My buddy has a 1975 RD350 when both spark plugs are on we only get spark to one cylinder.When you pull one the side thats firing off the side that was not running previously will run just fine what could be causing this?
how do you know its not firing? pipe not getting warm? or you have the plug out and you are grounding it and aren't seeing a spark at the tip of the plug with your eyes? doesn't really make sense except for when you are unplugging one plug, more voltage can "jump" the gap on the other plug. got new correct plugs in the bike? fuel is getting to the non-firing cyl in correct quantity?
ps....i love b13 sentras. messed with my fair share of those beauties. got anything done to it?
pipe does not get warm changed out both plugs while I was there and were getting fuel to both cylinders.say if the bike is running with both spark plugs hotted up the #1 cylinder will not fire if you pull the plug wire off of the the #2 cylinder the #1 cylinder will start running just fine.then hook them both back up and one of the two will quit firing.
as for the Sentra it was my little auto-x track slut for a while it's been put back to daily status for now.not much motor wise just a crap load of suspension and brake work.
How is the battery? The alternator might not be putting out and if the battery is weak there won't be enough to fire both plugs under load. It will always take the path of least resistance. Never try and chase an ignition issue without fully charging the battery first. Never assume the battery is good until you charge it and check it under load. It may have a slight static charge that will read as about 12V until you put some draw on it.