Despair shop 22 – Feelin’ hot, hot, hot
This week in the despair shop I have mainly been playing with a 2002 Honda Vigor 650. It’s a strange old beast – single cylinder 650 single overhead cam, 4 valves, twin exhaust port hi torque low power (49bhp) half scrambler half tourer. It had been sitting for a couple of years, has had only one owner and apart from a bit of cleaning being needed is in really good nick.
As is normal for something that has been sat the battery was as flat as a witch’s tit and it wouldn’t take a charge so a new one was procured. With that in place it turned over freely.
The petrol that had been left in it absolutely stank and when I opened the drain tap on the bottom of the carb a thick green fluid that used to be petrol oozed out all over my shiny engine. The smell was most unpleasant, it was hardly surprising it didn’t want to start really. A quick blast of quick start had her firing though so that was nice.
I fully drained the fuel and refilled with some of Esso’s finest and the bike seemed to run quite well but needed some choke even though the engine was now warm.
It was getting dark, I was about to give up when I glanced down at the exhaust headers, to my horror they were both glowing red. Not a dull red but an OMG they look like they are about to melt red.
I took a photo, it had cooled down a bit but you get the idea.
Now, I have heard of this happening on large single cylinder bikes but I have never seen a case quite like this, I am pretty sure something major is amiss. I did a quick internet search and found several threads on various forums where similar issues have been discussed. In some cases it has been dismissed as normal, in others contributors have suggested it’s a sign that the end of the world is nigh. I think it isn’t right and needs looking in to.
My first thought was that the cam timing could be out allowing the exhaust valves to open too early thereby allowing gasses that are still combusting to exit the chamber and heat the headers up. I find it hard to believe it’s that though as it starts ok on choke and runs fairly well except at tick over.
If I apply choke it runs better but still seems to be too hot.
The other school of thought says the mixture is way too lean which is why choke helps. The thing bugging me though is for the mixture to be that lean it would have to be an air leak or lack of fuel. Usually either of those conditions cause the revs to rise or hang up when you rev and release the throttle and that’s not happening. Definitely going to have to look further in to this one, watch this space.
Meanwhile an opportunity too good to miss raised it’s head the other day in the form of a Suzuki GSXF600 for sale on Facebook marketplace. The advert was very brief but the photos looked pretty decent so I got in touch. The ad had only been up for about 20 minutes but I was still too late, which is the story of my pathetic life. I asked the seller to keep me in mind in case the sale didn’t go through and then forgot about it.
The next day I got a message saying that the “buyer” hadn’t got back to him and so the bike was available again. I hopped in the van and drove the 60 odd miles to the middle of nowhere and bought the bike on the spot. It’s only done 9600 miles, was in really good condition and has just had a complete carb rebuild and balance. It even has a bit of MoT left on it, having only done a couple of hundred miles since it’s last one. It starts, runs and sounds really smooth, I don’t have any workshop space right now so it will have to stay on the van for now. I didn’t intend to buy any more bikes right now but sometimes they are just too good to miss.
Article provided by David Powell of Boston Bike Bits.
