Author Topic: What to choose.. HM300 or HM 341 (Read 3684 times)

Lars · « **on:** January 31, 2010, 09:22:42 AM »

Finally, I purchased my first CB 750 K4, 1974 model. Only 10 000 miles and in good shape, but not the orignal mufflers. I know the HM 300 was only for the first models, but many seems to like the sound of them better that the HM 341. So, I am thinking - should I stick to the original HM 341. What is the difference?
Lars

Gordon · « **Reply #1 on:** January 31, 2010, 09:26:47 AM »

Two main differences: 341's are more restrictive and quieter. 300's will cost you more.

There's a post here somewhere describing how to make the 341 pipes perform and sound more like the 300's.

Duke McDukiedook · « **Reply #2 on:** January 31, 2010, 09:31:41 AM »

Yep, money. You have about $1200US lying around not counting shipping?
Maybe you do, I don't right now.

MFHP · « **Reply #3 on:** January 31, 2010, 09:47:41 AM »

If money isn't an issue then I would recommend the HM300. They have a louder and throatier sound. If you care about 100% original looks the HM341is the choice. But you could also just take the baffles out of the 341.

Mike

Lars · « **Reply #4 on:** January 31, 2010, 09:51:59 AM »

But not any differences regarding size and mounting? Restricting meaning less sound AND less power? The bike has 4-2 mufflers, any adjusting on needle circlip necessary? Is the middle position the standard one? I have experiencensed that 4-muffler not uses the standard needle hight, but not sure on 4-2. Anyways, I will find out when I cleand them.

Lars · « **Reply #5 on:** January 31, 2010, 09:53:55 AM »

Money is no issue, can I afford the HM 341 I can also dig up some more for the HM 300. Or rob someone, he he

Any volounteers?

MFHP · « **Reply #6 on:** January 31, 2010, 10:37:28 AM »

no difference in size and mounting. Jetting shouldn't be affected as well. The mild stock cam with its small overlap makes it quite unnecessary to adjust carbs to any exhaust. Only for the race Marving 4-1 it was recommended to rejet.

Mike

andy750 · « **Reply #7 on:** January 31, 2010, 01:09:14 PM »

I have both the 300s and the 341s...the sound of the 300s is much better (to me).

have fun!
Andy

petercb750 · « **Reply #8 on:** January 31, 2010, 01:32:01 PM »

The 300s sound heaps better, in fact I don't know why i bought new 341s, I guess I was trying to keep the bike "correct".
Back in the 70s I swapped a 4into1 for a set of 300s on my K2. I was proddy racing then so had to fit baffles - the only ones I had were from 341s, so I managed to squeeze the cones into the 300s (the diameter of the 300s was very slightly less than the 341s), and it actually sounded very nice, in a baffled sort of way.

Toxic · « **Reply #9 on:** January 31, 2010, 03:51:10 PM »

If I had 1200 bucks laying around I'd buy BCR's 4 into 4 SS system.

It's strickly a personal taste thing but I can't stand the look of the tips on the stock pipes.

Visit youtube there are lots of sound ciips for both pipes. It will only give you a vague reference on how different they sound but it will give you an idea.

Bowswell · « **Reply #10 on:** January 31, 2010, 04:29:25 PM »

i put used hm 300 on my cb750k4 with main jet 110.reguler jet was 105.

Lars · « **Reply #11 on:** February 01, 2010, 12:33:12 AM »

OK, I think I will go for the HM 300. Were there any changes in main jet through out the 1969-1976 range of the CB 750? Or any other carb changes?

Regarding the needle hight, I once bought a CB 550 K76 with a 4-1 muffler on it. Replaced it with an original 4-4 set and the engine would not run well. I opened the carbs to find that the needle hight was changes, so I reset the circlip to the middle position. The engine ran fine after that. This little experience leads me tho think, that changing mufflers to anything else than the original 4-4, might need an adjustment of the needle hight. Maybe 4-2 less necessary to adjust than the 4-1, so the carbs might be untouched. Anyway, I will clean them up, and will need to find out what jet sizes were stock on this model.

Thanks for all the replies, guys!

Raul CB750K1 · « **Reply #12 on:** February 01, 2010, 07:40:10 AM »

Money is no issue. They both are available now and the price difference should be around 100 euro, that is, 800 against 900 euro or so if memory serves me. We are not talking about double or triple price.

I have been using my HM300 with no baffles for a while, more than one year. I loved the loud sound of it, heads were turning all the time. One day, I finally painted the baffles black and put some new baffling cloth that was missing. Installed them to check how it sounded. The sound was the same, but only at a lower level. Now I'm not deaf while riding on the highway, and I can always blip the throttle at stoplights to get some heads turn -they always sound more and different than modern bikes-. What is more, now the bike low range is stable and not like before. I'm not planning to remove the baffles anytime soon.

