Derbi GP1 Resurection

[buzzscoot]

I picked up a Derbi GP1 50cc LC (Piaggio motor) a few years ago for a few hundred that was in pretty rough shape. It had been sitting out for years and the owner had lost the keys. I got it rekeyed and it would turn over but I couldn't keep it running even after cleaning the carb. Because of the mechanical shape, body condition, rusted out exhaust, etc., I decided to take it all apart and start from scratch to rebuild much of it and fix up and paint the body. I took everything apart and put it in boxes. 

I have a Scarabeo and I am familiar with working on the carb, switching out exhausts, and everything in the cvt but I have never tackled this much work. This site and everyone's input have been valued in giving me the confidence to get it done.

Well, weeks turned into years, and now a few years later I am finally getting around to fixing it up.

I planned on adding
Malossi Sport Kit 70cc
Malossi Multivar 2000
Malossi Torque Convertor
Malossi Fly Clutch
Yasuni R exhaust
It had a Dellorto 19 PHBG which I am keeping

I planned on a lot of CVT work as I was never really happy with my stock scarabeo cvt (Minerelli) and I thought the stock Piaggio would be similar. I had already bought the new parts, when I took the CVT apart. After looking at the piaggio torque convertor, variator, and looking at all the measurements, I am not so sure I am making as much of an upgrade as I originally thought. I am also impressed with the venting of the CVT case which I don't have and have not gotten around doing on my Scarabeo.

Well a couple  a few weeks into the rebuild, cleaning out the cruddy tanks, etc. I find that I have a lot of problems. Most are easy to fix like a broken speedo cable, non functioning fuel petcock and thermostat, temperature sensor, starter (I think) and several others.

I installed the sport kit, and CVT parts, and thoroughly cleaned the carb and put the scoot back together.
Compression was tested to be about 130, and though maybe a little low? I decided to fire it up. Is this too low or once the rings get run in will it go up?
I put on the old exhaust and started her up .
The electric starter would work off and on then died completely despite a new battery.
Luckily after a few kicks it started ,idled , and seem to run great. 

I noticed after about 5 minutes or so it would idle slower and I had a hard time keeping it running without giving it a little throttle.
I worked for a while with the carb but with no luck.   I also noticed a little bit of wetness at the the case seal right below the intake boot. I thought my intake seal was leaking so I reset it with the gasket and some sealant.  I started it again and had the same problem.
I realized that before putting everything back together I should have performed a leakdown test after the kit install. 

This time I made a homemade leakdown tester out of a cheap blood pressure kit and fittings and tested. I had no leaks anywhere except 1/2 to 1 inch below the intake. There is a slight leak in the case seal about and inch below the intake.
I guess this means I have to disassemble everything and split the case and reseal it and put it back together. I am a little worried about doing that but I can try. Is there any other option from the inside or outside the case near the intake without opening it up?

Here is a pic of the scoot disassembled and pic of the leak. Thanks.

[spaz12]

With the reed block removed can you get your fingers down in there enough to maybe put some sealant where it's leaking? Not even sure that it's a good idea? If yes to both, then you'd have to get the area real clean so that the sealant would stick and not come off. Hell, I would probably try it.

[niz76]

Is the leak real bad?
How long will the engine hold 6 psi when pumped up?

Yes the stock Piggy vari parts are pretty nice!

[buzzscoot]

Thanks for the advice, I put some sealant over the leak  night before on the outside and retested last night. No more leaks in that spot, but I was still losing pressure. I sprayed soapy water everywhere and found no leaks, I took off the variator and had no leaks on the crankshaft seal. I started to open up the fly wheel but instead decided to take the scooter back apart, put the motor on the stand and investigate what was going on because on the ground it was hard to get to the underside of the scoot to see well.

I sprayed water underneath on the case seal and no problem there. Then I noticed a small bubble on the backside of the freeze plug at the exhaust port. I thought I checked it well before, but with the scoot together and the kickstand in the way, I didn't see it. I fiddled with the freeze plug but couldn't stop the leak. I then made a rectangular steel plate with two drilled bolt holes and a thick gasket to seal the port. It still bubbled slightly but with more tightening, I got it to stop. I then did another leakdown at 6 psi, even came back 30 minutes later with no pressure loss. So all is well. While I had the motor on the table, I took out the bad starter. I'm glad I had easier access because it was stuck in there pretty good.

Lesson learned-I will never do any kind of motor work again, without doing a leakdown test while everything is disassembled and the motor on the table. Wasted a lot of time and now need I need to put it back together.

Still waiting on some more parts, hope to have back together and then some pics. Need to get the body parts painted up next.

[buzzscoot]

Well, I have had some problems.

After putting it back together, I could get the scoot start easily but I couldn't get it to maintain idle like before at the beginning. It seemed like it wouldn't hold the rpm up high enough. It would idle well with just a slight turn of the throttle though. No matter what I did with the mixture screw or idle adjustment screw, nothing changed anything. I took out the idle jet and it was perfectly clear, but I noticed it was fairly big- 45- for this scoot where stock is 32. I had a 38 and put that on and it idled perfectly without even changing the screw settings of 1 1/2 turns out . I am thinking that because of the leak maybe they went up on the pilot jet and now that I had good pressure I didn't need as high an idle jet size??

