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Derbi GPR50 2003 France project

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benito brz
Posts: 118
Joined: Fri Sep 20, 2019 1:26 pm
Location: France
Replica: Derbi GPR 50 2003
Aprilia RS4 125 2014
x 64
x 77

Re: engine assembly part 1

Post by benito brz » Sat Dec 18, 2021 10:44 am

Hello everyone, I did the assembly of my engine, everything is new or rebuild,.
I had some issues but I solve all the little problems

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User avatar
benito brz
Posts: 118
Joined: Fri Sep 20, 2019 1:26 pm
Location: France
Replica: Derbi GPR 50 2003
Aprilia RS4 125 2014
x 64
x 77

Re: engine assembly part 2

Post by benito brz » Sat Dec 18, 2021 10:52 am

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So here I had some problem to put correctly the crankcase because of my gearbox bearing

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User avatar
benito brz
Posts: 118
Joined: Fri Sep 20, 2019 1:26 pm
Location: France
Replica: Derbi GPR 50 2003
Aprilia RS4 125 2014
x 64
x 77

Re: engine assembly part 3

Post by benito brz » Sat Dec 18, 2021 1:34 pm

So lets build something to remove the crankcase

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User avatar
benito brz
Posts: 118
Joined: Fri Sep 20, 2019 1:26 pm
Location: France
Replica: Derbi GPR 50 2003
Aprilia RS4 125 2014
x 64
x 77

Re: engine assembly part 4

Post by benito brz » Sat Dec 18, 2021 1:39 pm

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User avatar
jkv357
Posts: 213
Joined: Fri Dec 01, 2017 6:47 am
Location: WI
Replica: '99 GPR EBE-075
x 393
x 110

Re: Derbi GPR50 2003 France project

Post by jkv357 » Mon Dec 20, 2021 7:12 am

Wow - that's a ton of work!

Looking good now!
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User avatar
benito brz
Posts: 118
Joined: Fri Sep 20, 2019 1:26 pm
Location: France
Replica: Derbi GPR 50 2003
Aprilia RS4 125 2014
x 64
x 77

Re: Derbi GPR50 2003 France project

Post by benito brz » Mon Dec 20, 2021 7:48 am

jkv357 wrote:
Mon Dec 20, 2021 7:12 am
Wow - that's a ton of work!

Looking good now!
Thank you so much jkv
Now I have to adjust my carburator, my principal idle is 100 (90-95 are too low) any advice ?
Also I have coolant leaks from the downside of the cylinder, also from the headgasket , everything is New but its leaking :rage:
May I put some silicon paste ?
After fixing all that, just have to fix and paint the fairings and I'm done with it.
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User avatar
jkv357
Posts: 213
Joined: Fri Dec 01, 2017 6:47 am
Location: WI
Replica: '99 GPR EBE-075
x 393
x 110

Re: Derbi GPR50 2003 France project

Post by jkv357 » Mon Dec 20, 2021 8:27 am

benito brz wrote:
Mon Dec 20, 2021 7:48 am

Thank you so much jkv
Now I have to adjust my carburator, my principal idle is 100 (90-95 are too low) any advice ?
Also I have coolant leaks from the downside of the cylinder, also from the headgasket , everything is New but its leaking :rage:
May I put some silicon paste ?
After fixing all that, just have to fix and paint the fairings and I'm done with it.
Not sure I'm following about the idle - is it idling at 1000 RPMs or something else?

Did you torque the cylinder? It's possible the mating surfaces are not perfectly flat. I've had engines (heads) that needed the surfaces to be lapped with lapping compound on a very flat surface (Quartz or Granite) in order to get a flat surface that will seal properly.

No matter what, it's going to need to come apart again to cure. Maybe someone has a good fix, but I would start with lapping the surfaces.
0 x

User avatar
benito brz
Posts: 118
Joined: Fri Sep 20, 2019 1:26 pm
Location: France
Replica: Derbi GPR 50 2003
Aprilia RS4 125 2014
x 64
x 77

Re: Derbi GPR50 2003 France project

Post by benito brz » Mon Dec 20, 2021 10:33 am

jkv357 wrote:
Mon Dec 20, 2021 8:27 am
benito brz wrote:
Mon Dec 20, 2021 7:48 am

Thank you so much jkv
Now I have to adjust my carburator, my principal idle is 100 (90-95 are too low) any advice ?
Also I have coolant leaks from the downside of the cylinder, also from the headgasket , everything is New but its leaking :rage:
May I put some silicon paste ?
After fixing all that, just have to fix and paint the fairings and I'm done with it.
Not sure I'm following about the idle - is it idling at 1000 RPMs or something else?

Did you torque the cylinder? It's possible the mating surfaces are not perfectly flat. I've had engines (heads) that needed the surfaces to be lapped with lapping compound on a very flat surface (Quartz or Granite) in order to get a flat surface that will seal properly.

No matter what, it's going to need to come apart again to cure. Maybe someone has a good fix, but I would start with lapping the surfaces.
When I talk about my idle its about my principal idle jet in the carburator, i must choose the correct idle jet to adjust the carburator

Yes I torqued the cylinder and checked several times but maybe it need to be lapped like you said, the cylinder is new from 2018, but the rest upside and downside is original from the Factory, so it is "old"
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User avatar
jkv357
Posts: 213
Joined: Fri Dec 01, 2017 6:47 am
Location: WI
Replica: '99 GPR EBE-075
x 393
x 110

Re: Derbi GPR50 2003 France project

Post by jkv357 » Tue Dec 21, 2021 6:12 am

benito brz wrote:
Mon Dec 20, 2021 10:33 am

When I talk about my idle its about my principal idle jet in the carburator, i must choose the correct idle jet to adjust the carburator

Yes I torqued the cylinder and checked several times but maybe it need to be lapped like you said, the cylinder is new from 2018, but the rest upside and downside is original from the Factory, so it is "old"
What does it do that makes you think the current jet isn't correct?

Have you made adjustments to the idle mixture screw? Can you get it to idle?
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Jaxx
Posts: 46
Joined: Wed Jun 19, 2019 1:41 am
x 38
x 16

Re: Derbi GPR50 2003 France project

Post by Jaxx » Wed Dec 22, 2021 11:59 am

Which carb is this? It looks like Dell'Orto PHBN/PHVA 17.5 to me... Are you sure you're talking about idle jet? Idle jet size should be around 30-36. Size 100 should be main jet.
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