Derbi GP1 for Track Use

It's show and tell for your custom scoot! Post photos of your project scooters, etc.

Moderators: SLOWRIDER, Areomyst, scootertrog, mikal

User avatar
Areomyst
Site Admin
Posts: 5275
Joined: Tue Jul 10, 2007 11:39 pm
Location: Haw River, NC United States of America!
Contact:

Derbi GP1 for Track Use

Postby Areomyst » Sun Jul 31, 2016 9:36 pm

Hi guys!

I finally took the better part of one of my days off and started working on my Derbi GP1. There's a track day coming up next week, and I'd like to have the bike ready to run by then - but we'll see. :) My wife is pregnant also, and she's due on the 15th of August - so baby could come along at any moment and postpone my racing fun for a little while.

I took some photos of the progress. Please keep in mind that the parts aren't as clean as I would normally like. My parts washer isn't in yet (I ordered a good one a while back) and I figure I'll be back into the engine soon enough anyway, and I can get it cleaned up better then. Up until today, I hadn't worked on the scooter since I bought it, and didn't know everything that was wrong with it. I purchased the scooter cheap because it had a broken crankshaft.

IMG_2026.JPG
IMG_2026.JPG (592.58 KiB) Viewed 5875 times


IMG_2027.JPG
IMG_2027.JPG (461.86 KiB) Viewed 5875 times

I was surprised to find a Naraku clutch bell installed.


IMG_2028.JPG
IMG_2028.JPG (526.86 KiB) Viewed 5875 times

The broken crankshaft...


IMG_2030.JPG
IMG_2030.JPG (618.85 KiB) Viewed 5875 times

Finally got the engine out. Everything went along fairly smoothly.


IMG_2031.JPG
IMG_2031.JPG (549.93 KiB) Viewed 5875 times

Here, things got interesting. I was planning on building a 50cc track bike, but noticed that the scooter had a big-bore kit from Malossi installed... I suppose that I may eventually build a 50cc engine for this, but for now I just have to go with what I have. I thought it was funny that the cylinder head was installed upside down. :P


IMG_2032.JPG
IMG_2032.JPG (660.76 KiB) Viewed 5875 times

IMG_2033.JPG
IMG_2033.JPG (603.23 KiB) Viewed 5875 times

Before and after a quick cleaning.


IMG_2035.JPG
IMG_2035.JPG (634.75 KiB) Viewed 5875 times

IMG_2036.JPG
IMG_2036.JPG (494.24 KiB) Viewed 5875 times

Above: The broken crankshaft... I believe that it was broken by someone working on the bike, as it had several incorrect components on the splined side of the crank - including a stripped out and wrong sized nut. It looked like whoever had worked on the scooter before just wailed on the crankshaft with an impact gun...


IMG_2047.JPG
IMG_2047.JPG (564.28 KiB) Viewed 5875 times

Hey, it's ugly, but it passed a leak down pressure test!

IMG_2048.JPG
IMG_2048.JPG (634.23 KiB) Viewed 5875 times

Retiring on the engine for the night. It's been a long day!

IMG_2050.JPG
IMG_2050.JPG (576.96 KiB) Viewed 5875 times

After I get the engine installed and running again, I'll likely go ahead and install the Heidenau K61 tires. I opted to go with a premium street tire for the track instead of a race slick for two reasons. First, they're a lot less expensive than slicks. Second, I am not sure that at my skill level I'd really take good advantage of what the slicks have to offer. If I do end up switching to slicks, I think I'd like to find some NRG wheels or something so I can go with 12" tires... there are much better options for race tires in 12".

Anyway, I hope the build is interesting to some of you out there! I will chime in with details on the setup soon.

~Josh
"The more a man learns, the more he realizes how little he knows."

User avatar
Areomyst
Site Admin
Posts: 5275
Joined: Tue Jul 10, 2007 11:39 pm
Location: Haw River, NC United States of America!
Contact:

Re: Derbi GP1 for Track Use

Postby Areomyst » Mon Aug 01, 2016 7:51 am

The primary goal with this scooter is to race it on the kart track. If I'm going to do that though, I have to do it low-budget. The setup will change over time, but for now it's:

Malossi Sport Iron Cylinder Kit
RMS Stuffed Crankshaft
Tecnigas Q-TRE expansion chamber (Thanks for the great deal on the exhaust Triesandluth!)
Stock Dellorto PHVA 17.5mm carburetor

The CVT is stock for now, except for the Stage 6 Torque Control clutch and wing bell which is robbed from the Super 9.

