Motorcycle Carburetor Cleaning and Adjustment

The “Poor Man’s” Carb Adjustment

Sometimes, you can get lucky and a simple can of carb cleaner works magic.

The Triumph Tiger had been sitting in the dealer’s showroom for several months with a half-full tank of gas when I bought it in the Fall of 2004.

The dealer didn’t start it, nor did he offer a test drive.

The entire transaction was over in the blink of an eye — I forked over the cash, loaded it on a trailer and took off for home.

After all, what could be wrong with a motorcycle that was showing only 1,800 miles on the clock?

Over the next couple of days I went through all of the mechanical bits just to make sure nothing was out of spec.

I took it out for a couple of quick test rides (without license plates) and everything worked fine, except for some pretty obvious flat spots in the carburetion.

I didn’t have the time to tear into the carbs, so I brought it over to our local Triumph dealer and asked him to check it out while it was in for the inspection, which is a requirement to obtain plates in Maryland.

He told me he cleaned and adjusted the carburetors and installed a new airbox with air cleaner and, unfortunately, I believed him.

Riding it home from the dealership a few days hence made it obvious that it was running worse, not better. Hmmmm….

The Expensive Method Doesn’t Always Work

So it was back to the dealer for another round of adjustments.

It’s kind of like going to the doctor nowadays; if you don’t walk in with a broken arm or a bloody gash, they don’t really believe you until you come back the second or third time with the same symptoms.

This time the dealer swore that everything had been fixed. I’ll admit that the Tiger did run better, after a fashion, but it still had a big flat spot under normal acceleration starting around 2,500 RPM.

And it wouldn’t idle, but that was easy to fix by simply twisting the nice little dial that sticks out of the left-hand side of the Keihin carb bank.

A string of emails to the Tiger owner’s group resulted in several responses, most of which were of the “they all do that” variety.

So I accepted their general wisdom and figured that someday I’d install a set of performance jets to wake up the triple.

In the meantime, I ran a can of Sea Foam through it, which seemed to help. Since I had never ridden a Tiger before, I didn’t have any basis for comparison.

Fast forward to a few weeks ago: on the way home from a pleasant ride, I stopped and filled the Tiger with gas, parked it in the garage and took off on vacation.

Two weeks later I pulled it out of the garage, gave it the once over, checked the tire pressures and lights, pulled out the choke and fired it up. It started right up, just like always.

But as soon as I would ease off the choke just a tiny bit or if I twisted the throttle only slightly, the engine would quickly stall.

I tried every trick I could think of, including checking the fuel lines, the fuel overflow and the air filter.

Nothing.

I was puzzled, because I’ve parked motorcycles for much longer than that without problems. Possibly a bad tank of gas?

So I removed the fuel tank, drained the gas and checked the filter in the petcock.

I rested the tank back on the bike, connected the lines and tried again but no dice. It started and ran great on full choke, but it would die as soon as I touched the throttle.

Anyone who’s pulled the carbs on a Triumph triple would agree — you really, really want to avoid removing the carburetors, but at this point I had no choice.

I figured I may as well get to it and, at the very least, I’d end up with a webBikeWorld tech article. By coincidence, I had a brand-new point-and-shoot, so I set it on a tripod and went to work.

I should have read the owner’s manual for the camera, because the photos didn’t come out, which is a real shame.

And I didn’t realize it until I had everything back together.

In any case, pulling the carbs from a Tiger is not much different than the same task on a Thunderbird Sport of similar vintage, and we covered that a while back in this article.

But after going through all the trouble of removing the airbox, air cleaner and the bank of carburetors, giving everything a thorough cleaning and then reassembling the whole mess, nothing had changed!

My gut told me it had to be the carbs, so I figured it was time to break out the heavy-duty chemicals.

The Poor Man’s Carb Cleaning Method

Off came the fuel tank again and I first ran the bike dry with only the fuel left in the supply hose.

I came up with the idea of spraying some aerosol carb cleaner into the hose (Berryman B-12 Chemtool), which would hopefully fill up the carbs with the cleaner.

I planned on letting it sit all night and hopefully the carb cleaner would break up any varnish and crud inside.

I’m not sure why, but after the hose was full, I pressed the starter button and the engine started right up! I guess there’s enough mojo in the carb cleaner to combust in the cylinders.

I let the engine run until it started to stall, then gave it a few more shots of carb cleaner. The engine was now running on carb cleaner only. I used the entire can.

Then I figured that if it would run on carb cleaner spray, maybe it would run on carb cleaner liquid. Out came the can of Sea Foam. I carefully poured it into the fuel line and then hit the starter.

With the choke on, the engine idled with no problem, although it still died if I gave it any throttle. I kept it running until I had used up about 3/4 of a can of the Sea Foam.

I let the bike sit overnight and as I thought things over, I picked up the can and discovered that Sea Foam actually recommends exactly the same procedure.

