Cold exhaust. Back fires. All in the left cylinder.

[alex f]

Honestly my bike has no issue starting. 2 or 3 kicks and 10-15 seconds choke. Its when i let off throttle that i get the back fire. But at idle is when i get the cold exhaust.

 

[xjwmx]

With 90 lbs it can't be worse if you just throw in some rings. Very inexpensive from a guy in Japan on ebay. Takes about half a day. Ok, two days the first time. Don't even worry about cylinder wear. Then next...fix your carbs if you still have a problem. (since you maintain your carbs are just a-ok).

 

[Bob Kelly III]

Thanks 2M..... yes like that....
Bob..........

 

[SlowMaintenance]

make sure your vacuum ports are plugged or hooked up correctly if so equipped, massive air leak low float height fuel not flowing from the petcock

Can you explain what vacuum ports you're referring to? I'm having similar issues on my bike as well and I'm wondering if that's something I've neglected to do. I'm running a single VM36 carb.

Also wondering if you are supposed to clean brand new carbs. I just bought mine for this build and did not clean it as it looks pretty immaculate, but having the same hard starting and cylinder dropping issues OP mentioned so maybe I ought to.

 

[Twitchknaf]

Like i said I'm new to the xs650 just offering advice based off my experience, that being said on the factory carb rubber boots there might be a vacuum barb that if uncapped would completely kill a cylinder from firing

 

[Bob Kelly III]

on my '83 its the left carb holder that bolts to the head it has a brass tube sticking out of it that should have a line to the petcock vaccuum port at the back of the petcock.... earlier versions do not have the vaccuum petcock so there is no line but if that tube is there it definately needs to be pluged !
I have vaccuum tubes from the carb holders on each side Rt & Lft cylinders.... the right side has a rubber plug over it the left side has a hose connected that goes to the back of the gastanks petcock. those vaccuum ports are there for vaccuum syncronization.... very handy to just plug into and balance the Carbs very accurately....
.....
Slowmaintance : your new carb shouldn't need cleaning but it may well need setting, floats , re jetted and airscrew adjusted to just name a few.... never seen a New carb you could slap on and get away with it, they alwayse need re jetted and set up !
Bob........

 

[alex f]

anybody wana guess where my back fire was comming from? Think i figured it out lol. Looking back I think somebody in this post may have hinted it at.

 

[gggGary]

Missing vacuum cap is VERY popular.

 

[Bob Kelly III]

I'll go with a missing vaccuum Hose completely and it was sucking air !
Bob........

 

[TimeMachine]

Ya I'll guess, a plug lead/ plug ?

 

[TwoManyXS1Bs]

Failed to pay homage to the "Motorcycle Gods"?

 

[Bob Kelly III]

2M That's gott'a be it !!!!!!!
....Bob....

 

[alex f]

Gasket between pipe and head missing. Leaking exhaust lol. Found one and no more back fire.

Still getting a cold exhaust though. Put a new plug in and let it idle for 20 then ran around my parking lot. The right plug was black ish with slight tannish color at the tip. The left was wet but looked brand new. No burning or nothing. Just wet and gassy smelling. The left smokes up real bad with throttle. Am i rich?

 

[TimeMachine]

Cold exhaust, wet newish plug.. I still say you don't have left side spark.. hook a timing light on it ?

 

[Bob Kelly III]

Alex F.... sounds like that one cylinder is completely dead , Timemachine is right check that timing and spark again
if it has good spark and at the right time ( don't assume it is at the right time KNOW it is) then go to the carbs something is amiss in them
.....
Bob.......

 

[TwoManyXS1Bs]

The motorcycle gods meet every third monday evening at the corner of cloud and big dipper.


Bring a virgin...

 

[Twitchknaf]

Lol need to sacrifice my first born to get this rear wheel spacing right

 

[alex f]

Alex F.... sounds like that one cylinder is completely dead , Timemachine is right check that timing and spark again
if it has good spark and at the right time ( don't assume it is at the right time KNOW it is) then go to the carbs something is amiss in them
.....
Bob.......

How do i make sure its at the right time? Because there is for sure a spark. I know this for certian. Also why would it be smoking if its not igniting?