Hi team,

I'am facing an issue that I previousely did not have with the BSA,
I cannot sort it out

The BSA starts correctly, idle is OK, but when I open the throtthe, the engine starts to suffer and goes out
When putting a sock with a ziptie or my hand before the air inlet of the carb (so reducing the air) the engine goes better and I
am able to open the throttle and ride, did several kilometers with the sock yesterday

even screwing the pilot air screw fully does not change anything

I assume that air is coming from somewhere

any tips or ideas ?

email (option): its.me.twixi[AT]gmail[DOT]com

Have you checked that the flange is completely flat on flat surface?

Or that the tiny pilot drillings are clear. The jet block needs to be removed to clear the drillings properly.(more information on request) Ron

email (option): ronpier@talk21.com

For the drillings I'm sure at 99% they're OK as the carb was completely cleaned 2 weeks ago

Will check the flange and see to set a new gasket, I'll come with the feedback

email (option): its.me.twixi[AT]gmail[DOT]com

If the small drilling was blocked/partially blocked that would reduce the amount of air not increase it, as the pilot adjustment screw and the associated drillings are metering the air supply not the fuel....If the pilot airscrew has no effect at all even when screwed fully home you have an air leak elsewhere or, less probably, a problem with the fuel supply...
If you have weakness throughout the range then it won't be related to the carb settings but will be an air leak causing generalised weakness....If there was a problem with the pilot for example, that would not be apparent further up the rev range where other parts of the carb are controlling the strength of the mixture...
Apart from the carb there are other possible problems that could cause weakness...Have you done any other work lately?...Is there 'spitting back' in the carb when the engine is running at the lower end of the range?..(without the sock!)..Ian

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

I also completely stripped and cleaned a carb on one of my Royal Enfield's. At the same time I re-corked the petrol taps. The bike was running fine for our Sunday ride out. But then it sputtered for 15 miles and eventually died 3 miles from home. I knew exactly what the problem was and was hoping to make it home rather than a roadside repair.

I tiny sliver of cork must have shaved off and got into those drillings. It's happened to me before, but I'm too stubborn not to use the original taps. You have to use some very fine wire to poke out the drillings in the jet block and carb throat......I use fuse wire. Ron

PS Ian. The tiny drillings I referred to are the pilot fuel feed

email (option): ronpier@talk21.com

One if the actions that was Taken by my wife's father was to thighten the valve lifter with the nut near the tappet box

Since i found it was also much more difficult to start

Previousely i could start it with max 3 kicks

PS if someone here is near Liège in belgium, he's welcome to Come sort this out in exchange of some beers :)

I need this bsa for an event the weekend of septembre 9 :)

Cheers

Check that you still have enough clearance between the valve lifter shaft and the tappet head...If the seating of the exhaust valve has been compromised that would result in the symptoms you describe...Ian

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

Hmm unfortunately, my mechanic knowledge stops there :D

I tried to screw/unscrew the valve lifter nut without any results
Very difficult to impossible start

Is there a standard setting to set or any knowledge of a video explaining step by step how to set this up ?

email (option): its.me.twixi[AT]gmail[DOT]com

It's a difficult one Yannick. The M20 valve lifter is not one of BSA's best designs and can be really fiddly to set up. Sorry I am nowhere near you to help. You need to find an old M20 owner near you to show you some tips.

In the meantime you could disconnect the cable which will mean pushing the piston past the compression stroke with the kick starter, before kicking to start. This is what I am doing with my Royal Enfield CO, since the nipple popped off the cable. It's fairly simple actually. I know it's only a 350 but it does have a high comp piston. Ron

email (option): ronpier@talk21.com

Valve lifter is easy
With the engine at running temperature slip your finger on the valve lister and pull just enough to take all of the slack out of the cable
If you feel a tapping on the lever it is too tight so you go to the front engine bolt that anchors the cable & back it off 1 turn ( easier said than done ) then repeat the above test till when you take the slack off the cable you feel nothing on the lever
For some weird reason people think the vlave lifter has to raise the valve a large amount when in practice a couple of thou is all you need and I find that is better because you can hear the charge whooshing out of the cylinder better

I really wish I was as clever as you Trevor!! Ron

email (option): ronpier@talk21.com

I would not go that far Ron
I don't think I have ever replaced the valve lifter in exactly the same place in 30 years of riding the bike .
Thus I get a lot of practice in adjusing the cable
A current project is to make a front engine bolt with a bigger offset for the valve lifter as the angle on mine fouls on the crank cases

I have found the standard engine plate bolt a little too long on the shank so fit a spacer under the head to prevent the adj. screw touching the crankcases...Ian

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

email (option): its.me.twixi[AT]gmail[DOT]com

That’s exactly what I ended up doing, was all a bit tight 👍

email (option): markmayo63@yahoo.co.uk