VFR400 – Fuelish Boy

After the brakes were sorted I actually got the chance to ride the VFR in the dry, although doing so immediately revealed another problem, this time with the fuelling. I found that when I was keeping the engine at constant revs for a while, in any gear, it would bog down, like it was getting too much fuel and want to cut out. I figured it was time to strip off the carbs for an inspection and clean.

I rode over to maison de Fagan and enlisted Alastair’s help. Removing the carbs was a bit of a pain since they are such a tight fit (and the screws for the air box were completely chewed up) but once removed and taken apart, they revealed themselves to be in good condition and free of gunk. We cleaned them using carb cleaner and an air line and replaced one knackered float spring. Having a look at the main jet sizes immediately revealed why it was fuelling badly – they were much too big.

My bike’s got a Beowulf can on it and I can only assume that whoever fitted it decided to put in larger jets to accommodate for the extra bazillion horsepower it would probably unlock… It was running 122s in the front two cylinders and 124s in the rear; much larger than it needs. I got some new, smaller Dynojet jets from JHS and now the front two run 118s, while the rears are on slightly larger 120s.

Paying some attention to the carbs has drastically improved the bike. When it was running rich it was never happy starting from cold and had to be run on full choke for it to stay running and it was always threatening to cut out when sat just idling, which was very annoying on the road. With the new jets it fuels cleanly, doesn’t bog down and happily runs from cold without full choke for an eternity. Lovely.

Based upon what a difference servicing the carbs has made, I’d recommend paying them some attention because even though it’s a pain removing / fitting them, the potential difference it could make might sort out any irritating fuelling anomalies, especially if they’ve never been cleaned before or have been messed around with. Also just getting to grips with the carbs and how they go together and fit in the bike was useful, not as daunting as I first thought and means that I’d be happy to take them off and work on them again if I needed to.

Pip

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