Support GPR Camp!!

DRP: Derbi Reactivation Project

The Return of the Wicked GPR

Create a thread about your bike.
User avatar
jkv357
Posts: 172
Joined: Fri Dec 01, 2017 6:47 am
Location: WI
Replica: '99 GPR EBE-075
x 344
x 90

Re: DRP: Derbi Reactivation Project

Post by jkv357 » Thu Dec 20, 2018 7:01 am

Why does it look so wet?

Is it 4-stroking when you back-off at WOT?

What oil and ratio are you running?
0 x

Tags:

User avatar
toratora
Posts: 3103
Joined: Wed Oct 11, 2017 1:05 am
Location: San Francisco
Replica: Derbi GPR
Cagiva Mito
Cobra CX65
Aprilia RS50
x 1657
x 1896
Contact:

DRP: Derbi Reactivation Project: Moist

Post by toratora » Thu Dec 20, 2018 4:34 pm

I too was rather surprised that it was wet, because it had been a few days since the bike was ridden. The way the bike is now it cannot get to WOT. At about 9K, where it would be getting on the pipe, it stutters harshly. The fuel is either Redline, or Motul at 32 to 1.
0 x

User avatar
jkv357
Posts: 172
Joined: Fri Dec 01, 2017 6:47 am
Location: WI
Replica: '99 GPR EBE-075
x 344
x 90

Re: DRP: Derbi Reactivation Project: Moist

Post by jkv357 » Fri Dec 21, 2018 6:35 am

toratora wrote:
Thu Dec 20, 2018 4:34 pm
I too was rather surprised that it was wet, because it had been a few days since the bike was ridden. The way the bike is now it cannot get to WOT. At about 9K, where it would be getting on the pipe, it stutters harshly. The fuel is either Redline, or Motul at 32 to 1.
It's got to be way rich then - I would think - but could there possibly be an ignition issue (I think you said it's possible)?

My GPR fell on it's face anytime I was at mid-throttle, but idled fine and once past the major stumble pulled to redline fine.

I leaned the jet needle and needle jet a bunch, and now it pulls clean the entire way.

Do you have anything to go by for jetting - factory recommendations or anyone running a similar set-up? It's surprising it's that far off.
1 x

User avatar
toratora
Posts: 3103
Joined: Wed Oct 11, 2017 1:05 am
Location: San Francisco
Replica: Derbi GPR
Cagiva Mito
Cobra CX65
Aprilia RS50
x 1657
x 1896
Contact:

DRP: Relations

Post by toratora » Fri Dec 21, 2018 10:39 pm

Image

Image
The thing about this bike is that there are no other bikes like it. That’s been a regular issue for finding information, and illustrates the struggles of being a pioneer. The challenge here is the combination of the HPI ignition. If a stock ignition was employed this sort of situation wouldn’t exist. However, supposedly, with the HPI ignition the bike will run better, because the temperature of the exhaust will be controlled providing a wider power band.

Unfortunately, the HPI docs are severely lacking. They are in this thread somewhere, as are the docs for the kit. Nothing in the Derbi manuals is going to cover this situation, because very little on the bike is still stock. The rear brake system is for the most part stock—except for the res, pads, powder coating... :?

Hopefully, tomorrow I’ll borrow a timing light, and find out what the HPI is actually doing. Not having a garage, or properly working diagnostic tools, and the rainy cold weather has turned this into much longer struggle than it should have been.

Based on the wash readings the engine is currently setup in a rich condition. The solution is going to be something along the lines of adjusting the timing, and/or continue to try leaner and leaner jetting. Changing the timing can directly effect how rich or lean the engine is running. My current understanding of this is that more advancement will effectively lean it out, less will make it richer.

However, HPI is notoriously prone to putting the timing marks for their 2Ten ignition in the incorrect location. Which means until I can get a functioning timing light on it I have no real way to know what it is doing, or where it is set. Previously when I’ve put a timing light on the HPI 2Ten things didn’t work out, but I’ve learned that it is firing twice (I have no idea why), and this knowledge should allow me to get a proper reading. The HPI does look really cool, but it has been an expensive nightmare with with to work.
2 x

User avatar
XERO
Posts: 1
Joined: Fri Feb 16, 2018 9:06 am
x 1

DRP: HPI Docs

Post by XERO » Thu Dec 27, 2018 5:39 pm

Something I found on HPI’s website awhile back when messing with mine ...

My Ignition happened to be of this “faulty batch.” I reinstalled the Factory Ignition, and Top Red Box before finding this, perhaps in the spring I can revisit mine.

Anyways, it's worth a quick look at yours to see if it is wired wrong.

