Buell carburetor repairs – The ExhaustNotes Blog

By Joe Gresh

After years and years of tinkering with engines, my whole life really, I’ve come to the conclusion that I am not very good at fixing carburetors. The Buell’s multiple personality disorder carburetor has really illuminated my carb inadequacies.

Considering it sat for who knows how long the Buell carburetor was fairly clean inside. I blasted it out with spray carb cleaner and installed a few new parts just because it was apart. The bike started up easy and seemed to run ok. And then the oil tank blew all over the place. I got sidetracked cleaning up oil and it was a few days before I got around to starting the Buell again.

The aftermarket needles have slightly longer springs. I’m not sure this matters.

After a few moments of running, the bike started getting richer and richer. Black smoke poured out the muffler along with popping and farting sounds. I shut the engine off and fuel began leaking out the carburetor intake mouth. This was unfortunate because I installed a new needle and float earlier.

Off the carb came for the second time. I re-checked the float level, installed another new needle and bench tested the carb. No leaks. Plugging the carb back into the motorcycle and reconnecting all the bits, I turned on the fuel valve from the remote tank and gas poured out the carb. It was like there was no needle at all.

The seat didn’t look too bad to me but I could not get the thing to stop leaking.

Third time: I pulled the carb and put the old float and needle back into the carb, maybe the aftermarket stuff is junk, right? I re-installed the carb. No leaks. Good. Started the engine. Bike ran rich and the longer it ran the richer it got. Lots of backfiring and flames. Fuel started running out the carb.

At this point I gave up and ordered a new carb from Amazon. It was on sale for $38. I pulled the carb again and it sat on the bench for two days. You have to understand, there is no simpler carb than the one on this Buell. Despite appearances my pride can be hurt. If I can’t fix the Buell carb, then I can’t fix any carb. I decided to take one last shot.

For some reason, the float bowl o-ring enlarged from my ham-fisted ministrations. Stuffing the ring into the bowl groove became a Sisyphean task: push one side in and the other side popped out. I didn’t want to wait for an internet gasket, so I drove down to our friendly neighborhood Harley shop, Liberty Cycles on Highway 70.

Liberty is a real old school Harley shop. Independent, scruffy, populated by guys that might beat you up for mistaking the year Panheads were first manufactured. 99% of the bikes in the shop were big twins. Sportster riders are suspect. I asked Father Time, a grizzled, white-bearded mechanic for a bowl of-ring.

Father Time dug around in various drawers and came up with the o-ring, handed it to me and said “Just take it.” Maybe these guys aren’t so scary.

Harley needle-seat burnishing tool. A center punch on a Ryobi cordless.

On the bench, the needle seat looked okay to me but I wanted a more polished look. Using a center punch on a drill motor I burnished the seat to make it smoother. Back go all the pieces after checking float level. No leaks. Start the bike and it runs good for a few moments then starts loading up on fuel again. It’s maddening but at least fuel is not leaking out of the carb. Progress.

After a steel-to-brass burnishing session the seat looked smoother. Most importantly the carb stopped flooding.

The enrichener plunger was dingy but not terribly dingy. It was enough to cause problems.

After cleaning the plunger sealed off the enrichener circuit, greatly reducing black smoke.

Fourth time pulling the carb. I removed the enrichment plunger; it looked a little dingy. Maybe the plunger is not seating? I used 800-grit wet-or-dry sandpaper to remove any deposits and cleaned the enrichener bore. Reassembled again and installed on the Buell. Bike starts up and runs well for a few minutes. Install the air cleaner, fire up the bike and after a minute or so the bike starts running rich, black smoke pours out the muffler.

Arrow points to the float bowl vent. This is the only vent as there is no bowl overflow tube.

Fifth time pulling the carb, thank goodness it’s easy to do on the Buell. I examine everything. My repair manual shows a float bowl overflow tube in the bowl. My float bowl has no overflow hose. My bowl has no tube. This is why fuel runs out of the carb throat when it floods. A normal carb would piss the fuel into the ground. Which got me thinking: How does the float chamber vent to atmospheric pressure?

The air cleaner back plate blocked the bowl vent. I didn’t grasp this until much later in the process.

Facing the intake side of the carb there is a hole at the 10-o’clock position. This is how the float chamber vents and this is the hole that is covered up when the air cleaner is installed. It sounds easy and logical reading this now, but it took hours of confused staring at the Buell to figure out what was happening.

Drilling a vent hole in the air cleaner back plate allows for atmospheric pressure in the float bowl.

I drilled a hole in the air cleaner where the vent exits the carb. Reassembled the entire mess yet again and started the bike. It ran better but was missing on one cylinder. With a single carb if you have one cylinder missing it pretty much has to be ignition, so I removed the spark plugs. They were covered in fluffy black soot. Chunks of soot nearly bridged the electrode gap on the front cylinder sparkplug.

A quick session with a wire wheel and douching the plugs with carb cleaner had them looking like new. I reinstalled the plugs and the bike started up easily, ran smooth, both cylinders ticking off nicely. It idled well, as well as any Harley idles. Maybe I have finally fixed the thing.

To recap, the carb had three issues:

1. 1. The first was the needle seat. It must have had some microscopic flaws that prevented the rubber needle tip from sealing. The leaking needle caused a rich condition.
  2. The next issue was the enrichener plunger. It was not seating completely. This allowed extra fuel into the intake, causing a rich condition.
  3. The final issue, extra confusing because sometimes I had the air cleaner installed and sometimes I had it removed, was the blocked float bowl vent. Without a vent to atmospheric pressure the float chamber is under a vacuum. I’m not sure but I think the bike runs rich as extra fuel is sucked in. The vent on the fuel tank becomes the atmospheric pressure inlet.

The Buell seems to be running fine now but after pulling the carb so many times, I’m a bit gun shy. I’ll call it fixed with reservations.

I haven’t received the Amazon carb yet but if the thing has a bowl overflow and the parts interchange I’ll be swapping the bowl. The Buell leans left on the kickstand, the carb towards the (downhill) intake manifold. Without a float bowl overflow, a sticking needle could run gas into the engine. Not good.

A smarter man could have figured out the Buell carb in less steps. He would have analyzed the symptoms and made a logical plan to address them. I am not that man. I threw everything at that damn carburetor until something stuck. I had to grind through obvious processes until the correct answers were all the answers that remained.