THE CARBURETOR OVERHAUL (der GASENSPITSER FIXEN)
I know a few of you still have them. With my riding buddy (Don) being
in the hospital, I decided to spend my idle time rebuilding my ill-running
carbs. I pulled into my BMW dealer's parking lot and counted the number
of bikes with carburetors. It seemed like my '91 R100RT was an antique!
Only nine bikes out of about thirty parked in the lot were not fuel injected.
The Tools and Supplies
- A gasket/o-ring kit (such a deal! $12.00 for both carbs on the RT)
- Perhaps a manual such as Clymer or Hayes
- Phillips and straight blade screwdrivers
- 8,10 and 11 mm open-end box wrenches
- A 1.8 mm (.070") pin punch
- Solvent or carb cleaner
The Disassembly
Remove ONE carburetor from the bike. You want to have the other carb
to look at when you can't figure out where that one last piece goes. Assemble
all your tools and the carburetor on the dining room table or any other
clean level surface and proceed with the disassembly.
- Remove the dome cover from the top of the carb, pulling out the spring
and throttle slide with diaphragm. Inspect the diaphragm for holes or tears.
(We don't want holes in ANY diaphragm, do we?) Unscrew the needle retention
screw and pull the slide needle out. Inspect the circlip and needle for
wear. One of my needles had a groove four times wider than normal; the
circlip had bounced up and down wearing the soft brass.
- Turn the carb upside-down and remove the float bowl by sliding the
wire bail off. Remove the floats by driving out the small pin with a 1.8
mm (.070") pin punch. (At last year's Range of Light, Lars and the
gang who stopped to help me used a sharpened rusty nail off a farmer's
fence.) Remove the pin and floats. Inspect the rubber tip of the needle
and the spring pin at the rear. Sometimes the swagging around the spring
pin wears out and the float stays down, starving one of you cylinders.
- Unscrew the idle jet (replace o-ring), check position of the idle mixture
screw and remove screw (replace o-ring), remove the main jet, mixing tube
(replace o-ring) and the slide needle jet.
- Loosen up the 11mm nut on the choke housing and remove the housing
(four screws). Remove the shaft and replace the o-ring. Reassemble back
into housing.
- Loosen up the 11mm nut on the throttle shaft and remove the spring
bracket (two screws). Unscrew the two screws that hold the butterfly to
the shaft, mark butterfly and shaft so you can reassemble correctly, pull
out butterfly and shaft (replace o-ring).
The Cleaning
Clean all the parts in solvent - NOT GASOLINE! - in a well ventilated
area. (This is the safety part of the article.) Solvent cleaned my parts
very well, but if yours are really full of crud use a carburetor cleaner
found at your local auto parts store. I left the old o-rings on each part
as I cleaned so I could match up the sizes as I reassembled. Do not soak
new o-rings in solvent or cleaner. Using a source of pressurized air, blow
out all orifices, jets or passages.
The Reassembly
Just like the books say, "put all the parts back together in reverse
order." I have a hard time with that so I just grabbed the parts closest
to me. Reassembly is pretty straight forward and idiot proof. (I did manage
to install the throttle spring bracket upside down.) Continue the process
and rebuild the other carburetor.
Coming Next Month: Careburetor Installation
and Adjustment
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