Xs650 backfires at 2k-3500 rpm on left side

[Jim]

I just put brand new ones in before firing it up

Doesn't matter... fuel fouling can happen to any plug. Try going back to basics... key on, kill switch on... gas to On or Both? Maybe try Reserve?
If the plugs are fouled, take 'em out and dry 'em off... kick it through a half dozen times, reinstall the plugs and try again.

 

[Djfknwoo]

Doesn't matter... fuel fouling can happen to any plug. Try going back to basics... key on, kill switch on... gas to On or Both? Maybe try Reserve?
If the plugs are fouled, take 'em out and dry 'em off... kick it through a half dozen times, reinstall the plugs and try again.

It seems like that was the case I have them drying right now. What is confusing to me is it has all the right stuff now but is basically not able to run without the choke on. I'm going to put the plugs back in after work and try one more time

 

[5twins]

Don't rule out Jim's suggestion of switching to reserve. I've worked on several bikes where their issues turned out to be nothing more than they were running out of gas on the main feed and needed to be switched to reserve. When the main tank is running out, it's not like an on-off switch. Fuel flow will lessen, not stop completely, and this can cause running issues. Your only running with the choke on is a perfect example.

 

[Djfknwoo]

Don't rule out Jim's suggestion of switching to reserve. I've worked on several bikes where their issues turned out to be nothing more than they were running out of gas on the main feed and needed to be switched to reserve. When the main tank is running out, it's not like an on-off switch. Fuel flow will lessen, not stop completely, and this can cause running issues. Your only running with the choke on is a perfect example.

I'll try that today also. The tank sounds like it has quite a but of gas but ill switch it to reserve and see what happenes

 

[Djfknwoo]

Okay so I let the plugs dry out put the petcock in reserve and fired it up. It fired up on choke but had the same issue dies when choke switched off even with a bit of throttle and seems to be starting to foul the plugs again. Only thing I can think I might of done is when I moved the needle clip the springs popped out and I wasn't sure if it went on top of the needle under the white plastic thing or under the needle clip. I put it it on top of the needle under the white plastic was really hard to get the circlip back into place I'm wondering if I have put it in the wrong order resulting in the new issues

 

[5twins]

Yes, that's probably it. You have the needle assembled wrong. The little spring goes under the e-clip, not on top. Also make sure the thick plastic spacer washer is on top of the e-clip.

The way you've got it assembled, with the little spring on top, the needle is sitting way too low (and lean). That's probably why it only runs with the choke on. Here's what the washers on the needle should look like - thick plastic one above the e-clip, regular thin metal one below it .....

 

[Djfknwoo]

Yes, that's probably it. You have the needle assembled wrong. The little spring goes under the e-clip, not on top. Also make sure the thick plastic spacer washer is on top of the e-clip.

View attachment 213616

The way you've got it assembled, with the little spring on top, the needle is sitting way too low (and lean). That's probably why it only runs with the choke on. Here's what the washers on the needle should look like - thick plastic one above the e-clip, regular thin metal one below it .....

View attachment 213617

I did exactly that and she is now idling good. Still sputters a bit when I pull the throttle. Might try to go up one size on the pilot jet to see if that makes a difference

 

[Jim]

I did exactly that and she is now idling good. Still sputters a bit when I pull the throttle. Might try to go up one size on the pilot jet to see if that makes a difference

Try tuning that out with the mix screws first before you go up on the pilots.

 

[5twins]

Yes, that 2.25 turns out recommended setting is just a starting point. From there, you need to fine tune the screws for what your bike likes best. On the couple of sets of '78-'79 carbs I've fooled with, they seem to like about 2 1/2 to 2 5/8 turns out.

 

[Djfknwoo]

Yes, that 2.25 turns out recommended setting is just a starting point. From there, you need to fine tune the screws for what your bike likes best. On the couple of sets of '78-'79 carbs I've fooled with, they seem to like about 2 1/2 to 2 5/8 turns out.

I had them turned out 2.5 all the way to 3.25 turns and it didn't seem to matter. Now the bike has died again and won't start. I'm going to probably just have to take it to someone as I really don't know what I'm missing

 

[Tinker Taylor]

If at first you don't succeed, try, try again. If at last you don't succeed, time to call the specialist! Good luck.
'TT'

 

[Mike Melvin]

Hi

Djfknwoo I'm new to the site I don't claim to be a good mech but reading your post was like reading my own story.​

I have a 79 XS650SE. did everything you have. Mine was right side, after all that I left breather off, started motor and looked into the carbs wile throttling,
I think Tinker Taylor is on the right track. My slide on right side was working but fully, once I replaced it no more Problems.