Is it possible to use a 626 on a M20 ? If so, does anyone know which main jet, needle position, etc. I have to use for a Concentric 626 carb. ?

John.

email (option): john.kater@chello.nl

Hi John..You can fit a Concentric as it is essentially the same carb without a seperate float chamber...Use a throttle cutaway the same as for the 276..Main jet the same as a monobloc for the M20 and put the needle clip in the middle position for initial start up. Set the Pilot airscrew 1-1 1/2 turns out from fully screwed in..and fit an insulation washer between the carb and barrel as you would for a 276..Amal carb specs are, in fact, a guide for initial setting and may need 'tweaking' to suit the individual engine once running.....Ian

email (option): ian@wright52.plus.com

Thanks Ian,for your quick reply. The reason for a 626 carb, is that I want my M20 so modern as possible. Also it is a lot cheaper
One final question: do I need a airfilter

John

email (option): john.kater@chello.nl

Hi John..If you want the engine, and particularly carb, to do the maximum before replacement/refurbishment an air filter is definitely beneficial...and if you fit a new one the bike will be even more modern.. ...Ian

email (option): ian@wright52.plus.com

I have been running a 626 for 14 years on my M20 and it runs great with it on.
However you will need to fit the longest spacer you can find or it will boil the fuel.
I fitted an old carb from my WD B40 complete with the 1" manifold and 2 x 1/2 " Tuffnol insulating spacers.
With this set up I had to make up new mounting studs but still had enough space to run a pill box air filter from a Firebird ( A65F ) the ones with both off set and indented inlet.
If you want to use the original twist grip you will have to shop around or make your own cable as the 276 has a different end to a concentric and concentric cables have a bigger throttle barrel than M20 ones.
Easy option is to use a later model throttle twist grip.
Finally get a 900 series bowl with a drain plug as the position of the cable encourages water to run down the cable dribble down the needle and fill up the float bowl.

email (option): wariron@tpg.com.au

This is the type of filter.
To make it look more "proper" find an old perforated plate and swap the pretty chrome one for an old one painted either drab or matt black. You can usually find an old one at a swap meet ( auto jumble to some ) for less than a quid.
A normal one will not fit with the spacers and without the spacers the heat from the barrel will boil thee fuel in the carb causing the engine to run very lean till it ventilates the piston crown.



Here is the whole lot on the bike
From the barrel there is a paper, a thin Tuffnol, a paper , a thick Tuffnol , A B40 spacer , a soft composite gasket.
All this was done , one bit at a time till the carb got far enough away to prevent fuel getting too hot.
There is no " O " ring on the concentric as the soft gasket will conform to the grove for the "O" ring and make a good seal.
The WD B 40 ( B40GA ) replaced the WD M20 in the Australian army.
As they had a lot of problems with fuel boiling on the M20's they specified the long alloy manifold to get some more cooling on the carb at slow speeds on the replacement bikes.
The carb was also at a slight down angle so if the float stuck the cylinder would fill with fuel so they modified the manifold to take a drain tube which I have removed as it makes the tuning a bit of a PIA. This is the bolt you can see 1/2 way along.
You will also note the 900 series bowl with the drain plug

email (option): wariron@tpg.com.au

Thanks Trevor, I will keep it in mind. Although overheating is not much of a problem in the Dutch weather I use a 20 mm spacer. Since I use elbows on the carb, there is not much change of waterleaking I think. I keep you informed on this.



John

email (option): john.kater@chello.nl

Ian Wright

Use a throttle cutaway the same as for the 276..Main jet the same as a monobloc for the M20 and put the needle clip in the middle position for initial start up. Set the Pilot airscrew 1-1 1/2 turns out from fully screwed in..Ian

email (option): john.kater@chello.nl

i have done in a mag with the concentric carb because when tickling it the petrol comes out of the tickler in quite a large ammount straight down into the mag where as the 276 carb bowl sit more over the edge of the timing case and the overflow hole is small going to get a drip tray at stafford this weekend

email (option): roger.beck@node6.com

Hi John..Pilot jet will be the same as specified for the Monobloc...Ian

email (option): ian@wright52.plus.com

Thanks again Ian, I presume the needle jet will be no. 106

I understand there will be some changes once riding

John

email (option): john.kater@chello.nl

roger

Going to get a drip tray at stafford this weekend

email (option): john.kater@chello.nl

Have you got a left or right handed concentric ?
On mine the over flow from the tickler flows down onto the timing cover which should be obvious by the staining ( which I will polish off shortly ),
The long inlet tract brings the bowl back past the end of the maggy in any case which also makes it easier to pull the float bowl off the carb.
I am running the standard 30 primary jet
But I took a bit off the bottom of the slide so it is some where between 2.5 and 3 cut away now.
The main ended up at 260 but that is probably a bit big to compensate for the air leaking down the sides of the slide.
It ran quite well with any thing from 220 to 280 and for a long time was a 240 as I early run it WFO but on a long ride from Torquay ( Victoria ) to Walla Walla ( NSW ) up the Hume I decided that I really needed a bigger main.
The easiest way to sort it out is to fit the air slide to the carb and keep going up in size till it stops going better when you use the air slide on full throttle.

roger

i have done in a mag with the concentric carb because when tickling it the petrol comes out of the tickler in quite a large ammount straight down into the mag where as the 276 carb bowl sit more over the edge of the timing case and the overflow hole is small going to get a drip tray at stafford this weekend

email (option): wariron@tpg.com.au