I hope you can help me, my 1932 BSA W32-6 (500cc side valve) is losing power when I change up to third or fourth gear, but only when riding on the flat.
The bike is not easy to start but when it does start it pulls away just fine in first gear then pulling strong in second. However when I change to third or four gear the engine revs drop and the bike would stop if it did not change down to second again.
I find this strange but what I find even stranger is that the bike works fine when either going up or down hill in third gear.
I would suspect some kind of fueling issue. In that going up hill somehow dislodges crap in the carb or float or tank and on the flat the crap goes back to where it was.
In summary, I have no idea, but would like to know how you eventually get to the bottom of it.
That was also my first thought, a fueling issue. Did you check the vent hole in the fuelcap is not blocked?? Good luck!
Thank you Patrick and Michiel for your support; I’m new to old British bikes and need as much support as I can get.
I also find it puzzling it does not match any rational or any of my current life experience. But here are a few things people have suggested and I’m going to check.
1, Is the fuel cap breather clear (thanks Michiel)
2, Are the fasteners around the carbuttetor tight, are there air leak issues
3, I’ve just replaced the rear tyre, could I have set the chain tension so tight that it can’t pull in 3rd and 4th
4, The problem has happened when running the bike in 29C heat. Could this just be a coincidence? I’ll try riding the bike when the weather gets cooler, which in Britain will mean waiting two days.
Thank you so much for the kind help offered by the members of this (and two other) forum. Today I rode my bike for 10 miles in the glorious sun.
With your advice I’ve been able to identify and correct the problem of losing power when in high gears. It was a small head gasket leak which resulted in insufficient compression when dropping down the rev range in higher gears. A new head gasket and some advice on torque setting and I have a bike that runs sweet.
This type of support is invaluable for inexperienced vintage bike mechanics like me.
Did you buy a solid copper head gasket? If not, the composite ones can burn through quite quickly and you may encounter the same problem (the lack of compression can be so bad that the bike won't start).
Also, did you re-torque the head once the engine had cooled down again?
