NSR 125 ran out of two stroke oil and got hot, engine still kicks over, head gasket has been replaced, new plug with good spark, fuel seems to flood back into carb rather than getting through reeds. Any ideas what could be the cause. Cheers Colin

Get a cylinder compression test done to check head gasket and to check head is not warped or cracked.
if head gasket or head problem = one cylinder may be affected causing fuel could get into the oil via a blown head gasket. if one cylinder not firing it would run rough.

Has the engine been over heated recently ?

Jesse,
The engine is seized up, that tinkling sound was it seizing up getting to hot probably not enough oil either two stroke or engine reservoir or it was rusted up in side u shud of taken out plug and pored in some redex oil and leave 4 ....24 hrs then kick it over with rag over to catch oil then put plug back in and start it would of smoked a couple minni'ts but would of been ok, Now u will have to take of head and see what damage u have done u mite be able to take out piston u will need to pull of barrel but first pour some oil mixed with petrol to hepl loosen of stuck piston , good luck
..

check oil to see if there is rad fluid in it. if there is you have a cracked head or head gasket. if no rad fluid in oil, check for a spark.pull out a spark plug attach spark plug wire hold close to engine block with gloves and turn over engine. it is best to have someone with mechanical know how to do this,i.e. friend or nieghbor

This may help you determine the problem.
1. is sprkplug oil fouled? wet? dry? superhot and white electrode?
A sparkplug will always tell you whats going on.
if its too wet then its not burning all the fuel and oil and flooding out.
if its extremely hot and white, then its running lean , and needs more fuel.
also make sure your running 50:1 fuel oil mix.
a hot two stroke is hard to start.
if plug is dry, then its not getting enough fuel.

2. make sure your fuel oil mixture is 50:1.
to much oil is okay but it may smoke alot
way to much oil will oil foul the plug and plug will have oil on it.
to little oil will make the bike run hot and start damaging the bottom end crank bearings as well as your rings , then piston and cylinder walls.
the plug will be whitish and hot.

3. as for the timing , the rotor is resting on a keyway on the crankshaft and will only move out of time if the keyway is sheared.

4. make sure you have good spark when bike wont start.
a coil that is going bad will work cold but may not when it gets warmed up

to sum it up check to make sure you have correct fuel mixture
check you sparkplug to see how its burning
make sure you have good spark

if you have good spark, good fuel, good compression, then it should start within 2 kicks everytime.
i have a blaster 2 stoke 4 wheeler, starts everytimesince i rebuilt it.
i hope this helps you out and you can enjoy the rest of the summer with your dirtbike.
best regards
Big Al

You could have a carbon problem .Try checking your silencer for blockage or it maybe the engine need a good decoke .

Sounds like your oil/ fuel mixing valve may need to be replaced. New gaskets for it at least. Hopefullly your engine gaskets are ok, that's the first thing I thought of until I saw it was a 2 stroke.

Could be low compression due to head gasket leak, worn piston rings. Or bad spark due to dirty plug, wrong gap, plug breaking down, lead or cap breaking down, ignition fault. Choked air filter, fuel filter.
Try these in easiest order I.E. remove air filter and see if it starts easier, do a compression test, cahnge plug, lead cap. Check the fuel filter.
I am sure it's a simple solution.(high milage engines tend to be difficult to start so take this into account)

Get a new NGK spark plug one heat range hotter than stock. Be sure the fuel mix is 32/1 using two stroke engine oil ( not motor oil ). A 32/1 mixture equals 4 ounces oil to 1 gallon of gas. Remove the cylinder head and de-carbon the top of the piston and head.

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