G80S Concentric jetting?

[Drongo]

Can anyone help me with the correct jetting and slide cut away for a G80S 1954, I was sure there would be many discussions on this site but found one only that was not very informative
Denny

[dave16mct]

Use the settings for a 1955 monobloc and go down 20% on the main jet.
http://archives.jampot.dk/book/Owners_m ... ingles.pdf
Dave.

[Drongo]

Can anyone help me with a simple question on what jets exactly to use on a G80S with a Mk1 Amal 930 Carby, Main Jet ??? Needle ???? Needle Jet ???? Slide Cut away ???? No one seems able to supply this basic info which I thought would be a very commonly asked question for the thousands of owners who have changed out their Mono Blocks but it seems to have everyone scratching their heads???? I was expecting someone replying with, this this and this will make it run sweet???

I have 280 main, 2 ringed needle with 3 circlip slots, needle jet 1C7, side has 928 MB4 3, I tried to post an image but I cant work the system, click Img above copy my jpg image and it wont accept it when pasted???????

[dave16mct]

OK the link above works now. Go to the manual by clicking on the link. Go to Data. The monobloc carb settings are listed there. Use those settings but reduce the main jet, which I think from memory is 260 down to say 240.
Dave.

[Drongo]

Thanks Dave, what about the needle jet and needle sizes as well as recommended slide cut away, these still have me stumped??

[Andy51]

Hi, I used a 30 mm Concentric on my '54 18S. I bought it from a fellow cub member who had originally bought it ready set up by Amal Carbs. It worked straight from the box and apparently used Monobloc settings apart from main jet, which was, as Dave said, 20% down on Monobloc setting - this 20% rule wa confirmed by Surrey Cycles, purveyor of Amal Carbs, at Kempton autojumble. Hope this helps, Andy

[Drongo]

Thanks Andy and Dave, std amal monoblock has 260 - 20% = 208 main jet say 210 should do. Throttle valve say 3 and I have 3. Needle jet says 1065 I have 1C7 ?? pilot jet should be 30 but its a pressed bushing and set. Lets see.

[ajscomboman]

i suspect that is a 107 needle jet. Bigger than standard.

[Andy51]

210 main jet sounds about right. Earlier Concentrics had fixed bush for pilot jet, later ones had changeable ones, the fixed one can be a bit small and cause popping on the overrun. Surrey Cycles in UK drill it out to 19 thou (costs £15) to rectify this. Looked at doing this myself, but needed extra long drill, so paid the man to do it. Not a huge problem running without enlarging pilot jet, just make sure exhaust pipe is well sealed in the head with ordinary silicone sealant. To make sure sealant wouldn't blow out, I fitted one of those alloy finned exhaust clamps beloved of cafe racers back in the day - they just fit over the pipe, pushed back to head before silicone sets. Andy