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Bike 2007 RS125

Here is the problem

Bike packed in apparently with a bit of a bang. This is what I was told (I presume a backfire)

This is what I have done so far

I have had the carb apart and cleaned it and refitted
Checked the compression and that seems fine
Felt for some suction through the intake manifold (this seems weak to me)
Fuel has been replaced with fresh fuel (what was in there was old fuel syphoned from a car that has been broken for scrap)
Checked the plug (good spark and good electrics)

Now when I try to start it it will spit and fart, then it just turns over and will not start.

I have taken the plug out and it is flooded. This is my problem, I have only filled the float bowl up and do not have any other fuel going to the carb. It should not be a soaking wet plug (has a good spark). I dry it off with heat and refit, same thing happens again.

Only thing I have not looked at yet is the reed valve.

Other than that has anyone got any suggestions

This is the bike in question

Thanks

If its got a spark, and fuel is obviously getting through I would suspect the piston / rings.

Could be some sort of electrical problem (ECU / coil etc) causing the timing to be out - or a dodgy earth / side stand cut out but I would expect that to prevent a spark.

Also worth checking for any leaks around the head / base gasket.

if the plugs getting wet then i would'nt worry about your intake manifold or rings as the piston on it's stroke is drawing in fuel.i'd put a new plug in first even though you say your getting a good spark.plugs can fail under compression.failing that if it is flooding then i'd say the problems in the carb,i'd be looking at the float,jets etc. hope that helps.

fastasfcuk wrote:if the plugs getting wet then i would'nt worry about your intake manifold or rings as the piston on it's stroke is drawing in fuel..

If its nipped up rings it will still draw fuel through - just not enough compression to fire.

Did it lock the back wheel?

flooding could be a sign of low comp, do a compression test, my nsr and rgv did it and it turned out to be low comp
it should be around 180 psi, if its lower then replace the rings


my 2 cents

sms

Paulh wrote:

fastasfcuk wrote:if the plugs getting wet then i would'nt worry about your intake manifold or rings as the piston on it's stroke is drawing in fuel..

If its nipped up rings it will still draw fuel through - just not enough compression to fire.

it's my understanding paddyz1 as checked the compression and that it's fine.

If it stopped with a bang it definitely seized momentarily and will need it's innards looking at.

Should got an RXS100!

Troo.. and a black leather jacket, ogri helmet and a dog to sit on the back

Thanks for the replies people.

Here is what I have so far

Compression. I can't get a reading because my tester is knackered so I used the thumb over the hole method. Pressed as hard as I could and it nearly blew my thumb off when turned over. In the past that has usually been sufficient

I turned it over again without the carb or plug fitted (plug connected to the HT lead and ground out). I put a blowtourch near to the plug hole and it wanted to fire a mixture every so often. The rings must be in good condition here because the piston is causing pressure in the crankcase then forcing it up to the chamber. This led me to believe there was fuel in the crank so I took out the reeds. When turning over I could see fuel splashing about. Not much but enough.
Backtracking from there I checked the tank and found the vacuum fuel tap had a very small amount of fuel passing. I think I have found the root cause now.
At present I have blew out as much fuel from the crankcase as possible (short of turning the bike upside down) and will let the rest evaporate. Other than that I can't think of anything else.

From about 3 months new, we had problems with it starting after being laid up over the weekend. I can only presume that the tap and the float valve have failed to some degree causing fuel to pass into the motor.

I'll keep you posted as to the outcome.

ps, it was recently serviced where we brought it from so it could have a defective plug (that will get replaced).

Interesting problem........it would help if the "Bang" in question could be expanded upon...was the bang a noise, exhaust or engine??

my thoughts so far are:-

1, Could be a duff plug, sometimes a dud will not spark under compression
2, Timing? could have slipped
3, Lots of fuel and a spark and still no start could mean the crank seals have gone and the motors pulling in air
4, I thought these prilla 125's were a disc valve motor?, obviously not, but even a mis-set reed valve shouldn't stop the enging from starting

F9

I had wondered if the bang was as it hit a brick wall.

Can't go any further on the 'bang' it was discribed by the person in the photo. Women and mechanics
Al

have you checked the float level??
take carb off, remove the bottom, get some 1 to blow down the fuel inlet and close the float, it should close level any more and that may be the cause off the flooding

sms

i had one and the reed valve stuck together, years ago , if i remember right there were 2 one witch opens on high rev, it was the smaller of the 2 stuck , easy fixed, wd 40, it would start but i had to rev it