Author Topic: bsa a10 650..the problem child !  (Read 13179 times)

Offline a10sausage

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bsa a10 650..the problem child !
« on: 13.06. 2010 18:09 »
i purchased a rather nice a10 that has had a full rebuild at some point but came with one rather persistant problem...i can fix that i thought....mmm...well i cant so i need the forums help, this bike is driving me nuts..i have a pile of hair on the floor next to me !
Here we go...are you all ready for this..the bike starts almost first kick and will cruise all day around 40mph..if i give the bike anything like a bit of prolonged higher speed running it
starts to miss then sometimes back fires and the cuts out..i the let the bike rest for 5 mins and it will then start...but its just the same scenario,magneto i thought_so i went and bought a thorspark electronic ignition..i spent a full day fitting it and guess what...the a10 has the same fault...i have checked the valve clearances and they are fine..it has new ht leads..caps..plugs..srm rebuilt head...rebuilt crank..bores pistons..new pushrods..rebuilt dyno..12v conversion...the list goes on...any ideas please.

cheers
andy
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Offline mike667

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Re: bsa a10 650..the problem child !
« Reply #1 on: 13.06. 2010 18:22 »
simple but  - restricted gas flow? have you checked the petcocks and  made sure the gas cap vent is working -  my old ducati did the same damn thing it turned out there was rust/debris in the carb float bowls that got sucked up at higher RPMs and  restricted top end

m
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Offline a10sausage

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Re: bsa a10 650..the problem child !
« Reply #2 on: 13.06. 2010 18:30 »
hi..there is good flow from the tank and i swapped petrol caps with another a10....it made not a hoot of difference  *sad2*
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1959 bsa bantam d1
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1975 honda cb750
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Offline andy2565

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Re: bsa a10 650..the problem child !
« Reply #3 on: 13.06. 2010 18:50 »
if it runs all day at 1/2 throttle then i guess its a carb problem,is it a monobloc,never that keen on those for riding just try another carb maybe.
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Offline LJ.

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Re: bsa a10 650..the problem child !
« Reply #4 on: 13.06. 2010 19:30 »
Sounds exactly like my M21! and the problem there was that the needle had dropped out of its clip, has yours done the same? What's happening is that your running around on pilot jet... (I think!)
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Ride Safely Lads! LJ.
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Offline mike667

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Re: bsa a10 650..the problem child !
« Reply #5 on: 13.06. 2010 19:44 »
....is it a monobloc,never that keen on those for riding ......

thats crazy talk!
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Online groily

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Re: bsa a10 650..the problem child !
« Reply #6 on: 13.06. 2010 19:48 »
Probably is a fuel problem/carb problem - but are you sure the ignition is set right and is giving enough advance?
Does it rev well in the lower gears or does the same thing happen as revs/throttle opening rise in any gear?
Whatever, it's not a big deal and it'll be fine when you've sussed it.
Check the air slide (choke) if it has one is not part-closed even when you think it's open; check the plugs are correct; but above all check the timing's right at full advance and that the needle and main jets and throttle slide are correct, ditto the needle (in the correct groove) and there are no blockages on the taps or at the carb. Btw, there's owt wrong with a Monobloc IMHO - excellent devices!
Hope you didn't spend all that money on all those bits just for this!
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Bill

Offline a10sausage

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Re: bsa a10 650..the problem child !
« Reply #7 on: 13.06. 2010 20:02 »
Hi the needle is set perfect..choke is perfect...timing is spot on...engine purrs and revs out a treat...if i get on it and ride i can ride with gusto for about a mile...motor runs beautiful..revs out in every gear..no smoke ect... then its curtains...misfires then stops...just cuts out....argghhh   *sad2*
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Offline a10sausage

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Re: bsa a10 650..the problem child !
« Reply #8 on: 13.06. 2010 20:09 »
i should do a you tube video for you all
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1959 bsa bantam d1
1956 ariel huntmaster
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1936 bsa q21 500 bluestar
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Offline trickytree

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Re: bsa a10 650..the problem child !
« Reply #9 on: 13.06. 2010 20:24 »
No offence meant at all but I have just had exactly that problem with my lawnmower *eek*

That turned out to be a blocked fuel pipe. It would run a bit, splutter to a halt...leave it (while carb filled up again) then off it would go again. I have no idea what it was but it took the air line to blow it out and whatever it was landed miles away...it went with a right pop.
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Offline a10sausage

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Re: bsa a10 650..the problem child !
« Reply #10 on: 13.06. 2010 20:32 »
i have installed  new fuel pipes and fuel delivery to the carb is very good...i have also fitted a brand new battery..the bike is charging ok and the oil flow is very good..i did a test today...when it cut out i closed the taps and took the side cover of the float chamber on the monobloc to see if it had run dry...nope it was full of petrol... *conf*
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1959 bsa bantam d1
1956 ariel huntmaster
1922 triumph model h
1930 sunbeam model 8
1936 bsa q21 500 bluestar
1939 velocette mac
1975 honda cb750
2013 victory vegas

Offline coater87

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Re: bsa a10 650..the problem child !
« Reply #11 on: 13.06. 2010 20:36 »
 Hi,

 This sounds like a heat build-up problem. And after everything you have done its probably not going to be an easy to find one either.

 Like old Chevys, here is a couple of things I would look at first. Is the petrol pipe routed too close to the the engine and its picking up heat? Does the carb have a very good gasket at the head mount, and is it tight? (heat opening a gap where they meet after a short run).

 Another thing I would try before I tore everything apart again, is build some type of quick heat shield, (like a piece of tin) and slide/strap this between the carb and the head- try to protect as much of the fuel system as possible (underside of the tank and fuel pipes too). Then go for a ride and see if it makes any diff at all. This will eliminate an awful lot of things and its quick to do.

 I could be way off base here, but I have seen this twice on different vehicles now. Its not that the engine is overheating at all, its just something very minor that heat effects.

 Lee
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Offline MG

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Re: bsa a10 650..the problem child !
« Reply #12 on: 13.06. 2010 20:45 »
Andy,
It looks like you have a problem that is caused by high engine temp.
If it was a blocked fuel line the engine wouldn't run when cold.

After you have made sure that ignition and fuel supply/carb/carb-head-connection are okay (also at high engine temps!), a possible failure that comes to mind is a sticking (presumably exhaust) valve. The valve stem expands and once the engine temperature reaches a certain level the valve is stuck in the guide if there is insufficient play (or carbon deposits/corrosion in the guide).
Next time the bike stops take the inspection covers off and see if the valves move freely and close properly. If the backfiring and missing happens on just one cylinder, that is where you will have to look first.
If both cylinders are affected, it is more likely to be a carb problem I'd think.

Good luck, Markus
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Offline a10sausage

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Re: bsa a10 650..the problem child !
« Reply #13 on: 13.06. 2010 21:45 »
the problem is worse when the weather is hot...if its a  hot day the fault occurs quicker...i did wonder myself if it is a sticking  valve as we tried a carb of another a10,although it was off a 1960 model and the fault did not go away..i am just looking at some reciepts that came with the bike and the head was repaired by srm in 1995 and the bike has coverd 2000 miles since...it had a repair to the actual ..head and 4new valve guides ..2 rockers..valve seats...4 new valves with hard chrome stems and new valve springs..i wonder if when the bike cuts out the valve slackens off as the engine cools...cheers to everybody who is helping
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1959 bsa bantam d1
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Online bsa-bill

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Re: bsa a10 650..the problem child !
« Reply #14 on: 13.06. 2010 21:52 »
Hi a10sausage
Have you tried a hotter plug
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All the best - Bill
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