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 19mm PHBG copy carb issues

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markyB

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Number of posts : 67
Age : 47
Localisation : Norwich ...... GP3 Rep Owner
Registration date : 2006-08-21

PostSubject: 19mm PHBG copy carb issues   Fri Sep 15, 2006 3:25 am

Hi all, here is some info that i have learnt myself, or have been told by Shotaway/Jeff, about the copy carbs that are fitted on the GP3 reps.

1/. First of all to sort out the over/under fueling the bowl you need to set your floats up, for this you will need a vernier. Remove the carb from your bike, and float bowl. Rest the carb on a level surface with the air filter side on your level surface.
You now need to measure from left to right, from the carb base to the end of the float.
The distance should be 16mm, give or take 0.5mm.
Mine was pissing out petrol from the back of the carb into the air filter, and when i measured mine it was 19mm, since i adjusted it i have not had any problems.
Note: you must check both sides of the float, as i have known one side to be 19mm and the other to be 16.5mm.
Check this diagram out if your not sure:
https://2img.net/h/i76.photobucket.com/albums/j4/minimotomark/GP3/motorcycletechnicalpicture1.jpg

2/. Yes there's more! The choke when turned off does not close correctly. If you look at your choke and you can see the o-ring when the choke is off you know you need to adjust this. The O-ring should sit under the cap
To adjust you need to measure from the bottom of the black cap, past the O-ring seal. Mine measured 2.5mm so i got 2 fibre washers that were 1.5mm each put them on and it then closed correctly. This one is hard to explain so i have attached some pictures.

With the choke fault:
https://2img.net/h/i76.photobucket.com/albums/j4/minimotomark/GP3/Chokefault.jpg

Choke removed with spacers:
https://2img.net/h/i76.photobucket.com/albums/j4/minimotomark/GP3/Chokespacers.jpg
Carb with choke fitted correctly:
https://2img.net/h/i76.photobucket.com/albums/j4/minimotomark/GP3/Chokereseated.jpg

3/. And there's more! At the back of the carb where the air filter goes on, there are two holes next to each other. The most center and lowest of the two, has a brass insert pressed in.
This is restricting the fuel flow and should not be there. To remove this you need to insert a small self tapping screw, tighen into the brass insert until you see it rotate, then pull out with a pair of pliers.

Updated info for section 3/. You do not need to remove the insert, but it does not matter if you already have. If you remove it you will have to put in a bigger Main jet.

4/. The main Jet is an 89, i have been told you can put upto a 120 in, i am now running a 103 at the moment but have just ordered a 105.
I will follow up with any info the soon as i have got a definate answer.

Updated Info: I have had my bike dyno'd at MiniMoto Racing by Scott Finlay. We managed to gain an extra 2.3hp just by changing all the brass inserts to the carb for genuinne Dellorto parts. This is a must as we also noticed they run very rich from standard.
I believe that Scott Finlay will be selling carb kits for the GP3's that have the 19mm PHBG copy carbs fitted. These will be available mail order, but when ordering you must let him know if you have removed the insert at the back of the carb, as this makes a big difference to what size main jet you use.

MiniMoto Racing:- http://www.minimoto.co.uk/

01666 838234

Hope this can help!!!!!!!!

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