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I have a 1984 Honda GL 1200 standard wing and I am going to put straight pipes on it, however some forums say I will need to upjet the carbs, and others say I will not.

  • Has anyone on this site ever put straight pipes on a GL1200?
  • If so, how did it run on the factory jets?
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2 Answers 2

I'm not much of a motorcycle person but by straight pipes you are referring to the exhaust correct?

If so then if you are planning on going to a higher flow exhaust you probably don't need to change too much on the intake side. Less restriction exhaust frees up power by reducing the power losses from the piston having to push air out. It doesn't actually increase the total CFM of air through your engine (not significantly).

Anytime you actually increase the amount of air going into the engine you need to adjust the fuel to suit the new amount of air (A/F ratio). In your case I don't think it would be necessary. With motorcycles I bet it would be easy to stick something in the exhaust pipe to check the A/F ratio like a Wideband sensor so maybe do that after and check to make sure it is within safe levels.

If "straight pipes" are something else then just disregard this answer.

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Nope, straight pipes are just exhaust pipes without bends. Or actually with the least number of bends possible. –  Juann Strauss Sep 14 '13 at 12:34
    
I think my answer still applies changing a straight pipe to a larger straight pipe isn't going to significantly change the performance of the engine to the point where you have to retune the engine. –  Mike Saull Sep 14 '13 at 20:14
    
Hey, I wasn't arguing. You're right. The most extreme thing that could happen is such a loss of back pressure that the exhaust starts sucking oil through the oil seals and into your exhaust, causing smoke. –  Juann Strauss Sep 15 '13 at 11:49
    
@JuannStrauss Huh? how can the exhaust "suck" anything? Which "oil seals" exactly are you talking about? –  mac Oct 14 '13 at 18:08
    
I am talking about exhaust velocity and how if affects low and mid-range power delivery. –  Juann Strauss Oct 15 '13 at 7:58
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You don't have to upjet your carbs, but you could if you wanted to. Because straight pipes can handle a larger volume of exhaust, you can tweak your carbs to allow more air/fuel into your engine to produce more exhaust. It's part of the fun, but entirely optional.

It's a different story with electronic fuel injection though. EFI engines constantly monitor exhaust gases and readjust the air/fuel mixture and ignition timing to allow for optimal efficiency. An uprated exhaust would cause the EFI to freak out, especially if the catalytic converter was upgraded or removed completely.

None of that applies to carbs however.

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