Of course, once I get it going I'll tune it on the dyno. :)

~Josh
"The more a man learns, the more he realizes how little he knows."

User avatar
wireburn
Posts: 638
Joined: Mon Jan 07, 2008 2:34 pm
Location: Muskegon, MI USA
Contact:

Re: Derbi GP1 for Track Use

Postby wireburn » Thu Aug 04, 2016 1:46 pm

Wow, nice bike! Be careful out there and watch for squid.

New baby on the way, huh? You really HAVE been busy :lol:

-Mike
2007 Ruckus BIG BORE
2002 Metropolitan II w/Ruckus Swingarm
2006 Yamati Strada RX8 103cc LC stroker, PG power pipe, Keihin PWK28, Custom Intake, V-Force3 MX Reeds, Polini 14/41, Malossi OR, DC conversion (Sold!)
2000 Harley-Davidson Road King Classic

User avatar
Areomyst
Site Admin
Posts: 5275
Joined: Tue Jul 10, 2007 11:39 pm
Location: Haw River, NC United States of America!
Contact:

Re: Derbi GP1 for Track Use

Postby Areomyst » Fri Aug 19, 2016 4:24 pm

wireburn wrote:Wow, nice bike! Be careful out there and watch for squid.

New baby on the way, huh? You really HAVE been busy :lol:

-Mike


If I really want to watch for squid, I'll leave my mirrors on and point them right at myself! :P I hope I can do decently out there - I practice my technique often, and constantly read literature on staying safe on the road and improving skills for road and track. That said, I always look forward to learning more!

Not long after my last post, I got the engine installed in the GP1, and the tires mounted as well. I got a few more small parts in for this the other day, and Daniel.O was kind enough to machine the brake caliper piston that I was having trouble with. I've got some more pictures to share as well, I just haven't had much spare time lately. I'll get them posted up next week most likely.

~Josh
"The more a man learns, the more he realizes how little he knows."

User avatar
F10Pilot
Posts: 275
Joined: Thu Apr 03, 2008 6:22 pm
Location: Maine

Re: Derbi GP1 for Track Use

Postby F10Pilot » Sun Aug 21, 2016 4:53 pm

Woah nice Derbi!

Must post pics of Kart track racing though sir. Congrats on the family additions the baby and the scooter.
Malaguti F10 - Flies like a butterfly - Sounds like a bee.

User avatar
Areomyst
Site Admin
Posts: 5275
Joined: Tue Jul 10, 2007 11:39 pm
Location: Haw River, NC United States of America!
Contact:

Re: Derbi GP1 for Track Use

Postby Areomyst » Wed Aug 24, 2016 9:51 pm

Here's the update that I intended to provide a while back!

IMG_2190.JPG
IMG_2190.JPG (667.67 KiB) Viewed 5651 times

I had an order with SIP a while back, and as a dealer I have certain minimum requirements. Needless to say, a variator kit ended up in my shopping cart, so there's that. No, it's not the Polini 9 roller vario or a high end overrange - but it's a nice part and for my entry-level trackdays it should certainly suffice.


IMG_2191.JPG
IMG_2191.JPG (515.67 KiB) Viewed 5651 times

I also scored a Stage 6 drive face and a set of brake pads for the rear, as my rear pads were shot.

IMG_2192.JPG
IMG_2192.JPG (504.95 KiB) Viewed 5651 times

IMG_2193.JPG
IMG_2193.JPG (398.21 KiB) Viewed 5651 times

The previous owner of my scooter had a guy working on it who did a lot of poor work to the bike... The brake lines were full of air, and the pads weren't installed the right way at all. The end result was a pad that was worn with a heavy "slant" on the pad's friction surface, and eventually the caliper piston got ruined. Thankfully, Daniel.O was willing to machine the damaged part off of the piston. I prefer both pistons to be the same, but parts availability (or lack thereof) forces me to go this route. In the above photo, the newly turned part is on the right, and the old (but still good one) is on the left.

