BSA A65T trying to sum up the causes of the misfire, now fixed & thoughts on the fuel tank's origins 

Back in summer of 1970 I bought a working Triumph Tigercub 200cc. It wasn't long before the battery went flat. New battery also went flat a few days later. And in between lots of back firing! Lucky my mate had a dad that loved tinkering and was a boy racer in his day. He took the head light off and started his air compressor. You should have seen the water come out of the Lucas ignition switch! Lots of WD40 and recharging the battery, a quick points clean and timing check, and wouldn't you know it. I started and kept running. And to think my local bike shop wanted me to buy a new alternator? I was and forever remain in Ron's debt bless his sole 👍. Good vid and your not giving verbal for nothing. Always a learning curve when it involves old Brit bikes. Good luck getting her running 👍...

Interested in listening to you on this one Paul, as with all your vids , but I've been struggling with an almost identical issue with a 69 A65 Thunderbolt...completely rebuilt motor, properly and with great Care ,I've done 4 before so I do know my stuff, but without writing a monologue it turned out to be a duff Silicone Lucas HT lead , the ones that came with the bike from America, I just never thought about the leads until I'd exhausted every avenue, did a resistance test on each lead and bang ...totally different readings, fitted some old copper core traditional leads and it's absolutely fine. On points too..never trusted complicated electronic ignition systems. Anyway just thought I'd share that Mate , I have my own ' Black Dog' too so I'm fully with you pal .

it's never like a well-controlled experiment where each variable is examined individually by lab-coated technicians with clipboards... glad you got it running.

Agree with mattmathews4070 wholeheartedly your channel gets better with all your rants and explanation of problems you encounter.

I have a 70 A65 Firebird this tank was standed on these and yes it has the same gap between the seat and tank. I remember well when these bikes were new but can't remember seeing a Lightning or Thunderbolt fitted with this tank..

Thanks for passing on all that info, especially for those of us with unit twins. A pain in the arse for you, there's no doubt! But hopefully it's all fixed now that your summer is almost upon you.

As a fan of old Brit bikes, may I say this channel just gets better and better. Thanks Paul.👍

British cycle supply was selling those tanks 15 or 20 years ago for about $150 new old stock. They were the same color as yours. It was a great price for a beautiful tank and I picked up one for my Starfire and it has it on there now.. I have a similar problem to you on my Firebird scrambler, but I also have a problem of it overheating. I know the head gasket is leaking oil and now I can hear air chuffing in and out, so that’s definitely bad. Thanks to you. You gave me the push to get started on it today. Thanks for sharing all your knowledge.

I'm no professional but I have owned Triumphs for 55 years and always done my own repairs on them. My experience may help nail your issue down to one thing. Coils are notorious for playing havoc. Wiring both the wire itself and the connections are also a main culprit. Whenever I purchase a new coil I check it for proper resistance and 50% of the time I've found new coils to be out of specified limits. Do they still work? Sure they do most of the time, but when out of exact resistance specifications they heat up and problems recur until they cool down or are replaced. Vibration plays havoc on wiring when it comes to internal corrosion which cannot be seen and connectors are simply a hellish nuisance. Original wiring on Triumphs is pure garbage. I rewire with quality aftermarket copper wire on all of my bikes and do not use clamp on connectors at all. Everything gets silver solder and I upsize wire gauge as well which completely stops any issues with wiring. So I agree with you that the problem was with the coil. Two pole coils (1 coil feeding 2 spark plugs) have two internal resistance feeds as well so going out of spec will not carry enough spark to feed both plugs. Switching the spark plug wires on single coil applications will identify a bad coil because the problem on a Triumph will switch cylinders because as you said it is a spent spark system. It works the same on BSA's That's my two cents on the issue. I enjoy your videos as there are not many people left who truly understand these old classics anymore these days and it is enjoyable to watch a mechanic with a common sense approach no matter the labor involved in finding the problem. Cheers from Canada.

Had an a65 t 1970 model in 1970. It had a chrome side tear drop tank gray paint. Eastern Canadian supply. Nicest running A 65 I ever rode. Was an insurance wtite off too. Didnt have those nice alloy rims

I’m with you, that it’s a handsome machine. And also happy that it is now reliable. There’s one like it in the corner of my shop, sitting for quite some time. You’ve made me think about doing something about that by now. Thanks

Hi Paul regarding the Pazon ignition I seem to remember reading that if you run the bike for too long with one cap off it can cause issues so perhaps the oiling thing did have something to do with the unit going down, glad you got it sorted it's a fine machine & did I hear that the 20 mph limit is being dumped. Tony

Had I had a problem like that I can tell you I would have put it back in storage in disgust and retired to a bottle of beer. That tank looks exactly like the one on my 1968 BSA Shooting Star only mine was red/white. Great information!

