Topic: HM300 and HM341 Mufflers

[ZTatZAU]

I thought it best to ask this question here rather than my ongoing 1971 CB750 K1 resurrection thread.

I need to replace my current 4 into 2 unmuffled aftermarket exhaust as the header pipes are quite rusty with some pinholes at the bends just below the exhaust ports.

Of course, I'd love to find a nice, affordable set of OEM HM300 pipes but don't really see that happening.  I do see individual HM341 pipes here and there in varying condition and I've read a lot here about the repo's from Busso in Italy which as I understand are all copies of the HM341 exhaust.

My questions are:

Other than not being "correct" for a K1, is there any problem installing HM341 pipes on a K1?  I've read the HM341's are more restrictive above 5K rpms but are the HM341 style, fitment and attach points all the same as the HM300 systems?

I don't see my K1 project as a full-blown restoration to original condition, mostly because the OEM paint job is long gone and what it would take to duplicate the original candy red paint.  I'd just like to wind up with my 750 roadworthy and reliable again and looking nice; if not OEM perfect.

Thanks for any info/advice on how to proceed.
ZT

[ekpent]

The attachment points are the same for the HM330's and 341's so no worries there. Busso I think also does no number pipes which some like the best.

[ZTatZAU]

The attachment points are the same for the HM330's and 341's so no worries there. Busso I think also does no number pipes which some like the best.

Thanks ekpent!  I assume your HM330 was just a typo and you meant to write HM300.  I also assume the "no number pipes" from Busso are what I see referred to here as "No-No's".  Is that correct.

Other than number stamps, or lack thereof, do the HM341 pipes and shields, etc., look exactly like the HM300 pipes?

Thanks!  ZT

[BenelliSEI]

The end baffles are different, but lots of early bikes have replacements using HM341’s. They fit and work just fine. They are significantly quieter than HM300’s.

[ZTatZAU]

The end baffles are different, but lots of early bikes have replacements using HM341’s. They fit and work just fine. They are significantly quieter than HM300’s.

Thanks (John?) BenelliSEI,
I'm still trying to connect names with screennames around here.
ZT

[BenelliSEI]

Yes…. John D.

[PeWe]

Yamiya No Numbers are like the HM300 with same baffles (diffusers).
Better flow and sound than restrictive HM341 style. 
Need richer jetted carbs too.
My K2 has Yamiya no numbers.
Air screws 1 turn out
Pilots 40
Needles 4th from top
Main jets 115

A friend  with HM341 could not run that jetting, too rich.
Had to set needles middle (3)
Main jets 105



DSS had Yamiya no number style not that long ago. They might get new sets?

Well worth too look for.
Possible with tuned engine too. I have used them with 836 and 1000cc, ported head, hot cam etc.

[newday777]

There's still a few days if you are ready to get the Busso no numbers, no stamped 300 set for 850€ which was $940 on Monday when I paid for mine. You can pay half now and the other half when the run is made and ready to ship(@August)
That is @ 1/2 price of what you can get them already made in the 341 or 300 with BS341 or BS300 stamped on them.
If you are ready now, send an email to Busso at the group buy address in the screenshot.

[Phoenix]

I have a 71 built in August.  It came with 341 pipes and 120 jets.

[ZTatZAU]

Yes…. John D.

Thanks John!  I appreciate your replies!

Yamiya No Numbers are like the HM300 with same baffles (diffusers).
Better flow and sound than restrictive HM341 style. 
Need richer jetted carbs too.
My K2 has Yamiya no numbers.
Air screws 1 turn out
Pilots 40
Needles 4th from top
Main jets 115

A friend  with HM341 could not run that jetting, too rich.
Had to set needles middle (3)
Main jets 105

DSS had Yamiya no number style not that long ago. They might get new sets?

Well worth too look for.
Possible with tuned engine too. I have used them with 836 and 1000cc, ported head, hot cam etc.

Thanks Pewe!  I appreciate the info you provided on the Yamiya HM300 repos as my only CB750 experience has been with the K1 I bought new in 1971.  I'm not familiar with "DSS".  Is that the full name of an aftermarket Honda parts supplier that I can find online?

There's still a few days if you are ready to get the Busso no numbers, no stamped 300 set for 850€ which was $940 on Monday when I paid for mine. You can pay half now and the other half when the run is made and ready to ship(@August)
That is @ 1/2 price of what you can get them already made in the 341 or 300 with BS341 or BS300 stamped on them.
If you are ready now, send an email to Busso at the group buy address in the screenshot.

Thank you too David (?) I hope that's correct Stu!  I'm still getting to know all the contributors around here and my memory isn't what it once was.

I may jump in on that HM300 group buy from Busso.  I've just gotten my K1 running again after a 12 year slumber and still have a few more things to sort out.  So, I can certainly wait until August.

Do you have any notion or personal experience on how the Yamiya and Busso HM300 repos compare in price, quality, fitment, etc.?

I have a 71 built in August.  It came with 341 pipes and 120 jets.

Thanks for your reply Phoenix!  My 1971 K1 was manufactured in December of 1970 so I'm fairly certain it started out with HM300s.

