I'm happy to report that my new(to me) Yamaha VMax is legally on the road, woohoo!
VMax Tuesday 17 June 2025 by
Terry Prendergast, on Flickr
I rode it home from Spotty's place in heavy traffic, and I was disappointed that it was running like crap. I lost a lot of sleep on Tuesday night trying to work out why it wanted to idle at 4000 RPM every time I stopped at the 9 traffic lights between his place and mine. On Wednesday morning I decided that it might be a flat battery problem, one or two of my bikes with ECU's will increase the RPM's to provide power to lights etc when the battery is marginal. As it turned out, the battery was holding 12.5 volts in very cold (39 degrees F) weather. I decided to start it and check that the charging system was OK, and realised my error straight away, as opposed to every other bike with carbs that I own the choke is on when it's up, but a VMax is the opposite, and I'd ridden it all the way home from Spotty's place with the choke on. Du-oh! I fired it up and checked the charging voltage, and it was fine.
Another issue was that the VBoost system didn't appear to be working. What's "VBoost" you ask? The VMax is a 1200cc V Four, with 4 carbs in the valley between cylinder banks. The manifolds for cylinders 1 and 3, and cylinders 2 and 4 are linked, but with a butterfly valve blocking flow from 2 carbs into 1 cylinder until the engine revs to around 6K RPM, when a little servo motor opens the valve, and suddenly 2 carbs are feeding fuel/air into each cylinder. It's a really simple system, a bit like the vacuum secondaries on a 4 barrel carb, and the BHP's suddenly increase from around 100, to around 150, which is scary fun when you crank open the throttle. The most common cause of the VBoost system not working is the soldered joints on the circuit board for the VBoost controller will eventually fail due to vibration, so the test is to unscrew the little controller box and flex it, and if it suddenly starts working, well, there's your problem. Luckily enough with mine, it started working just by me removing it from the frame, then screwing it back on. If it's working, you'll hear the servo motor working as well as the fuel pump.
I screwed everything back together and found another controller on Ebay that the owner said works well, so I ordered it as a backup. I fired the VMax up and put all of my cold weather gear on, and headed up the road. The word "VMax" and the phrase "Fuel Economy" can't be used in the same sentence unless "Fuel Economy" is prefixed with "Sh1thouse", so my first stop was a gas station. I then headed out on one of my local circular routes where I take all of the bikes that Spotty and I bring back to life for a "shake out" ride, just to make sure that I'm not too far from home if it breaks down. As it turned out, there was no issue with breakdowns, and the VMax went like a raped ape. It doesn't have the massive torque of the Triumph Rocket III, but when that VBoost kicks in, it doesn't matter as you are suddenly catapulted forward, and all you want to do is hang on and survive the experience. I had to stop and take some pics of course.
VMax Wednesday 18 April 2025 2 by
Terry Prendergast, on Flickr
I wore my heated gloves, but thought that the batteries were flat. It turns out they were fine, I just hadn't pushed the buttons in the right place, but when I got them to work when I got home, they warmed my cold fingers a treat. Yes, I'm an idiot. Anyway, ride #16 is done, and tomorrow's supposed to be a nice day, so I might take the VMax out for another blast, it's a fun bike.
VMax Wednesday 18 April 2025 1 by
Terry Prendergast, on Flickr
