Possible seizure!!!

[Minto]

Cheers Jules and Kiwi GF, it’s definitely not completely blocked for sure, when I stop I can hear it sucking through the vent, but would that mean it isn’t venting as well as it should? Hard theory to test on the driveway.
I’m not going to get anything done for a few days due to feeling a bit Ropey with the COVID lurgy. I’ll update with test results as and when I get into the garage.
Thanks everyone for all the suggestions and advice. As always, awesome forum!

[berger]

minto, the throttle would have been wide open trying to get up the hill, WHY?? don't you have gears on your bike. keeping the throttle wide open if the engine is struggling is a no no. you might have washed the oil from the bores and  made it overheat and grab up

[RDfella]

when I stop I can hear it sucking through the vent

Sounds to me like problem solved. Shouldn't do that.

[Minto]

minto, the throttle would have been wide open trying to get up the hill, WHY?? don't you have gears on your bike. keeping the throttle wide open if the engine is struggling is a no no. you might have washed the oil from the bores and  made it overheat and grab up

Mr Berger
I’d just dropped it into third but she was still slowing so gave it a bit more throttle.
I’ve just ordered an endoscope so I’ll take a look at the bores when it arrives.

[Minto]

when I stop I can hear it sucking through the vent

Sounds to me like problem solved. Shouldn't do that.

Cheers RDFELLA
Here’s to hoping it’s that simple.
I’ve a spare tank cap on my old tank in the loft, I’ll swap it over and try it out over the next week when this COVID eases off.

[Worty]

Can't really add to the excellent comments on here Minto, but I can offer you some solace on the vagaries of riding BSA twins.  My Flash ran beautifully on Friday for a faultless 140m trip up all sorts of hills etc, pulled like a train.  However, on Sunday I went for a 100m trip round Derbyshire Dales.  Heading up Snake Pass, every single time, the bike starts to 'ping', I always have to bang it down to third where it is fine and winds up as much as you like.  The road is about a two mile ascent with sharpish corners, and I can rarely get it to top without it complaining.  Add in a headwind and it's pointless trying fourth.  What puzzles me is that on another stretch of road, with a similar incline, it sails up in fourth and even accelerates - just don't get it (unless it's an altitude issue).  Just to add that I use Tesco Momentum 99 RON with Castrol Valvemaster Plus - the extra octane transforms the bike's performance.

[Triton Thrasher]

I’ve a spare tank cap on my old tank in the loft, I’ll swap it over and try it out over the next week when this COVID eases off.

The reliable test is to loosen the cap when the problem occurs.

[Minto]

It’s going to be a day or three before I’m going to get out on it, but I’ve fought my way to it through all the crap in my garage waiting for my new wood shop to be built, took the cap off and blew through the vent which seemed to be totally clear. Feel so ropey today that it’s all I could manage with the bike.
I’m off to bed with a bottle of cheap rum now, save the good stuff for when I get my sense of taste back.

[Worty]

Good luck Minto, hope you feel better soon. 

[Greybeard]

Something else to try, open both petrol taps.

[BagONails]

Just to add that I use Tesco Momentum 99 RON with Castrol Valvemaster Plus - the extra octane transforms the bike's performance.

Yep I agree,  my A10 prefers the 98 Ron BP Ultimate. Not sure what the equivalent fuel is in UK but its about the best you can get in Aus. I've always found not only does the old stuff (1965 Austin Healey Sprite) go better on it but also it tends to keep better than the crap 93 octane standard unleaded. The old girl will invariably still start after a few months winter lay up whereas on the rubbish fuel after 3 months forget it. Even the lawn mower goes better on it!

[Worty]

Too true.  We now have 10% ethanol on standard unleaded, but the Super Unleaded is still 5% and with higher octane.  The Tesco Momentum is the highest I've seen at 99 RON, but many are 97 RON.  I am on the generous side with the Valvemaster, but I can't fault how the A10 goes.  As I say, it's only on specific roads where it may start to ping a little, but on the whole it's very good.  With the Valvemaster, the petrol is fine even over 6 months - starts and runs as it should.  Having said that, I do put some tape over the filler breather to keep it as airtight as possible, the theory being that it keeps better in a sealed container!

[Minto]

Something else to try, open both petrol taps.

Cheers Neil
Did that about 3 seconds before it gave up.

[Minto]

Yep, since the introduction of the 10% ethanol crap they pretend is fuel, I’ve had to swap to Tesco extortion on both bikes. The other has a plastic tank which are known to swell and distort with too much ethanol.

Endoscope thingy arrived today, so hoping to poke it down a couple of holes before the weekend. I’ll keep you posted.

[sean]

Just to add that I use Tesco Momentum 99 RON with Castrol Valvemaster Plus - the extra octane transforms the bike's performance.

Dont forget unless you can find a dedicated high test pump there will be a litre or so of ethanol crap in the  plumbing of multi choice ones ….we are at 10% in Canada but high test is available with no ethanol and rumors of 15% ethanol on the horizon.

Yep I agree,  my A10 prefers the 98 Ron BP Ultimate. Not sure what the equivalent fuel is in UK but its about the best you can get in Aus. I've always found not only does the old stuff (1965 Austin Healey Sprite) go better on it but also it tends to keep better than the crap 93 octane standard unleaded. The old girl will invariably still start after a few months winter lay up whereas on the rubbish fuel after 3 months forget it. Even the lawn mower goes better on it!