Get It Rolling Again: Carb Rebuild and Service

Many of us have a great older bike that we used to ride the wheels off of, and then something—a newer, sexier machine, work, kids, etc.—intervened and ol’ faithful ended up under a tarp in the back of the garage. At the time you swore it would be temporary, not “storage,” no way, but then the weeks turned into months and the months into years, and before you knew it 3-4 years had slipped by. Not a serious problem if the bike was properly stored, but because we often fool ourselves that it will only be “a little while” at the outset, the motorcycle was simply parked at the end of its last ride without an effort to prepare it for a longer nap. Leading to that famous statement….

It Ran When I Parked It

These days putting a carbureted motorcycle away “wet,” with unstabilized fuel in the tank and fuel system, for more than 2-3 weeks is asking for trouble. In the article below, Matthew Wiley of Moto-Services.net explains why. Wiley offers a long list of “mail-in” services for vintage and touring bike brakes and suspension. But Moto-Services is perhaps best known for its carburetor rebuilding services. While the typical do-it-yourselfer probably won’t shy away from changing oil, spark plugs or tires to get an old bike going again, servicing a bank of 1-4 gunked-up carburetors is beyond the skills of most shade-tree mechanics. Wiley accepts components for service such as carbs, brake calipers, master cylinders, forks and shocks—you have to remove and ship them, but complete installation instructions are included when they are returned.

Removing the bank of carburetors from this Kawasaki was fairly straightforward, but it always helps to have a shop manual. (Photos: Mark Tuttle and Matthew Wiley)
Removing the bank of carburetors from this Kawasaki was fairly straightforward, but it always helps to have a shop manual. (Photos: Mark Tuttle and Matthew Wiley)

Among the staff and contributors, we have a number of vintage bikes here at Rider, some that are ridden regularly and others, well, not so much. Much to my horror, the other day I realized that one of our vintage multis from the early ’70s had been sitting for three years, so I took it upon myself to change the oil, charge the battery and get it rolling again. Fortunately the bike had been properly prepped for storage by draining the tank and carbs (here in SoCal we don’t worry about tank rust too much unless the bike is stored outdoors or near the beach), but long-term “dry” storage can also dry out O-rings, rubber fittings, etc. and cause them to fail. When I filled the bike with gas and opened the petcock, fuel began leaking out the “T bars” in between carbs 1-2 and 3-4 that connect the dual fuel lines to them. Not good. This meant that the carbs would have to come off the bike and be removed from the “rack” that holds them tightly together and in-sync to replace the dried-out rubber T-bars.

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Since this bike’s carbs had last been rebuilt in 1996, it made sense to do it again while they were off the rack. I’ve done a few carb rebuilds, but this one was just too involved to tackle at that particular time, so I removed the bank, boxed it up and sent it to Wiley. Matthew performed a thorough cleaning and rebuild that included rebuild kits for each carb from K&L Supply Company (available through Matthew or your dealer), new T bars (fortunately available NOS), new synchronizing lock tabs, and some custom work including drilling out a seized enrichener holder. The carbs were bench tested for fuel flow through all of the passageways during the cleaning process, statically synchronized, and the fuel mixture and idle speed were set. Finally, they were checked for leaks with a remote fuel source for 30 minutes before Wiley boxed them up and sent ’em back.

Our carburetors inverted with the float bowls removed on the workstand at Moto-Services, ready to be cleaned and have their various replaceable bits replaced with parts from K&L Supply and other sources.
Our carburetors inverted with the float bowls removed on the workstand at Moto-Services, ready to be cleaned and have their various replaceable bits replaced with parts from K&L Supply and other sources.
Before returning the carbs, Matthew Wiley at Moto-Services checks them for leaks with a remote fuel source for 30 min.
Before returning the carbs, Matthew Wiley at Moto-Services checks them for leaks with a remote fuel source for 30 min.

 

 

Moto-Services includes a very thorough instruction sheet and checklist for reinstalling freshly serviced carburetors to make sure that the effort isn’t wasted. Things like rust in the fuel tank, stale fuel, petrified or cracked intake manifold boots and even incorrect cable routing can create problems, so Matthew goes over everything that might rear its head.

On this particular bike, the carb rack removal and installation are pretty straightforward, and I had the bike back together in short order. It runs like a champ again, with a total time investment on my end of about two hours.

Carburetor rebuild kits like this one from K&L Supply generally come with everything you need to fully service the typical carburetor, though sometimes the odd part will need to be sourced elsewhere (e.g. drain plug O-rings were not included in the kits for our carbs).
Carburetor rebuild kits like this one from K&L Supply generally come with everything you need to fully service the typical carburetor, though sometimes the odd part will need to be sourced elsewhere (e.g. drain plug O-rings were not included in the kits for our carbs).

