[Zweihammer]

80 CM400 Scrambler

Hey, I'm picking back up a project I started in 2013 with a pair of '80 400s I was given. I did a mix and match between the two to get one back on the road. Didn't have a good tank or carbs, which started me on modifying parts I did have. Put an early CB350 tank on and made a 2 into 1 manifold to use a carb left over from another project. Rode the resulting mongrel for a year.
I can never leave well enough alone, and the bike was too far gone to make restoration feasible, and truth be told I love design. I am an engineer and former fabricator by trade.
So, wanting a CL style exhaust caused me to start screwing with a perfectly fine commuter.
Well, as of last night, here we are

I will try again later, have to get back to my day job.
Cheers, Erick

 

[ScramblerCurtis]

Ooooooh. I really like your exhaust. Is that a custom fabrication?

 

[longdistancerider]

Interesting, a few questions for you
1) what did you do to get the 350 tank to fit over the frame bulge?
2) I'm guessing you're running the GM ignition coil since the plug wires go backwards and the original coil would never fit under the tank
3) did you add a stopper to the center stand to keep the chain from rubbing on it?
4) single carb? care to share what and how since it's been asked several times over the years with no answers
5) have you considered bracing the swing arm to eliminate flex since you've gone with the mono shock

 

[Zweihammer]

To drop the Cb350 tank I trimmed the bump off inline and welded across the resulting hole with some sheet. You can still pass an extension through, though I would drop the engine if I had to service the head. These bikes are so simple. I also trimmed the rubber up front. I haven't made the rear mount yet. When I was using the stock CM seat it just trapped it down. I will include a picture later.

I apologize for the lack of updates on the single carb mod. I really have to re jet it, as it will only run with the choke on. However, with the choke on it starts right up, idles and runs smooth. The carb is really too big, as I have to roll it on or it will stumble for a couple seconds otherwise. But the plugs are tan. I'm only getting 30 mpg, but I am a big boy and I only used it to shoot around the back roads up in the hills. I don't have much in the way of highway miles on it.

On the swinger, I am going to extend it 3 inches and under brace it with some 1" .065 wall tube. I was looking at putting the shock on as it was on the GSXR it came off of, but there isn't any frame underneath to put the linkage.

Still debating whether or not I am going to keep the center stand once he mods are done. I like having one, but it looks out of place.

Yep on the GM coil, one of the first mods I did (thanks to all who worked that out before me on here, it was very easy at that point!), as my original coils were dry cracked from being parked in the sun for 20 years.

Cheers, Erick

 

[Zweihammer]

Here is what I did to put the early CB350 tank on the CM400 frame. I trimmed the bulge off flush and TIG welded a 12ga patch back in. I trimmed the tank rubbers down to the width of the "new" tank as well. Sits tight now and I plan on hiding some of the wiring in the space above the spine.

I am machining some 3" extensions to put in my spare CB400 swingarm. Once I have those, I will extend and underbrace the swingarm before I finalize the shock mount. As I mentioned in the last post, I have some spare 2009 GSXR shocks but I am looking for recommendations for other, direct acting, shocks. I don't think I want to go through creating a mount for the rising rate linkage. Any suggestions would be welcome.

 

[J. Wright]

definitely want more info on the single carb. I was wanting to do that but wasnt sure where to start. Was thinking a 38mm flatslide with a custom intake manifold

 

[Zweihammer]

I think something in the 30 to 32mm range would be more than enough for a stock 400 or 450, possibly even a 28. I just used something I already had. I still need to jet it properly and make a hanger to support the carb, right now it's just held on by the boot and without a support for the filter side,that's it.
Runs fine for me, the manifold condenses drops of moisture whenever I ride and is cold to the touch.
The downside is it is right at my knee. With the stock CM400 seat I either had to ride with my leg out or sit up on the passenger step to be able to tuck my leg in. I picked up a stock '70 CB350 seat to let me sit further back but didn't like how it blended with the janky frame and stock side covers.
So, chop chop, no turning back now.
Now I am looking to make a long brat seat to let me sit further back.

 

[Zweihammer]

A little further down the rabbit hole...

'05 GSXR1000 forks using the all-balls sets.
If any one else does the same mod, just remember to put the spacer under the bottom inner race as the outer race seats very deep in the Cm400 headstock. I didn't catch that before I put bearing on the triple, so I need to decide whether to buy another bearing or trim the headstock.
I want to use the 305 headlight, but the bulb I found is for the baby dream. I did try cutting off the bulb and putting in a LED headlight bulb. What a difference!
I realize this is a rolling contradiction. I wanted to source a later XL500 fork, but I had the GSXR and I needs me some big brakes.