So Lars, you either put HM300 and change the jetting, or use HM341 and keep the jetting. If I were you I would put HM341's if only to keep it "period correct". Bikes are for riding and for looks, sound is the icing on the cake but I doubt anybody here has ever bought a bike just for the way it sounds. I don't plan to put a "ducktail seat" or a later tank because it is more convenient to have the petcock at the left side. Mi K1 is period correct and that's what counts for me. I just replaced the master cylinder thinking it would improve braking. It didn't and I will probably replace it when the time to change the brake fluid comes, but I don't really care much about it. What counts is that I have both the new master cylinder AND the original one. If you can afford to buy one set of HM300 and enjoy them, and buy a set of HM341 for the day you want to put your bike on display, then go for it!!!

Lars · « **Reply #13 on:** February 02, 2010, 12:58:14 AM »

Raoul, thanks for your opinion - do you need to rejet using the HM 300? Is there a difference in mainjets for the first years and the following?

Raul CB750K1 · « **Reply #14 on:** February 02, 2010, 07:21:33 AM »

Quote from: Lars on February 02, 2010, 12:58:14 AM

Raoul, thanks for your opinion - do you need to rejet using the HM 300? Is there a difference in mainjets for the first years and the following?

I think so. Talking by memory, it is like 105's with the HM300 and 120 for the HM341, or the other way round.... :-)

Seamus · « **Reply #15 on:** February 02, 2010, 03:48:16 PM »

Have a look through the FAQ at Hondaman's thoughts

http://forums.sohc4.net/index.php?topic=7401.0

There is info regarding exhausts and carbs. May be worth a look to explain the history and sizes etc. before making a decision

Cheers

Seamus

hondaseven · « **Reply #16 on:** February 03, 2010, 03:06:19 AM »

Lars, I have a k4 I fitted new hm300s ,k&N air filter in standard k1 airbox Less restrictive sucks more air in,125 mains,std40 slow jets,needle clip std in middle,and it goes and sounds the same as my k1,dont waste your time and money on 341s.

Lars · « **Reply #17 on:** February 03, 2010, 03:51:05 AM »

Hondaseven, I am most interested in the HM 300, but the rest of the bike will be stock. My worries is:

1. Do I need to replace the mainjets and to which size?
2. Do I need to change the needle hight for standard middle position?

I am not going to tune the engine racing style, simply keep it original and to idle nice and have good power in all ranges of RPM. You know - just wants the nicest sounds since I am buying a new set anyways. I am familiar with opening the carbs, clean and change the jets if necessary from my work on the CB 550's, so no problem to do the work.

andy750 · « **Reply #18 on:** February 03, 2010, 04:06:43 AM »

Hi Lars

I wouldnt worry too much about jetting. First get the pipes and then go for a ride and do a plug check and see if you are running lean/rich. Then you can change the jetting if need be. For me, I have a K4 as well with K&N air filter, 110 main jets (40 pilot) and have stock HM341s. I run quite rich and should really drop my jets to 105 (which was stock). Ive had my HM300s on the K4 as well with no other changers and it ran very well. Still a little rich. I dont know yet where my needle position is but I now have the carbs off the bike and will be checking soon.

The earlier bikes - K0/K1 had 120 mains and then they decreased in size over the next couple of years to end at 105 for the 74-76 bikes (Raul got it round the wrong way). But your jetting can vary depending on your particular set up...for example on my K2 it should be 110 mains but after trying 110 - 112.5-115-116-117s...I finally ended at 120s (HM300s, K&N air filter, Dyna ignition).

There is a good resource on the website - dont recall where - its a PDF that talks about carb set up/tuning. Its good reading and will answer more in depth your questions. Needle position can be kept stock or raised/lowerd depending on your riding.

good luck
Andy

bwaller · « **Reply #19 on:** February 03, 2010, 04:18:24 AM »

We used to hollow the 341's when racing production. I always wittled through a couple baffling layers and left the end cap off, but you can modify the 341 cap to eliminate the smallest center tube also.

It will not turn them into 300's but as your hearing weakens you may want to adjust your exhaust note to compensate.

hondaseven · « **Reply #20 on:** February 03, 2010, 12:45:08 PM »

Lars, 125 main jet ,a k1 air box or enlarge the 2 inlets front and back from the bottom of your own air box to let more air in,LEAVE THE NEEDLE CLIP ALONE,only then your k4 will sound magnificent and go like a bat out of hell ,mixture screw 1 turn out.

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Author Topic: What to choose.. HM300 or HM 341 (Read 3684 times)