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Derbi GPR Track Bike

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toratora
Posts: 3161
Joined: Wed Oct 11, 2017 1:05 am
Location: San Francisco
Replica: Derbi GPR
Cagiva Mito
Cobra CX65
Aprilia RS50
x 1768
x 1977
Contact:

GPR Track Bike: Simply Little Progress

Post by toratora » Fri Sep 29, 2017 9:39 am

More little progress today—and the ants came back!

I thought I took more photos, but apparently I didn't! Most of the time was spent sanding. It takes forever to sand. The painting didn't go all that well, but it's fine for now. The ants showed up climbing all over one of the tail section halves.

Finally removed the pins that hold the controls. These where in the way of the controls I wanted to employ. So I removed them with the rotary tool, then shot a bit of paint on them.

The clutch lever I had came with one of the source bikes. It looked nice enough, but I needed to drill it out to fit the cable. This was a bit more difficult than I expected, but eventually I got it working. The clutch level is okay. It could be the cable, but it feels a bit tight.

I went to take out the thermostat. It was really grunged up, and stuck inside the head. Eventually I was able to remove it one piece at a time. But now all of the coolant lines are connected.

I was also able to get the chain in place. Turns out I didn't need any additional links. Which was nice. ;)

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User avatar
toratora
Posts: 3161
Joined: Wed Oct 11, 2017 1:05 am
Location: San Francisco
Replica: Derbi GPR
Cagiva Mito
Cobra CX65
Aprilia RS50
x 1768
x 1977
Contact:

GPR Track Bike: Close, but this isn't Horse Shoes

Post by toratora » Sat Sep 30, 2017 9:39 pm

Got a lot done today, but not enough to go to there track tomorrow. ¯\_(ツ)_/¯

I ran into a number of gotchas. Kind of what happen with used bikes.

Started today with checking out how the tail section was going to look.

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Then set in on repairing the cracks. I didn't have the stuff around to do this before the paint, or I would have done this first! lolz It's good to have some source materials. I was out on a group ride some many years ago and this idiot crashed his 748 into a bunch of other riders. I picked some one of the fairing pieces knowing that it would come in handy. I've used this on a number of bikes! lolz

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There were lots of little things to clean and paint too.

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Then it was time to drain the tranny oil. To make this jorb easier take an oil bottle, cut a tongue, and use it to keep things from spilling. This works great because these trannys only take about 650ml.

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This was working great until I open up the drain plug at the clutch cover. Then a huge amount of fluid came out! I had planned on revisioning the water pump because these things go out, and one of the bolts holding the pump cover on was quite oxidized. Clearly something had failed, and the clutch cover was full of nasty shit. Took a really long time to clean out. The clutch plates were all stuck together too. Eventually it was serviceable again, but by that time I was far too late in the day to expect the bike would be ready for tomorrow.

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Trying to figure out how to fit a kill switch into the mix.

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Tail Section Assembly

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The bike is coming along. ;)

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User avatar
toratora
Posts: 3161
Joined: Wed Oct 11, 2017 1:05 am
Location: San Francisco
Replica: Derbi GPR
Cagiva Mito
Cobra CX65
Aprilia RS50
x 1768
x 1977
Contact:

GPR Track Bike: Got Sprung

Post by toratora » Thu Oct 05, 2017 9:39 pm

Made some tiny progress today. I made some progress on the water pump as well, but didn't take photos of it yet. Still lots to do! lolz

Finally made it over to Treats to pick up the clutch springs. They are stiffer than stock, but look almost the same. The coils are same, and the springs are the same high, but the thickness of the wire is slightly larger.

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Picked up this gasket remover--it didn't work very well at all.

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Finally installed the fuel line and filter.

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User avatar
toratora
Posts: 3161
Joined: Wed Oct 11, 2017 1:05 am
Location: San Francisco
Replica: Derbi GPR
Cagiva Mito
Cobra CX65
Aprilia RS50
x 1768
x 1977
Contact:

GPR Track Bike: Forward Movement

Post by toratora » Sat Oct 07, 2017 7:39 pm

Made a lot of progress today. Even got the bike started! It runs great. It's going to be a lot of fun. But I wasn't able to finish enough of it to go to the track tomorrow. I needed to finish some brackets for the body work. I was out of time and had to call it quits for the day--still it was a great day of wrenching, because I got to ride it.

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First up was was getting the water pump assembled. The revision kit had a shaft that was too large. This gotcha was pretty bad because I wouldn't be able to use this kit. I ended up using the old shaft with the new seals.

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So with that worked out I went at the timing. This was rather difficult, and I even bent my new tool! But I kept at it, and eventually I was able to modify things enough to finally get it set.

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Once that was taken care of I was able to button up the clutch cover.

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Then I was able to tighten up the pipe again.

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The next issue was the 23mm CP carb. The slide was sticking. I've never run into this previously. It took me quite a while to figure it out too. What was happening is the stop where the idle screw contacts the slide. The slide was deforming and then causing it to stick when the throttle was pulled. I was finally able to get the carb to work correctly with some rotary tool and 1200 grit sand paper action. Not happy about needing to do this sort of thing on a brand new carb. I didn't get any photos though, as I was trying to meet my deadline.

Then I went around torquing bolts, and nuts. I also added oil to the tranny, coolant to the cooling system, mixed up some fuel and poured it in the tank, oiled up the filter, and, added a kill switch. A lot of little things had to be done.

