SimonFordman
XS400 New Member
EDIT: I think I found the issue, the new battery I installed is bad.
For the life of me I cannot figure this out. Sorry for the long read but I feel like I should include everything I did, which is a lot.
I recently replaced the coils on my Yamaha (1977 XS360) because the bike didn't really want to rev above 8,000 rpm, the revs would just level out. It also would slowly die at idle when turning on any of the lights (alternator was feeding 13-14v still) so that also pointed me to the coils. Replaced coils, then it doesn't rev above 5-6000 rpm and it now backfires once it gets there. Put back the old coils, revs up to 7-8000 again then a few minutes later it's backfiring at 5000 rpm. I check the battery because I figured it was a couple years old, tested bad, put in a new one, no change with the issue. Because of this, I reinstalled the new coils I bought. Now I move on to other issues, the carb would drip if I left the petcock on for a few hours with the bike off, the bike would also shut off with any amount of choke, so I figured it was flooding. Took the carbs off, cleaned them (they looked fine), adjusted the float to 26mm from the gasket surface (was set way too high), and the replaced needles and seats. I also replaced the old intake boots/carb holders at this time. Reinstalled everything, bike runs smoother now but still acts like it's hitting a 2-step rev limiter at 5000. I noticed the left cylinder seems to be doing most of the backfiring, I can pull off the spark plug wire at Idle and the rpms barely change. Now I look into the points/timing. Set point gap to .012. Set timing to the LF/RF marks, was a tad off. Also adjusted all the valves, but they weren't far off spec. Also replaced spark plugs. No change. I hooked up a timing light just to see what the spark was doing while I revved the bike in neutral. The light goes out around 5000 rpm, so I look back into ignition. I unhooked the new coils and temporarily connect my old coils again, just twisting all the connections together. The bike then revved right up, no problem, I let off when it touched 10,000 rpm. Now - the tank was off and it was just running from the float bowls, so before I installed the old coils for good, I reconnected the new ones to make sure the bike didn't rev because the fuel was leaning out. The new coils cut out at 5000 like before. I put the old coils on for good and tried to take the bike around the block. In gear it barely ran, popping and sputtering like it had no gas. I got it back to the garage, confirmed fuel flow, got it fired up and now it's not revving past 5000 again. I confirmed voltage to the coils, bypassed wires, no change.
For the life of me I cannot figure this out. Sorry for the long read but I feel like I should include everything I did, which is a lot.
I recently replaced the coils on my Yamaha (1977 XS360) because the bike didn't really want to rev above 8,000 rpm, the revs would just level out. It also would slowly die at idle when turning on any of the lights (alternator was feeding 13-14v still) so that also pointed me to the coils. Replaced coils, then it doesn't rev above 5-6000 rpm and it now backfires once it gets there. Put back the old coils, revs up to 7-8000 again then a few minutes later it's backfiring at 5000 rpm. I check the battery because I figured it was a couple years old, tested bad, put in a new one, no change with the issue. Because of this, I reinstalled the new coils I bought. Now I move on to other issues, the carb would drip if I left the petcock on for a few hours with the bike off, the bike would also shut off with any amount of choke, so I figured it was flooding. Took the carbs off, cleaned them (they looked fine), adjusted the float to 26mm from the gasket surface (was set way too high), and the replaced needles and seats. I also replaced the old intake boots/carb holders at this time. Reinstalled everything, bike runs smoother now but still acts like it's hitting a 2-step rev limiter at 5000. I noticed the left cylinder seems to be doing most of the backfiring, I can pull off the spark plug wire at Idle and the rpms barely change. Now I look into the points/timing. Set point gap to .012. Set timing to the LF/RF marks, was a tad off. Also adjusted all the valves, but they weren't far off spec. Also replaced spark plugs. No change. I hooked up a timing light just to see what the spark was doing while I revved the bike in neutral. The light goes out around 5000 rpm, so I look back into ignition. I unhooked the new coils and temporarily connect my old coils again, just twisting all the connections together. The bike then revved right up, no problem, I let off when it touched 10,000 rpm. Now - the tank was off and it was just running from the float bowls, so before I installed the old coils for good, I reconnected the new ones to make sure the bike didn't rev because the fuel was leaning out. The new coils cut out at 5000 like before. I put the old coils on for good and tried to take the bike around the block. In gear it barely ran, popping and sputtering like it had no gas. I got it back to the garage, confirmed fuel flow, got it fired up and now it's not revving past 5000 again. I confirmed voltage to the coils, bypassed wires, no change.
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