Poping and erratic running there then gone.

Started a ride. Bike started popping and erratic firing. Turned around got home. Saw the clear fuel line to the single mikuni was only partially filled with fuel. Put a stick in the tank to check. Plenty of fuel. Got a can, removed line to the Mikuni, opened the taps (they were open when I rode) and watched about half a small coffee cans worth flow out. Noticed the flow from the left tap was slow. Put the line back on the carb and it ran fine. Well that's great, but where will I be if and when this happens next. Could it still be the taps or was there a sticking float or did one plug just get loaded up?

After relacing the fuel lines and every thing came good then I be pulling the taps out and give them a good clean and inspection as crap in the tank will get caught in the fuel tap filters I also would pull the bowl off the carbie and make sure no crap in the bowl, stale fuel can also be a problem, but usually with stale fuel it don't run good till the fuel has been drained and replaced with fresh, anyway the tank and taps be the first thing to look at, drain the tank and give it a good flush out with clean fuel.
If any crap in the tank it won't take long to clog the tap filters again, checking your taps and filters should be all part of your maintenance when doing a oil change and service.

Ashley

I don’t know what fuel taps you have and assuming you didn’t have something from the tank get into the line. The fuel taps from Taiwan have a rubber gasket inside that tends to rotate then the fuel pathway is restricted.

illf8ed said:

I don’t know what fuel taps you have and assuming you didn’t have something from the tank get into the line. The fuel taps from Taiwan have a rubber gasket inside that tends to rotate then the fuel pathway is restricted.

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I do believe these taps come from Asia somewhere. I couldn't get the taper fitting of the metal adaptor tofit tight enough on the tap no matter how hard I dared to tighten it. Then I noticed a small flattened spot at the tip of the taper on the tap. It was bottoming out! Now that was easily fixed with a file, but showed the manufacturing tolerances were pretty bad. I'll take out the taps and check for clogs. But whats this about the rubber washer you mentioned rotating. Not.sure I understand.

Joe Schlaberdowski said:

I do believe these taps come from Asia somewhere. I couldn't get the taper fitting of the metal adaptor tofit tight enough on the tap no matter how hard I dared to tighten it. Then I noticed a small flattened spot at the tip of the taper on the tap. It was bottoming out! Now that was easily fixed with a file, but showed the manufacturing tolerances were pretty bad. I'll take out the taps and check for clogs. But whats this about the rubber washer you mentioned rotating. Not.sure I understand.

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Not a washer. It is more like a rubber insert the taper fits into. It should not but does rotate in the tap body. There are holes at top and bottom. When the hole in the taper lines up, fuel flows...unless the rubber rotates to block flow.

Proper taper taps do not have the rubber cylindrical seal, although they may have a small o ring.

Joe, you say you filed the bottom of the taper off as it was ‘bottoming out’... I’d now suggest that you check the fuel flow holes still line up. You’ve allowed the taper to move inwards, taking the hole with it, whilst the hole in the tap body has remained where it was...

One other thought, could the rough running have happened due to a plugged petrol tank cap vent? This would self cure after stopping for a bit or when opening the cap like you did to check the fuel level. If you look carefully at underside of cap you should see a tiny hole in the sealing plate. That is the vent and must be clear when blown on or spraying some aerosol through like WD40.

Fast Eddie said:

Proper taper taps do not have the rubber cylindrical seal, although they may have a small o ring.

Joe, you say you filed the bottom of the taper off as it was ‘bottoming out’... I’d now suggest that you check the fuel flow holes still line up. You’ve allowed the taper to move inwards, taking the hole with it, whilst the hole in the tap body has remained where it was...

