Hi all,
My BSA a10 1958 keeps running ritch. As the sparkplugs keep turning black.
I've pulled all my tricks out of the bag to sort it out.
Without any result. Could someone please advice me what else i can do?
The bike response the following way.
Ignition timing is spot on. Easy starter. Guess the pilot jet is ok 🙂
Pulling away she stutters and a full throttle it picksup again an runs ok and pulls well.
The airscrew is 4 turns out, which is too much.
So I already did the following to the Amal Monobloc 376
- cleaned the carb (ultrasone) and fitted new gaskets
- checked the floatlevel with a seethrough plexi (level is right on the dot)
- fitted a velocitystack airfilter (open)
- took away the choke as I didn't want an extra lever on the handlebar.
- went through different jet sets (currently she runs the best with a MJ 240, NJ 105, PJ 25 and a 3.5 cutout throttle slide.
- Checked that the float is smooth and isn't hanging up on something in the carb.
- replaced the needle (C type)
Anybody have any idea what could be causing the faul sparkplugs?
I'm out of ideas.
Kind regards,
Piston Jockey
It sounds as though you have a fairing standard set up for the carb -presumably using needle position 3? Have you tried to reduce the main jet to see what effect this has? Although you have checked the float level, have you checked the condition of the float needle and valve to make sure this is working ok and isn't causing the carb to flood?
Thank you ADJW thumper for your reply.
I have renewed the valve needle and valve needle seat.
Sorry i didn't mention this.
Just checked again with the transparent floatbowl cover and this works as it supposed to work.
I have tried the following jetting.
Standard setting
MJ 240 - NJ 106 - PJ 25 - cutout 3.5 - needle 3 from top
Sparkplugs black, doesn't pull fluidly
Smaller setting
MJ 220 - NJ 105 - PJ 25 - cutout 3.5 - needle 2 from top
Sparkplugs black, holds in
Bigger setting
MJ 250 - NJ 107 - PJ 25 - cutout 3.5 - needle 2 from top
Sparkplugs black, to much fuel to handle
Kind regards,
Piston Jockey
If you are using an original monobloc which takes a thick O ring make sure that you have not included a fibre washer between float seat and carb body. If you have the fuel level will be too high.
The washer in the gasket set which fits under the seat is for the new monoblocs which take the thin O ring.
Thank you Julian S for your reply.
To get the floatlevel correct i had to shim the floatseat with thin metal shims.
As the dot on the cover indicates the approximately right fuel level i know this is done right.
Do gou have any other ideas what might be the case?
Kind regards,
Piston Jockey
What spark plugs are you using.
Hi Idie,
Thank you for joining the conversation
I'm using Champion L82C but going through them pretty fast!
Which I use on all my BSA's
Kind regards,
Piston Jockey
Quote from: piston jockey on 21 Jul, 2020, 18:01
Thank you ADJW thumper for your reply.
I have renewed the valve needle and valve needle seat.
Sorry i didn't mention this.
Just checked again with the transparent floatbowl cover and this works as it supposed to work.
I have tried the following jetting.
Standard setting
MJ 240 - NJ 106 - PJ 25 - cutout 3.5 - needle 3 from top
Sparkplugs black, doesn't pull fluidly
Smaller setting
MJ 220 - NJ 105 - PJ 25 - cutout 3.5 - needle 2 from top
Sparkplugs black, holds in
Bigger setting
MJ 250 - NJ 107 - PJ 25 - cutout 3.5 - needle 2 from top
Sparkplugs black, to much fuel to handle
Kind regards,
Piston Jockey
When trying to sort out a carb, it's best to vary only one setting at the time. Also, you have to be careful when interpreting plug colour because if you go out for a ride and come back and let it tickover, the plug colour can end up being a function of the pilot circuit only. To determine the plug colour for the bigger throttle openings, you need to run it for some distance at that throttle and then stop the engine quickly. It would be good to determine the differnce in the plug colour for at least a couple of throttle openings.
Does it start when hot? Have you a weak spark due to a poorly mag or using suppressed caps or leads. A weak spark will give you sooty plugs due to insufficient combustion. As you seemed to have tried all leads to the carburetor.
pilot jet 25 may be too large if the silencers are restrictive types. i have a 2 into one with restrictive silencer and i had similar problems mid range until i fitted a 15 pilot
Quote from: piston jockey on 21 Jul, 2020, 18:21
To get the floatlevel correct i had to shim the floatseat with thin metal shims.
As the dot on the cover indicates the approximately right fuel level i know this is done right.
shim the seat? dont you just normally bend the tab?
presumably the choke cable holes are blocked , but that would make the mixture lean, more air.
as AJWD says you are best off doing a "plug chop", racers do it to get results after passing the chequered flag and keep the revs on half way round the track, then they kill the ignition and coast in often paddling in . mainly a two stroke thing and club racers as GP riders have expensive kit for the purpose.
No tab to bend on a monobloc carb
Hi all, thanks for the replies
@idie
yes it's an easy starter and gives bright sparks.
Just double checked and i noticed that the right side gave a more clear and stronger spark compared to the left. Switched the cables around to rule out any magneto failure out and guess the left cable wasn't up to specs and gave a spark less bright. Replaced the cable so i'll give it a try tomorrow.
@edie simpson
I've bend and welden 2 stainless pipes in which I incorporated db killers.
Might be a good idea to change the pilotjet. But first going to try the new sparkplug wire.
After as 5k ride i'll kill the ignition when in 3rd of 4th gear and see how the sparkplugs look like.
Thanks all! Keep you posted
Grtz Piston Jockey
:) :) :)
Just a stray thought. If you are, as suggested, overfuelling to such an extent I would expect to see a smokey(black) exhaust and some greasy residue in the end of the silencer. However if you have everything else relatively OK then I too would be thinking spark plug.
However something in my mind is suggesting that even with all your checks and balancies in place your carb is maybe in a very minor flood condition. Is the float actually completely shutting off properly or when running is it allowing it perhaps to overfuel. I assume the float is in perfik condition.
Mike 8) 8) 8)
Know this may be a long shot but what is the origin of the jets you have? Genuine new AMAL, acquired used, or non-genuine? Some non-genuine jets are of dubious accuracy, and if they're "used" they may have had a drill though them. Just a thought.