QuestionI have a Honda magna that i have just recently purchased the bike starts fine but as the bike runs the tachometer begins to jump and act sporadic and the bike does not idle correctly. It seems like when the fan comes on and the more lights you turn and the more load you put on the bike the better it runs.Any help would be much appreciated
AnswerI realy have no experience with Magnas, but I will make a few general suggestions.
Check the ground connections. An intermittent or poor ground connection can cause all kinds of electrical problems.
Is your engine rubber mounted? If it is make sure that the ground connection from the engine block to the frame or battery is in good condition. Even if the grounds look OK it doesn't hurt to loosen their bolts, wiggle the lugs around and re-tighten the bolts - this can break up dirt or oxide and re-make the connection.
Does the bike have any electrical accessories? If it does you might try disconnecting them one at a time to see if the problem goes away.
If your ignition system has a mechanical timing advance it could be hanging up. If it is easy to get at you could inspect it and clean & re-lube it. Information on how to do this should be in yout shop manual.
If you don't have a shop manual you should get one - your bike is an antique and you will have a hard time finding a shop that will work on it. The sad fact is that a lot of the mechanics working now are too young to remember bikes this old and aren't interested in learning about them so that they can do a proper job since yours may be the only one they see this year. This means that you will have to do most of your own work, and working on a bike without a good shop manual is just not worth the headaches. (My bikes are from the same era - that's why I fix them myself.)
I recommend that you get two manuals - a Factory Shop Manual and a Haynes or Clymer. That way when you don't understand the explanation in one you will probably figure it out when you have read the other too. If you spend some time on Google you might even find a factory manual available for free download.
The best piece of advice I can give you is to spend some time on Google and find a good online usergroup (discusson forum) that caters to the Sabre/Magna family of bikes. Forums are usually free to join and the people there are willing to share their knowledge & experience about keeping their bikes on the road.
