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Won't rev past 5,000: Solved!
I didn't post this problem when it was still happening, but I searched and read and tried several things from the wealth of information here. I'm posting this so someone with the same problem might also be helped.
The problem: I have a '79 GS750E, bought by me in 1980, stock but for a Dyna III ignition and a one-piece K&N in the stock airbox. I decided to get it back on the road this year. It's been kept inside, but I didn't ride it for a few years. It wouldn't rev past 5,000 on the road in any gear, and I think it was doing it before I stopped riding it. I couldn't tell if it was fuel starvation, or an ignition problem (I had spark at all 4 cylinders, but couldn't tell if it was "weak"). Here's what I did within the last month, none of which solved the problem:
Disassemble and dunk carbs, reassemble with old parts (I know, I know). Set proper float levels. Didn't know to bench synch, but did mercury synch. New spark plugs. Check ignition timing and valve clearance. New gas. Check gas tank screen. Newish battery with full charge.
One (or more) of these things solved the problem. Unfortunately, I did them all at once, so I don't know what did the trick:
Carb kits (didn't know about the o-ring kits), dunk, bench synch, mercury synch. Exchanged 1/4" ID fuel line for 5/16" ID. New intake boots and o-rings.
Voila! My old friend is back! Still needs a few tweaks, but the problem is gone. I'd like to thank Paul Musser's VM carb rebuild document, and anyone else who unknowingly helped me out.
Next up: freshen up the suspension, brakes, and tires, and spend more money than the bike is probably worth. To anybody but me, that is.8-)
The problem: I have a '79 GS750E, bought by me in 1980, stock but for a Dyna III ignition and a one-piece K&N in the stock airbox. I decided to get it back on the road this year. It's been kept inside, but I didn't ride it for a few years. It wouldn't rev past 5,000 on the road in any gear, and I think it was doing it before I stopped riding it. I couldn't tell if it was fuel starvation, or an ignition problem (I had spark at all 4 cylinders, but couldn't tell if it was "weak"). Here's what I did within the last month, none of which solved the problem:
Disassemble and dunk carbs, reassemble with old parts (I know, I know). Set proper float levels. Didn't know to bench synch, but did mercury synch. New spark plugs. Check ignition timing and valve clearance. New gas. Check gas tank screen. Newish battery with full charge.
One (or more) of these things solved the problem. Unfortunately, I did them all at once, so I don't know what did the trick:
Carb kits (didn't know about the o-ring kits), dunk, bench synch, mercury synch. Exchanged 1/4" ID fuel line for 5/16" ID. New intake boots and o-rings.
Voila! My old friend is back! Still needs a few tweaks, but the problem is gone. I'd like to thank Paul Musser's VM carb rebuild document, and anyone else who unknowingly helped me out.
Next up: freshen up the suspension, brakes, and tires, and spend more money than the bike is probably worth. To anybody but me, that is.8-)
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