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Hello... I hope I can pick everyone's brain and get an idea of what's going with my bike... thanks in advance for any suggestions

I have a 1970 A65L... When I first take it out after sitting a day, it will start after a kick or two... and it runs great when it first starts. Comes off the stop light/sign strong and sounds awesome. I go a few miles on it though and it starts to get "tired". Which is the best description I can think of.... When I stop at a light or stop sign, I need to keep giving it some gas or it sounds like it will stall out... It will need a lil finesse to come off a light/stop sign by giving it more throttle than normal.... It might be unrelated, but it will develop a knock for the first 10-20 yards when I'm first coming off a stop. By the time I get to my destination, which is typically under 5 miles, the thing is ready to stop running. I'll release the throttle and it will stop running. If it matters, I live in a huge city and am forced to make regular stops at lights/stop signs

Could someone share their opinion or offer me some guidance of what this might be? Once again thanks

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Guessing a burned valve. Try a compression test.

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The symptoms could also be due to the ignition system acting up. First question what type of system does it have?

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If it has points the symptoms are that of failing condensers, went it starts getting tired look at the points when running , big sparks at points= failed condensers.
Other things it might be, carbs set too rich.
Motor slowly seizing. lets hope its condensers.


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Another possibility is fuel vapourising in the float chamber. Have you got an insulating spacer between head and carb?


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Sounds like the engine is getting hot with all the stops and starting at the traffic lights.

Some things I would check:-
- are the carbs fitted with the tufnol washers between the carb and inlet manifold? These are designed to prevent heat transfer from the head to the carb, if missing the fuel could vaporize as already mentioned.
- check the tappet adjustment, if too tight the valves may not be closing and sealing. Note that the best way to do this is to turn the engine until one of the inlet valves is fully open then adjust the other inlet valve, same with the exhaust, turn the engine until one exhaust valve is fully open then adjust the other exhaust valve.
- check the petrol tank filler cap isn't blocked, if it is blocked a vacuum may form in the tank and prevent fuel from reaching the carbs
- check the taps and filters aren't gummed up this can happen especially if the tank has been lined with sealant.
- is the oil return to the tank ok? It may be that you are getting a partial seizure


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sure sounds like overheating to me but you havent mentioned if it seems really hot?

compression test for sure (hot engine)

sounds very similar to an issue i had with mine ,,, i messed around with everything and nothing helped .

Finally i noticed that the fuel line lay out was pretty dodgy so replaced all the lines in an inverted H pattern ,, problem gone never to return! .... i figure it must have been getting a vapor "bubble" in the fuel lines when it heated up.


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If the clutch is tight then heats up it will kill the motor at a stop sign. Had a bike do that. It's unlikely but unlikely happens sometimes.


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hope I'm wrong .
Your symptoms sound a little like a soft piston seizure .
where poor ignition timing or inadequate cold piston clearance
Allows the hot piston to expand into the cylinders
... causing excessive friction and power loss . .. goes away when cold

if not too bad , or caught in time , damage is minimal to none .
if bad ... piston material smears onto the cylinder wall .
( some guys like to run their bikes on the rich side ) ... the cooling effect
helps to mitigate some of the piston Heat

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Originally Posted by Chitown guy
......I have a 1970 A65L... When I first take it out after sitting a day, it will start after a kick or two... and it runs great when it first starts. Comes off the stop light/sign strong and sounds awesome. I go a few miles on it though and it starts to get "tired" When I stop at a light or stop sign, I need to keep giving it some gas or it sounds like it will stall out...............Could someone share their opinion or offer me some guidance of what this might be? ....
This sounds like the idle may be way too rich. Does it idle nice when it is cold? .Lackluster mid range can be worn needle jets.

Easy starting combined with fading performance as it warms up and bad hot idle can be as simple as those two things. Idle usually speeds up when the engine is warm.

Originally Posted by Chitown guy
...... It will need a lil finesse to come off a light/stop sign by giving it more throttle than normal.... .... it will develop a knock for the first 10-20 yards when I'm first coming off a stop..........
But this knocking is more worrisome. A65 bottom ends are known to be a bit tender.

It could be pinging from low octane fuel, OR a loose con rod, or hopefully a loose primary chain.

I would first be making sure the ignition timing was not too advanced and that it had oil pressure. Run at least a 20-50 oil.

Keep in mind these bikes barely tolerate modern 91 octane fuel at 9 to 1 compression. Some of us run race gas to eliminate this problem and retarding the timing from the stock setting helps too.

Hopefully it isn't seizing up on you as mentioned by Quinten.

Best of luck with it. Let us know what you find.

Stuart


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