BSA B31 timing

[Derek996]

Not that I know of, I've always just tightened up until it feels right to me. But I would think that around 45Nm wouldn't be far off and about 24Nm for the screws retaining the support plate.

[briancairns]

Cheers Derek

Thanks

Brian

[briancairns]

Hi,
Set timing according to book ( at fully advanced, checked that it was definitely advanced) :

7/16th ( 38degree) BTDC.
Spark plug 0.48 mm
points ; 0.3mm at widest opening. ( set magneto timing just as points opened)

Now bike hard to start, no real power and if i retard even the slightest bike splutters and pops.

new to this , but what i am doing wrong?


Thanks

Brian

[Derek996]

Were all the cam marks were lined up correctly? Did you change anything?

[briancairns]

Checked the cams all perfect . Only thing I changed was new points and adjusted magneto as originally timing was set at 57degree BTDC, point gap was 0.6 mm . However bike started ok but couldn't get over 50mph and struggled with the slightest hill

[Derek996]

It seems like you have the mag points gap and timing set correctly so I'm struggling to see where else you can check. Is you retard cable tight or slack for full advance? If the cable is on the cylinder side of the mag it should be slack, if it on the side away from the cylinder it will be tight for full advance. It is possible that you are setting it for the wrong advance direction.

[briancairns]

Ok   Derek .

I will recheck.

Cheers

Brian

[Jim S]

Just to clarify, the points face cam in the magneto should be rotated fully counterclockwise for the magneto fully advanced setting, regardless of the advance cable configuration. At 7/16in before tdc, the points should be just starting to open with the face cam rotated fully counterclockwise.

[briancairns]

Ok thanks Jim,
Not sure if I did that but or not.
Will re-time .

Cheers
Brian

[Pete C]

I would strongly recommend that you visit the technical section of the WM20 website at http://www.wdbsa.nl/.
much of the information is also applicable to the OHV models.

with regard to timing the sections linked below are very informative and should help you with any such problems.

http://www.wdbsa.nl/ignition_timing.htm
http://www.wdbsa.nl/download/Ignition%20setting.pdf

good luck
Pete

[briancairns]

Thanks so much Pete

Cheers
Brian

[Pete C]

Hi Brian
so long the ignition and cam timing are OK the only other issue could be the carb. What carb have you fitted? The settings are pretty basic to get it going reasonably well.
You mentioned at the beginning that the bike is OK up to around 55mph but bogs down on hills. The B31 should be good for around 70mph max but the engine does need to be spinning  to get the best performance. Unlike a B33, it isn't really a slogger.

cheers
Pete

[briancairns]

Hi Pete,
It's an Amal carb.
When bike was able to reach 50-55mph, it would really dive at the slightest hill.
I'll check your links and go through process again.

Thanks again

Brian

[Pete C]

Hi Brian

You could have one of a variety of Amal carbs  ,  pre-monobloc, monobloc or concentric. Do you know which you have? They all work OK but your tuning strategigy might be a bit different for each.

this link is a good start for tuning info.   https://amalcarb.co.uk/downloads/

Concentrics are cheap and easy while pre-monobloc or monobloc are more "authentic"  Enter your bike details here in "vehicle search" to get info on which carb would be "correct" for your bike           https://amalcarb.co.uk/

[briancairns]

Great Pete!

I have a look in the next day or so .

Thanks so much

Cheers