The typical cost is $300-$400 for parts and labor, and turnaround time is 10-14 days, but it depends upon how many carbs need service, and the cost of vintage NOS or repop carburetor parts can vary dramatically as can the parts required for CV carbs vs. these simple slide-throttle types. Wiley has a labor cost table on his website and a complete listing of his services. My cost was about $400, including $222 in parts such as the K&L rebuild kits ($24.99 each). Matthew also insisted I replace the intake boots, which were an additional $100 for four (grand total about $500). This bike’s petcock is a new aftermarket unit, but if it had been as neglected as the carbs it should have been serviced as well. Moto-Services’ prices seem very fair, and for your money you’re getting the attention of a master mechanic with 35 years of experience. –Mark Tuttle

FOR MORE INFORMATION: Matthew Wiley, moto-services.net, (928) 245-8149 or sales@moto-services.net

If you’d like to try your hand at servicing your own carburetors, read on for expert advice from Matthew Wiley himself:

Carburetor Rebuild and Service

Overview

Carburetor maintenance and tuning has become something of a lost art. Over the last 15 years, fuel injection has become mainstream, and many dealership technicians have little experience and understanding of them. The “old timers” and service shops specializing in older motorcycles of the ’70s through ’90s are much more adept at handing carb problems and tuning.

Current Conditions

Today’s gasoline is much different chemically than what we burned in the past. As a result, rubber parts on older bikes not designed to resist modern fuels, such as O-rings, float needle tips, enricher plunger tips, air cut-off diaphragms, petcock diaphragms, etc., can all suffer.

Slide-throttle carbs like these are generally easier to rebuild than CV models that have more parts.
Slide-throttle carbs like these are generally easier to rebuild than CV models that have more parts.

Storage

There are two schools of thought in regard to motorcycle fuel system storage: wet or dry. Wet storage requires treating the fuel with a stabilizer so it does not break down. However, today’s gas can still break down in a few months, even weeks, despite being stabilized. The advantage of wet storage is that the rubber parts do not dry out and harden, and full fuel tanks do not rust. But storing wet for more than 2-3 months, even with stabilized fuel, can still result in some level of fuel breakdown that causes hard starting, drivability issues, fuel leaks, clogged passageways and sticking float valves, etc. I do not recommend wet storage for more than 90 days.

Dry storage requires draining the fuel system completely, both carbs and fuel tank. It is critical to ensure all fuel is removed from fuel tanks, the fuel valve (petcock) and carbs. The engine must be cranked over several times after draining to pull residual fuel out of carb passages. The fuel tank should be well coated with oil, too—I use fogging oil from the watercraft/marine industry. The weak link with dry storage is that rubber parts often harden as a result, and even with oil treatment gas tanks may rust internally over time. Dry storage is best for long-term storage, like 6 months or more.

Carburetor Service

Once the bank of carbs is removed from the bike, if one or more has to be removed from the support “rack,” afterward it can get tricky making return springs and linkages work again.
Once the bank of carbs is removed from the bike, if one or more has to be removed from the support “rack,” afterward it can get tricky making return springs and linkages work again.

This becomes necessary when drivability issues or leakage mandate the effort. When dealing with 20- to 40-year-old motorcycles that have multiple carbs, it often becomes necessary to separate the individual carburetors from the “rack” to facilitate replacing O-rings and seals at the cross connectors, or T bars. Air cut-off (coasting enricher) valves often require separating the carbs in order to access them for inspection and replacement. This is a tricky process, since making linkages and return springs work properly afterwards can be difficult. Parts for older models are often discontinued, making aftermarket rebuild kits your best bet to obtain all the various parts at a reasonable price. Kit contents vary, however, and may require matching up O-rings, screws, etc. in order to complete the job properly.

Intake Manifold Boots

The rubber boots connecting the carbs to the cylinder head should not be overlooked. They can harden, making carb removal and installation difficult, and may tear or separate during disassembly. Air leaks (vacuum leaks) resulting from rock-hard intake boots or the failure of the gasket or O-ring that seals them to the head can cause drivability issues or even engine damage due to lean fuel mixtures and overheating. The boots connecting the carbs to the airbox are critical for proper operation of CV (constant velocity) carbs as they depend upon a strong vacuum from the airbox to operate well and provide good drivability.

Don’t overlook the fuel valve (petcock) when servicing a fuel system—they often have seals and/or a diaphragm that can deteriorate, too.
Don’t overlook the fuel valve (petcock) when servicing a fuel system—they often have seals and/or a diaphragm that can deteriorate, too.

Fuel Valve a.k.a. “Petcock”

Petcocks should be rebuilt anytime there is seepage from their outlet, external seepage and whenever carbs are rebuilt. Don’t overlook fuel and vacuum lines during this process.

Starting Motorcycles After Wet Storage

If the motorcycle has been stored more than 30 days, carefully drain the fuel from the carb bowls prior to turning the engine over, as the small quantity of fuel they hold will deteriorate faster than the several gallons in the tank. Prime the carbs after draining, then attempt start up. If the storage period was long, it is often worth draining the fuel tank as well and filling with fresh fuel. This removes rust, sediment, etc. lurking in the tank before it reaches the carbs. There are some fuel restoration additives that can help restore borderline fuel when tank draining is difficult. It may be necessary to fine-tune the fuel mixture and idle settings initially and then re-adjust later if needed. –Matthew Wiley

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