first of all an apology: i know it's likely that this topic has been discussed in the past. i HAVE tried to do a search, and read many threads already, but have been unable to solve my problem so am posting a new thread. please be gentle with me i have a speedfight2. it used to run. then it sat in my shed for a couple of years. now i cannot get it started. i currently have it connected to a good battery, i have checked spark (both seen spark on cylinder head and using a spark tester), i have fuel flow (with fresh fuel - checked carb, pulled hoses, observed fuel flow), i have removed exhaust in case it was blocked, when winding engine over using starter can see exhaust/unburnt fuel exiting exhaust port. i have checked compression and it has 60psi (i do not know the spec for this though so this may be too low?) do all speedfight2's have an immobiliser? i didn't think mine did, but have read this as a possible fault on previous threads. could it be the auto-choke? i don't know a lot about these electrics on scooters aren't a strong point, but i would expect that if fuel is getting in, there's a spark, and a free exhaust... then the engine should run surely?? i am at a loss... can anyone help?? many thanks in advance! Andy
60psi you should be around 90 psi , 60psi is way to low spark - fuel - air the three main units require to run the motor, BUT there is a fourth its compression , if the fuel and air is not compressed enough it wont be able to catch . and tahts why your seeing unburnt fuel from the exhaust, low compression due to ring failure. re-do a compression test, make sure the test plug is nice and tight in the head. OPEN THE THROTTLE FULLY and kickstart the scooter with ignition off, keep kicking it untill the pressure does not go any higher, you should be seeing atleast 90 psi . what ever pressure you get you leave it in the cyclinder and do not disconnect the pressure gauge or release pressure. you want to leave that pressurized for around 10 mins to see if there is any low level leaking. if your still seeing a low 60psi, remove exhaust grab a light and have someone slowly turn the motor over with ignition off untill you can see the piston rings passing the exhuast port , have a look at them. let the piston travel down to bottom center and glance into the port see if there are any signs of scoring. you may even have to remove head and cyclinder for a full inspection.
ok so i reattached the exhaust just to double check the compression stayed the same. it stayed at 60psi. i then noticed my compression tester was using a rubber extension hose... surely that would swell and affect the pressure reading?? so i removed that and connected directly to the metal connector. compression went up to 80psi. better but still too low. so i put a little bit of oil in plug hole and refitted the spark plug. when i thumbed the starter it still didn't fire but did cough, once. encouragement! i put my thumb over the exhaust and after a few spins the engine fired! it started!! i can only assume that blocking the exhaust momentarily, increased the pressure in the cylinder and helped the fuel ignite? lot's of smoke but it's running. happy days!
Check the vacuum pipe from the inlet manifold to the fuel tap. It may be leaking air in and not allowing fuel to flow properly. Also weak reed petals can cause starting issues, so they may be due for replacement. I think by back-pressuring the exhaust, you forced the reed petals shut, increasing the amount of fuel mixture.
hi merlin, i've never looked at reed petals before, pretty simple to remove and check tho?? ill have a gander at the weekend
Yeah. Just unbolt the manifold where it meets the main engine - 4 bolts. You can even leave the carburettor bolted on the manifold. Just check that they sit flush with the V block as they should seal against it when they aren't open. They fatigue over time, the metal ones bend and the fibre ones crack.
