For the last 2 weeks since I've been riding and working on my 1978 XS1100 with 36,000 miles. I've been stumped. I've spent about 40 hours on the XS1100 trying to figure out why the number 4 plug is dark and pretty much dry black. I've replaced the choke valve even. I pulled the exhaust hoping to find the exhaust port plugged. Nope. The decided to once again pull the carbs for the 15th time probably. What I found was the sync tube has slipped into the intake about 1 inch. Would this cause it to want to suck in extra fuel or restrict air? Bernoulli's Principle? A 1/4 inch tube 1 inch into the intake would have what effect? Can't ride it yet and need to bead blast the plug off first to see if this fixed it. It would also cut out and sputter at a 4 to 5 thousand rpm band with some throttle opening up. I think that this is the result of to much fuel gong into the 4 cylinder. Carbs are perfect. Compression is 160 warm. pickups good. fuel visible at 3 mm before joining surface with the float height set at 25mm. The other 3 plugs are clean. Even traded the 1 for 4 plugs wires so ruled this out. This bike was built at Merriam Cycle about 6 years ago and has performed great till now.
If this fixed it then we all could learn from this as it could happen to others. I think my tube pulled out a while back and I pushed it back in without comparing the height against the other 3
If this fixed it then we all could learn from this as it could happen to others. I think my tube pulled out a while back and I pushed it back in without comparing the height against the other 3
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