Topic: 1975 750 K5 - Stock exhaust not fitting

[BackIntoBikes]

I purchased my 750 a couple of months ago and wanted to put the 4-4 stock exhaust back on. I found some on craigslist that I *think* are correct, here are the part numbers:

Left:
HMCB750 1L HM341 (inside pipe)
HMCB750 SL HM341 (outside)

Right:
HM300 (inside, number seems wrong...?)
HMCB750 SR HM341 (outside)

Is that inside right pipe wrong? I bought them from a guy who said the whole set came off a buddy's 750 years ago.

Right pipe aside, I've been having a heck of a time with getting the left set to fit. It's exacerbated by lack of documentation, which leads me to think this must be supposed to be easy, which doubles my frustration... I have the Clymer book and Hondaman's My CB750 Book, but neither seems to address installing the pipes. (Clymer has 750F which is no help anyhow.)

I did get the parts schematics from a parts store, so can kind of see from that how they're supposed to fit. My problem is that when I install the inside pipe, I can't seem to get it to align with the frame for the pillion bolt to seat.



I am re-using the flanges that were on there -- they seem correct, but perhaps they aren't?




I'm not positive how the pipes are supposed to fit with the frame. They seem to have to push up against it at the bottom front:



Anything obvious I'm missing? Are these the right parts? Do I need different flanges? My fear is that there may be something wrong with my frame... Thanks for any and all tips!!

-Tom

[Johnie]

The 75 should have all HM341's. That HM300 is for 69-71 CB750. I am not sure if the sizing of the holes will be the compatible to combine a 300 & 341 on the same side. I can tell from your pics you are trying to position the #2 pipe to far to the outside. It goes on the backside of the frame. I will load up some pics that might help. Click the pic to enlarge it. The flanges look correct for the bike.

[Johnie]

You will need the rubber bumpers that go on the bottom of the exhaust for both side stands to rest against when they are in the up position.
There was a thread that some of the OEM exhaust built in the last year or so were not properly bent to specs. I hope you did not get one of those. Do not tighten everything up until all is seated. You may have to slide a pipe off the flange a bit to get all to line up. And still you may have to push a bit to get that long rear foot peg bolt into position.

[pdrides]

Glad to see I'm not the only one to run into this, same thing happened with me the first set I put on. The inside pipes (2 and 3) come of the flange, go down to the INSIDE of the frame then they work their way out so when you run the bolt thru the upper and lower pipes and finally thru the frame they align vertically.

[BackIntoBikes]

Thanks so much guys, I'll go give it a try!

[Bowswell]

Johnie picture is good.
hm300 and 341 fit on your bike,just check your spark plug on hm 300 because the muffler is less restrictive...Ihave 4 hm300 on k4 with 110 main jet.

[BackIntoBikes]

Johnie, thanks so much for the pics and info! pdrides, thanks for the confirmation and commiseration -- nice to know I'm not the only one. Threading that inside pipe behind the side stand was the key.

I have them all together and the 300 does fit. I will need a new diffuser for it as I'd bought 4 for the 341s and it's a little smaller. I also need all the little screws to hold in the diffusers -- think they can be had at the local Ace? I'll give it a go.

It wound up taking less time to install them than it did to take the pics and formulate that post! I guess it is easy if you have a clue what you're doing.

Boy, do I like how the bike runs and sounds now! I'd had an uneasy feeling with it all along as it ran very rough and felt like it was missing or something in the 4-6K range. Much, much smoother now! I don't think the PO adjusted the spark or fuel mix after installing the 4-1 system. He'd also drilled extra holes in them for sound effect I guess.

Bowswell, thanks for the info on your settings for your HM300. I may have to vary a bit as I'm at 5280 ft elevation.

So much better now, thanks! It sounds and feels like what I'd expect a genuine Honda to do. Ahhhh.

[pdrides]

excellent!!

[Johnie]

Glad you got it sorted. The OEM 4-4 is such a cool looking exhaust!!! You will really like the sound and look!!!

[nancy]

I had a mixture of 3 x HM341's and 1 x HM300 on my 750 K3 for a few months and finally got around to replacing the 300 with another 341. There is a performance/tune difference. It is now smoother, less erratic. Fitment is no problem though, all mounts etc are the same.