IMG_2201.JPG
IMG_2201.JPG (648.98 KiB) Viewed 5651 times

Finally, here is the scooter just waiting on me. I'm sure that if it had feelings it would feel neglected - just like my Jog... Meh, I'll get it out to the track soon enough. :)

Ciao!

~Josh
"The more a man learns, the more he realizes how little he knows."

User avatar
Areomyst
Site Admin
Posts: 5275
Joined: Tue Jul 10, 2007 11:39 pm
Location: Haw River, NC United States of America!
Contact:

Re: Derbi GP1 for Track Use

Postby Areomyst » Tue Nov 08, 2016 12:39 pm

Well, I got the rear brakes fixed up today. If I had time, I'd have painted the caliper, but the bike will surely be apart again before long anyway. For now, I just want to get the bike going so I can get on the track...

~Josh
Attachments
IMG_2485.JPG
IMG_2485.JPG (565.68 KiB) Viewed 5167 times
IMG_2487.JPG
IMG_2487.JPG (565.28 KiB) Viewed 5167 times
IMG_2486.JPG
IMG_2486.JPG (510.7 KiB) Viewed 5167 times
"The more a man learns, the more he realizes how little he knows."

User avatar
Areomyst
Site Admin
Posts: 5275
Joined: Tue Jul 10, 2007 11:39 pm
Location: Haw River, NC United States of America!
Contact:

Re: Derbi GP1 for Track Use

Postby Areomyst » Sun Nov 13, 2016 3:24 pm

IMG_2556.JPG
IMG_2556.JPG (614.2 KiB) Viewed 5116 times

IMG_2557.JPG
IMG_2557.JPG (467.19 KiB) Viewed 5116 times

IMG_2558.JPG
IMG_2558.JPG (482.79 KiB) Viewed 5116 times

The Derbi came with no means of starting it, as the starter bendix was ruined, and the kick start components were missing. I was able to get a bunch of RMS replacement kickstart parts installed and the kickstart now works great. The CVT is all put together, and ready for testing.

IMG_2560.JPG
IMG_2560.JPG (594.19 KiB) Viewed 5116 times


IMG_2563.JPG
IMG_2563.JPG (593.68 KiB) Viewed 5116 times

Dyno tuning is next! The setup is very tame and mild. It's basically a sport setup, and from my quick test drives around the driveway and yard, the throttle response is very smooth and predictable. That should work well for now! After tuning, I will give a track day a try. :)

~Josh
"The more a man learns, the more he realizes how little he knows."

DanielO.
Posts: 180
Joined: Fri Sep 07, 2012 1:19 am
Location: Efland NC

Re: Derbi GP1 for Track Use

Postby DanielO. » Sun Nov 13, 2016 5:16 pm

Looking good man! glad you got some time to work on it... I'll probably have to clean my fuel system again when we finally get a chance to go ride... the track usually closes down for a few weeks around the holidays so we'll have to see how it goes...

dan v
Posts: 358
Joined: Thu Nov 05, 2009 5:45 am
Location: Grand Rapids, Michigan USA

Re: Derbi GP1 for Track Use

Postby dan v » Wed Nov 16, 2016 8:27 pm

Areomyst wrote:The primary goal with this scooter is to race it on the kart track. If I'm going to do that though, I have to do it low-budget. The setup will change over time, but for now it's:

Malossi Sport Iron Cylinder Kit
RMS Stuffed Crankshaft
Tecnigas Q-TRE expansion chamber (Thanks for the great deal on the exhaust Triesandluth!)
Stock Dellorto PHVA 17.5mm carburetor

The CVT is stock for now, except for the Stage 6 Torque Control clutch and wing bell which is robbed from the Super 9.

Of course, once I get it going I'll tune it on the dyno. :)

~Josh


Pretty similar to the set-up on the SR50 I have been working on for so long........let me know what jet for the 17.5 you settle on.
How many scoots is too many?

