RS 125 wont start just backfires

[monty16v]

have a 98 rs125
bike has been going 100%

today it felt although i was running out of petrol, although i had petrol in the bike so i pulled over
bike wont start now seems to be turning over a little slower on the starter
tried new plug br10eg, still the same
tried a push, with choke on/off, throttle open/closed still no joy just backfires when pushing it
i took fuel pipe off valve on the tank and fuel is making it that far at least
plug is sparking as well

anybody got any ideas
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OffTheClockMotorSport

[SuzukiTom]

was the plug wet when you pulled it out? might be worth checking your getting a spark to - you can remove the plug and then connect the ht lead back and make sure the plug is in contact with the fream and turn the bike over, needs a nice blue spark (do not put your hands on the plug!! rest it on the fram making contact but deffo font hold it!) sorry if you know all this or have tried it

also what does the air filter look like?

[ClockworkJesu...]

RS huh?
Hows your oil level? And (hate to ask this) did you fill up with petrol, or diesel? Had a mate who fuelled up with diesel on an RS. It didn't kill it; but it didn't turn over until we got some neat petrol into it.

Guessing you've checked the kill-switch already.
The ignition timing okay? And, it being a 2-stroke; how long has it been since your last rebuild?

[monty16v]

[SuzukiTom]

aha, 'compression seems good' have you used a guage to test? i would do just incase its a good point.


When was the last time the carbs were apart for a clean? its a dead simple carb, a dellorto i think.

[lihp]

RS125? Checked your cam/valve timing?

[P.addy]

[lihp]

[monty16v]

[Livefast123]

Fuel tap is on?

Check your fuel tank breather in case it is blocked stopped fuel supply to the engine.

You can't test compression by 'I think it's good'. It may have snapped a ring or the piston may have started to break down. Take the exhaust off and have a look through the exhaust port to see what the state of the piston / powervalve if fitted are like.

Is your oil pump working well?
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Current ride - Yamaha MT-07

[P.addy]

But a crap battery will result in crap running on most things.
Do you have a tester? How old is the battery?


Also the compression being fine and the bike running one minute and not the next... Compression could have disappeared.

Charge battery to be sure, pull out spark plug, put thumb over spark plug hole and crank it over. My RS was at 130psi (was dead though, so compression isnt the be all and end all test) and it was sucking my thumb in and forcing it off, I couldnt press against it.

[andy_uk]

Have you put the correct 2T oil in?
i.e. Fully synthetic, not semi
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Aprilia Classic 125, GS500E, ER5-A1, ER5-C4, ER6 & an XJ6 project frame...

[P.addy]

[andy_uk]

[lihp]

[monty16v]

sorted it out yesterday when i got it home.
air filter had started to disentegrate and small bits of foam were in bottom of airbox, must ogthen blocked the carb
took carb off, flushed out bowl, set float, blew out the 3 jets with copious ammounts of carb cleaner
bike was going well again after that

sold it today and bought a better one with 34mm carb and full stainless exhaust, much nicer to ride
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OffTheClockMotorSport

[SuzukiTom]

knew it was carbs!