Well I idled and reved it a few times over about 10 minutes with everything looking good, and then the scoot died and I couldn't get it restarted.
The cylinder felt very very hot. I drained some of the coolant from the hose before the pump and it was cool. I started thinking that the water pump wasn't working though I know that the shaft turns.
I let the scoot cool for a couple of hours, retested the compression and leakdown test. The leakdown test was great, the compression a little lower than I got before, now at 120 psi.
I also looked at the cylinder and rings and had no problem there.
I took off the hose at the top of the radiator . This hose comes from the cylinder head . I tried to keep the coolant tank at this height so I wouldn't loose too much fluid.
I am not sure what path the coolant follows but I guessed that it goes from the pump through the cylinder, out the head and into the top of the radiator.

I next started up the scoot as this was the only way I thought I could see if the coolant was flowing. I couldn't observe the temp gauge because I didn't have a temp sensor on the scoot as it was missing and I have a replacement on the way. I only had it idling for a minute but no coolant flowed out.

So I have the question, is this the correct flow direction and is this the correct way to test. I also thought that if the thermostat didn't open up then maybe I wouldn't get flow from this hose. Should I have tested this without the thermostat, or should some coolant flowed into the radiator from the other loop? Even after a minute the cylinder did seem quite hot. I can't find good info on how to test this so any advice is welcome, thanks.

[spaz12]

I would test it without the thermostat.
Not sure either what path your coolant flows. There is at least one other guy here with a GP1 and as soon as I remember who, I'll tag him so that maybe he can tell you.

[buzzscoot]

Thanks Spaz,

Took out the thermostat and bled the coolant system at the cylinder head, and made sure the radiator outlet and hose had coolant filled to the top, started up the scooter and no flow. The water pump shaft is turning but I think the pump impeller is buggered up. There also was evidence of a leaky seal but not leaking at present.
I'm just going to try an electric pump cause I don't want to split the case if I don't have to, and I took out the oil pump as well because I intend to run premix.
,

[buzzscoot]

Did I say how I hated the design of the piggy water pump, geeezzz! I think if I ever do another one I'll just throw on an electric pump from the beginning and be done with it.

[pinkscoot]

The Derbi engines water pump is no treat either.

[stepthrutuner]

I started to suggest early in the thread that you'll probably have to replace the water pump. I've seen it time and time again. And sitting up and out like it did almost made it a sure thing.

[buzzscoot]

Almost done. Installed the starter, electric water pump, and Koso Tach/Temp gauge.
The pump works great and keeps the temperature very low.
I"m still too rich at idle with a 38 jet. I'm spitting out a fair amount of spooge from the old exhaust and the plug looks wet and black. I thought it might be from oiling the cylinder so much during install or/and saturating the filter. I've now have gone through nearly a gallon of fuel so I don't think that is the case any longer. I did start at 30:1 premix but now I am at 45:1 with the same problem so that's not it. My main is 75 so I wouldn't think I'm overly rich there though I haven't been revving much. Awaiting some more idle jets so I can reduce the jetting to leaner as I still think I'm still too high as it barely keeps an idle.

All that's left is rebuilding the rear master cylinder and caliper and putting on my new Yasuni R. I want to wait till I get the spooge spitting solved before I put on the new pipe. Of course after that is the painting ,putting on the body parts, and final tuning. Keeping my fingers crossed!

[buzzscoot]

I’m not sure I understand what is going on. Maybe you guys can give me your two cents.

Got the idle jetting straightened out , maybe just some slight tweaking left. Still waiting on the parts to rebuild the rear break, but I put on the yasuni R and rode the scooter some. With 5.5 gm weights my acceleration was very good. I don't have the speedometer hooked up so I don't know how fast I was going in the videos below, but it felt fast. I recently upgraded my scarabeo with a malossi sport 70 and it seemed quicker. I was surprised to see a peak of 13,000k rpm within a few seconds of starting on a short stretch and it kept between 12000 and 13000. The pipe is pretty loud too with these high revs.

It seemed to drive well and fast and I was hitting 12,500 to 13,000k rpm at WOT toward cruise speed but I didn't run long at WOT and I don't know what my top speed is , but I guess I'll increase my weights to hold the rpm's down? Any other options to hold the rpms down other than maybe changing gears? I am running a stock crank and am worried about the high revs. I have never experienced really high revs before so I don’t know what to think. I thought over revving due to light rollers would also not have good acceleration or good top speed, but I don’t know what to think here. Also I am running the white malossi torque spring and yellow clutch springs.

[buzzscoot]

It didn't add the videos in my previous post.

[buzzscoot]

Tried half 7.2 rollers and half 5.5. Rpms went down to 11.8k max on acceleration but averaged 11-11.5.
Short cruising around 11k but it seemed like I kept up the speed backing off the throttle and keeping the rpm at 10,500.
Acceleration seemed just as good if not better. Overall driveability seemed better. So it seems like I reduced rpm about 1200 with this change.

Tried all 7.2 rollers and I had a noticeable power and acceleration loss. Scooter didn't feel right. Rpm's went down around 800 more.

It looks like this setup is about a 11k rpm +, which is a bit more in the safer range. I think I'll wait on doing anymore tuning until I put on some body parts and hook up the speedometer.

[spaz12]

Glad that ya got it sorted out. And I would never of figured a Yasuni R and that cylinder for those kind of RPM's. Crazy, but cool