hi, all
I am after a bit of advice, just recently got an m20 and today was the first day out on it rather than just up and down the street but its not as quick as
i think it should be. Doing about 45mph. It does not run with the choke closed and it runs better or pulls stronger with the choke open it is fitted with the amal 276 aw/1bb carburetor but with a 170 main jet .
I have seen on this forum somewhere about fitting a smaller main jet because of the bigger carburetor.
The needle has four groves and i have moved it up and down but to no improvement, it is running rich at the moment.
any advice welcome, before i start porking about with it.

realy like the forum thanks in advance
steve

Steve normal running is with the choke open.(lever towards you). In fact I never close mine, even on cold mornings. Ron

email (option): ronpier@talk21.com

Thank you Ron, i think that might be it. had only opened just enough to run

Rode mine down to Devon for the Bank Holiday weekend clocking up another 400 miles . According to my GPS I cruise at around 45 mph and the most I saw was 51mph. Averaged 57mpg. There not fast bikes but you get far more smiles per gallon as well.

I've found that getting the timing spot on at 7/16" btdc make a noticeable difference to the way she goes.

Stuart

email (option): stu.gibbins@btinternet.com

It sounds like you've found the problem with the choke being on, but I've been saying my 16H will only do 40-45mph but I've now had 2 different mates follow me on bikes and told me I'm doing 50-55mph. So my speedo is reading 10mph slow even though I've just had it reconditioned. so something else to check out.

email (option): horror@blueyonder.co.uk

I know when my 16H is doing more than 45, all my fillings fall out.

Steve I would check out gearing if everything else is spot on ,if you a running std 18 tooth engine sprocket (or less) then your bike will revving hard at 45-50MPH. The first time I ride my rebuilt WM20 with a 18t sprocket I though it was gutless & underpowered compared to my 1950 ZM20 which has a 20 tooth engine sprocket fitted.I now have a 21 tooth sprocket fitted to WM20 and bike can cruise nicely at 50-55 mph with a nice gentle thump with 65mph possible in right conditions ie slip streaming / backing wind.I think for all round gearing best sprocket is a 20 tooth one.The old WM20 was once clocked by a mate riding with me at 75MPH but he was reading this from a harley speedo Dave

keith have you not got a ww2 army issue gum shield finding an unused one might be hard and cleaning the cosmoline off does leave the taste of petrol in your mouth for a while

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

Hi Steve,have you moved the advance / retard lever to fully advanced?this also will help.
cheers Rick

email (option): richardholt@rocketmail.com

Hi, went out and tried the bike again tonight, it was that or cut the grass, anyway it makes sense to pull the choke right in otherwise you have a large piece of alloy in the way if you don’t :) Never seen a choke work the other way round.
Went out on to the road and it pulled a lot stronger, especially in 3rd looked at the Speedo and it was reading 40 mph. I could feel it building up so I looked again and it was reading 40 mph it eventually topped out at 45mph
In the next week or so I will check the things you have suggested
Thanks for the input guys.

I two run a 20 tooth sprocket.
With the 6 spring clutch and 32 mm concentric it would pull to about 65 / 70 mph and gradually rev out to 75 /80 on the flat or slow decline at the cost of a LOT of fuel ( there is no such thing as a magic pudding )
With the same clutch & a 626 concentric it pulls to 60 & revs out to 70 but uses a lot less fuel.
With the single spring clutch & 626 it pulls a lot quicker up to 65 and that is it, not one foot/hour faster, up hill down dale or tail wind down a mine shaft.
There is an absolute limit to how fast these engines can rev without serious modifications which is around the 5000 rpm mark ( sure some one will know the actual figure ) .
You can gear them faster but if a sparrow farts in front of you, you stop dead in your tracks.
On step hill it will actually coast down faster than I can drive it down

With the tall gearing I was oft forced down to 2nd gear on any thing other than a short hill.
With the lower gearing it was just the occasional pop back to 3rd and funny enough I get a lot better fuel economy with the lower gearing I am running now.

The bloke I ride with most often has an A65F with a tiny 2 US gallon tank which used to go further than my 4 US gallon tank as we found out coming back from the BSA National in Torquay ( Victoria ) on the boringly flat Hume highway.

Coming back from the ABR this year with the lower gearing I was getting a lot further than him so he was just about dry & I was not yet on reserve when we refuled.

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

Hi Trevor...Interesting observations on the various set ups. My 720 is running a standard crank, M21 carb/port and standard cams with a 21T engine sprocket...Pulling power up hills is greatly improved and downward gear changes a lot less frequent. Normal (easy) cruising speed is about 50-55mph but with less revs. Top speed around 75mph. Over a long run its ability to maintain its speed up hills improves journey times considerably.
On one trip to Normandy I rode my WM20 with a standard M21 engine and lent the 720 to a friend...We rode the same route at the same speed and interestingly the 720 used approx. 20% less petrol in identical conditions.
I can only put this down to the fact that most of the time it is revving a lot less...
As you say, with both sidevalve and OHV BSAs of this age you can go so far and then come up against a 'brick wall' in terms of engine revs..
Substantial lightening of the flywheels is, in fact, the key element in building a performance version...Ian

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

There waas no seroius attempt for higher performance , it ws just as things unfolded.

The 276 had more leaks then a confidential cabinet meeting and the only donor bike handy was the B50 hence the 930 carb.

Eventually I dug out the 626 from a B40 and over the next few years did a very slow jet appraisal till I had it what felt right.

By this time the the clutch sprocket was a bit "gummy" so an A 10 six spring went in ( as it was handy).

ran like that for years till the box packed it in ( ran out of oil & killed top fork ).

By this time the old single spring had been rebanded so it went back in as the 6 spring hub had to be cut off the mainshaft.

However I do have a spare barrel , a VW piston and a copy of the Victory files, so you never know what might happen.

Bike Beesa
Trevor

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

Ian
I have the same setup as you, using the piston you supplied me with. I'm still running it in but I have a few 100 miles on it so far and it's soooo nice to ride! Loosening up nicely and doesn't seem to notice hills at all.
The only thing is the exhaust note which is like the crack of doom and it sends the neighbour's dog mental

email (option): petercomley@web.de

Hi Peter,.. ..Yes, the soft M20 sound is sharpened up somewhat with the bigger engine...Tell you neighbour to get a Dalmation..they frequently suffer from inherited deafness.... ....Ian

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

Hi Trevor,

I have a NOS 626 Amal as a backup for the M20, which I run original 500cc now.
Can you tell me what you found to be the best jetting for it?

You also talked about the lower gearing which was better for fuel consumption.
How low was it?

I use now a 19T engine sprocket and 18T gearbox, usually with a sidecare.

Thanks!
Noam.

email (option): noam10@gmail.com

Does anyone else have the same problem as me- flies hitting the back of my helmet, not the front!!!???

email (option): davmax@ntlworld.com

showing off again??

email (option): petercomley@web.de

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