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Jul 5, 2008
OK, I preface this by saying that I am marginally competent with working on my bike, actually, I am arguably completely incompetent.

I can rebuild carbs, set the valve clearances, replace a kickstart shaft and bypass shorts with the best of them but thats about as far as I have had to go so far. To be honest, have the stuff on this forum is generally well beyond my limited vocab.

While riding back the other day, my bike stalled out. Pulled over and was horrified to see my left float bowl hanging on by the fuel lines. As luck would have it, I had one screw still hanging in there and with my trusty allen key, I managed to get the float back in and cinched up. The bike was not happy but I managed to get it back the last 8 miles to my house.

Once home, I pulled the carb off, burned my hand. checked the carb out, reseated the bowl, burned my hand yet again, slapped it back together and fired it up. Bike not happy I would say.

Left side running poorly/intermittent etc. Throttle it up and the left side is shooting fire out the ass like I had fed it a spicy burrito. I have removed the carb again and am soaking it in cleaner however I am slightly worried that I may have damaged something more serious.

As mentioned, the left cylinder seems to be back-firing and I swear that when it was running, there was an ominous metallic ticking noise that I don't remember ever having. Seemed to be coming from the cylinders. When it was running, the oil seemed to be pumping ok (return line is clear plastic variety). I pulled the valve covers off and the valves seem to move correctly and be gapped ok. ie no obvious large chunks of metal were present.

OK, I know this is a vague question but do you guys think I could have messed anything up in the guts? Anything I should look for without ripping the head off?

At this point of the story you can probably smell my fear of the unknown crankcase. Please be sure to type slowly and use big words.

Humbly, B-Stone
Well! the last thing you did was replace the float bowl, I would start there.

Get hold of a good manual take a little time out and read the carb section. Remove the bowl completely check the float is free to swing and undamaged that everything is still there and tight.

Don't worry in a few months you'll be as nutty as the rest of us.

Did the float bowl gasket survive intact, or did you replace it with a new one?

Because an air leak (air being sucked in) at the float bowl-carb body joint could cause running problems?

Did you also check the face of the float bowl was completely flat (place it against a piece of glass and try rocking it) as they often need rubbing down on a sheet of abrasive paper to flatten them so that the gasket joint seals properly?
Check your float needle tip and the seat.
I had a grumpy, flooding carb for a season. Flatened the surface, replaced screws, needles, gaskets, swapped wasn't until I realized I must have damaged the float seat adjusting the height.

Check your viton tip, it could be near the end of it's life, or was damaged but rattling around when the bowl loosened.

Good luck sorting it out!
I checked the float level and it still looks ok. Snaded the float bowl gasket surface as well as it was a bit warped.

Will take a good look at the float needle and seat. They looked ok when I took it apart last night bit will do a closer inspection.

My biggest fear is the percieved ticking sound (almost like the valves are way out) but seems to be coming from lower down the jugs.

Thanks for the tips...and please keep em coming. This is a kick-ass site!
If your fuel bowl came off, you weren't getting any fuel into that cylinder, causing a lean situation and a temperature spike. Does the head look discolored on that side? Did the exhaust on that side turn blue?

I would check out the carb first, and make sure all is well with it. Then I would check the valve clearances. Once you know the valves are gapped properly, run a compression check.

If the compression is down on that side, you may have burned a valve.
Put the carb back together and made sure it was squeeky clean etc. The left side is still acting up and backfiring and burping back out the carb. She'll run but it aint pretty.

I had checked the valve clearances the other day and they seem to spec.

Great idea re the compression check...should have thought of that one. Off to the shed to check it out

OK back from garage...

Maybe my compression technique ain't the greatest but here is what I did.

Plug in right, comp tester in left. Kick bike over (without key in of course) about 10-12 times. Tops out at 120

Right side came out at 120 as well.

With the ignition on (and now both plugs back in) it backfires on kick from either the pipes or the carb.

No weird discoloration on either jug or pipe.

