Sputters and dies out of nowhere

After letting the bike sit for about a week, i took it out and after about 4 blocks, it just died. Couldnt get it started again and had to push it home. I could kick it over and get it to run poorly for a couple of seconds but would backfire and die. If i gave it some gas it would even out a little bit but sounded like it was backfiring through the carb. At one point i actually blew the baffle out of my exhaust. Pulled the plugs, they where black so i replaced them. Charged the battery. Pulled the carb and cleaned it all up. Same thing. Think maybe the boyer finally went? Its a 72 frame/69 engine. Ran like a top before i let it sit.

Check for water in the fuel. Pour some in a clear glass. If there is you'll see it.
Thats the easiest thing to try first. Happened to me.

Boyer's had or have a fragile wire problem by the pick ups.
I have one on my other bike. Been there for years. Never a problem.

Then check grounds and connections.

Start with the fuse , spin it , check for corrosions. Yes Boyer pickup area wires too. You can bypass the harness running a wire to ign. direct from battery (fuse it) then if the problem persists you can concentrate on harness and it's switches. :?

Are you still running your ignition through the kill switch as per standard? The points corrode and only let limited power through and a Boyer needs decent voltage. Try running a line direct from the battery to the ignition and see if it solves the problem. I always put a relay in my bikes and use the kill switch just to trigger the relay off when needed.

It could be so many things but I had a similar situation. Turned out to be residue from a bad tank liner system plugging up the fuel filters on the lower end of the Amals. Check also the filters at the petcocks on tank.

sound like some intermittent electrical issue to me. When a bike has fuel igniting in the exhaust pipe that's usually because it's pumped some fuel through the cylinder without igniting it. Then when a charge finally does spark in the cylinder, that hot exhaust charge ignites raw fuel in the exhaust pipe too. It's usually louder than just a "POP" and can blow flames out the tail pipe... (ask me how I know that... 8) )

I had a similar symptom a long time ago. The issue turned out to be an intermittently bad spark plug that tested as "good" when it was spring clamped against the head for testing, but must have had a cracked insulator up inside the plug, because under compression it didn't always spark at the tip. It would pump fuel into the exhaust pipe, then it would finally spark and "boom"... scarey results.

Put new plugs in, then try to get it to run. Then pull the plugs and see what they are showing you. Are they wet with fuel? Is one wet and one firing?? Is there no fuel on them??

For a boyer, Use a pair of spring clamps and clamp your spark plugs against the head, then turn the ignition on, then off. Did you see a spark on both plugs? Was it a decent spark? clean your kill switch if you have one. Run extra grounds for your engine and your boyer. Isolastic means rubber mounted engine... If you have a poor ground, you'll get a weak spark.

The newer Boyers don't guarantee a spark at grounded plugs when switching on and off at ign. switch. Just to screw us all up.

Thanks for the replies everyone. Theres no kill skitch, the orignial gas had some black powdery sediment in the fuel line so i drained it and put a few fresh gallons in. Changed out the plugs, checked the fuse. Still nothing. Starts for a couple seconds, theres some popping every couple seconds if i hold the throttle and then eventually it dies. Sounds like popping from the exhaust as well as carb. Thinking maybe the boyer is about ready to be swapped out but ill do some more testing first.

Are the sparkplugs dry or wet after it conks out?

How many miles on the Boyer ? Maybe pickup magnets getting weak. The black box is encapsulated. It either works or it doesn't. Trigger diode dies but can't be replaced due to encapsulation. Said before ,run a wire to ign. directly and try again. Clean up ground point as Boyers need a good ground.

OK, I'll fall for it - choke left on?

OK, I'll fall for it - choke left on?

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that my guess too ! amazing how many times something as simple as that is the problem, worth checking

I had the choke cable break right at the handlebar lever end.
No way was the engine going to run right until fixed.