Q: I’ve just acquired an old Suzuki RM250 two-stroke, which is an air-cooled model. I only paid a 4k for the thing and I’m not even sure what I’m going to do with it, and I think it’s from the late eighties.
Besides that I’m sure it’ll be fun to ride and I’ll probably hurt myself. But the reason I’m writing is that a guy told me to fit three to four base gaskets under the barrel to improve performance. So, quite simply, is this true because it’s easy to do on these old engines, and will it affect reliability? Just wondering….
A: This has been done for years on many two-stroke engines, and all it does is to raise the transfer ports and exhaust port by a few millimeters, depending on how ‘high’ you lift the barrel.
What this tends to do is increase top end power, sometimes? But the trade off is it makes the engine more ‘peaky’ at the top end and therefore you’ll get a loss of bottom end power. It will also lower the compression ratio and squish band, which isn’t a good thing either.
So it all depends on the type of riding. Personally I’d leave it alone because Suzuki knows what they’re doing better than the ‘guy’ in the pub. Shouldn’t affect reliability though, if you fancy fiddling around.
Q: I own a Yamaha V-Max from the eighties and it was running a bit rough to say the least. So I decided to check things out and replace the spark plugs, air filter and give it a general clean. I have worked on the bike before so I have good idea on how things work and fit.
But when I took off the air box I noticed two of the rubbers that connect the air box to the carbs’ are stiff and well out of shape causing air leaks. I asked my Yamaha dealer to order new ones but they’re not sure if they can get anymore, and it will take forever if they can.
I’ve heard of different ways of ‘repairing’ them and wondered if you guys knew of anything about this issue, I understand they’re old parts and all of that?
A: We’ve seen this problem many times with old bikes because these items always become brittle and perish with old age. But there is one thing you can try.
Take the rubbers and soak them in thinners until they swell up to about ten times their normal size. It’s a bit scary to see but don’t be worried. Then take them out and leave them overnight and you’ll be surprised in the morning that they’re back to their normal size and soft and supple once more.
It’s certainly worth a try especially seeing as they’re hard to find, have a go you have nothing to lose seeing as they’re in such a state?
If any of you have the same ‘rubber’ problem on any sort of motorbike give it a try as well, no guarantee though folks.
Q: I’ve just bought a Yamaha BWS, 2006 model, with 30,000km on the little clock. I’m very happy with it but recently I decided to clean the air filter because of the mileage.
It was indeed very dirty so I cleaned it, oiled it, and washed out the air box, which is a standard one. But now the scooter has become sluggish and oil is dripping out of the air box! So should I now replace the filter for a new one?
Pierre De Wet
A: The stock filter is a paper element and therefore requires no oil. So if it is you’ll have ruined it and it will certainly need a new genuine Yamaha replacement, which aren’t too expensive. After fitting it the stock performance will return.
Also, screw the airscrew in and back out one complete turn, which seems to give a better pull-off in stock trim. You might have to raise the idle a bit to compensate. Give that a try as well?
Q: Hi guys and I hope you all have a great holiday because I’ve enjoyed your site all year so keep up the good work in 2019, I’m sure you will?
Anyway back to my question. I own one of those Honda FMX 650 Supermoto fun bikes from around 2007, I believe. I’ve owned the bike for many years and it’s never given me any problems. However, it’s covered in a ‘thousand’ pipes surrounding the engine in the name of reducing emissions I suppose, and I like to take them all off.
I’ve been told this will increase power and living in Jo’burg, at altitude, it also needs a jetting change because the plug seems to run ‘black’? So is this correct and what sort of jet sizes should I be running to get a bit more power from this old 644cc single? The bike also runs the stock air box and exhaust (filter is clean), in case you’re wondering.
Thanks for your time and don’t get too ‘hammered’, which I’m sure you will.
A: We’ve taken all this emission pipe work garbage off before and on the dyno it makes no difference at all to improving power output. The only advantage there is it tends to save a few kilograms of weight. So we wouldn’t bother unless you desire a less cluttered engine to look at?
Regarding jet sizes we tend to drop the size by around 7 to 8% for our 1500m altitude. So take out the main jet and see what the size is, it will have it engraved/stamped on it, and drop accordingly. We also recommend some sort of less restrictive exhaust because the stock twin cans are also very restricted for emission control. They could also affect jetting so try to do that first and check the plug colour as this could lean the bike off considerably.
Hope that helps and thanks for the comments and have a superb holiday too.