roscoe_bass Posted May 15, 2008 Share Posted May 15, 2008 I just bought a 1978 Yamaha XS400. I'm completely new to motorcycles. It only has 4400 miles on it, but it's running a little rough. The guy I bought it off of said it was running a little rough when he brought it to me. (He actually rode it down to our meeting). It had been sitting awhile because he had bought a new bike. It sometimes dies while idling. I took it out the other day for my first ride beyond a mile. It seemed fine for a while. When I got on the highway, after about 1/2 mile at 60 mph it started to lose power. It seemed doggish. When I was able to pull off in a parking lot, as soon as I got off the throttle it died. It didn't want to start up again. I sat there for about 5 minutes, and then it took off again. I rode it straight home, and it died as soon as I pulled into the driveway. Again, it didn't want to start up. So I parked it. Tried it the next night. This time I just drove on country road at about 40-50 mph. Everytime I would go to stop at an intersection, if I would let off of the throttle it would die and not want to restart. There's a strong smell of gas, too. Also, the tank has a little rust in it. Any advice? I thought I would start w/ cleaning the tank out, and then cleaning the carb, but I'm a beginner so any advice would be welcome. Link to comment Share on other sites More sharing options...
bralkan Posted May 15, 2008 Share Posted May 15, 2008 I just bought a 1978 Yamaha XS400. I'm completely new to motorcycles. It only has 4400 miles on it, but it's running a little rough. The guy I bought it off of said it was running a little rough when he brought it to me. (He actually rode it down to our meeting). It had been sitting awhile because he had bought a new bike. It sometimes dies while idling. I took it out the other day for my first ride beyond a mile. It seemed fine for a while. When I got on the highway, after about 1/2 mile at 60 mph it started to lose power. It seemed doggish. When I was able to pull off in a parking lot, as soon as I got off the throttle it died. It didn't want to start up again. I sat there for about 5 minutes, and then it took off again. I rode it straight home, and it died as soon as I pulled into the driveway. Again, it didn't want to start up. So I parked it. Tried it the next night. This time I just drove on country road at about 40-50 mph. Everytime I would go to stop at an intersection, if I would let off of the throttle it would die and not want to restart. There's a strong smell of gas, too. Also, the tank has a little rust in it. Any advice? I thought I would start w/ cleaning the tank out, and then cleaning the carb, but I'm a beginner so any advice would be welcome. Get an in-line fuel filter. It sounds like there may be some debris in you float bowls or the jets are gummed a bit. Do you have any gas going into your air filters? If you get fuel going into your air filters, try tapping the float bowls and seeing how it does. How do the plugs look? Is it charging? Lights stay bright, etc? If you have a multimeter, make sure you have ~14.5 volts across the terminals at about 3k RPMS. Link to comment Share on other sites More sharing options...
roscoe_bass Posted May 15, 2008 Author Share Posted May 15, 2008 Where can I get an in-line fuel filter? Link to comment Share on other sites More sharing options...
bralkan Posted May 15, 2008 Share Posted May 15, 2008 Where can I get an in-line fuel filter? any bike shop should have them. they are about $3 USD. I prefer the clear filters, pancake style. It should keep the rust in the tank out of the carbs. Link to comment Share on other sites More sharing options...
XSwheels Posted May 15, 2008 Share Posted May 15, 2008 On these '70's XS360/400's a no charge condition is common. Your pilot jets could be plugged too. Link to comment Share on other sites More sharing options...
bralkan Posted May 15, 2008 Share Posted May 15, 2008 On these '70's XS360/400's a no charge condition is common. Your pilot jets could be plugged too. When I got my bike I could get on it for a bit of a ways and then it would die. I let it sit, it would crank back up to rinse and repeat. It was a charging problem - replaced the voltage regulator and it was fine. Like I said, check for ~14.5volts across the terminals. With yours, your regulator will be mechanical and you may be able to adjust it. Link to comment Share on other sites More sharing options...
jrhendryx Posted May 17, 2008 Share Posted May 17, 2008 When I got my bike I could get on it for a bit of a ways and then it would die. I let it sit, it would crank back up to rinse and repeat. It was a charging problem - replaced the voltage regulator and it was fine. Like I said, check for ~14.5volts across the terminals. With yours, your regulator will be mechanical and you may be able to adjust it. also, your petcocks have a tiny (but not that great) filter built in most likely. if you pull the back cover off the petcock, you might be able to clear out any rust that has built up in there. thats what I do whenever mine starts trying to run rough/backfire. good luck Link to comment Share on other sites More sharing options...
Jonesy_10 Posted June 2, 2008 Share Posted June 2, 2008 also, your petcocks have a tiny (but not that great) filter built in most likely. if you pull the back cover off the petcock, you might be able to clear out any rust that has built up in there. thats what I do whenever mine starts trying to run rough/backfire. good luck On the note of the petcock, call up your local Yamaha dealer. There was a recall on the 78/79 Yamaha XS400 on the petcock, I called my dealer the other day and they're just giving me one for free. This is a small shop that I know the owners of, so I don't know if your shop would do the same. Link to comment Share on other sites More sharing options...
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