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Jetting an AMAL GP2 for a Silverstone RDS

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  • Jetting an AMAL GP2 for a Silverstone RDS

    Can anyone please help me with the jetting on the AMAL GP2 for my Silverstone RDS? The engine has been refurbished by Simon at Nametab and he looked-up the following: Main 420, Pilot 25 & Needle 109.

    I have taken the existing main jet out which came with the bike to find it is a 320! I called AMAL (Burlen Ltd) and they say the original main jet for the Silverstone is a 350 – they did agree the Pilot & Needle at 25 & 109 respectively.

    Obviously I don’t want to risk seizing the new motor but I don’t want to run it over-rich either. Can anyone running a GP2 in a Silverstone please give a sense-check? It will have an exhaust made by Andy Bacon and silenced to 105db for CRMC parading.

    Also struggling to find paper manifold gasket at 1 3/8” – who may be able to supply?

  • #2
    Will check with a friend who runs a GP on his RDS. As I run a Mk2 concentric my jetting is a 360, bit rich but play safe for parading. Gasket is easily cut from gasket paper or a thin smear of Threebond. Dogsbody


    • #3
      Always amazes me that owners try to search out ready made paper gaskets, I have always made my own (like Dogsbody) from brown paper or ever cornflake boxes, a dab of the dreaded red or brown Hermetite and job done. Gasket paper in various thicknesses is still available from car part shops like and of course on the internet.


      • #4
        He runs 400/420 depending on weather. He also has an Andy Bacon system so start at 420 and see what colour you get with a plug chop unless you do a dyno run. Dogsbody


        • #5
          Thanks Colin. I also want to fit a kill switch for the PVL - where is a good place to get the switch to fit 7/8 bars?


          • #6
            You don't need a kill switch. A GP carb does not have a tickover screw, let go of the twistgrip and it will stop ( assuming a little free play in the cable ). Dogsbody


            • #7
              Is it not a ruling for racing these days that a kill switch needs to be fitted, ie in the case if the rider comes off and the throttle jams open.
              There are loads of kill switches for sale on the internet. Like this one
              Its just a push button earthing switch same as used for a horn


              • #8
                When I was using the 5GP2 on my RDS the main jets were always in the 400-450 range to give the correct plug readings, depending on weather conditions. GP jets always seem enormous compared with the same bore Mikuni and, as I believe Amal and Mikuni both use flow to calibrate the jet sizes not the hole diameter, they should be comparable. I think the reason Amals run such large main jets has something to do with the remote needle and the indirect air flow that doesn't draw the fuel up in the same volume.

                According to the RDS service notes the main jet is 420, pilot jet 25, needle jet .109, a #3 slide and the needle in the #2 groove, so Simon was right.

                Make sure the float level is correct. The petrol should be level with the bottom of the scribed circle on the body, at the bottom of the enrichening slide.

                Yes, we have to run with a kill switch on race bikes in Canada. I found a similar universal push button here that was a quite small with a round red button. The red wire on the PVL ignition module is the wire to ground to kill the spark.


                • #9
                  Thank you all - lots of information and tips covering exactly what I need. Finishing touches next week and then - gulp, fire her up for the first time. Then hopefully on the track for my first ride at CRMC Mallory Park 31 August & 1 September


                  • #10
                    Dearly beloved has decided we need our bedroom decorating...… means going through half a ton of old records receipts etc, but amongst them I have found original Greeves service notes for the RDS and RES Silverstones (must be from when I borrowed the bike nearly 30 years ago, oops! , sorry Ian give them back to you at Cadwell). The book lists the same settings as above, might be the same book. What might be more use is an exploded diagram for the five speed box. Copies could be available for the requisite fee in real ale.