For carb service help, go here:www.amckayltd.com/carbguide.pdf
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Xs650 backfires at 2k-3500 rpm on left side
- Thread starter Djfknwoo
- Start date
Djfknwoo
XS650 Enthusiast
Alright I little update on the bike situation I cleaned the carbs (bs38s) with carb cleaner and compressed air checked the diaphragms and they are in great condition. I had to change a rubber washer on one of the jets (I'll attach a photo of that) I also changed the spark plugs. The bike now idles fine on both sides but has a bit of a sputter between 2-3k rpm anything before that runs great everything after that runs great pulls hard. I'm thinking I just have a bit of fine tuning in the carbs left or it might just need another deep cleaning.
New issue that seems to arise now and then is when the bike warms up and I've ridden it for a while the clutch seems to stick. I can find neutral easy but even then the bike seems to still be engaged and slows down. It doesn't cause me to stall at all but just curious as to what that may be
New issue that seems to arise now and then is when the bike warms up and I've ridden it for a while the clutch seems to stick. I can find neutral easy but even then the bike seems to still be engaged and slows down. It doesn't cause me to stall at all but just curious as to what that may be
Clutch adjustment needed. As cases warm up and expand, clutch plate separation diminishes. On my ‘76 I often do a quick adjust on the lever after I’ve warmed it up well, then back it off when cold.
what slot are the needle clips in.
What air filters are you using?
What air filters are you using?
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Djfknwoo
XS650 Enthusiast
I'd have to check the needle placement when I get back home. They are bs38s from a 1979 xs650 special and I'm using these filters here.
Attachments
Those filters may be responsible for your minor glitches. A K&N type pleated pod doesn't play nice with CV carbs. Straight foam UNIs work best. Take a test ride with the filters removed to see if they are the issue. If you switch to UNIs, get the 4" long ones with the open ends, not the shorter ones with the capped ends.
The open ended ones flow through the sides and ends, the capped ones only flow through the sides. The capped ones really don't flow much, if any, more than stock. I know this to be true because a local guy put them on his '78 and we didn't have to re-jet at all.
The open ended ones flow through the sides and ends, the capped ones only flow through the sides. The capped ones really don't flow much, if any, more than stock. I know this to be true because a local guy put them on his '78 and we didn't have to re-jet at all.
Djfknwoo
XS650 Enthusiast
I took the filters off and it seemed to run worse lt wont let me attach a video. Haven't checked the needle hight on the bike but I thought the 79' bs38s don't have an adjustable needle?
Yes they do, but you’ll need a special pair of long nose circlip pliers to remove the plastic hold down disc inside the slide. Got mine on Amazon for reasonably cheap and quick.
Djfknwoo
XS650 Enthusiast
Also I can pull the left side spark plug wire off and the bike will continue to run but if I leave the left on and pull the right spark plug wire the bike will die also the right exhaust pipe is definitely hotter than the left
Did you remove and check/clean the pilot jets?
valves set, spark strong?
Djfknwoo
XS650 Enthusiast
I did yeah fully removed and cleaned with carb cleaner and compressed air. I double checked with a light to make sure all the holes were good.
I've been messing with the adjustment screws on both carbs the right is the recommended 2.5 turns but the left seems to backfire immediately if it's anything less that 2 right now it seemed to run a tad bit better at 3.5 turns out but still isn't running its best.
I am going to order those pliers and see what my needle is set to but im not sure why the right side is running quite well but the left isn't.
Before you order the pliers, remove the diaphragms and make sure they are the type that have the clip in them. If they are an earlier generation BS38 they may not be needed.
Post up some pics of the engine, carbs etc. someone might see something that will help you out.
Sounds like the pilot circuit in the left carb is still blocked or partially blocked. Your carb sync may be off as well (left running slower than the right). There's more to cleaning the pilot circuit than just the jet. You have to clear the passageway from the jet to the main bore in the carb.
confirm the float bowl choke orifice is open?
Spray carb cleaner on the throttle shafts and about the intake manifolds while it's running.
Spray carb cleaner on the throttle shafts and about the intake manifolds while it's running.
Djfknwoo
XS650 Enthusiast
I'll take a bunch of pics this weekend of thr carbs off the engine and everything inbetween.
Djfknwoo
XS650 Enthusiast
I'm out of carb cleaner but I will grab some and some starting spray and do that test this weekend here also. It dies as soon as I apply the choke. I start it with no choke every day (10°-15° in Vancouver Canada) and it starts up well.
It should need choke for a cold start.
When it's running on just one side, shut down pull the dead cylinder plug, what do you see, show a pic?
did you replace the float needle valves? it's pretty much a must do on old BS38's, the steel on brass seats tend to leak with age.
do a HOT water float dip, leak test. It's another old carbs issue especially up here in the great white north, brass floats fine cracking/ leaks.
Djfknwoo
XS650 Enthusiast
I have replaced the floats and the needles with brand new ones from xs650direct I'll send a pic of the left spark plug tonight (I changed them out last week)
