Topic: Exhaust pipes of K0, K1, K2, K3, K4, K5, and K6

[Nanahan_Rider]

hello,

Is there any difference between the exhaust pipes of K0, K1, K2, K3, K4, K5 and K6 models?
If so, could some one in the forum please educate me about the differences.

Thanks for your time.

Regards,
Nanahan

[Shenanigans]

KO had the "HM300" K2-K6 had the more restrictive HM341. Cant remember if the K1s had the 300 or the 341.

[Nanahan_Rider]

Thank you Shenanigans.
Can you please share some links to know more about HM300 type and HM341 type.
I do not have much idea about what these types are and how they are different from each other.

Thanks,
Nanahan

[meloni.racing]

Even the  K1 has the HM300: a very cool 4-4 megaphone with a small DBkiller on the back, lout but very nice performance-wise.

[coolgoose]

Are all HM 341 exhaust pipes same? I read somewhere in this forum that as you go forward from K2 to K6 the number of expansion chambers in the HM341 pipes also increases. Is this true? Also the baffels are same on all the HM 341 pipes? Can someone please post a cutaway diagram for the HM300 and HM341 pipes?

[Johnie]

Yes, I have both and the 69-71 HM300's are louder and sound very nice. My K4 has the HM341's and are quieter. Sometimes that is a good thing. HM300's will cost you more than the HM341's, but both sets are available from Honda, DSS, etc. for over $1,000.

[Kevin D]

My K1 came new with the 300's but they rusted out pretty quick. I got a set of take off 341's with the end caps removed and it sounds pretty nice, in my humble but biased opinion. Certainly louder, but far from too loud.

[scrapvalue]

Are all the baffles the same, or were some years more restrictive then others?

[mycb750k6]

It's actually more complicated than that. There were at least two, maybe three pre-341 pipes. The first had no number indicator followed by one or two HM300s that persisted late into 71. The HM341 went through three generations with the first on the 72s followed by a version with an additional chamber that slowed the bike down so much Honda went back to the original 341 configuration. Thanks EPA for this and so many other great improvements to the bike. Actual facts and dates are in the H-man book if you're really interested. So it's really tough to know what you're getting after market if that's what you're after and yes, it does matter. The back pressure differs significantly.

[Johnie]

Yes, mycb750K6 has it right. I read on this board that if you put 300's where 341's were the stock exhaust you will have to rejet the carbs.

[GammaFlat]

Baffling dilemma!  The baffles are modifiable.  ...just to make things more confusing.  HondaMan also covers the mods in "thoughts of hondaman" in the FAQ.  ...but you won't be sorry if you buy the book.   

[754]

 So mixing and matching 341s, you may end up with inconsistent baffling..

 restrictive.. .. no wonder this K4 feels like a tired dog..

[co425]

1969 and Very early K0 had no number pipes as well. Early 69 have no number pipes with a lotus root baffle.

[mycb750k6]

Taking the end caps off the 341s should make little difference - besides making the pipes ugly as the baffles are internal. The 300s are a different story as taking out the glass packed baffle will be ALMOST strait through like the lotus. I think this was another EPA regulation so you couldn't make the pipes any louder. I've thought of  pulling the 300 baffles out and sticking 341 caps on. What do you think of that idea?

But as H-man points out, breathing is the name of the game. To get a 75-76 to run like the early guys, you'll need to improve breathing all over the place, not just the pipes.

[coolgoose]

What is a lotus root baffle? Any pictures? This is totally new term to me 

[754]

I run 341s with the end caps out. Its throaty and not real quiet.. sounds like a bike..

 Not too worried about tickets with the way it sounds.

[Kevin D]

These are early 341's, I think 3 baffle, with the end caps removed. I counted the spot welds on the back side of the mufflers once upon a time.

If I was going for a show bike I'd lose points for not having the 300's, or even having the end caps, but this bike is a rider, and unless you get close enough to see or have a well trained ear you won't know the diff.

Its throaty and not real quiet.. sounds like a bike..
Not too worried about tickets with the way it sounds.

+1.
The growl from a set of 6500rpm shifts puts a smile on my face every time.

So whats your intention Nanahan_Rider?

[Old Scrambler]

There are numerous other differences.........the first pipes have no numbers and no flattened area near the kickstarter. The 300s seem to appear somewhere in the early months of 1970 but some of the June production K0s and some of the K1s came with unstamped pipes.  All unstamped and 300s have asbestos-wrapped removable baffles attached to the end-caps.  The size of shape of the 'dent' in the pipe near the frame-boss on the left changed for the 341s as did the shape of the kickstart flat area on the right. The K3s and most if not all K4s came with the extra baffle-plate. I defer to the Hondaman for more exact info.......

[fire113]

...I like the sound too but do I need to rejet? feels like the bike has more power with the end caps in.

I run 341s with the end caps out. Its throaty and not real quiet.. sounds like a bike..

 Not too worried about tickets with the way it sounds.

[754]

 Do a plug chop and see how it looks.. if you have 105 mains you can probably go up a bit.

[fire113]

...plugs are looking good but if I put the caps back the bike has much more power.
I am wondering how can I get this sound and full HP ?

[Nanahan_Rider]

Thank you all for your inputs!!

Kevin: - I just want to know more about these models.

Thanks,
Nanahan_Rider

[sandcastcb750]

HM300s are designed for #120 jets and, you can remove the baffles. 1972 and later had 110 and smaller jets, so restrictive HM341s are used.

If you lean the engine out too much it will overheat it (if at least turn your pipes yellow)

NEW HONDA PIPES COST HAVE THE VALUE OF YOUR CB750, AND INCREASE THE VALUE OF THE BIKE BY A FRACTION.

[mycb750k6]

sandcastcb750,
Could you be a little more specific on the cost thing?

[GammaFlat]

NEW HONDA PIPES COST HAVE THE VALUE OF YOUR CB750, AND INCREASE THE VALUE OF THE BIKE BY A FRACTION.

sandcastcb750,
Could you be a little more specific on the cost thing?

I think he means that pipes will cost you a ton of money ($1200-$1400) or half the investment in your bike and only increase the sell price of the bike by a small amount (fraction).