[lcfj888]

Hello everyone. Im sorry if this question has been answered already but I have been searching for a while and have not found a definite answer. I have a 1971 Cb175. I am installing straight pipes soon and would like to know what size jets i will have to run and what else i will have to do to make the bike run properly. The set up will be straight pipes with stock air filters.

 

[J-T]

You haven't found a definitive answer because none exists. Every bike and it's setup is unique and requires some trial and error testing to arrive at the right setup. You will probably need larger main jets but how much larger you will need to determine through a series of plug chops.

This thread is for a different bike and refers to pod filters but the ideas are valid for your project as well. Hope it helps.

http://www.hondatwins.net/forums/63...4-cb400-cv-carbs-pods-how-make-them-work.html

BTW welcome to the group. Got pictures?

 

[66Sprint]

The 175's actually run nicely with straight pipes IF they are of appropriate length........
Just removing the mufflers and running only the headers will decrease performance and cause a "rich" situation...
ONLY your engine can tell you what is correct for it with the way your whole breating system (intake and exhaust) is set-up.....
"Plug chop" testing/readings will be the easiest way to determine what IT needs .....Buy a BOX of plugs.....

 

[lcfj888]

Whats the appropriate length? Also if you guys have run this setup what size main jets did you guys run? I just want to get an idea of what size or sizes i will have to try.

 

[66Sprint]

We aren't deliberately witholding information...... Everything depends on what you install on, and any changes made to your engine.....
Exhaust length is dependant on what RPM range or ranges you are tuning the engine to run best at, and the ID of the pipes, the displacement, and valve sizes (amoungst other factors).....
Exhaust systems are a science and an art unto themselves......

AS an initial "starting point", I WILL recommend you go up one size on the main jetting ( numerically add 2.5 to whatever jets you have originally), but that is just to compensate for modern fuel......
From there, make individual changes and read the plugs......

For the pipe length all I can do is show you what worked on a stockish engine for me....BUT, I was running K&N filters (not shown in pic)...

 

[lcfj888]

Thank you so much for the help!!

 

[lcfj888]

You haven't found a definitive answer because none exists. Every bike and it's setup is unique and requires some trial and error testing to arrive at the right setup. You will probably need larger main jets but how much larger you will need to determine through a series of plug chops.

This thread is for a different bike and refers to pod filters but the ideas are valid for your project as well. Hope it helps.

http://www.hondatwins.net/forums/63...4-cb400-cv-carbs-pods-how-make-them-work.html

BTW welcome to the group. Got pictures?

Thanks!!!

Here she is

 

[Simo]

Nice bike
Those pipes look good. once you've cut them off , be sure to store them safely so you can put them back on once you get sick of doing plug chops and syncing

 

[lcfj888]

Nice bike
Those pipes look good. once you've cut them off , be sure to store them safely so you can put them back on once you get sick of doing plug chops and syncing

Thanks yea the pipes are in excellent condition. I will definitely store them inside my house

 

[lcfj888]

Another quick question would these main jets fit my carbs?

Main Jets 99101-393 Only :: Keihin type Main Jet 9101-393 Select Size - Jet kits for Carburetors

 

[Simo]

Keihin 393's is right but the mains only effect the tune 3/4 throttle to Wot