Hi, this is a project I’ve been working on for a few months~ an 02 Derbi GPR50;) This is a quick post about the running and exhaust. I’ve had a great deal of help from my friends on the Apriliaforum.com in the build section.
The problem I ran into was the running, despite re-jetting with different jets, I could not get the engine to get over 8k rpms! The new exhaust I had purchased was called a Doppler. I suspected it, but just didn’t want to fork out another 300 for another system.
I decided to try the old exhaust that it came with, but it wouldn’t work with the fairing, so out with the cut off wheels and get ready to weld it into a usable shape.
below: I re-situated the upper part to match the cylinder head so it had to be shortened the re-welded.
The lower cut was done with a cut off wheel, like a piece of pie, the bent back to make the angle I needed.
Obviously here the lower segment is welded back up. Will it last? who knows, it was a trial and error thing to see if I could get the bike running correctly!
Relocation of the mount below:
Using a VHT 2000 degree paint, dressed it up a bit;)
Fortunately, the newly re-designed exhaust fits with the body plastic~!
I didn’t have a hanger for the Metrakit silencer, so the Doppler silencer fit perfectly, but rotated the silencer to where the Doppler decal didn’t show. I had a Yosh “emblem”, I hope will stay put and not melt off!
The end of the story is the new exhaust will send the rpm’s up to 12-13rpm’s with the blip of the throttle! This bike rocks now!!!
Short n sweet and with success~