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The filing of the taper was a while back and a very small amount. Just enough to let it tighten enough to seal with the intended metal to metal contact. The other option would have been a washer of some sort or a replacement. And it was only on one side. But with only an inch level of fuel showing in the vertical part of the transparent fuel line just above where it enters the Mikuni it was, at least to me, as if the fuel had stopped flowing from what had to be both taps. When I saw that I checked both taps that they were open. Maybe it's the cap. One other thing. The inside of this tank was lined with some white stuff. A white coating. And that is now peeling up at its edges

Joe Schlaberdowski said:

The filing of the taper was a while back and a very small amount. Just enough to let it tighten enough to seal with the intended metal to metal contact. The other option would have been a washer of some sort or a replacement. And it was only on one side. But with only an inch level of fuel showing in the vertical part of the transparent fuel line just above where it enters the Mikuni it was, at least to me, as if the fuel had stopped flowing from what had to be both taps. When I saw that I checked both taps that they were open. Maybe it's the cap. One other thing. The inside of this tank was lined with some white stuff. A white coating. And that is now peeling up at its edges

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Have to add I the peeling mentioned above was near the lip of the tank where the cap fits. It didn't seem to be disintegrating, just separating. But that could be coming apart down in the tank where I can't see and plugging the tap filters. I guess I'll just have to bite the bullit and take the taps off and look at the tap screens. To note, whenI took the line off the Mikuni and poured some fuel in a coffee can it did seem to flow fast enough and did seem clear (the cap had been opened). Still, gotta look at the filters, I know. Rather ride before the snow flies. By the way, does anyone know what that white stuff, that coating might be. It does seem rather thick.

If you’ve got white stuff peeling in your tank, you’ve probably got some of that same stuff in your pilot jet...

Mikunis are FAR more sensitive to particles in the fuel, and / or partial blockages in jets than Amals.

You have to remove the pilot jet to ensure it is properly clean. Blowing carb cleaner etc through it simply proves it’s not fully blocked, it can still be partially blocked and that will have a MASSIVE effect on running (look at how precise jets are, then think what happens to that precision when it’s half full of crud).

If your white stuff is dissolving, you need to sort it. Filters don’t solve it. If it’s dissolving it’ll pass through filters and gradually apply itself to the inside of jets etc.

Once the deposits were made inside jetsbthey would not go away just by letting the bike sit for half an hour. Yet it starts popping and banging and loosing power and then stalls. Looked at the transparent tube to the fuel line and, again it looked partially empty. Tank was full. Took the fuel line tube off the Mikuni and without hesitation thefuel began running out. There couldn't have been a blockage in the taps. It was as if the Mikuni had vapor lock. Except why would the fuel tube look partially empty? Tomorrow I HAVE to empty the tank and check the filters. By the way, after waiting half an hour (again) it started two kicks and ran perfect.

FWIW, the clear fuel tube(s) on my 850/twin Amals, using the right-side OEM petcock on my fastback tank is always about 1/2 full. Fuel flows as necessary into the carb as the needle/float requires but the fuel level does not rise to fill the tube. The engine operates normally with no issues at all at any RPM/load. Your description is how my fuel system has always looked. The fuel level in the tube stays at the same point even though the top of the tube remains "empty."

Something to do with physics/air pressure/hydraulics!

Best way to 'fix' it is to replace the clear fuel tube with black fuel hose.

I have gone to opaque fuel lines , with clear ones the bubble makes you think you have an air lock but look closely and the fuel flows around the bubble, must affect flow but not enough to cause an issue.

MexicoMike said:

FWIW, the clear fuel tube(s) on my 850/twin Amals, using the right-side OEM petcock on my fastback tank is always about 1/2 full. Fuel flows as necessary into the carb as the needle/float requires but the fuel level does not rise to fill the tube. The engine operates normally with no issues at all at any RPM/load. Your description is how my fuel system has always looked. The fuel level in the tube stays at the same point even though the top of the tube remains "empty."

Something to do with physics/air pressure/hydraulics!

Best way to 'fix' it is to replace the clear fuel tube with black fuel hose.