User avatar
Areomyst
Site Admin
Posts: 5275
Joined: Tue Jul 10, 2007 11:39 pm
Location: Haw River, NC United States of America!
Contact:

Re: Derbi GP1 for Track Use

Postby Areomyst » Thu Nov 24, 2016 11:05 pm

DanielO. wrote:Looking good man! glad you got some time to work on it... I'll probably have to clean my fuel system again when we finally get a chance to go ride... the track usually closes down for a few weeks around the holidays so we'll have to see how it goes...


Thanks for the kind words Daniel. I'm getting closer to having it ready for a real ride. Today I did some work on the dyno and got the carburetor dialed in to where I'm comfortable thrashing it, and I got some blocked CVT runs in. I'll post the results below.

dan v wrote:
Pretty similar to the set-up on the SR50 I have been working on for so long........let me know what jet for the 17.5 you settle on.

Hey Dan, it's good to read from you, as always! The jet specs:

    Stock airbox
    32 Pilot
    30 slide
    A22 Needle 4/5 (clip is in the 4th position of 5, 5/5 being richest)
    80 Main

After tuning a bit, I decided I'd rather do away with the stock airbox in favor of a Doppler setup. The jetting specs were adjusted as follows:

    Doppler airbox
    32 Pilot
    30 slide
    A22 Needle 5/5
    118 Main
"The more a man learns, the more he realizes how little he knows."

User avatar
Areomyst
Site Admin
Posts: 5275
Joined: Tue Jul 10, 2007 11:39 pm
Location: Haw River, NC United States of America!
Contact:

Re: Derbi GP1 for Track Use

Postby Areomyst » Thu Nov 24, 2016 11:47 pm

IMG_2588.JPG
IMG_2588.JPG (2.59 MiB) Viewed 4922 times

The first order of business was to remove the cable going to the oil pump as I am premixing the oil and fuel.

IMG_2583.JPG
IMG_2583.JPG (3.16 MiB) Viewed 4922 times

Onward to dyno tuning!

IMG_2584.JPG
IMG_2584.JPG (2.89 MiB) Viewed 4922 times

IMG_2585.JPG
IMG_2585.JPG (2.88 MiB) Viewed 4922 times

IMG_2586.JPG
IMG_2586.JPG (3.18 MiB) Viewed 4922 times

Above: The Doppler airbox. I rather like this one! It's quieter than some of the others I have messed with, and it is easy to modify for more airflow if desired. I went ahead and removed the plastic that was blocking the two additional intake ducts on the filter box. It was very simple to modify, and the only tool needed was a razor blade.

IMG_2587.JPG
IMG_2587.JPG (2.96 MiB) Viewed 4922 times

The carburetor saw a fair amount of time removed from the scooter today.


gp1pretune.jpg
gp1pretune.jpg (85 KiB) Viewed 4922 times

Above: This is a pull with the stock airbox and the carburetor settings shown in my previous post. The CVT was operating normally (not blocked), but I haven't tuned the CVT yet with proper weights, etc... I wasn't surprised that the power was that low. I have built 50cc engines with ported OEM cylinders that made more power and torque.

gp1BLOCKED.jpg
gp1BLOCKED.jpg (77.33 KiB) Viewed 4922 times

Above: This is a dyno run with the CVT blocked (so the CVT isn't "shifting" during the run). From this graph, I can see that peak torque is at 8800 RPM, and peak power is at 8900. Therefore I will aim to have the clutch engaging close to 8800 RPM, and select rollers that will keep the engine around 8900 as the CVT "upshifts" during acceleration.

I could get more power out of this setup with a larger carburetor, a better exhaust, and porting. Any one of these things alone would certainly improve the output. I may port the cylinder, but for now the exhaust and carburetor will remain the same unless I find a really really crazy deal on different parts.

One thing that I noticed pretty quickly while running the scooter on the dyno, is that my rear wheel needs to be removed and balanced. I should have done that before putting it on the bike...

Next up is CVT tuning! When the opportunity arises, I would like to get a torque drive pulley (also called a movable sheave, or movable pulley half). With the stock torque drive pulley I will not be able to get the CVT dialed in quite as well as I'd like, though I should still be able to get it close.

I'm not sure when I'll have another chance to work on the GP1, but I'll be sure to document the work and share it when I do! I'm getting awfully close to being ready to take the scooter to the track. The more I think about it, the more I feel I should go ahead and get some basic porting done to this cylinder. We'll see how it goes. :)

~Josh
"The more a man learns, the more he realizes how little he knows."