The information you discussed will definitely be utilized in future troubleshooting. It’s something we all can refer to! When you have multiple gremlins you have to look more places!👍

I lay under the cat on the sofa enjoying the films. Thanks Paul Also that is best shape tank ever

Paul it some time just a game of guess the part I was having a problem with my lightning it would start then cut out in the end I found out it was the fuse holder not the bike fault but mine for overlooking the obvious ps the tank is the same shape on my bike

I know this has been a trying experience. Findung the problem is a reward in itself.. I do not remember seeing a gas tank like this on an A-65 stateside. Thanks for all you do !

Many thanks for the honest warts and all summing-up Paul. Its the same old story with electricary, fault finding takes time and try's your patience but you won in the end!!

I've always liked BSA's, superior frame, etc, plus single carb bikes are far more sensible!

I had a misfire on my 750 commando off idle mainly , iturn out to be too much outer throttle cable clearance and one cable at the splitter sat cocked and this meant one slide was about 5mm higher when you reved it .cheers glad you got it sorted .

Some A65’s came with that fuel tank my 1970 lightning has the same style tank but with Crome sides after doing some research I found a few bikes got that style tank . The misfire issues was probably a few things at once good to see it’s running better now

I bought a BSA 650 Thunderbolt as a rolling chassis with the engine in a milk crate. The speedometer said 6,000+ miles on it. I thought maybe the crankshaft was bad. My buddy who raced Ducati and he checked it out and the crankshaft was on standard. How someone could take apart a good motor l had no idea. People do stupid stuff. What can l say?

Oh yes one other thing. While the headlight was off, Ron checked every connection. He showed me how them old connectors could short out on themselves or the headlight. So using petrol he cleaned every connection and all those showing ends were covered over using insulation tape. Seems he's been there and done this before in his past. Hope this helps?

not sure but the tank looks to me to be a C25 250cc starfire tank. I had one of these on my C15 which had been fitted prior to my owning the bike.

love that bike !!

A good idea to make this video. Reviewing what you've done is never wasted time, especially when there has been a combination of problems. You certainly have a nice A65 there now. I had wondered about the tank but had seen that shape of tank on other A65s so didn't give it a second thought. It seems likely to me that it could be a 250 tank but, as long as you're happy with it, why worry about that? It's a minor consideration which you might eventually follow up or not, depending on how you feel.

Enjoyed your video. Don't have British machines but some of that information is helpful for my collection of other bikes.

Okay, you answered my query about any exhaust smoke.

That is a nice BSA. I also very much like the shouldered rims.

The oil leak sounds most likely thanks for explaining it all

The only thing left is the HT lead.

There are A65T photos with a tank-seat gap, but they tend to be with the teardrop tank models. The only A65 models with a tank like yours seem to be the Scrambler variants.

You changed the coil but not the plug. You still had a misfire , possibly due the plug being previously under stress, so you put a Bosch in. End of problem, hopefully.

I wonder. Where the coil is mounted behind the side cover.do they get more heat than if they were up under the petrol tank. ? Def lovely lookin bike wishing u well with it

Starfire tank, mine was a darker blue ink like colour 1969 model. I bought an a7ss it had a chrome starfire tank which I changed to a new thunderbolt export tank same dark blue chrome sides and petrol cap with twist handle to remove I got that from if I remember called the graveyard west London.

Just prior to losing the cylinder, did its exhaust pipe begin to smoke...and during the diagnosis period, did ya install a HOTTER sparking plug in place of the recalcitrant one ?

Hi Paul do you prefer the lighter bsa twin to the big trident, I am finding the appeal of lighter more nimble bikes as i grow older. Thks

In retrospect for anyone suffering such a suspected oil leak across the head gasket, would you suggest first a re-torque of the head bolts vs the very time consuming job of head removal?

How does it compare to that Constipation you had in a few weeks ago? I realise this particular Thunderbolt is newer than the R.E. but I think there was a bit of overlap, before the Connie morphed into the Interceptor.

What does the wireing harness look like?Can you test the charging system?

Does this bike have points or electronic?What about the charging system?Are the electrics breaking down under heat?

Curious what the wires dangling near the zener diode are ?

Are the plug wires bad?

Is the petrol tank steel or fiberglass?