I sure appreciate everyone's replies here!  I now have a lot to consider!
ZT

[ZTatZAU]

There's still a few days if you are ready to get the Busso no numbers, no stamped 300 set for 850€ which was $940 on Monday when I paid for mine...

Just so I'm clear on the Busso Group Buy options...

Are all the exhaust systems built the same (HM341 style) with the only options being 1) No Stamp, 2) Stamped 300 or BS300, 3) Stamped 341 or BS341?  Or do they actually make different style HM300 repros as well as HM341 Repos?

TIA, ZT

[newday777]

I think the 300 no numbers are indeed as the 300 with the bigger baffle and not just the short diffusers that the 341 have.

[ZTatZAU]

I think the 300 no numbers are indeed as the 300 with the bigger baffle and not just the short diffusers that the 341 have.

So is that what you'd recommend for my early K1 (mfg'd DEC 1970)... Busso 300 style, no stamp?

[newday777]

Yamiya is closer to $1900.
No I don't have any experience of the comparison of Yamiya and Busso, just that the Busso is a bit tighter to the frame of the outer header pipes. There's a thread of a member who got a set from the original group buy last year. He is the one who got in touch with Busso to see if they would make a run of no numbers no stamped 300 pipes.

[grcamna2]

I think the 300 no numbers are indeed as the 300 with the bigger baffle and not just the short diffusers that the 341 have.

So is that what you'd recommend for my early K1 (mfg'd DEC 1970)... Busso 300 style, no stamp?

Does Busso still offer them at a discount? I thought that was part of a 'group purchase' here on the forum ?

[newday777]

I think the 300 no numbers are indeed as the 300 with the bigger baffle and not just the short diffusers that the 341 have.

So is that what you'd recommend for my early K1 (mfg'd DEC 1970)... Busso 300 style, no stamp?

The no numbers no stamped are what I ordered and it's what this group buy is about getting the minimum of 30 sets to start the production run of them.

Here is David's write up on them

http://forums.sohc4.net/index.php/topic,131225.msg2246068.html#msg2246068

[newday777]

I think the 300 no numbers are indeed as the 300 with the bigger baffle and not just the short diffusers that the 341 have.

So is that what you'd recommend for my early K1 (mfg'd DEC 1970)... Busso 300 style, no stamp?

Does Busso still offer them at a discount? I thought that was part of a 'group purchase' here on the forum ?

David just said yes to get the 30 minimum orders(deposits). You will need to email them directly at the address in the attachment above.

[MauiK3]

My K3 has Yamiya no number pipes. They sound great, I leave the baffles in.
Good quality stuff.

[ZTatZAU]

...
I think the 300 no numbers are indeed as the 300 with the bigger baffle and not just the short diffusers that the 341 have. ...
David just said yes to get the 30 minimum orders(deposits). You will need to email them directly at the address in the attachment above. ...

Thanks again Stu!
I'm about ready to email BUSSO on the 300 style - no numbers group buy, but have questions...

Do you know for sure that this 300 no stamp group buy includes the decorative heat shields?

And I just corresponded with someone who recently received their delayed BUSSO order due to the chrome issues.  Apparently Busso included a hardware kit (rubbers and clamps) at no charge to make up for the delay... which sounded pretty fair to me and a good indication of Busso trying to "make things right!" for the delays.

I'm now wondering, if I should order their hardware kit along with my group buy email?  If this is something I'll likely need, it would make sense to include the hardware kit in the same shipment?

Looking for some guidance for this newbie here but perhaps David would be best able to answer these questions.
TIA, ZT

[newday777]

The hardware and covers are included

[ZTatZAU]

The hardware and covers are included

Great! That's good to know!  I just posted my questions on David's thread and sent him a PM as well.  Just wanted to confirm what I am about to buy here.

In my email, to Busso, under KIT QUANTITY & MODEL NUMBER: I put...
1 KIT - HM300 STYLE  (NO STAMP)
Is this correct?

EDIT: And do you happen to know how close we are to the minimum required 30 orders?

[newday777]

As of 2 hrs ago there were 21 order deposits in
I sent David a message on the messenger group page to reply to your questions

[ZTatZAU]

As of 2 hrs ago there were 21 order deposits in
I sent David a message on the messenger group page to reply to your questions

Thanks so much for your help Stu!
I'll be emailing Busso momentarily.
ZT

[newday777]

As of 2 hrs ago there were 21 order deposits in
I sent David a message on the messenger group page to reply to your questions

Thanks so much for your help Stu!
I'll be emailing Busso momentarily.
ZT

You are welcome bro. 😊
That's what this forum is about.

[Don R]

 I heard today that they are expecting to be close to the 30 needed to start a run of them by next week. This will supposedly be the last group buy at this price. I ordered two sets of no no. pipes. You can get no stamp, 300's or 341's. The numbered ones will have Busso or B-something on them. 
  Several guys are having trouble with the international wire transfer of the funds. My bank charged me $75 for doing it, the exchange rate is going in our $$ favor and the recent difference almost covered my fee. Some guys have found Wells Fargo and other ways. Western union was using an old exchange rate which may or may not cost more.
 I've been watching Yamiya, Webike, and DSS for some time and have managed to miss any 4-4's that were available. No one is running a waiting list as far as I know. I almost ordered a set of Mugen/Yoshi daytona 4-4's from Webike!