Derbi GPR 50 Belson project

[jkv357]

No drain in the crankcase. It holds the air/fuel charge on its way up to the cylinder.

If it leaks you have problems.

Was the spark plug out when you got it? If it's not coolant in the crankcase I would think it is rain water.

[mace]

Spark plug was in, although the exhaust gasket was weeping slightly after I attempted to turn it over so exhaust might have been previously disturbed. Coolant tank was empty, and first section of exhaust was brimmed with water.

I did wonder if it could be rain water, but the rest of the bike doesn't really show any major signs of having been left to get wet for a long period of time, and with the empty reservoir and lack of antifreeze (hence rust) in the system I reckoned probably not rain water.

Either way though, with there being water in the crank case, that'll have knackered the bearings in there so they'll need doing now. Crank itself contains a bearing too so as toratora suggested that wants replacing. I guess the rest of the bearings and seals in the engine (gearbox etc) should probably get done too since it'll be in pieces.

[mace]

Bonus points, looks like it might have an arrow exhaust system. That appears to be a 'performance' option from a quick google.

[toratora]

The Arrow pipes are a nice mid pipe. I have one on the Malossi bike.

The DRP has an Airsal crank because I went for their Xtreme kit. That didn't work out so well. Currently that bike is getting set up to run the Stage6 88cc kit. Neither of these would I suggest for your setup. I would say though that you should replace the crank with a good 40mm stroke (standard) crank, and get a nice 75cc or so top end. These will make the bike fun to ride, but still reasonable to build. You'll probably need to upgrade the carb/intake, and a few other things, but these are manageable too.

For bearings yes everything around the crank. The transmission stuff should still be okay. But you'll find out when you open things up. Thankfully bearings aren't very expensive, so if you want to replace them it shouldn't be much.

[mace]

I can't go the 75cc route, if anything I need to lose some power, rather than gain it. License in the UK for a 16 year old is 50cc restricted to 30 mph.

Made some more progress this evening, bike is now pretty much torn down, engine is out, wheels are off etc.

I didn't get a chance to check the jets in the carb, so don't yet know if that's been fiddled with. I'm assuming of course that it's the original carb, not sure if people put on different ones?

[jkv357]

I can't go the 75cc route, if anything I need to lose some power, rather than gain it. License in the UK for a 16 year old is 50cc restricted to 30 mph.

Made some more progress this evening, bike is now pretty much torn down, engine is out, wheels are off etc.

I didn't get a chance to check the jets in the carb, so don't yet know if that's been fiddled with. I'm assuming of course that it's the original carb, not sure if people put on different ones?

How would they know the displacement? All the paperwork would say it's a 50.

Even with a 75cc kit it isn't going to be hard to handle. A good running 50 should top 30 anyway, so how do they control that? I'm guessing it should have a restrictor of some kind.

I'm sure tora tora will have some ideas for you if you decide to stay with the stock bore. Different (bigger) carbs are usually a good idea when you increase the displacement looking for more power.

Me, I'd open it up and let her know she need to hold it down.

[mace]

I've heard they sometimes rolling road suspect scooters en-masse, not sure how true that is. The biggest problem is that it /looks/ like it can go fast, so it'll gain unwanted attention from the fuzz automatically.
From the factory the exhaust apparently has some kind of 'restrictor disk' welded in, to reduce the exhaust flow and thus restrict the speed. Carb jets are probably also suitably underrated too, but not sure.

Anyhow thinking I might swap the cogs around and lower the gearing to get more torque; will make it more fun to ride and limit the top speed. I'm not going to replace the arrow exhaust unless it's excessively loud, getting an original exhaust with restrictor will be pretty much impossible now, so seems pointless taking off an exhaust in good condition.

[mace]

Just going through the stuff I took apart today. All the photos are in the album here: Album
I'll label them another time, I'm knackered

[toratora]

In markets where there are restrictions the bikes are fitted with super tiny 14mm carbs, the pipe is fitted with an obstruction device which is basically either a washer, or a small tube to severely restrict flow at the exhaust manifold. You can also get a device that regulates the RPM. This is probably the best way to regulate the power on the bike. But it totally sucks to ride these bikes when these things are in place. My 05 would do about 45mph when I first got it.

I run a 12 tooth front sprocket on my track bike which has a stock 50cc top end. That will reduce the top speed quite a bit, but probably not down to 30mph. The Arrow might have the restrictor in it, and if not you can get one from Maxiscoot, and weld it in place. It basically keeps the bike from getting on the pipe.

I saw three albums in your link, but no Derbi action.

[mace]

Oops should be fixed now?