I re-installed the fuel tank, the lines, the overflow and everything else. I started up the bike and after several attempts, I could finally get it to run under some throttle, but it ran very poorly.

After several minutes of revving, I figured it might be good enough to try taking it down the road to “blow out the cobwebs”.

This I did, and I felt comfortable enough that it would continue running to ride it down to the gas station.

I filled it up with high test and poured the rest of the Sea Foam into the tank.

About half-way home, it all of a sudden smoothed right out. I ran it up and down through the gears, giving it all the throttle I could. Wonderful! Just like a new engine!

All of those modern chemicals finally overcame several years’ worth of varnish and blew it right out the exhaust.

The Tiger now runs fantastic. It’s a huge difference from what I thought was normal.

Conclusion

So, what’s the point of this long story? I thought I’d share this “poor man’s carb adjustment” with others.

If it saves just one other rider some money, it’s worth it.

I’ll bet that a lot of motorcycle carburetors have way too much varnish and crud inside of them.

Rather than bring your bike to the dealer for a $450.00 “carb adjustment”, you may want to try running the engine on pure carb cleaner first. Total cost?

About $10.00. I’m sure there are plenty of smart shade tree mechanics out there that knew about this, but I have never heard it mentioned on any motorcycle interest groups that I belong to.

I had no idea that running an engine on carb cleaner alone is actually a recommended practice by some of the carb cleaner manufacturers, nor that it would actually work!

One word of caution – whenever you’re messing around with fuel, carb cleaner or other chemicals, read and follow the manufacturers instructions to the letter and use every precaution regarding fire, smoke and fumes!

Got a carb cleaning tip or a comment on this article? Send it to editor@webbikeworld.com

Publication Date: August 2006

See Also: Sea Foam Carb Cleaner Review

Owner Comments and Feedback

More comments also available on the Sea Foam review page.

From “J.C.” (November 2012): “I read with interest your articles on the use of Sea Foam and Berryman B-12 Chemtool for carb clean up.

For many years I have used the B-12 in all gas that goes in my lawn mowers, weed eater, chain saw, and gas powered welder.

These are all fairly old — the mower and welder are over 25 years old. No carb rebuilds or tear downs for cleaning; they all start easily even after sitting idle for months.

I recently bought a 2005 Triumph Bonneville America. Like your advice on oil and owner’s manuals, I have studied the Triumph book as if I was going to take a test. The fuel section states that fuel with methanol is not be used.

The second ingredient on the B-12 Chemtool can is methanol.

Maybe there is something in the Triumph fuel system that can be damaged by methanol.

So I have opted not use my old favorite in the Triumph, but will put an occasional cup of Sea Foam in the tank to help keep things from gumming up this winter.”

From “M.S.” (8/09):  “Note about Constant Velocity, or CV carbs with rubber diaphragms.

Spray carb cleaners such as “Gumout Carb and Choke Cleaner” and “Berryman B-12 Chemtool” have the capability of weakening and/or dissolving the thin rubber diaphragms attached to the slider pistons.

Some carb cleaners are so caustic that just the fumes can dissolve the rubber. Read the directions/warnings and always avoid spraying carb cleaner down into the airbox unless recommended by the manufacturer.

I also recommend running all the carb cleaner out of the float bowl as the float is plastic and, depending upon the carb cleaner, can become brittle and even melt.”

From “D.D.”:  “I did much the same thing with my 81 Suzuki GS450. I had always winterized the gas with Sta-bil, and every year when I brought it out it would start up on the first try.

This year, however, it would run, but it would bog down when I hit the gas. I ran Sea Foam and Techron through it, with some improvement, but I still had to rev the bike over 4000 rpm just to get moving.

I siphoned the gas out of the tank and removed it, then ran the bike until it stopped.

I injected Sea Foam straight into the carbs, and ran the bike on that for a while. I then injected more Sea Foam into the carbs, and let the bike sit for 3 days. I put the bike back together and tried to start it.

At first it would only run for a few seconds, then after about 20 or 30 tries, I finally got it to idle. I let it warm up, then took it for a ride.

The difference was amazing. It now runs better than it ever has. I swear by Sea Foam now.”

From “J.W.”:  “Several years ago, while working as a mechanic in auto service, I learned that Chevron owns the patent for “Fuel System Cleaner” and sells the stuff to every one else who then dilute it, package it, and sell it to us.

Consequently, Chevron Techron is the best additive for fuel systems.

1 fl.oz. per gallon every 3000 miles is sufficient; oil thickening may occur at shorter intervals. Adding some to that Tiger tank should have also helped.

It did for my ’74 Norton 850 that had been sitting idle for a while when I first purchased it. If a carb-off teardown is the only option, Valvoline Synpower Carb Cleaner is the best.

It will even dissolve Craftsman brand plastic hand grips; Snap-on and Mac tools are un-affected. Fuel injection systems require a pressurized delivery system which is probably best left to a shop or some one who does “side work”.”

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