Ignition Problems

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FatsMccarthy
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Ignition Problems

#1

Post by FatsMccarthy »

This is my first time posting here so I beg your pardon if I am doing it incorrectly. I recently bought a 1979 Yamaha xs750. I don’t know when the last time it was ran. Or where the factory air box is. But it wouldn’t start, so I began by squirting it with some starter fluid and it fired up on two occasions for a short period of time but wouldn’t stay running. Next I checked the spark plugs they were black but still sparked. But I ended up replacing them just to be punctual. They are gapped properly and spark. But the bike will not start it just turns and turns. Nextly I noticed the fuel was bad so I drained the old fuel added knew, and cleaned the carbs that were very dirty and green. After reassembling I tried to fire the bike up again. But it still just turned and did not start. Even after hitting it again with starter fluid it would not start. Occasionally it will let out a backfire but that is it. Currently I have the air pods taped 3/4 of the way shut, there is no muffler, and the battery has a strong charge and is less than a year old. Should I be worried about compression or electrical?
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Track T 2411
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Re: Ignition Problems

#2

Post by Track T 2411 »

I'll take a stab at this, having owned a '79 for some time. Mine has always been a bear to start, especially after sitting for long periods. My recommendation would be to start with one 'system' (such as the electrical system, fuel system, etc) at a time and work your way through. There is likely going to be no 'easy' fix.
Like any 40 year old bike, the electrical connectors throughout the system get corroded and start to cause issues. The kill switch is notorious for failure, as well. While the plugs may be fine, the plug wires and caps may not be. Even a poor ground connection can cause issues.
You've stated you had old fuel in the carbs, and drained the tank, but did you clean it thoroughly? The fuel filters are plastic mesh jobs that mount on top of the petcock inside the tank. They suck. The petcocks themselves are often a problem as well.
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