lost of power in Cylinder after 10 min at 100km/hr

[murphy92]

Hey guys! i just purchased a custom yamaha xs 650 chopper. unfortunately my xs 400 got run over so i joined the 650 crew! anyways i took it out on the highway and as soon as i was up to 100km/hr for maybe 10 minutes, the bike would lose power in one cylinder. some time both and sometimes it would change cylinders. it seems like its running really hot and i thought maybe it could be the points not being upgraded. the bike runs fine in the city. alittle bit of backfire due to the straight pipes but i need to sync the carbs yet still. it seems to not be buring the fuel proper . but Any ideas why only at this speed it would shut a cyclinder down. sparks are brand new and have good burns on them. carbs have been clean inside and out.

 

[GLJ]

Check your fuel tank vent.

 

[murphy92]

The tank has been swapped for a sportster tank

 

[GLJ]

All tanks have a vent. Make sure it's not partially plugged. Easy way to test is to crack the cap open when it's acting up. A lot of bikes not just 650 Yamaha's have had the same symptoms. It happened to me once on my Hodaka. Ran great in the woods, on roads it would start missing after a few miles.

 

[murphy92]

Okay I'll give that a try! Yeah I believe the tank was purchased off TC bros. So it would just be the gas cap that is vented right?

 

[jetmechmarty]

So it would just be the gas cap that is vented right?

Yep!

 

[murphy92]

Okay great! hope this works! I started buying stuff for the charging system. Cause I thought the points were shot. So I have a new condenser on the way. Haha thanks guys I let you know how it clogged it is

 

[murphy92]

Capacitor*

 

[murphy92]

But this does make sense now, cause I did notice my fuel line coming out of the tank would drop so it was half fuel and air in the line.

 

[GLJ]

Something that has caused problems. Very cheap and easy to rule out.

 

[Paul Sutton]

Capacitor or Condensor?? Either term is correct, just depends on where you are. A bit like Accumulator and Battery. If the vent is fine then just check your fuel line is not too close to the cylinders and getting hot enough to form a vapor lock - This happened to me once upon a time.

 

[murphy92]

Would an online fuel filter being clogged cause this too?

 

[murphy92]

Here's kinda what I'm working with. I didn't check the inline fuel filter when I cleaned the carbs. So that could be an issue. And I'm not sure how to check how the tank cap is clogged

 

[GLJ]

Would an online fuel filter being clogged cause this too?

Yes that could also. To check the tank vent just loosen the cap when it acts up. I know pics can be deceiving but your inline filter doesn't look so good. I had mine ( 2 of them ) plug up on my 650, when that happened it would run on one and then die. Replace filters, crack cap. Easy cheap things to do.

 

[Jim]

And I'm not sure how to check how the tank cap is clogged

Another way is to place the fuel line in a gas can and turn the fuel on. Should get a steady stream pouring out. If it slows to a dribble, remove the cap and see if it picks up again.
If it starts out a dribble and doesn't improve with the cap off, most likely clogged filter.

 

[X77S]

The fix is easy for a clogged cap as well. Just grab a new cap!

 

[Paul Sutton]

Your fuel line looks very direct so should be fine regarding vapor locking. Try the suggestions above.

 

[murphy92]

Yeah the fuel line is clogged beyond belief, Ill clean Tonight and check the flow of fuel and let you guys know. Thanks so much for the help! Really appreciate it

 

[Paul Sutton]

You may need to waste a few liters of petrol and give the tank a thorough rinse to remove any particulate material. When you look in the tank is it rusty, slightly rusty, shiny, full of dust or perhaps a peeling tank liner?

 

[kopcicle]

Not directly related but the bike is new to you .
Adjust the valves.