 

[Zweihammer]

Does anyone know why the images I uploaded are upside down on some formats? I uploaded from my iPad and now one is upside down, though never in the preview window. From my Windows based workstation, they are both upside down, still not from the preview screen.
I guess I need to get a Photobucket account, again.

 

[Lefty]

I think it might have somthing to do with how you're holding the idevice when taking the picture

 

[dtsmjr8dan]

I've mostly seen this happen with Apple products.

 

[Zweihammer]

I started to modify the swingarm this weekend. I made two stepped extensions to add 3". I have to say I was annoyed after machining those to realize the swingarm from Honda is sleeved, not the heavy wall tube I thought it was. So I made sure to rosette all three of the parts together and at least the brace will be .120 wall 1".
I SWAG'd a quick bracket from an existing clevis I had to get an idea of how far off the spring rate would be. I have used the same spring, along with the whole swingarm and linkage on another project, and as you would expect, it worked as designed in that application. Without the stock GSXR linkage, it is stupid soft right now, like '80s dirt bike soft. Now, I am not a small person at 230, but my first SWAG was it would be too stiff. However, as is here, it sags 4" under my weight alone. Time to work up my options.

 

[Zweihammer]

I just got some '82 Cr480 footpegs to change out the soft rubber stockers. Since I have to add new clevises to the mounts I might move them back a couple inches.

My next idea to make this more difficult than it has to be is to use another GSXR front rim I have for the rear. I want a 17 (for the wider modern tire selection) with a disc, and the GSXR rear is very wide, both at the rim and the hub. The 3.5 x 17 front matches and fits well proportionally, it just lacks a cush drive. I think I can adapt one from another hub to the unused disc pattern.

I just can't leave well enough alone. This was supposed to be a quick, cheap build of a free bike.
It's all relative.

 

[danno]

That bike is going to be awesome! I'll stay tuned (no pun intended)...

 

[66Sprint]

Are you planning on a jackshaft for chain alignment?....Otherwise, I believe you'll hit the tire with the chain if the wheel is centered on the frame......

It may just be the picture angle.....

 

[J. Wright]

I am working on the same issue with using a front rim for the rear. My plan was to have an adapter laser cut that will mount to the disk brake mount holes and then the sprocket will mount to that. I dont plan on any type of cush drive as mine is a hondamatic and shouldnt have the jolt of the standard transmission

 

[Columbus78CB400t]

I hope to someday I have the amount of skill you do. This bike is going to be very neat. I have a hard time selling things, so maybe in a few years I'll have the cash to convert my bike a vintage modern. Keep up the good work.

 

[Zweihammer]

Hey, J. Wright, years ago, an friend of mine used two 21" dirt bike front rims on a early Triumph hard tail bobber build, a '61 I believe. Made for a sweet, narrow profile. He didn't bother with a cush drive, opting for a sprocket straight to the hub, just like the matching rear he wasn't using. I don't remember the hub he used, he didn't use the rear hub as it was a different spoke count. He also ran the knobbies that were on the rims. Didn't see much use outside of riding around car shows and bar hopping around Hollister. It was a handful, a scary, beautiful handful. He sold it on to a kid looking for a replacement for his recently wrecked CBR600, I often wondered if he tried to ride the old Triumph the same way he rode the CBR. I am going to keep working my options. I've heard of "Cush sprockets" but haven't actually seen one.

 

[Columbus78CB400t]

Hey, J. Wright, years ago, an friend of mine used two 21" dirt bike front rims on a early Triumph hard tail bobber build, a '61 I believe. Made for a sweet, narrow profile. He didn't bother with a cush drive, opting for a sprocket straight to the hub, just like the matching rear he wasn't using. I don't remember the hub he used, he didn't use the rear hub as it was a different spoke count. He also ran the knobbies that were on the rims. Didn't see much use outside of riding around car shows and bar hopping around Hollister. It was a handful, a scary, beautiful handful. He sold it on to a kid looking for a replacement for his recently wrecked CBR600, I often wondered if he tried to ride the old Triumph the same way he rode the CBR. I am going to keep working my options. I've heard of "Cush sprockets" but haven't actually seen one.

If the ole knoggin serves me right, a cush drive on the rear sprocket dampens the shock from each compression stroke. I actually thought my rear sprocket was bad on the DR, given how much play was in it. Went up to buy a new one and the shop owner told me to go home! Said the cush probably wasn't bad and if it was I'm not going to notice a difference when on dirt.

 

[J. Wright]

In running matching yamaha swirl 19" front mag rims.(link in sig) was thinking about oversizing the holes and using something like shock bushings to mount the sprocket would add a little cush but I dont know if it would be enough to actually make it worth while