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Then it was time for a test ride. Oh boy oh boy oh boy! Lots of fun. I first rode it in the parking lot with out any gear, and it was obviously too fast, so I put some gear on. Then ran it up and down the lot more than I probably should. It doesn't feel like a 50cc. It's got a lot more drive. It even wants to lift the front. This is probably due to the 12 tooth front sprocket. The clutch lever is garbage and I'll need to replace it with something better. The brakes work, but they need to be a lot better. So I'll have to attend to them. I have some Ferodo pads which will probably get put in there, and the fluid really needs to be changed out.

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Okay after the fun I still had a bunch of work to do as the body work need to be fitted. I was only going for the tail section and the faux tank, but because I needed to make brackets I wasn't able to get done before I had to pumpkin. One of the previous owners did some interesting stuff with cutting up the stock tank and fitting in a tank from another bike--probably a Derbi Senda. He also had some velcro to hold things in place. I decided that I would use some of these parts, and see if I could make it slightly better. I've not finished yet so photos will be in a later post.

This is taking a lot more effort than I had initially expected, but I'm very happy with the progress, and how much fun the bike is to ride. I'm really looking forward to taking it to the track even if it wont be tomorrow (Saturday). ¯\_(ツ)_/¯

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User avatar
toratora
Posts: 3161
Joined: Wed Oct 11, 2017 1:05 am
Location: San Francisco
Replica: Derbi GPR
Cagiva Mito
Cobra CX65
Aprilia RS50
x 1768
x 1977
Contact:

GPR Track Bike: Approaching

Post by toratora » Wed Oct 11, 2017 11:39 am

The faux tank and tail section are installed. This means that stage one is complete. I can now take this bike to the track! Obviously it's going to get updates, and more features as I have time to implement, but there's now enough there that I can start riding it.

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For the faux tank mount I needed to make some mods. But I didn't really take many photos this time either. So I don't have any photos of the brackets. But in the future I'll be painting them so all in due time. I will say this, the faux tank is the most stable I've ever felt on this style GPR.

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To gain access to the fuel tank I need to cut a hole. I decided to try a flap. This seems to be working. Eventually I'll install the fiberglass tail section, but until then I'll be running this stock plastic section.

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Are you ready boots? I did ride it some more in the parking lot today. This is going to be so much fun!

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User avatar
toratora
Posts: 3161
Joined: Wed Oct 11, 2017 1:05 am
Location: San Francisco
Replica: Derbi GPR
Cagiva Mito
Cobra CX65
Aprilia RS50
x 1768
x 1977
Contact:

Re: Derbi GPR Track Bike: Future Track Day

Post by toratora » Tue Oct 24, 2017 3:39 am

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Track Day

This Sunday October 29th we’ll be taking it to the kart track at Stockton Little 99. Join us for some full throttle action on the track. Expect it to be warm so bring shade, beverages, snacks/lunch, and other supplies.

Prep the track bikes, get the chains lubed up, the tires checked, and get that riding gear ready. Smaller (50~85cc) two stroke replicas like the Derbi GPR, and the Aprilia RS50 are very much encouraged. Fast mopeds, pocket bikes, Groms and such are okay!

Meet up Sunday October 29th
The track is open from 10am to 5pm. Open track, ride all day for $40.
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User avatar
toratora
Posts: 3161
Joined: Wed Oct 11, 2017 1:05 am
Location: San Francisco
Replica: Derbi GPR
Cagiva Mito
Cobra CX65
Aprilia RS50
x 1768
x 1977
Contact:

GPR Track Bike: And...

Post by toratora » Sat Oct 28, 2017 11:39 pm

Are you ready boots?

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User avatar
toratora
Posts: 3161
Joined: Wed Oct 11, 2017 1:05 am
Location: San Francisco
Replica: Derbi GPR
Cagiva Mito
Cobra CX65
Aprilia RS50
x 1768
x 1977
Contact:

GPR Track Bike: At the Track!!

Post by toratora » Sun Oct 29, 2017 11:39 pm

We had a good time out at Stockton today. For the most part things went really well. The bike were running good, although Mike's need some serious mid throttle tuning, and mine had a clutch cable fail. It started to bind up--which is unfortunate since it was a brand new cable. I'll be checking into it, and will probably put an older OEM unit on the bike.

There were a lot of people out there today. I didn't get much in the way of photos because I was rather busy doing riding. I was surprised how many LARGE cc bikes (over a liter) were out there. That track is just way too small for those bikes--and it's not safe having them out there with the pocket bikes.

Ed picked up Max's MetraKit for Alex today. It needs some fixing up, but I'm excited to see what Alex can do now that he'll be on a two stroke again.

Photos from today at the track!

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User avatar
Karim
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Re: Derbi GPR Track Bike

Post by Karim » Sat Nov 18, 2017 1:06 am

Sure is nice to have a track nearby.
Damn NIMBYs
Can't even have a proper go cart track
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User avatar
toratora
Posts: 3161
Joined: Wed Oct 11, 2017 1:05 am
Location: San Francisco
Replica: Derbi GPR
Cagiva Mito
Cobra CX65
Aprilia RS50
x 1768
x 1977
Contact:

GPR Track Bike: Tracks

Post by toratora » Sun Nov 19, 2017 3:39 pm

Yeah we are pretty lucky around here as now there are four tracks within driving distance for a single day adventure.

Stockton
Sonoma
Dixon
Le Grange

In SoCal they have some rather nice tracks too.

Adams
Apex
Apple Valley

I should probably do a proper track listing thread in the Track section. :P
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