User avatar
Areomyst
Site Admin
Posts: 5275
Joined: Tue Jul 10, 2007 11:39 pm
Location: Haw River, NC United States of America!
Contact:

Re: Derbi GP1 for Track Use

Postby Areomyst » Fri Nov 25, 2016 10:28 pm

I just couldn't leave well enough alone. I didn't want to be disappointed by poor performance. My wife didn't need me for anything after work, so I went back out to the garage to play with the GP1.

IMG_2592.JPG
IMG_2592.JPG (498.8 KiB) Viewed 4888 times

IMG_2593.JPG
IMG_2593.JPG (455.91 KiB) Viewed 4888 times

This is how I laid out the exhaust port. The corners will not be sharp as the scribed lines indicate. I usually just use the radius of the cutter I'm using to shape the corners of the ports. I didn't do much with the intake. Here's a list of what I did copy/pasted from Walter's Porting-programs.com software.

    Malossi Cast-Iron Sport Cylinder Specs
    lengths: mm
    areas: cm squared
    durations: degrees

    Stock Engine
    ===============
    Bore: 47.0
    Stroke: 39.3
    Conrod: 80.0
    Deck Clearance: 1.04
    Exhaust PortTop-BarrelTop: 23.40
    MainTransfer PortTop-BarrelTop: 31.70
    AuxTransfer PortTop-BarrelTop: 31.70
    Boost PortTop-BarrelTop: 32.60
    Exhaust duration: 178.5
    MainTransfer duration: 124.9
    AuxTransfer duration: 124.9
    Boost duration: 118.0

    Porting Mods
    ===============
    Raise barrel: 0.00
    Raise exhaust: 2.34
    Raise main transfers: 0.42
    Raise aux transfers: 0.42
    Raise boost port: 1.32
    Exhaust duration: 192.0
    Main transfer duration: 128.0
    Aux transfer duration: 128.0
    Boost duration: 128.0

I also widened the exhaust port to 70% of the bore.
IMG_2602.JPG
IMG_2602.JPG (457.97 KiB) Viewed 4888 times


Surely the next dyno test will be a little more exciting. :)

~Josh
"The more a man learns, the more he realizes how little he knows."

User avatar
Areomyst
Site Admin
Posts: 5275
Joined: Tue Jul 10, 2007 11:39 pm
Location: Haw River, NC United States of America!
Contact:

Re: Derbi GP1 for Track Use

Postby Areomyst » Sun Nov 27, 2016 1:28 pm

I meant to post these photos of the cylinder the other day:
Attachments
15259619_10207876490218635_2042262000130770405_o.jpg
15259619_10207876490218635_2042262000130770405_o.jpg (276.9 KiB) Viewed 4864 times
15156840_10207876480018380_454330002332151636_o.jpg
15156840_10207876480018380_454330002332151636_o.jpg (277.22 KiB) Viewed 4864 times
"The more a man learns, the more he realizes how little he knows."

dan v
Posts: 358
Joined: Thu Nov 05, 2009 5:45 am
Location: Grand Rapids, Michigan USA

Re: Derbi GP1 for Track Use

Postby dan v » Sun Nov 27, 2016 6:37 pm

Thanks for the heads up on the jet size. I have a 90 in there now - what the PO was using with an Airsal. Guess I'll keep it in there for now. Interesting how the airbox to your doppler setup changed the jet size so much.

After working on the above mentioned Aprilia for almost 2 years now, I finally got to fire up the new engine this afternoon. So apparently no problem running that 12 mm piston in the Polini kit, just as you said. A few other minor things to work out before trying it on the road, probably won't happen till spring. Thanks again for all your help on that project.

Nice work on the porting. I wish I had that skill. I was going to give it a go on the Polini, but only found info on porting for the Piaggio model, and no confirm that porting info was the same for Mina. So left it stock.

Please pardon the minor threadjack. Looking forward to see how you make out at the track!
How many scoots is too many?


Return to “Scooter Showroom”

Who is online

Users browsing this forum: No registered users and 5 guests