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by Mal Marsden - 06/16/22 7:00 pm
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ChiefRider, Chitown guy, gavin eisler
Total Likes: 6
Original Post (Thread Starter)
by Chitown guy
Chitown guy
Hello, and thanks in advance for anyone patient enough to read my post.... And I'd greatly appreciate any advice anyone can offer me about my 1970 Lightning

I'm a new BSA owner and I'm doing my best to learn about how they function.... I have 4 initial questions/issues with my bike

1) It bogs down in 1st gear when it's hot when I start moving from a stop sign or light
2) It's been requiring multiple kicks before it starts
3) Unsure how to remove the bracket on my tank holding the rubber knee guards in place
4) Do I keep both petcocks open when I ride my bike

1) Let me explain some of the history here. When I first got it up and running it would stall at a stoplight or sign once it got hot. I had to keep the throttle revved up to keep it running. I took it to a local garage and they said the values were tight. Their adjustment seemed to help a bit and didn't require me to apply as much throttle when I was stopped... but the problem didn't go away. I have AMAL 930 carb's, and after doing some research I started suspecting it was running lean. I discovered the air intake screw and adjusted it a 1/2 turn, which helped a lot and now it doesn't require the constant throttle when it's hot and I'm stopped. But now I noticed the bike is bog'ing in 1st gear when it's hot and coming off a light or stop sign. I have to slowly release the clutch while applying a lot of gas to get it moving and to keep it from stalling. I'm unsure if this issue could still be related to the carb's or if it might be another problem

2) When I first got it back from the garage it would start on the first kick with me holding the throttle open about a 1/4 turn (There is no choke on it). After a couple weeks it required 2-3 kicks. After approximately a month I have to kick it 6-7 times before it will start. It SEEMS like the compression has gotten higher, but I'm not 100% sure if that's the case or in my head. It doesn't seem like it wants to start, and it might backfire once during a kick before it does start. When it does start it seems to run fine. I have a small hill I can go down to get it running with a rolling start, and it doesn't seem to have any issues starting like this. Could someone suggest what this could be? The fact it went from turning over right away to being so hard to start over a short period of time has me a bit confused... I think it might be points or the magneto but I'm not sure

3) The rubber knee guards are old and I'd like to replace them. I found an old parts manual online and I see they're screwed into a bracket that's attached to the tank somehow. ... I don't see any obvious way to get them off the tank and I don't want to just start yank'ing on things. Can someone let me know if the bracket will just slide out of what's holding it to the tank? Or if there's any trick to getting them off

4) The mechanic I took the bike too told me to keep the petcock on the primary side turned off when I ride. He said this was a "reserve"... That doesn't seem right to me. Can someone clear this up for me?

Anyway... Once again, thanks to anyone that took the time to read my post. I'd greatly appreciate any hints or suggestions that anyone can offer me about my bike!
Liked Replies
by Adam M.
Adam M.
Before your answer Leon, I'd like to point out your chokes should be reinstalled. Much easier to keep A65 one / two kick bike with them, specially in Chicago.
2 members like this
by Allan G
Allan G
I’ll answer easy ones first.

4) yes he’s right. Keep the left side off, that way if you start running low you can hold the throttle open and switch on the other tap with your left hand. Look at a Japanese bike... it’s always on the left.

3) if they are the original type rubbers they are held on at each corner if it’s the rounded tank, if it has the sides scalloped for your knees then they are glued on.

1/2) if your issue is getting worse without adjustment then it’s likely an electrical issue. If you don’t know the battery history, replace it. If you do and your confident it should be ok, get it charged up. You might have a charging issue on the bike which isn’t giving enough output back to the battery to charge it. Assuming your bike has electronic ignition and not
1 member likes this
by leon bee
leon bee
A couple quick points: we should know if you have the original ignition points setup. Also, 6 kicks is the point at which I reach for a clean pair of Champion N4C plugs. I imagine you'll be getting plenty of replies.
1 member likes this
by DMadigan
Are you priming the carbs with the tickler before starting? You did not mention it.
"70 had push-pull fuel taps. I do not remember if they are marked for reserve. If you do not know you should take off the fuel lines, open the right tap and let it drain on the centre stand. Then open the left and see if there is more fuel, somewhere around a pint. Bad idea to wait until you run out of fuel to find out.
Are the holes for the choke cables blanked off? Air leakage past the top will make it run lean. I think people delete the chokes because they need new cables and are too cheap to buy new. Whatever, it starts easier with the choke.
You did not mention the ignition, sounds as though you still have points. Your advance may be stuck or someone put in a Triumph, or ?
Magneto - do you mean the generator or an actual magneto ignition? The '70 had points with 12M17 coils. Low voltage could cause problems also. You should have at least a cheap meter (ChinaFreight has them for a few dollars, for a time they were giving them away). Unless you know the shop really well it is best to do your own maintenance. At least you will have an idea of where to look if something goes wrong on the road.
My '70 Thunderbolt had a chrome tank but no knee pads. I thought '68 or so were the last time they were put on US bikes. A parts book (check out CBS above) will tell you some things.
1 member likes this
by Mark Z
Mark Z
I think you need to go through the entire tuning regimen yourself, starting with timing. I would have said starting with valve adjustments, but it sounds like that's been taken care of, assuming you can trust that your mechanic knows what he's doing. Ignition timing is next, because it's measurable, and it's not affected by carburation etc.

I also didn't mention having a healthy, fully charged battery, and making sure your charging system is working.

If you don't have a timing light, get one; they're not very expensive. If needed, ask for references or help with timing procedure. In addition to gauging the timing, the strobe light can also reveal other electrical problems such as a misfire.

Turn your attention to carburation only after the ignition system is checked out. One common cause of poor idling when warm is wear on the throttle slides and carb bodies. You can check this by removing the air cleaners and pushing the slides back and forth sideways with your finger, seeing how much "slop" there is between the slide and the carb body. Also, if the throttle stop screw causes the slide to cock to one side as it starts to lift, this is another sign of a worn slide or carb body.
1 member likes this
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