Topic: 4 into 4 exhaust options

[rpyles]

Sometime I'll have to bite the bullet and buy a 4 into 4 exhaust system. I have a '70 K0, but I don't really mind if thhe pipes I install are 'correct' or not. What is the difference between a 300 numbered pipe and a 341? Or a no-numbered pipe, for that matter, and would all of these fit a K0? i've noticed that the 341s are less expensive.
Thanks for any help.
Richard

[Raul CB750K1]

Good question, I also want to know that. The HM300 in my bike have removable mufflers. I believe the 341 have different baffles and also they cannot be removed, but I'm not positive about this.

Raul

[Bob Wessner]

As far as I know, the unmarked pipes came first on the earliest 750's but I'm not sure when they stopped using them. My K0, frame #1017898, has them, well at least 3 of them, the #1 was rusted out. However, that said, I can't be sure because of other mods to my bike that they were orig. or put on at some time by a previous owner.I believe the 300 was less restrictive and, as you mentioned, the baffles were removeable. The 341's were used on the K2, more restrictive, the baffles were not removeable and would likely require carb modifications everything else being equal.

[Kevin D]

My 71 K1 - 106xxxx is fitted with 341 pipes with the baffles removed. The originals rusted out, if I remember, in 74 and I bought these 341 pipes second hand for $100 from a K2 owner who had fitted a 4-1 aftermarket header. The aftermarket 4-1 was a very hot item, and the 4-4 was not! The baffles were already removed when I got the pipes, and there remains a small bolt hole on the inside of the muffler at the tip of the cone where the baffles were bolted in, I am sure. The bike still runs good, sounds great. Yes, it runs rich, someday I will rejet. I have 120 main (standard), 38 slow (40 was std), needles have not been reset, foam air filter.

[Jonesy]

Good question, I also want to know that. The HM300 in my bike have removable mufflers. I believe the 341 have different baffles and also they cannot be removed, but I'm not positive about this.

HM 300 pipes had a long, perforated tubular baffle that was held in the end with a bolt. You essentially had an expansion chamber and baffle for each pipe and the pipes were interconnected at the rear for less net backpressure. The bikes with these pipes were usually jetted with 120 mains.

The HM 341 pipes were far different. There are a series of integral welded baffles inside the muffler portion of the pipe. All that bolted in the end was a diffuser which was basically decorative. The pipes with these were jetted with 110's and later 105's.

[rpyles]

So I could use the cheaper 341s if I rejetted to 110 of 105, depending on how it runs?
Richard

[eldar]

Well I may be off here but if you have LESS backpressure from no baffles or whatnot, you will run leaner.
THe more pressure you have, the richer you will run.

[Jonesy]

So I could use the cheaper 341s if I rejetted to 110 of 105, depending on how it runs?

According to the Honda books, you should be able to. You will also have to drop the clip on the jet needle down to the 4th notch to keep with factory setup.

Well I may be off here but if you have LESS backpressure from no baffles or whatnot, you will run leaner.
THe more pressure you have, the richer you will run.

You're correct. With the 300's (less backpressure) it runs leaner, hence the bigger main jet. With the 341's (more backpressure) you can size it down.

[pbelanger]

Hi all,

Here's what I found on another bulletin board.

http://www.greenspun.com/bboard/q-and-a-fetch-msg.tcl?msg_id=00BWbA

You can also make a search on this other board, using HM300 or HM341. I remember reading a lot of this issue. On my part, I have a set of HM341s on my 1976 CB750K. I can assure you that the baffles are indeed removable; there is a bolt on the side to maintain them. When I bought the bike a year ago, I noticed that the previous owner fitted something in there, ressembling more like 6 little metal tubes held together. I figure it was only for a "visual" aspect e.g., not to be too easily noticed by a police officer because, really, my bike is LOUD, almsot like 4 into 4 straight pipes.

Which is the reason why I bought a set of Mac 4 into 1 that I'm going to install during the week end, waiting for that affordable used set of HM341 to come along.

Regards,

Paul

[Tim.]

Hi all,

Here's what I found on another bulletin board...

Just so you know - that 'other' bulletin board is the predecessor to this board - many of the original members are still around

[Raul CB750K1]

Ummmm....  www.greenspun.com, I was thinking why that domain name sounded familiar...

[Bob Wessner]

Interesting about the removeable baffles on the 341 pipes. I had to replace an unmarked pipe that was rusted through and picked-up a 341 pipe, almost new, on eBay until I figure out a reasonable replacement for the unmarked. It's baffle "appeared" to be secured by a bolt on the inner side of the cone rim at the rear, but on closer examination it is welded under the bolt.

[Jonesy]

The 341 pipe does have a removable endpiece, but it's just a small diffuser- not a baffle.

[eldar]

Hey just to discredit that jpeg of your jonespd .  My 78 750K never had that tube between the exhaust mufflers. There was no connection anywhere between mufflers. But then like I said, I have a 78 and there were many changes because of the emissions changes.

[jsaab2748]

Bikes that came new with 341 pipes from the factory, as I understand it, had the diffuser's mounting bolt welded in, so the bolt broke off when you tried to remove it. Newer 341 factory replacements still have the bolted in diffusers, but the bolts are no longer welded. I have a set of these on my bike now. Sounds like Bob has a 341 original, very rare these days, as most have rusted out years ago...