[cb175guy]

I've got a question, actually, more of a thirst for information.

I've put a very unrestrictive exhaust system on my bike, and it runs very lean. The bike will start, and idle like a champ but putter when I decelerate and the plugs are WHITE indicating lean. I have a removable baffle which I am experimenting with for back-pressure...

Now my question is: can you tune the "lean" out with the mixture screw and needle height or is it a trial and error type of deal with main jets? How should I approach dialing the carbs in?

Also, anyone has anyone had any success with velocity stacks???

I want to know as much info on carb tuning the 175 as possible

 

[jbranson]

First...what part of the plug is white?

Second... the 175 in most cases likes some kind of filter installed. Not ALL 175's, but most.

Third: If the outer ring of the plug is white while running pump gas, yes you are probably lean. A crude test would be to put the choke on about 1/3 the way...see if it acclerates better. If so, you are probably lean on the main jet.

Fourth: if the accleration problem is evident at 1/4 - 3/4 throttle raise the needle one notch (lower the clip one notch).

Fifth: adjusting the idle air mixture screw will not cure the lean condition.

JohnnyB

 

[chrisf]

Assuming the 175 is similar to the CB/CL350, there doesn't seem to be provisions for raising the needle. I've heard they can be shimmed, but I cannot--for the life of me--figure out how this is done. Anyone have an suggestions?

--Cheers, Chris

 

[cb175guy]

quote:Originally posted by jbranson

First...what part of the plug is white?

Second... the 175 in most cases likes some kind of filter installed. Not ALL 175's, but most.

Third: If the outer ring of the plug is white while running pump gas, yes you are probably lean. A crude test would be to put the choke on about 1/3 the way...see if it acclerates better. If so, you are probably lean on the main jet.

Fourth: if the accleration problem is evident at 1/4 - 3/4 throttle raise the needle one notch (lower the clip one notch).

Fifth: adjusting the idle air mixture screw will not cure the lean condition.

JohnnyB

-the tip of the plugs are white

-threw the stock air filters on and it improved a lot...more that I would have thought

-I'll try messing with the choke and needle to see if I can find out if my main jets are too small

-one last thing, how well do these bikes respond to no back pressure in the pipes. I fired it up with no baffle in and the plugs seem to be less white. You were right, these are LOUD with no muffler on them. I can predict with 100% certainty that my neighbors hate me.

 

[jbranson]

Check this current topic on exhaust.
http://www.caferacer.net/forums/topic.asp?TOPIC_ID=7365

Yep sounds like it's a bit lean, but not excessively so. Adding filters can do two things....richen mixture a bit, and/or improve the intake system dynamics...bear in mind the engine was designed to run with some kind of filter in place.

The open exhaust probably changed the "tune" of the pipe....most of the time they will run crappy with open steet pipes. The plugs were probably less white because the engine was running less efficiently (not burning as much of the fuel...so it "appeared" richer).
JohnnyB

 

[parks61]

loud pipes make it easier to be hunted down by both neighbors and our friends in blue. a shrieking red sports car will get a ticket doing "5 over the limit" while a (quiet) gray mini van can often get away with more significant extemitties of velocity. and yes i drive a gray mini van. wish i had a red two-seater though i'd make sure it was really quiet...
-parks

 

[cb175guy]

yeah, by bike has already been to impound once...
I'm already off to a bad start with the boys in blue.

was tuning the carbs right when I first got it. Long story short, a police officer pulled me over a block from my house, I had no license on me (was in my garage), no insurance on me (was in my garage) and no registration (my bad). Cop would not let me walk the bike home with the ticket, full blown impound!! I had ridden the bike less than a mile. wrong place, wrong time.

anyways back to the subject.

Where do you guys find different jets for these carbs, just in case I need one???

 

[jbranson]

I've gotten old Keihin jets from these guys.

http://www.carbparts.com/index.html

A Honda 175 should use Keihin type 393 jets. Sizes go from 60 to 200.

JohnnyB

 

[cb175guy]

I have bumped my main jets to 95's with rubber "velocity stacks" same exhaust as before and still runs a bit lean. plug electrodes are a bit white still.

Keep bumping up main jets until I get into the ball park and fine tune it with needle height??? I have to order more jets, how high should I go when ordering??

 

[jbranson]

Next step will be 98's, but I'd order some 100's too. Can't imagine it needing more than 100's.
So...yes, keep going up on the mains.
JohnnyB

 

[krapfever]

Yeah. Open Branson pipes are LOUD.



JB, do you sell just the Supertrapp caps?

I picked up some universal baffles for mine but find myself too lazy to fab up a means of mounting them.

 

[jbranson]

Krap,
How many do you need and what size? I might have to order some materials..can't remember what stock I have left for those, last time I checked I think I was kind of low on it.
JohnnyB

 

[catboy]

quote:Originally posted by parks61

loud pipes make it easier to be hunted down by both neighbors and our friends in blue. a shrieking red sports car will get a ticket doing "5 over the limit" while a (quiet) gray mini van can often get away with more significant extemitties of velocity. and yes i drive a gray mini van. wish i had a red two-seater though i'd make sure it was really quiet...
-parks

amen brother! my tan minivan is INVISIBLE! ...probably to a fault!

 

[bfd]

I've been getting those jets from the local dealer as well. Sometimes they have them listed as SRS for small round slotted but they are still used in newer carbs.

 

[cb175guy]

102 the magic jet.

nice sound, tan electrodes, crisp acceleration

Thanks for the help ! ! !

My neighbors thank you too......