I love Amal carbs!!!
I would switch carbs , and see if problem goes to other cylinder or not. Then you would know if it was a carb problem or something else.
Comandos have a habit of throwing up multiple faults at once. I would never rule out coincidence.

You don't have a Boyer fitted, do you ?
On compression test the throttle should be held wide open. Also it is easier to kick over when you take both plugs out.

Would still stick with investigating carb that fell apart first. !st rule of troubleshooting is What has changed?
If the compression is OK - 120 is good - then check your timing.

Rough running could have caused the the nuts holding your stator plate (Boyer) or contact breaker assembly (points) to vibrate a little loose, allowing timing to go out.

Generally, backfiring is caused by the ignited mixture escaping past a valve. This normally happens when the valve can't close (bent or burnt) or the timing is off, allowing spark to occur with a partially open valve.

Since compression is good, valves must be closing.

Full advance on points is, I think, 28 deg BTDC

Boyer timing is 31 deg BTDC at 5000 RPM.
I have boyers on the bike so will check the stator plate to see how she is set. The previous owner installed the Boyer.

Will get back to you guys soonest.

Thanks for the great tips.

Back again frome the garage...

The stator seemed tight in place and the wires seemed ok. The wiring harness is a mess of wires and electric tape so not even sure where to start with trouble shooting the boyer.
While poking around the Boyers, I noticed that I have 6 volt coils. Is it 6 ar 12 V coils for the boyers?

6 volt coils are what you want for your Boyer.

Did you re-check your float setting? After it bounced around with the dangling bowl it might have bent the tang resulting in the wrong float height.
Yep. The carb seems sound as a pound with float at 2mm below lip.

I have not tried swapping sides yet. To be honest I am not sure they would fit with the ticklers in the way although I suppose I could start by swapping the bowls.

After tinkering for another hour and checking wires I think I am getting closer. I rechecked the stator and rotor and fine tuned it a bit. Adjusted the timing by ear for now. After a bit of flame shooting and revving the hell out of it I had it back and running without backfiring.

Earlier in the year I had issues with the left cyclinder not firing. I swapped out the left coil, left spark plug, and wire and thought that I had fixed this but now that the back firing seems under control, the left jug is still acting up (albeit not as bad).

It seems that if I pull the plug wire back from fully seated (actually almost just resting on the plug) the left side kicks back in although it is finicky as hall hell. Spark seems to be consistent when I stick a screw driver into the plug boot.
Swapped both plugs out. They were covered in black soot.

After playing with the timing and swapping the plugs, it seems to be running OK but, there is a distinct tapping sound coming out of the jugs that sure wasn't there before.

As previously mentioned, I checked valve clearance and it seemed good. Also pulled the exhaust valve covers off with it running and all seemed ok.

Milllion dollar question: Any suggestions as to the metal on metal loud tapping coming from the cyclinders? What the hell would have snapped when thye left carb's bowl fell off that still lets the bike run with good compression?

Thanks guys
I'm assuming dual Amals. If that's the case, and you start swapping things around, make sure you keep the slides in their original bodies. On the 650SS, and I'm sure it was the same on the Atlas and Commando series, the slides are individually lapped and honed to fit the body. Actually, I think that the body is lapped to fit the slide, since the slide is the harder material.

They are NOT interchangeable. I think I posted this once before, but it's short enough not to be a problem to do it again.

We did a test on the "hack" 650SS I was riding to and from work. A larger single carb was installed to see if we got better low end torque for sidecar use.

I replaced to original twin set-up after the tests were done. First time out, on my way home, I did a quick "squirt" to get between a car and a bus in city traffic. I was in second gear at the time. When I pulled in behind the bus abd rolled the throttle off, one slide stuck wide open. I was very glad it was a magneto-equipped bike and had a very accessible kill button.

I pulled the slides and swapped them over right there at the side of the road. Bike ran fine after that!
6 volt coils IN SERIES, no? Parallel wiring won't achieve the same result, methinks...?
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