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Howdy, all!
I just recently got my '79 GS1000L going (last weekend, in fact), and one of the first things I did was synch the carbs with a set of mercury column manometers. I just bought the bike last fall from one of those types who *thinks* he's the world's greatest mechanic. Well, turns out that 1 & 2 were way low, and 3 & 4 were way high on the scale. No wonder it ran rough! Couldn't get them perfect - the mercury columns would all surge and decline at different times, but I got it running a whole lot smoother than it did. Also got rid of a loud "clattering" noise that seemed to result from one or two cylinders trying to over-ride the others.
Then I developed a gas leak. Turns out the sharp end of the choke wire had poked a hole in my BRAND NEW clear-plastic fuel line near where it goes into the carburetor. Cut 1/2 inch off the damaged end, bent the end of the choke wire away from the fuel line, and that fixed that. Of course, I then proceeded to lay the bike on its right-hand side in my garage while trying to rock it up on the center stand and I lost my balance. No obvious damage other than some smudges where gas leaked out onto the top of the gas tank from the fill-neck vent, and those polished out OK.
The next couple of days were cold, and the bike had never started very well below 50 degrees since I got it, but I thought I'd see how well the bike would start now that the carbs were synchronized. Ended up running the battery down trying. Checked the plugs and found out that they were all sooty (one was also slightly oily, but the previous owner said it had a valve-seal leak on that cylinder). The gaps were around .040" and last I knew the spec was around .025" with a points-type ignition. Closed the gaps down to .025", checked for spark - all good, fat, blue sparks. The engine started, but now it was puking gas out through the overflow pipes on #2, #3, and #4 carbs! This stopped with a bit of thumping on the carbs, though (probably somehow stuck the float needles when I laid the bike over). No obvious smell of gas in the oil, either.
Problem is, the clattering noise is back. It goes away when I rev the engine, but comes back around 1500-2000RPM's. It also pops and backfires when I let up on the throttle after revving it up. #1 and #4 cylinders' exhaust pipes barely get warm, even by the manifold, while #2 and #3 are too hot to touch at the same time. I have to pull the choke partway out to keep the bike running, and while I had been able to get a reasonably smooth 1000RPM idle right after I synched the carbs, now it dies if I push the choke in enough to get it to idle down to that point, even when fully warmed up (except for #1 and #4 cylinder, as I mentioned). I even checked for leaks in the rubber manifold seals by spraying starter fluid near them. No chance in engine function. The ambient temperature was around 45 degrees Fahrenheit.
What should I do next next? My Haynes manual says don't touch the idle air screws and whatever that one is at the bottom of the carb (Mikuni flatslides, BTW) because they're close-toleranced for emissions reasons. Well, if it would help my bike to run better, bugger the emissions standards (Michigan doesn't check them except perhaps in some metropolitan areas anyway). Should I re-synch the carbs? adjust the screws? Get hotter plugs? Any or none of these? HELLLLLP!
I just recently got my '79 GS1000L going (last weekend, in fact), and one of the first things I did was synch the carbs with a set of mercury column manometers. I just bought the bike last fall from one of those types who *thinks* he's the world's greatest mechanic. Well, turns out that 1 & 2 were way low, and 3 & 4 were way high on the scale. No wonder it ran rough! Couldn't get them perfect - the mercury columns would all surge and decline at different times, but I got it running a whole lot smoother than it did. Also got rid of a loud "clattering" noise that seemed to result from one or two cylinders trying to over-ride the others.
Then I developed a gas leak. Turns out the sharp end of the choke wire had poked a hole in my BRAND NEW clear-plastic fuel line near where it goes into the carburetor. Cut 1/2 inch off the damaged end, bent the end of the choke wire away from the fuel line, and that fixed that. Of course, I then proceeded to lay the bike on its right-hand side in my garage while trying to rock it up on the center stand and I lost my balance. No obvious damage other than some smudges where gas leaked out onto the top of the gas tank from the fill-neck vent, and those polished out OK.
The next couple of days were cold, and the bike had never started very well below 50 degrees since I got it, but I thought I'd see how well the bike would start now that the carbs were synchronized. Ended up running the battery down trying. Checked the plugs and found out that they were all sooty (one was also slightly oily, but the previous owner said it had a valve-seal leak on that cylinder). The gaps were around .040" and last I knew the spec was around .025" with a points-type ignition. Closed the gaps down to .025", checked for spark - all good, fat, blue sparks. The engine started, but now it was puking gas out through the overflow pipes on #2, #3, and #4 carbs! This stopped with a bit of thumping on the carbs, though (probably somehow stuck the float needles when I laid the bike over). No obvious smell of gas in the oil, either.
Problem is, the clattering noise is back. It goes away when I rev the engine, but comes back around 1500-2000RPM's. It also pops and backfires when I let up on the throttle after revving it up. #1 and #4 cylinders' exhaust pipes barely get warm, even by the manifold, while #2 and #3 are too hot to touch at the same time. I have to pull the choke partway out to keep the bike running, and while I had been able to get a reasonably smooth 1000RPM idle right after I synched the carbs, now it dies if I push the choke in enough to get it to idle down to that point, even when fully warmed up (except for #1 and #4 cylinder, as I mentioned). I even checked for leaks in the rubber manifold seals by spraying starter fluid near them. No chance in engine function. The ambient temperature was around 45 degrees Fahrenheit.
What should I do next next? My Haynes manual says don't touch the idle air screws and whatever that one is at the bottom of the carb (Mikuni flatslides, BTW) because they're close-toleranced for emissions reasons. Well, if it would help my bike to run better, bugger the emissions standards (Michigan doesn't check them except perhaps in some metropolitan areas anyway). Should I re-synch the carbs? adjust the screws? Get hotter plugs? Any or none of these? HELLLLLP!
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