Inherited a 1956 B31, have little knowledge of mechanics. Bike in need of TLC. Was advised to strip carb, thorough clean required and renewed jets and needle. Bike started but not running smoothly at all. Can anyone please advise me how to adjust the settings via the screws on the carb?
Quote from: MJ1 on 10 Feb, 2025, 16:21 Inherited a 1956 B31, have little knowledge of mechanics. Bike in need of TLC. Was advised to strip carb, thorough clean required and renewed jets and needle. Bike started but not running smoothly at all. Can anyone please advise me how to adjust the settings via the screws on the carb?
They are simple devices but need clean and fresh fuel so check your tank filter gauze (attached inside the tap) is clean and you have a new filter on the carb. Check you have the correct sequence of washers under the filter mounting block to the float chamber as that ensures the float needle sits at the correct height. Iirc no washer under the chrome plated nut.
I presume you have cleaned and adjusted the contact breaker points to 12-14 thou you have a new spark plug of correct type gapped to 18thou. You have non-resistive plug cap and plain copper HT lead.
Here is link to basic monobloc adjustment:
https://www.manualslib.com/manual/828471/Bsa-B31.html?page=21#manual
After that you would need to dig deeper (tappets correct) and magneto needing service/rebuild etc.
Many thanks for your reply. I'll have another look and follow your suggestions.
Sucking eggs here, but have you checked that the oil pump rotates? They tend to nip up if left unused for a while.
Thanks for that but the oil pump is working fine.I thick it is something to do with the carburettor has I said have renewed all the jets and the needle it starts on first kick then dies and does not start again.May have to take carburettor off again and start from the being again.Thanks
Quote from: MJ1 on 11 Feb, 2025, 14:58 Thanks for that but the oil pump is working fine.I thick it is something to do with the carburettor has I said have renewed all the jets and the needle it starts on first kick then dies and does not start again.May have to take carburettor off again and start from the being again.Thanks
Check the pilot jet and the air way with it. Drown in carb cleaner and blow air through the tiny holes (I don't need to remind you not to poke wires through the jets!!)
Thanks, will try this at the wknd.
Quote from: neil1964 on 11 Feb, 2025, 15:17 [remind you not to poke wires through the jets!!)
They used to give that advice back in the 1920s/30s when fuel quality was worse and some riders were inveterate fiddlers. Doesn't really apply these days where people are less inclined to tinker for the sake of it, and fuel is cleaner, especially where a filter is fitted.
Some gas and industrial jets need a pricker to clean on a regular basis too.
Although solvents and compressed air are good initial steps in cleaning carbs, sometimes there's no alternative to poking through with a piece of wire to clean a particularly recalcitrant obstruction.
I've found a short length of High E guitar string to be most effective as it's both smooth and relatively stiff.
Thanks for info.I have purchased a full set of carb cleaning brushes and needle cleaners ....fingers crossed.
Whilst you have the carb in pieces, you should note the numbers on each jet. For a 250 it is usually 140 main and 25 pilot. The 350 could use a larger main. The needle position should be in the middle slot. The only reason you would want to change any of theses, would be if you lived on a high altitude plain, at 4000 feet asl.