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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
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Re: Derbi GPR50 2003 France project

Post by benito brz » Thu Dec 23, 2021 3:35 am

jkv357 wrote:
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?
Well I think my current jet is correct for the moment because its starting and running but the answer of throttle is slow
I havent tried idle jets over 100
I've tighten the idle mixture screw and loosed it 2,5 round
But the bike cant stay at idle I have to turn the throttle so the engine dont turn off
Also the bike is running good in the street and then the engine turn off after a moment because my gas filter is not filled enough so I have to change the part under the tank with "on/off/res"(dont know the name in english) that is leaking so i cant adjust my carburator if gas isnt coming properly
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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 » Thu Dec 23, 2021 3:37 am

Jaxx wrote:
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.
Yes its a dellorto phva 17,5
Yes you are right i talked about the main jet
Usually I dont touch the idle jet
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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 » Thu Dec 23, 2021 3:38 am

jkv357 wrote:
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?
Sorry i was talking about the main jet and not the idle jet
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jkv357
Posts: 213
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Location: WI
Replica: '99 GPR EBE-075
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Re: Derbi GPR50 2003 France project

Post by jkv357 » Thu Dec 23, 2021 6:48 am

If it doesn't idle, I would make adjustments.

If it's close to idling, first turn the idle speed up with the idle speed screw - which just lifts the slide. Then make the mixture adjustments.

When the engine is fully warm, turn the idle mixture screw to get the highest RPM at idle - then I like to richen it slightly (about 1/8 turn) to get a smoother transition off-idle. After that is optimized, set the idle speed back to the proper RPM (most likely it's going to be too high).

Depending on the carb, your idle mixture screw may be a fuel-bleed or an air-bleed - you need to know which in order to adjjust 1/8-turn richer.

Generally, if the idle mixture screw is behind the slide (closer to the air filter) it's going to be an air-bleed (turn IN to richen). If it in front of the slide (closer to the engine) or at the bottom it's going to be a fuel-bleed (turn OUT to richen).
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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 » Thu Dec 23, 2021 7:55 am

jkv357 wrote:
Thu Dec 23, 2021 6:48 am
If it doesn't idle, I would make adjustments.

If it's close to idling, first turn the idle speed up with the idle speed screw - which just lifts the slide. Then make the mixture adjustments.

When the engine is fully warm, turn the idle mixture screw to get the highest RPM at idle - then I like to richen it slightly (about 1/8 turn) to get a smoother transition off-idle. After that is optimized, set the idle speed back to the proper RPM (most likely it's going to be too high).

Depending on the carb, your idle mixture screw may be a fuel-bleed or an air-bleed - you need to know which in order to adjjust 1/8-turn richer.

Generally, if the idle mixture screw is behind the slide (closer to the air filter) it's going to be an air-bleed (turn IN to richen). If it in front of the slide (closer to the engine) or at the bottom it's going to be a fuel-bleed (turn OUT to richen).
Thank you for all these advices
First I have to buy a new fuel tap
And then I will adjust the carburator, i've got an air-bleed on it
And when you talk about adjustments, is it about the main jet or something else ?
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jkv357
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Replica: '99 GPR EBE-075
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Re: Derbi GPR50 2003 France project

Post by jkv357 » Thu Dec 23, 2021 8:23 am

benito brz wrote:
Thu Dec 23, 2021 7:55 am
Thank you for all these advices
First I have to buy a new fuel tap
And then I will adjust the carburator, i've got an air-bleed on it
And when you talk about adjustments, is it about the main jet or something else ?
In this case, just the idle mixture and idle speed.

Testing and adjusting (changing) the Main Jet is a bit more complicated. I would do some research to see what the general size range should be, so you have a decent starting point.

The Main Jet will be primarily controlling the mixture at wide open throttle (WOT), and needs to be correct before you can precisely adjust the remaining circuits. The idle circuit is mostly isolated, being controlled by the Pilot Jet and idle mixture screw setting, and is usually not affected significantly by a change in the Main Jet.
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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 » Thu Dec 23, 2021 11:58 am

jkv357 wrote:
Thu Dec 23, 2021 8:23 am
benito brz wrote:
Thu Dec 23, 2021 7:55 am
Thank you for all these advices
First I have to buy a new fuel tap
And then I will adjust the carburator, i've got an air-bleed on it
And when you talk about adjustments, is it about the main jet or something else ?
In this case, just the idle mixture and idle speed.

Testing and adjusting (changing) the Main Jet is a bit more complicated. I would do some research to see what the general size range should be, so you have a decent starting point.

The Main Jet will be primarily controlling the mixture at wide open throttle (WOT), and needs to be correct before you can precisely adjust the remaining circuits. The idle circuit is mostly isolated, being controlled by the Pilot Jet and idle mixture screw setting, and is usually not affected significantly by a change in the Main Jet.
Ok thanks you very much for the advices jkv
I'll keep you updated
Have a nice christmas :tada:
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Jaxx
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Re: Derbi GPR50 2003 France project

Post by Jaxx » Fri Dec 24, 2021 5:29 am

As I understand, you have replaced cylinder (barell) but kept original head? That's not the best idea, especially if head came from engine that was siezed/overheated... At least you should measure if it's completelly straight... Interesting, stock EBE engine have one-piece head, different than D50B which is segmented (head and cover).
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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 » Sat Dec 25, 2021 12:26 pm

Jaxx wrote:
Fri Dec 24, 2021 5:29 am
As I understand, you have replaced cylinder (barell) but kept original head? That's not the best idea, especially if head came from engine that was siezed/overheated... At least you should measure if it's completelly straight... Interesting, stock EBE engine have one-piece head, different than D50B which is segmented (head and cover).
Yes I kept the original head because I havent enough money 3 years ago to buy a new head with the cylinder-piston kit , so i bought only the cylinder-piston kit , wich was also leaking from the headgasket in 2018
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