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"Black plastic" the info above that was very relevant. As for the joke, ha ha. But the problem remains. Almost 100% localized now to the Mikuni carb. Go for a long ride. In the beginning everythings fine. Then, at slow speed or at a stop (just happened on the last two rides) popping and acting like running on one cylinder begins. Very quickly too hard to keep running and the motor dies. Kick it and try the choke, try opening the throttle a little without choke, all to no avail. Sit on the bike exhausted and call one of my kids. 15 minutes goes by beyond the time I kicked and fiddled with it. Decide to give one more kick. Starts immediately. Runs like nothing was ever wrong for the rest of the ride. Last night the rest of the ride was 25 miles with one one hour shut-off time in the middle. This rest of the ride was cooler. Sun was going down with most of it at night. Friends have suggested vapor lock, but no one here has ever mentioned that with either a Mikuni or an Amal. But has anyone heard of this with the Power Arc ignition? I only ask because I've just gotten that installed and got the bike running fine. 1000 or sub 1000 rpm idle. And steady. Plenty of power. No hesitation on acceleration from idle. But the last two rides have been the first real rides besides testing it going around the block then back up the driveway.

“Most carburetion problems are of the electrical type.”

Or something like that.

Have those friends who have suggested “vapor lock” explain exactly how that phenomenon works....

A blocked tank vent was mentioned back in post #7....

Any confirmation of this ?

Joe Schlaberdowski said:

In the beginning everythings fine. Then, at slow speed or at a stop (just happened on the last two rides) popping and acting like running on one cylinder begins. Very quickly too hard to keep running and the motor dies. Kick it and try the choke, try opening the throttle a little without choke, all to no avail. Sit on the bike exhausted and call one of my kids. 15 minutes goes by beyond the time I kicked and fiddled with it. Decide to give one more kick.

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A failing coil which stops working when hot will give these same symptoms, when its not starting have you checked for good spark at both plugs.

Joe Schlaberdowski said:

But has anyone heard of this with the Power Arc ignition? I only ask because I've just gotten that installed and got the bike running fine. 1000 or sub 1000 rpm idle. And steady. Plenty of power. No hesitation on acceleration from idle. But the last two rides have been the first real rides besides testing it going around the block then back up the driveway.

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NO, but if your bike ran fine on the previous ignition, and the power arc was the last change you made before this problem began, I'd suspect something changed with the ignition change. Whether it's an incompatible part that heats up and fails or a poorly connected or broken wire that fails, I would remove the power arc and switch back to your old ignition and see if your problem goes away. If the problem goes away, then you know it's ignition related. If the problem persists, then you can safely reinstall the power arc. If you have the luxury of a different ignition system, you only have to spend the time to swap it in to test by substitution. It may be time consuming, but it could rule out one entire avenue of the search for a solution.

Beyond that classic, "I changed X and now my bike has a problem" diagnosis, things like old ignition switches wear out and get corroded. Once it heats up, it could be intermittently feeding power to your power arc, which would screw it up completely since it's not a magnetic sensor type ignition... check that..

kommando said:

A failing coil which stops working when hot will give these same symptoms, when its not starting have you checked for good spark at both plugs.

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Haven't checked for spark. Both times I've been out on the road pretty far from home. AND because of the air space in the transparent fuel tube just before it goes into the Mikuni, I've thought the problem was with the fuel supply. To answer another post, bought it second hand. It had a Boyer MARK III. Never could get it to run right. Decided to buy the Power Arc. Got it sorted out. It ran great. But would kick back like a mule if you didn't watch the forward rotation. Still, everything was fine till the last two rides. After reading the post from mexicomike that a small airspace in the fuel line above the Mikuni was normal, it occured to me it might be the ignition. And both times it's been hot. I'll have to carry a spark plug wrench to check time it goes on me.

concours said:

“Most carburetion problems are of the electrical type.”

Or something like that.

Have those friends who have suggested “vapor lock” explain exactly how that phenomenon works....

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Ok. I'll try. The fuel vaporizes in the bowl and causes pressure -- and then -- and then -- something ??? But I do like the statement about most carburetor problems being of the electrical type.