I clean, inspect, update and tune all my projects' carbs as a matter of course, and recently began work on the carburetor set for Project 42, a Euro-spec 1986 VFR750. I thought I'd share a few tips and reminders I've stumbled upon over the years.
(Right) Here's a basic collection of tools I use in the rebuild process. The small pistol-looking device is a butane torch used to soften the adhesive on the tamper-proof pilot mixture screw caps.
(Right) Here's a basic collection of tools I use in the rebuild process. The small pistol-looking device is a butane torch used to soften the adhesive on the tamper-proof pilot mixture screw caps.
(Below) During carb removal, simplify your life by disconnecting the throttle cables via the bracket, not by the adjustment nuts. This preserves the throttle cable settings and saves time.
(click on an image to enlarge)
(click on an image to enlarge)
(Right) Two things here:
After about the third time dropping the choke cable bracket down into the bike's netherlands, I finally learned to leave the bracket and screw in place during removal and installation (I'm a slow learner). Just loosen the screw to remove and install the cable (red arrow).
On the 3d- and 4th-gen carbs, you will find refitting the air intake tubes easier by first marking them with their number & orientation. Here, I've drawn a reference line to line up with the upper diaphragm cover screw.
After about the third time dropping the choke cable bracket down into the bike's netherlands, I finally learned to leave the bracket and screw in place during removal and installation (I'm a slow learner). Just loosen the screw to remove and install the cable (red arrow).
On the 3d- and 4th-gen carbs, you will find refitting the air intake tubes easier by first marking them with their number & orientation. Here, I've drawn a reference line to line up with the upper diaphragm cover screw.
(Below) Before splitting the carb set you may want to mark the carbs with a small drill bit — I once wasted a half-hour struggling in vain to install carbs #1 & 4 in reversed positions (2d-gen). I quickly drill indentations on #1, 2 & 3, leaving #4 unmarked.
(Right) When removing the floats on Project 42, I was surprised to find they were black-colored with all-metal brackets, unlike the yellowed color and mostly plastic brackets on every other VFR carb I've dealt with. A UK thing?
(Below) When removing the pilot screws, it's imperative to remove the tiny washer and o-ring stuck deep in the recess. I have a proprietary "tool" to accomplish this — a bent length of wire with a sharp angle filed at the end. The metal parts are reusable but the o-rings will be replaced. At reassembly the order is: spring, washer, o-ring.
(Below) A major part of the rebuild process is to replace the fuel joint o-rings. The fuel and vent joints are shown here. Looking closely at the fuel tube pictured, you can see the issue — there's a residual fuel trail visible (pink arrow), and the leaking culprit is the crusty o-ring (red arrow). TIP: the joints are plastic — they're pretty tough but will only tolerate so much ham-fisted abuse, like forcing off a stubborn fuel line. After several decades those lines are stiff and often stuck in place. Running them under hot tap water or soaking in hot water for several minutes will allow a gentle twisting removal. I leave the vent lines and their o-rings in place, as they're not critical seals.
(Below) Pictured are the 2d-gen carb-to-plenum o-ring-style seals. They're reusable unless damaged in some way. Note that one side of the seal is grooved and the other smooth. The grooved side faces outward on the carburetor and is held in place by tiny nubs (pink arrows). This does not apply to later model seals, which are specifically shaped and can only be installed one way.
(Below) Lastly, I leak test the freshly assembled set before mounting on the engine. This is where you'd like to discover a leak, not dripping on the engine and shop floor. A plastic tub works great, in this case a $4 cat litter box. The fuel bottle is attached and the set is allowed to sit at least overnight, as tiny leaks may take some time to appear. I then install the set with the fuel bottle still attached, ready to start up for the tuning process.
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