k_alinovi Posted November 28, 2021 Posted November 28, 2021 Hi all, I am coming to the end of my project Aprilia rs125, the engine has been rebuilt properly and everything is set up correctly (eg carb jetted, oils bled). Today I decided to start the bike for the first time and checked the spark plug, engine oil, gearbox oil etc and poured fresh fuel in. As I attempted to start the bike, all it did was turn over with no sign of it starting at all regardless of using choke or throttle. I then attempted to bump start it but when it went into first the bike wouldn't move (clutch had no effect) and it was very difficult and still to get the bike back into neutral. I understand that the gearbox shouldn't be perfect as its sat for a while, but I had poured fresh oil in and there was absolutely no play in it, the clutch cable seems to be at the correct tension but again it had no effect. My guess is that once the engine starts, the oil warms and the gearbox works accordingly but I cannot test that as of now. As for the starting problem, the engine has spark, it has an open air intake so there should be sufficient air, the carb is brand new as are the fuel lines and most of the engine, I believe it is getting fuel through the lines and the engine turns over strongly as it has a new battery and starter motor etc. Is there anything Im simply missing? It is a 2t Aprilia rs125 (2009) but I cannot seem to find a fault. I would like to attempt a bump start but the gearbox stiffness would need addressing first. If anyone has any advice please let me know! thanks Quote
TimR Posted November 28, 2021 Posted November 28, 2021 Dont bump in first ...3 or 4 at least 2nd minimum ... Chances of bike turning in 1st via a small push is ZERO. Best thing to do is prepare is to start before starting .. Disconnect spark leads and remove plugs and attempt to start ... this gets all the required fluids flowing . Once you have established oil pressure is sufficent and fuel has filled the system then check for spark at plugs..if ok put plugs back in and go for start . If no spark Check idiot lights ie neutral light showing Check kill switch Check fuses Check wiring connectors and polarity Check clutch switch if fitted Still no spark .. check coils and all relevant ignition systems Spark but no fuel .. Check fuel is flowing to carb Yes .... carb maybe not correctly built No check fuel level, tap,pipework, pump Quote
KiwiBob Posted November 28, 2021 Posted November 28, 2021 (edited) 3 hours ago, k_alinovi said: Hi all, -------- I then attempted to bump start it but when it went into first the bike wouldn't move (clutch had no effect) and it was very difficult and still to get the bike back into neutral. I understand that the gearbox shouldn't be perfect as its sat for a while, but I had poured fresh oil in and there was absolutely no play in it, the clutch cable seems to be at the correct tension but again it had no effect. My guess is that once the engine starts, the oil warms and the gearbox works accordingly but I cannot test that as of now. ------ If the clutch lever has no effect then your clutch plates may have stuck together from the bike being stood for some time. .. Pull the clutch lever and hold it with a cable tie and leave it overnight, with luck the clutch plates will free themselves. Edited November 28, 2021 by KiwiBob Quote
fastbob Posted November 28, 2021 Posted November 28, 2021 I thought you said you rebuilt the engine . Quote
Bianco2564 Posted November 29, 2021 Posted November 29, 2021 As asked what work has been done on the engine? Do a compression check as you would a 4 stroke, will be lower ,maybe 100psi. If you have leak on the crankcase ,it will struggle to start or run properly. This could be crank seals or crankcase sealing. It is possible to perform a pressure test on the crankcase with bungs on the intake and exhaust and using soap bubbles to find any leaks. Any leak will also weaken the fuel mixture and cause poor running or seizure. How are the barrel and piston? The barrel is nicasil so cannot be rebored, it has to be replated. Piston clearance checked.? Ring gaps checked? Reed valves ok,? if not sealing properly will leak pressure back out the inlet. Has it an exhaust power valve? Is that set up properly? Is the exhaust clear? Any excess back pressure will stop airflow through the engine. You say it has a spark, but is the timing correct? Is it new plug? Do you have an air filter for it ? 2 strokes can be fussy beasts on carb calibration. It is normal to first fire up with a bit of pre-mix until the oil pump is bled. If that mix has too much oil, it can be difficult to ignite it. When I first went to start my RGV after a rebuild ,it was a tw@t to start, would fire on one cylinder but the 2nd intermittently fired. Ended up with new plugs, fitting the airbox and fresh fuel. Gearbox sounds like an assembly issue, should be able to click through the box with the back wheel in the air and spark plug out turning the wheel by hand. Quote
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