Q: Morning men. I’m about to rebuild an old Kawasaki GPZ1100 from 1982, the one before the Unitrack rear end arrived. I’ve taken off the head and barrels to check out the state of the piston, rings and valves. I’ll have the valve seats cut again for maximum compression and the piston and rings are within Kawasaki’s tolerances, so I’ll just hone the barrel.
But I’m thinking of raising the motor’s compression ratio by skimming the head and or barrel, which one would you recommend and more importantly, how much would you take off and what compression hike can I expect? Would this affect performance, and if so, by how much? According to the manual the standard compression ratio is 9.5:1.
Thanks for your time and now waiting for your reply.
A: First off all do not attempt to skim the barrel; it will cause all sorts of problems regarding the piston height and therefore clearance issues. So you can certainly skim the head and it will indeed raise the compression ratio to a more modern figure.
We’ve done a calculation and recommend taking off 0.5mm from the cylinder head, make sure a proper engineer does this though, because if the head is machined incorrectly you might as well throw it into the bin, you have been warned!
This will raise the compression ration from 9.5:1 to close to 10.8:1, which is quite an increase. Set the ignition timing to stock and use 95-octane fuel and you’ll certainly feel a difference in performance, possibly a 10% increase, or even more.
Hope that clarifies the process for you.
Q: Hello to you all. Please can you help me with a recent issue regarding my 1984 Suzuki GSX750?
I’ve owned this bike for the best part of my life and it has over 80,000km on the clock, I say over because the speedo broke about a year ago, but that is not why I’m writing.
My wife and myself have been on many trips with no problems, and the bike has always been serviced at the correct intervals. But recently when the bike is in top gear, and after a few kilometers, the bike just dies. I then have to shut off and rev the engine until it begins to run smoothly again.
I’ve fitted a new air filter because the old one is, well, too old, and drained the carbs by undoing the screw under the float bowl. I also fitted new spark plugs, but the problem still remains.
So please can you tell me what to look for next because we still want to keep the bike because we still enjoy it and don’t really have the money to buy one of these new and too complicated expensive machines?
Korbus (and wife).
A: It might be time to have someone, who’s a qualified mechanic, to take off those carbs and give them a thorough overhaul and service. You can still get some genuine parts from Suzuki, if you need them.
However, bikes of this age can generate problems with the vacuum fuel tap. If the diaphragm inside the tap is worn or leaking it will certainly starve the bike of fuel in a manner you’ve mentioned. There are vacuum tap rebuild kits for sale on the Internet, so check that out by taking the tap off, dismantle, clean and inspect it, and also the internal screen filter as well for blockage.
Another thing to easily check is the breather for the petrol tank, if blocked or restricted this will also cause this issue. So take of the fuel cap, strip it down, blow through all the parts with an airline, and see if that helps. Push the bike backwards and forwards to swill the fuel around and make sure you can hear air escaping from the filler cap to make sure it’s functioning correctly.
Go through these recommendations and I’m sure your loved machine will be fine again and give you many more hours in the saddle, with your wife of course.
Q: I was wondering if you guys could shed some light on ignition advancers? I own a very nice 2012 Yamaha R1 and I’ve seen an aftermarket ignition advancer that simply replaces the original one on the end of the crankshaft, and it looks very easy to install.
It’s quite expensive (R2,700) for such a small thing though, but they claim it’ll do ‘wonders’ for performance gains, which sounds a bit dubious if you ask me. But, if it does, I’ll eagerly go out and buy the thing.
So, come on guys, what’s your take on this piece? Is it worth it, or is it just another way of getting money from people, like me, who’re always looking for more power without too much effort?
Can’t wait to see what you have to say?
A: To be honest, with a stock bike that we presume you have, I’d spend the money on a holiday instead. Yamaha do most certainly know what they’re doing with their engine already, and something like this will make little or no noticeable difference.
It may add a tiny bit of midrange, but you won’t notice it when riding. These things are primarily designed for full-race modified engines – you know, cams, pistons, head-job, etc, etc. This sort of heavily modified engine will then run on high-octane race fuel, which you won’t have, and then you’ll see an improvement. And to do all of that will cost you more than the bike’s worth…
Spend it on a night out with the boys instead; you’ll feel a ‘bigger affect’ then.
Q: Hi guys and welcome to 2015, blah, blah blah…
Anyway, over the holidays my 1983 Suzuki GS1000G, the one with the shaft drive, has begun to piss oil all over my left foot!
Now this didn’t bother me too much because I had a new gasket for the stator/alternator cover and decided to have a beer or two and replace it, because the oil seemed to be coming from around that area. So off the cover came and I took off the old gasket and cleaned up the surfaces perfectly before installing the new one, and smeared a thin film of silicone on each side, just to be sure. I also ‘glued in’ the small rubber ‘half moon’ thing where the three wires pass through to the wiring harness, because I was told this can by-pass/leak oil and dump it around my left foot. I then put it all back together and tightened everything up nicely and went out for a ride…
Guess what? Yes, my left foot is still covered in oil – W.T.F! So what have I missed, or need to attend, because it’s really annoying me?
A: Yes Trevor you have missed out one thing from that side of the bike – the o-ring at the end of the starter motor. This leaks oil when old and runs through a hole beneath it and onto your left foot.
Don’t worry though because you won’t have to take off the cover again and use up your new gasket. Just remove the starter motor cover, undo the two bolts that hold it in. undo the feed cable, and wiggle it around until it comes out.
Then go to a bearing shop and match up the o-ring for a new one, do not re-use the old one because it’s too hard and brittle by now. Smear a bit of your silicone around the new o-ring once re-fitted and put it all back together. No more oil leak…