Derbi GPR 50 Belson project

[toratora]

Maybe it's the assembly. I'll see if I can get a photo for you.

Can you measure the length of the forks? I can try to measure my GPR50's stock fork length.

[toratora]

Here's what the clip looks like on my caliper. It should be similar on your.



And I did get a chance to measure the fork too. Looks like a bit over 73cm

[mace]

Ah slightly different caliper design to mine; is yours the 125? I've bent my clip into a "C" shape, so will unbend it into a dog leg shape like yours and try again when I get back near the bike next.

[toratora]

Yeah that caliper is actually from a MetraKit, but it's similar to the one found on the 2T 125 GPR. I had a caliper like your's, but I sent it to BW who's working on an adapter for older GPRs so that they can run radial calipers, and larger discs like on the newer 05+ bikes.

If the spring is bent then it wont be able to function correctly. EasyParts can source you a new clip if you can't get that one back to its proper shape.

[mace]

Ok cheers for the pics, I've bent that clip back to how it should be and it's all reassembled now.

I measured my old forks at approx 74cm, and the replacement ones are around 79cm. The difference is mostly in the top part of the fork tube; the lower part is near enough the same length.

[toratora]

This is very interesting. When I put the aftermarket forks on the 2012 GPR in Japan the bike looked to be sitting rather low. This 5cm would explain it. Are the forks now on the bike? Would be nice to see photos of which ones are which.

[mace]

Sorry for the delay. I've not had a chance to take pictures for you yet.

I've now gotten as far as reassembling most of the bike, minus the fairings and various electrical parts.

Also fed it some pre-mixed fuel today and got it to run for a minute or so. However fuel was dripping out the bottom of the carb, there's what appears to be a hose barb there.

I'm not quite sure how to set the carb up, or whether I have the hoses correctly connected. Are there any guides that might help?

Parts I still need to source:

Piaggio, TAILLIGHT, part no: 00H01011321
Piaggio, REAR RH TURN INDICATOR, part no: 00H01700531
Piaggio, REAR LH TURN INDICATOR, part no: 00H01700541
Piaggio, REFLECTOR, part no: 00G04403752
Piaggio, SWITCH, part no: 86144R

I'm also unclear on whether there should be a number plate light. There seems to be a recess in the tail plastic for one, but no obvious wiring.

[mace]

Getting there with the bike now..

Electricals mostly sorted now, still on the hunt for a rear indicator, but I can live without that for the time being, and use the existing ones.

Carb is the current sticking point. I've had it apart a number of times now, trying to clean it up. A fair amount of corrosion in it, and the float/needle valve was stuck.
Float is now working properly, which is good news, and the bike has run since then, to an extent.

However I cannot get the bike to run at all without the choke fully on, and I have to manually hold the revs at 2000 or higher to stop it stalling, even with the choke on. Revving it up in this state sometimes works, but anything near WOT and it feels like its bogging down and doesn't rev properly.

Current carb setup is as follows:

Dellorto PHVA 17.5
Needle A25 N5 (or F1 depending on your preference)
Main jet 95
Idle jet 32
Atomiser 208 HA
Choke jet - unknown, it's seized in pretty well, and I don't want to totally mangle it, since it seems to be working.

Would appreciate any advice on whether I should keep going with this carb, and if so, what I should look at adjusting?

Or should I dump it and buy a new one - if so do I go for another PHVA 17.5, or switch to a Polini CP 17.5 which seems to be recommended on the Aprilia forums?

Thanks!

[toratora]

Have you considered replacing the carburetor? The new Polini CP carbs are inexpensive, and work quite well. I'm running them on a few bike with good results.

EasyParts has Vicma indicators at nice prices. They also have a number of tail lights too!

[mace]

Have you considered replacing the carburetor? The new Polini CP carbs are inexpensive, and work quite well. I'm running them on a few bike with good results.

EasyParts has Vicma indicators at nice prices. They also have a number of tail lights too!

I have, yeah, all options are on the table. New carb is more expensive, but probably necessary given the condition of this one

Which Polini CP carb would you recommend? Does the 17.5 just drop in as a replacement, oil feed/throttle/choke just hook straight up?

Thanks.