Im not a mechanic however I am quite practical and have taken on quite a few more modern builds and maintenance.
I wanted an old bike to potter on and tinker with, and so decided to buy a 'fettled' bike that i could then get to know and maintain. That plan hasn't worked as i have only managed to get it going once..
Delivered from the dealer to me, it started off the van after a few attempts and had its maiden ride around town. A few days later after turning on the fuel tap, petrol was pouring out the carb and fuel bowl weeps.
Stripped the carb down and on rebuild cracked the solid fuel line from the tank.
Trailered it to my local specialist who fixed the pipe and fitted a replacement fuel bowl needle and managed to get the bike going again. He did say it was a nice bike!
This morning, turned on the tap and fuel pouring out of the carb again. Can only assume its the same issue.
Now thinking of ordering a new fuel bowl needle and giving it all a good strip down and clean again - unless anyone has a better suggestion?
Have you checked that the float is intact - no fuel inside it? Also, make sure the loat height is correct. Changing the float valve assembly is a good idea, but just make sure there's no debris from the tank stopping the needle from seating - if it has been seating reliably in the past then it's likely to be something intermittent causing the problem.
When the petrol is turned on give the float bowl a tap with a small , say 13mm , spanner and see if it stops . it could be the seat where the float needle is fitted to . A rubber tipped float needle is what you want in there .
Ive tried tapping the bowl and makes no difference - just annoying its the same problem.
Ive ordered a new needle and will try seating that, how do you set the float height?
Or should i just go straight to a rubber tipped needle and forget trying to fit the new 'standard' one ive ordered?
Also checked the oil and was very low, dropped the lid off and was full of oil so obviously wet sumping - was only in the garage on Tuesday so only took 5 days to happen.
Wet sumping is very common on older bikes. I have a few and have fitted a large bore tap to the oil feed pipe to cure it. Just don't forget to turn the oil on before starting the bike!
Which carb is fitted is it the pre monoblock or a later one .
The carb is an amal 75 / 145.
The float height should be pre-set by the float needle groove, but the needle may have more than one groove to allow adjustment. The club has a pdf on Amal carbs that might be worth reading: https://www.bsaownersclub.co.uk/bsaoc_forum/index.php?action=dlattach;topic=5667.0;attach=8749 (https://www.bsaownersclub.co.uk/bsaoc_forum/index.php?action=dlattach;topic=5667.0;attach=8749)
Is there any debris in the float bowl? I see you have already had a new float needle fitted, and have ordered another one. Part no. AM/14/024. Assuming it's a bottom feed float bowl, you should be able to unscrew and remove the cover, turn the petrol on and it shouldn't overflow. If it does, the needle is not seating. Remove the float bowl, turn it upside down and examine the seating closely. Check for dead flies etc. You may need to lightly polish the needle and seating with a little brass polish. If you disturb the Union Nut which screws onto the bottom of the carburettor body, be careful not to over tighten it, otherwise the bottom of the carburettor will break off. I understand the new needles have 2 grooves. The top groove is for copper floats, and the bottom groove is for plastic floats. Assuming yours has only one groove, and a copper float, the float height is non adjustable, but with the cover off, you will be able to see where the petrol level is. I think the petrol level should be just below the the top of the needle jet. Make sure that both tangs of the float clip stay in the groove. Often the top one springs out. Bend as required.
You may need to fit an inline fuel filter to stop debris getting into the float chamber. Also, check that the small horizontal breather hole in the knurled part of the cover is not blocked.
I would fit an inline tap in your oil feed line. You can buy one with a switch which earths the magneto when in the off position.
Properly cleaned the fuel bowl and rebuilt with the original parts, all seems good.
Didnt strip carb again but tried to fire up and nothing.
Damp spark plug, so definitely getting fuel through so hoping carb is ok now.
Checked spark and couldnt see it sparking, it might of been but if it was was very dim - its hard to kick and hold at the same time!
Thinking it might be a magneto issue, somewhere in the garage i have an inline spark plug flasher which should help me diagnose.
Just got a bit fed up / cross with it so packed up my tools in a huff and am ignoring it for a while
You could try cleaning and then heating the plug with a blow lamp or heat gun put it straight in a see if you have any joy. A new plug would be best of course.
But if you're not seeing a nice fat blue spark when you kick the machine over you need to investigate the mag. Have you checked that the magneto points are clean and set to the right gap? Also check that the slip ring is cleand and the pick-up brush etc. is good. Check that the earth brush is clean, but you'll need to remove the mag to do that.
I know you said the machine had been running, but it might be worth just checking the valve clearances.
Cleaned the points down with liberal amounts of contact cleaner, new spark plug and fired up 3rd kick!
Let her warm up and she settled into a steady idle, but only with a little throttle on. Adjusted the idle screw until idle was steady and held - i think its a bit fast, but will keep and eye and adjust as necessary.
Started to rain so no maiden voyage, fingers crossed its dry tomorrow night!
Nice work. BTW, contact cleaner will remove grease, but it's usually a good idea to get the mag into a position where the points are closed and draw a folded piece of 1200 wet and dry through the closed points to remove any corrosion followed by a piece of paper to remove any debris.
So all was going well, had a few short rides with no incidents.
Got her out tonight - started right up and i kept a few revs on initially and then she settled into a high idle, no amount of fiddling with the choke or retard helped also tried dialling out the idle screw slightly which didn't do anything
Was also backfiring like crazy so turned off with the valve lifter.
Then would not restart and the kick pedal felt a lot stiffer then usual.
She is back in the garage now
Check the ignition timing. Also check the valve clearances. Maybe do a compression test too.
When you back-firing, do you mean spitting back through the carb or unburnt mixture igniting in the exhaust?
What colour is you exhaust? A photo would be good.
The stiff kickstart is wierd. It could be unrelated to the running - have you checked the primary chain tension?
Its popping out the carb.
Earlier this week the throttle needle was sticking in the carb and i released it with some wd40, wondering if there is something stuck under the needle causing the high idle?
Exhaust is a bit of a bodge, mostly chrome - not got a pic to hand.
Will have a proper look tomorrow at the kick
Spitting back through the carb could be caused by a number of things including incorrect ignition timing - too advanced. In this case it sounds like it's down to a weak mixture. The needle shouldn't get gummed up. Is the tank lined with something breaking down due to the ethanol content of the fuel - the same goes for fuel lines which will leave a black gummy deposit in the carb. Foreign matter in the carb would also account for your flooding problem mentioned earlier. If the bike's been laid up for a long time, the evaporation of the fuel often leaves a brown varnish or sediment in the carb.
It's unusual for the needle to stick. More likely, it's the slide. This can be caused by overtightening the flange nuts, causing the body to distort.
I wonder if the slide is not bottoming on the slow running screw, perhaps the cable is holding the throttle open? Maybe give it a bit of free play?
You should be able to unscrew the slow running screw until the engine stops.
If you're sure the slide is bottoming, then another reason for a fast idle is an air leak. Spray WD40 over the flange with the engine running to check. Also spray grease on the inlet valve stem to check for leaks here. You may be able to grasp the valve collar with a pair of molegrips to check for play without dismantling.
I have found that laying the spark plug on the head doesn't tell you much. What you need is a spark gap tester. This is just an adjustable gap. I made one following the instructions in "The Motorcyclists Workshop", and it's saved me hours of grief. A reliable spark over a 3/16" gap indicates 8,000 volts, 1/4" gap 10,000 volts and 5/16" gap 15,000 volts. Don't go over 5/16" gap as you may damage the windings.
Have you tried screwing in the air screw to cure the spitting back?