Derbi Gpr 50 - 3k revs and no more

[snowdude2004]

A week ago my Derbi gpr 50 year 2000 would not start. I went for a long ride and when I went to go back out on it an hour later after leaving it on my drive it just would not pull away. A few days before the problem I had changed the gearbox oil for 10w40 gear oil from Halfords and about 1/2 weeks before that I put about 20ml of redex in a full tank.

Before this problem occurred I had a couple of issues on the bike, occasionally the starter button would not respond and the indicators would flash like mad. Also when in third gear onwards it would not go past 10k revs so I checked my sprockets and found out the rear was 50 teeth and the front was 14 teeth which seemed far from standard so I'm guessing that just needs the standard sprockets again. Was a bit crap up hills aswell but I believe it may of been because of this problem.

When I start it, it is at 1.5k revs or so with the choke open and when giving it full throttle it just about picks up to 3k revs and will just not go any further. The throttle seems to be unresponsive. When I took out my spark plug and put it on the cylinder to check for sparks it was a small blue spark as it should be as air pushed out of the spark hole plug as it should as well as a strong smell of petrol, if thats normal?

Since then I have done the following:

* Replaced spark plug
* Took off airbox and checked it
* Took apart carb and re assembled it
* Re charged battery
* De coked exhaust
* Checked fuel line from petrol tank and carb and both are receiving petrol
* Checked throttle cable to carb was still tensioning when twisting throttle
* Was almost on reserve so filled up the tank with petrol

I'm completely baffled for ideas now, Any ideas people?
____________________
CBT passed: 26/09/09, Theory Passed: 18/08/10, Mod 1 passed: 20/10/10, Mod 2 passed: 26/10/10.
Current Bike: Honda CBR 400 Nc23

[snowdude2004]

Bump...
____________________
CBT passed: 26/09/09, Theory Passed: 18/08/10, Mod 1 passed: 20/10/10, Mod 2 passed: 26/10/10.
Current Bike: Honda CBR 400 Nc23

[snowdude2004]

Just sprayed easy start into carb with airbox off and on the inlet on the airbox when it was on and there was no change on my rev counter what so ever.
Also just did a compression test and received a reading of 90 psi....
____________________
CBT passed: 26/09/09, Theory Passed: 18/08/10, Mod 1 passed: 20/10/10, Mod 2 passed: 26/10/10.
Current Bike: Honda CBR 400 Nc23

[N cee thirty]

maybe you need a new coil ?
____________________
'00 Aprilia RS50 > '92 Honda CG > '99 Yamaha Fazer > '91 Yamaha RXS > '79 Suzuki X5 > 01' Honda Cg > 07' Honda Cg > 82' Kawasaki Z200 > suzuki gsxr 400 gk73a > honda vfr 400 NC30 Mod 2 Passed 09/06/2011

Jewlio Iglesias wrote: I actually did vote BNP once

[snowdude2004]

already changed my coil over with other one which I broke ht lead off of so just transferred that across and no change
____________________
CBT passed: 26/09/09, Theory Passed: 18/08/10, Mod 1 passed: 20/10/10, Mod 2 passed: 26/10/10.
Current Bike: Honda CBR 400 Nc23

[snowdude2004]

Finally got a compression gauge and have now found out that its only getting 80/90 psi.... Don't know what I can do to increase it now though.
____________________
CBT passed: 26/09/09, Theory Passed: 18/08/10, Mod 1 passed: 20/10/10, Mod 2 passed: 26/10/10.
Current Bike: Honda CBR 400 Nc23

[P.]

[snowdude2004]

How would you go about rebuilding the top end properly exactly?
____________________
CBT passed: 26/09/09, Theory Passed: 18/08/10, Mod 1 passed: 20/10/10, Mod 2 passed: 26/10/10.
Current Bike: Honda CBR 400 Nc23

[N cee thirty]

[snowdude2004]

I don't know what it entails exactly, e.g new piston/piston rings.
____________________
CBT passed: 26/09/09, Theory Passed: 18/08/10, Mod 1 passed: 20/10/10, Mod 2 passed: 26/10/10.
Current Bike: Honda CBR 400 Nc23