I have a miss

[Lonerbtw]

  Hi guys. need some help. I have a miss. Soudns like left side backfire at idle. Changed plugs, have had the carbs off and cleaned awhile back. That was another problem, low speed jets pluged. Fixed that. Then petcock went bad and hydrolocked it. Luckily that was about the same time that I was reading alot of posts about that problem. Blew the gas out,changed oil and rebuilt petcock. Shortly after that it started missing. Thought that I might have tweeked a valve. But have good and equal compression on all.
  Yesterday took a can of carb cleaner and sprayed around carbs,boots and lines. When I got near the line comming off the back carb on left side the rpm,s went up about 500 over idel. Could this be my backfire? If so how much trouble is it to change lines. Please tell me that I dont have to pull the carbs again.
  Any other ideas ?
  Loner

[DFragn]

If your talking about #6 vac line [left rear] that is to the petcock. If it's cracked or split near the intake nipple a quick short term fix [if there's enough slack] would be to cut the bad 1/2" or so and reattach.

You'll really want to replace that line and most likely all the others.

[CajunRider]

That would definitely cause a problem.  Might be a good idea to replace all vacuum hoses (all those little 1/8 inch hoses). 

You can do it without taking the carbs out.  If you have a good needle nose with a bend in them... you can do it without taking the tank off. 

Definitely change those lines before spending time on anything else. Or... it may be a good time for de-smogging... if you're into that thing. 

[Lonerbtw]

  Thanks for the input. How many lines are there? If #6 was leaking would it not open the petcock?

[Ferris Leets]

It takes very little vacuum to open the petcock .  Even with a leak it will flow.

[Lonerbtw]

  Thanks DFragn . Cut the line back and stoped the miss. replaced that line and runs smooth again. How many lines are there that I need to replace?  And thanks to all that posted on this.
  Loner

[shortleg]

 There are only 3 lines the rest just have plugs.
   One fron each side and the one on #6 for pitcock.
                Shortleg[Dave]