XS650 w/ VM34s RPMs Spike on Start, Won't Idle

[LeonCrush]

Hey y’all — I’ve got a 1971 XS650 with VM34 carbs. Bike starts, but:

• RPMs spike uncontrollably, even with choke off
• Dies without throttle, won’t idle
• Idle screws are backed out, mixture screws 2 turns out
• Both carbs recently cleaned
• Spark is good, plugs new
• I found a loose vacuum barb on the left intake boot — it spins freely

Could that loose barb be causing the runaway rpm’s? Just want to ride — could I jb weld the barb back in until I can get another?

 

[Jim]

Uncontrolled revs with VM carbs is sometimes caused by the slides being swapped. Try swapping the slides and see what happens.

 

[Signal]

I have seen swapped slides a few times. It causes all sorts of strangeness.
The cutaways should face the air filter.
If the loose barb is threaded try some blue loctite so secure it.

 

[LeonCrush]

Uncontrolled revs with VM carbs is sometimes caused by the slides being swapped. Try swapping the slides and see what happens.

Bingo thank you kind sir, runs like a charm now. just trying to track down my left case leak now.

 

[Jim]

Don't ask how I knew that....