My daughter has a Derbi GPR50 that after a lot of money spent has been fine. Since its been getting damp and cold it's not firing on the button. We can bump start it but if I'm not with her she struggles to do it on her own. Just rang the mechanic and he said to turn the air/fuel screw half a turn but, not having to start with 50's and 125's I haven't had to do this on my bikes so question is...is this the correct screw?
I would say it is not the air screw it looks like the throttle stop/tickover screw,the air screw Should have a slot for a flat headed screw driver and be turned out 1 1/2 to 2 turns out.,look on the other side of the carb.
This is on the right hand side and I wasn't sure if it was the idle screw or air/fuel screw. Thanks for the reply
Fwiw I would expect that (with it being a 2 stroke) the spark plug would be the likely suspect for your poor starting. They tend to have a much shorter working life in two stroke engines. The air mix screw is possibly in the round recess forward & below the large knurled (tickover) screw that is prominent in your picture .
Spark plug was recently changed (about 4 weeks ago) No kick start on the bike which is frustrating. Thanks for the image, I'll have a gander in the morning on the other side of the carb. Didn't know if adjusting the air/fuel would help in cold weather as even when bump starting it needs the choke on
IMHO it would be good to know if the compression is low, does it seem to turn over quite readily on the starter (despite not starting).? Fwiw, when we used to blat around on stokers as lads, carrying spare spark plugs was as natural as wearing bike gloves is. Frankly I would be very reluctant to alter the mixture screw, and the choke would be needed from cold irrespective of the starting method. If it needed choke on to be able to tickover correctly when warm, then it may be worth considering. (Although I would be looking for the underlying cause first). Good luck Legs'.
Compression was tested at the time of changing the plug. It was 140 and new they are 150? So I don't think that's caused the problem although with this bloody thing it could be anything! Only 5 more months to go and she can have a decent 125!
Legacey you say its was running ok untill it got damp,i would check the surpressor cap (plug cap) that its not arching onto the cylinder head made worse with damp condition,if it is you can hear it ticking or run it in the garage with the lights off and you will see the spark jumping to earth also un screw the cap and check there is copper at the end of the lead if not snip the lead back a few mm untill you see copper,if you decide to adjust the air screw first count the screw turns in then you can always return it to original settings,like stmarks says the spark plug should be were you start.
Cheers fellas. It just seemed to coincide with the fog we had on Monday, that's the first time it failed to start. Started with what is in the cupboard, WD40! I'll get a new plug in the morning and check the HT lead whilst there
First off check what setting the mixture screw is at now. Count how many turns it takes to screw it in. I think it should be around 1 and a half turns.
