Q: We (as in my mates and I), all have old Yamaha XT500 singles in various states and conditions. We all sit down and talk about them over a beer or two and even though they’re old and relatively slow compared to today’s bikes we all still love the ‘rawness’ of an old air-cooled single with a kick-start, until it slaps the back of your leg and leaves a bruise the size of the moon!
As a rule all of our bikes are reliable except for a few spitting plugs out of the head and having to heli-coil them, and minor stuff like that, but I do have a question to run by you guys to see if you can shed a bit of light on this irritating subject.
Most of us have re-bored the motors with new rings and pistons and fitted new valve guides and seals and gaskets, to see if we can stop excessive oil use. As you know the oil is filled by putting it into the top frame rail but even after a couple of days of riding, mine especially, has dropped more than I thought it should. But there seems to be no smoke coming out of the exhaust pipe, or indeed any oil leaks from anywhere, pointing to why it’s dropped.
So do you have any idea where the oil is ‘going’? It would make a great talking point the next time we all meet, and thanks for a great site (best in SA by far), because we all log on daily for Bill’s silly, but entertaining, comments.
A: Bill says he had the same issues in England when ‘they’ all used to tear around on these bikes, and eventually they discovered in was in fact the bike’s oil pump at fault, which is interesting.
The oil pump sits at the bottom of the frame rail that holds the oil with no valve, of some sort, in-between. When the internal vanes wear, over time, the oil from the header tank seeps past the pump and straight into the crankcase, so check the level in there to see if the level inside has risen before you start the engine over night, to confirm this?
It can’t harm the motor unless the crankcase becomes over-full, which can obviously affect the seals in that area. So, if you guys want to keep the oil use back to original go and buy a brand new original oil pump and your problem is cured, simple as that. And yes, any Yamaha dealer can still get those parts for you.
Q: I’ve just taken control of my uncle’s old 1977 Yamaha RD400, after pestering him for many years to let go of his old two-stroke.
I’ve got it running but the pipes were falling to pieces, so I’ve imported a pair of cool looking expansion chambers from Australia, which will make the bike sound better and go faster. I’ve kept the stock air box, but fitted a new air filter and cleaned out the carbs. The bike also had an electronic ignition fitted around 10 years ago and the timing was set correctly, so I’m told, so for now I’ll leave that part of the bike alone.
But my question is about the jetting and how to choose the correct main jet size? Do you have any idea what jet sizes to use and how to get the correct mixture; is the old ‘plug-chop’ method still applicable in today’s world of modern fuels, etc?
Eric Musson Cape Town.
A: The only way to get the jetting correct is indeed to do a ‘plug-chop’. Hold the bike flat out in fourth or fifth gear and immediately kill the motor with the kill switch.
The plug should have a light brown tint to the white center piece, but if you see any sandy deposits or erosion of the centre electrode it can be dangerously weak and therefore cause terrible damage to your engine. If you blow a hole through the piston by running too lean it will spray molten aluminium all over the crank, and that will then become a major problem.
As a golden rule with old air-cooled two-strokes, if you’re not too sure what you’re doing please take it to a professional who does?
Q: I’ve just fitted a top box (maker’s name withheld because my brother sells them) to my 2005 Aprilia Caponord. I’ve wanted to fit one for a while now because my backpack gets wet in the rain and I live just outside Durban where it tends to rain a lot. So it seemed like a good idea to fit a waterproof carrying device.
The fitment of the accompanying brackets in the kit was relatively easy, if not a little fiddly, but I came right in the end. So then it was time to go and out test the new ‘box on the open road.
As soon as I get to 140km/h the bike has now developed a constant weave, which is a bit unnerving, and I didn’t feel like going any faster to see if it disappeared at higher speeds.
So, is this trait common when one fits a top box and more importantly is there anything I can do, or try, to cure the problem?
A: If the top box you’ve bought isn’t primarily designed to fit this particular bike problems, like this, can occur. Also, there’s probably a label, or sticker of some kind, on the ‘box, advising on speeds after fitting it. So it might pay to find that.
Also, if a pillion sits on the back it sometimes stops this ‘weave’ because it smoothes out the airflow after it passes over your body, try that? Also, move your body position backwards and forwards whilst riding to see if that improves things. But as a rule you’re going to have to keep your speeds down, live with it, or take it off when not really needed.
Q: I see you’re getting a lot of questions relating to older Japanese motorbikes, so I thought I’d throw another one at you.
I have a Suzuki GS550 from the late seventies, just because it’s all I can afford. It still has points and condensers, which are always giving me loads of problems. I’m forever cleaning them and settings gaps, etc, which is irritating to say the least.
I’ve just priced a new set from Suzuki (two sets of points and two condensers) and they come to nearly R1,000, WTF! And within a few years they’ll need to be replaced again, and the entire mechanism seems to be worn out anyway.
So what other options do I have? I’m thinking of replacing all of it for an electronic system, and would you know who to get in touch with, and will it work OK with the stock ‘points’ coils?
A: I would certainly throw away all that old stuff and replace with a modern conversion from Dynatek for example. You’ll get a much more accurate spark and better all-round performance, and it will work fine with your stock ignition coils.
Go to www.dynojet.co.za and order your parts from there, they are the official South African importer for the full range of quality electronic parts, like these, from the USA. Then your points problems will be over with your ol’ GS.