I just bought the bike. 1981 Yamaha XJ750 SECA. It was running a little poorly on the way home (I expected that) choking a little and stalling now and again, with the occasional backfire. I looked at the spark plugs and they looked very dirty, very black and sooty. SO I replaced them and it seemed to run better... for a little while until the same problem occurred stalling as I decelerated. I then took off the carburetor caps to see if that was a mess... looked fine and I sprayed a little carb and choke cleaner in there just in case. Ever since then I can not get it started at all. I am sure I put it back together too… no extra pieces!
It turns over... no visible spark when I checked that. Every now and again it sounds like it wants to go but doesn't. The thing that really gets me is the when I turn of the key, then back on after trying to start, it backfires... just by turning the key to the on position. Scares the crap outa me! There is gas, gas is on, getting a little frustrated.
I am new at this whole motorcycle thing and all I really want to do is learn to ride.. with that I need to get it running. Any suggestions??? Please?
you said there was no spark, Unscrew the plugs and the stick em back in the wires and ground the plugs to the head( tape them to the head so you can see the gap and the try starting it, If you don't see spark, then something is wrond witht the ignition system, points, coils etc.
Gas may be on but is it getting to the carbs? you might have a vacuum leak in the fuel lines from the petcock(fuel valve) to the carbs. If they are old and hard you may have cracked them when you removed the carbs, it happened to me. Try replacing those, they are cheap. If you can, find some clear fuel line, helps troubleshoot later issued.
Depending on how mechanically inclined you are your best bet might be to take it to a shop if you get too frustrated. It's most likely something small that you may overlook but a seasoned mechanic might look for.
Something disturbing bout your post ... did you take off the TOPS of the carbs and spray crap in there, or did you take the Float bowls off?
Your problem - if it's weak spark, is probably an electrical (resistance) problem w/ the wires or plug caps. I'd suggest 2 things.
1 Patience. You want to get riding, of course, but if you don't do this right, it could lead to big problems or some kind of failure when you are out on the road.
2 Get a manual and learn about your bike, especially the carbs.
I have the manual for your bike. If you would like the resistance numbers (so that you can test the caps and wires - if you have a multimeter) I will post them here. If you don't have a multimeter, and your problem is indeed weak spark, you can get a multimeter (and a manual) and do the electrical tests, or you can take it to a competant shop and have them do the tests.
Good luck!
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