1 x

User avatar
toratora
Posts: 3103
Joined: Wed Oct 11, 2017 1:05 am
Location: San Francisco
Replica: Derbi GPR
Cagiva Mito
Cobra CX65
Aprilia RS50
x 1657
x 1896
Contact:

DRP: HPI Docs

Post by toratora » Fri Dec 28, 2018 2:39 am

Hey Xero,

Thanks for that—I’ll check that out. I remember you posting that in your thread some time ago. I think I inspected the unit back then, but doesn’t hurt to take another look!
0 x

User avatar
toratora
Posts: 3103
Joined: Wed Oct 11, 2017 1:05 am
Location: San Francisco
Replica: Derbi GPR
Cagiva Mito
Cobra CX65
Aprilia RS50
x 1657
x 1896
Contact:

DRP: Timing 101

Post by toratora » Fri Dec 28, 2018 6:39 pm

Image .
Image

Image

Image
The Proper Tools
Today was another attempt at getting the timing set. I didn’t actually make any progress, but I did collect some confusing data! Ed let me borrow is new timing light. This one isn’t nearly as nice as his old one, but it works so much better. Today was the very first time that I actually able to get real readings from the bike.

This was because I had a proper battery in the bike, the tach set correctly to read the RPMs, and the timing light was powered with an external source. All of these things created a state where real data could be collected.

Fasteners and Access
In order to gain access to read, and adjust the timing the left lower side panel had to be removed. I had put thread lock on the panel screws because over the years with these bikes so many screws have been lost. With the thread lock they didn’t want to come out even with a proper tool. Hopefully this means that in the future fewer screws will disappear.

Leverage
While in there I noticed that the shift lever was loose. Since I wanted to adjust it this seemed like a good time to deal with the issue. Even though this is a Derbi shift lever the clamping mechanism doesn’t grab the shifter shaft enough to be tight. I didn’t want to break it so I tightened it as much as I dared, and called that good enough. It is tight enough that the bolt isn’t going to come out. However, the play in the system is annoying. I’ll have to investigate and address this issue when there is more time.

The Living Daylights
I basically got this far before it started getting dark. Which is to say I didn’t really get anything accomplished, but at least the stage is set for making some progress. Maybe tomorrow I can employ some Seat Dyno action.

Notes
The Derbi engine spins counter clockwise from this side. More advancement would mean turning the stater plate clockwise, less would mean turning it counter clockwise. I did a quick test each way.
. Readings
Since I wasn’t going to be setting the timing by checking the distance before TDC I set a pen mark on the stator plate as a reference. The pen mark was alined to the timing mark on the cases. For the first test I turned the plate counter clockwise. For the second test I turned it clockwise.


These readings were at roughly 4K RPM.

2 x

User avatar
toratora
Posts: 3103
Joined: Wed Oct 11, 2017 1:05 am
Location: San Francisco
Replica: Derbi GPR
Cagiva Mito
Cobra CX65
Aprilia RS50
x 1657
x 1896
Contact:

DRP: OMFG!!

Post by toratora » Sun Dec 30, 2018 9:39 pm


It was suppose to be just a short little test, but how could it be? The bike for the first time in ages was awesome, again. Sure there’s still a hiccup around 7k-8K, it isn’t very happy about short shifting, and the H2O needs to be up to around 50°C, but OMFG!! is it fun! :o

What was it? The HPI of course. Based on the work I did last week I realized that the markings on the HPI were off by about 5°. This is why I could never get the timing set correctly. I was unable to figure this out because until then I didn’t have both a working tachometer and timing light with which to test. Having both of those, taking some photos, and thinking about it a little bit allowed me to discover the issue.

I’m confident that with some effort the fine tuning to work out the hiccup at 7K-8K RPM can be worked out. I’ll need a working bore scope (both of mine have failed) to check on the wash as I go. I don’t want to fry things by going too lean.

This brings up the next issue which is the suspension. Both springs (there’s only one in the forks), are way too soft for my fat ass. The throttle now has access to enough power that the bike acts like a child’s seesaw. Riding it around requires extra effort with the smoothness. :?
3 x

User avatar
kaldis12
Posts: 233
Joined: Tue Jul 31, 2018 3:04 pm
Location: Hungary
x 21
x 138

DRP: Derbi Reactivation Project

Post by kaldis12 » Mon Dec 31, 2018 12:13 am

Happy to hear this :) Waiting for the video :)
0 x

User avatar
Rj_666
Posts: 50
Joined: Sat Nov 11, 2017 3:13 pm
Location: Tacoma, WA
Replica: 2 x Aprilia RS50
1 X Derbi Senda SM
x 21
x 23

Re: DRP: Derbi Reactivation Project

Post by Rj_666 » Mon Dec 31, 2018 9:29 pm

Great news, Tora !!
0 x

Post Reply