ok,, if no check compression and spark and muffler

will the unit run with 2 stroke mix sprayed into the carby throat ?

if it does sounds like you have a air leak somewhere in the intake system

could be at barrel base gasket, c/case joint, manifold boot/ block gasket, carby gasket , impulse hose ,if this unit has one , c/case main seals leaking

2 strokes need air tight c/cases in order to pump fuel / air / oil mixture from c/case to cylinder
and to create a vacuum for entry of fuel/ air / oil mix from carb to c/case

symptoms of air leak are -: hard to start, wont idle, stalling, low power, inconsistant idle, over rev

pressure and vacuum testing can be done by blocking off intake and exhaust with rubber and metal plates , then fitting adapter to spark plug hole , and placing piston at bdc , pressureise cylinder to 7 to 8 psi of pressure and check areas , base gasket, manifold joint, main seals, , impulse hose ? for leaks with soapy water - if leaking bubbles will be evident

if no leaks and pressure is held at 7 psi for at least 2 minutes with dropping - presure test is good
next do the same test using vaccuum again go to 20 - 30 inch / vaccuum

if vaccuum held unit is ok

suggest take a good look at carby particularly if P and V test are good and spark coil tests good with a coil load test using a spark gap of 6.00 mm to stress the coil ( simulates spark under compression load)

have a look and let me know what you find

cheers pauly46

Apr 30, 2011 | Tanaka Commercial Grade "Inspire" Design...

2 Answers

Bike chokes down after throttle is open past 20percent things i checked cleaned silencer cleaned intire carb things i havent checked fuel cutoff solenoid ex.port valves thrttl position sensor

hi ,
Is your carby well fixed? If your air intake is too big ,the bike will not run properly .
Make sure the carby is not taking additional air or not enough .
Clean the air filter , tune the carby with the mixing screw air/fuel

Jul 13, 2010 | 2004 Yamaha YZ 250

1 Answer

I have a 1988 carburetor that has a cloged idle jet and I need to unclog it How do I do it? What is the best way to do that?

unscrew the idle mixture screw,count the turns,blow down hole with compressed air,rescrew screw back in.if it works,ok.if it doesnt work,youll have to strip carbie and clean it inside,jets,galleries,everything thoroughly.may need new gasket set.lay it all out carefully,on large sheet of newspaper,.if two barrel,dont get jets mixed up from one barrel to the other..have clean container of petrol to rinse and wash each part.use fine wire to clean any jets/air bleed holes etc..blow dry bits away from work place..use widest screwdriver blade that will fit,saves damaging jets[in fact,buy a new set of screwdrivers]

Jun 20, 2010 | Cars & Trucks

1 Answer

Lawn mower

sounds like you unseated your needle valve. pull the bowl off the carb and ensure that the float is contacting the valve and shutting off the fuel when you push lightly up on it.

Feb 06, 2010 | Garden

1 Answer

Hi, This is probably a simple question but it has me baffled. I bought a cx500 1981 custom last week and I have had a couple of teething problems. The main one being that she looses power - at full...

you definately have a fuel problem .
clean your tank first as deposits in the tank might have made way to the carbi .
the fuel/air mixture is one thing but your bike may have also oil burning issues .
try first by making sure the carbies are clean , fuel tank clean , the air mixture adjustment is tricky but usually screw the air mixture screw on the carbi all the way in and undo it 1.5 turn back and no more .
try that first and see how you go . the vaccum menbrane in the carbi may be defective too and may have to be changed .
have a look at all that and see how you go

Sep 26, 2009 | 1981 Honda CX 500 B

2 Answers

After bike gets hot will quit running.

sounds to me that your coils are getting hot and quiting . replace both coils or do a diagnostic check on each coil to find out wich one is loseing reistance . i repalced both coils on my bike when it did this and it runs great now

Apr 26, 2009 | 1985 Honda GL 1200 Interstate Gold Wing

1 Answer

Carbies willn't set float level,right floods,left sets to low

I don't know if its any help but I've fixed my Honda with similar problem. It turns out I reassembled the rich carbys air cut off valve incorrectly. Have you checked yours? I'm wondering if the cut off valves somehow affect the other parts of the carbys. Mine is running sweet now.

Apr 13, 2009 | 2001 kawasaki ER-5

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