Normal behaviour for a little KH100
First post. A long one. I can't help but waffle :)
About 8 months ago I found a little 1979 KH100EL in a motorcycle 'recyclers' that needed a few bits and pieces and a little bit of work. I went ahead and bought it because it was a nice looking little thing and I've wanted a bike for quite some time and thought this would be an interesting place to start.
Having no prior mechanical knowledge has been fun. So after fixing quite a few things (ignition switch, cables, adjusting brakes, brake levers, battery, cleaning/greasing air filter cleaning the fuel tank/hoses et al) AND getting a mechanic to make sure it was carburetting properly, oil pump was doing the job, the timing was set right and the engine compression was otherwise OK it has been running pretty well.
However, it generally only runs well for maybe 35 minutes before it seems to get hot and starts struggling (acceleration stars to go, rev progression gets a little rough - it basically starts to get slower and grumpy). I try and ride it at varying RPMs as much as possible because I've heard that these little 2 smokers don't like to cruise. My mechanic has told me that 'this is just how they are, they need a rest every 35 minutes or so'. Is this true? It'd be nice to get it to a point where it will last 25 minutes before performance deteriorates or even to a point where I could ride it for say an hour without caring too much :)
There are a couple of other little things that may or may not be related to this performance quirk. The first being that I am having some trouble getting the tank cap to vent properly, blowing air through it with my mouth tells me air can get through but I think it isn't keeping up. To circumvent this, and avoiding fuel flow ceasing and the engine cutting - which has happened, I loosen the tank cap while riding every 5 minutes or so. Does the trick.
I'm fairly certain it is missing a regulator rectifier so I have been charging the 6V system every few days or so. I've heard someone say that not having the rectifier can affect engine performance in some of these types of bikes but I am unsure as to how.
Any help would be greatly appreciated. I'll also be diving in with a full respray of the tank and side covers because there is a little rust on the tank.