Topic: Starting in on a CB350 twin bobber

[JLeather]

So, I've tried and failed to get rid of this CB350.  I guess I oughta do something with it so this winter I'm gonna build a bobber/street fighter out of it.  I need a couple things.  First off, information.  I know a lot about the CB750's, but very little about this little guy.  I definitely need a wiring diagram, simplified if possible, cause all I need it to do is run and have a brakelight/headlight.  No electric start, no turn signals, etc.

Second thing is I need to freshen the motor.  It ran, but it smoked pretty badly from the right cylinder.  Maybe I can get by with just rings.  What can I do to the motor relatively cheaply?  Is there a source for overbore pistons/rings?  Cams?  I'll atleast need a gasket set for the engine.

Can I run the CB350 without a battery?  I know on triumphs, since they've got a fixed-magnet charging system, you can run them kick-only with a big capacitor (a mity-max or whatever it's called).  CB750's have a field coil that needs to be excited so you can't do this.  Anyone run a CB350 twin without a battery?

Does a CB750 front end fit a CB350?  Are the necks different?  Lastly, anyone got any 350 twin bobber pics to motivate me?  Thanks guys.

[mgmuellner]

The neck on my 350 is the same as on my old 500.  I actually took the fork/triples from it & they look the same as my 750. 

[JLeather]

Anyone who's messed with these got any wiring or performance suggestions??

[HondaMan]

Anyone who's messed with these got any wiring or performance suggestions??

I owned several, in fact my whole family had CL and CB versions, and I built them for street and road racing (and chops!). You can pull about 42 HP from them, if you're careful, which could take most CB750s in stoplight contests, because of the weight difference. What year engine is yours? The early Honda cams were good for 11,000 RPM.

The weak links are: cam bearings wear badly, the rubber diaphragms in the carbs get tiny cracks in them and become a difficult-to-tune situation until they are replace/repaired, and the early models through K1 had only 16mm oil pumps, which were replaced with 19mm oil pumps later. The early trannys, thru K1, had trouble shifting and dragging when hot: this got fixed by K2. The rings don't seal well until the engine is bored to 2nd oversize, because the metals used would warp a lot when hot, preventing round cylinders. For best results, we would go straight to 4th oversize after the engine had about 5k-8k miles, to stop the blowby and oil consumption problems.

The electric schematic is very similar to the 750 thru the 750K2. If you remove the electric start, you can use the same battery as the SL350K2-later bikes.

[JLeather]

Ok,
  The bike is, as I recall, a '71.  Can't remember exactly, but it's certainly no earlier than '71.  I had the bike running a couple years back.  The tranny shifts fine, but then again I never really ran it to operating temps cause it had no tags.  The bike does definitely smoke from the right cylinder.  It probably needs to be bored.  I'm not lookin' for a ton of performance, just a fun little machine.  I'm keeping the frame light.  Is just a top end good?  Maybe oversized pistons, replace the cam bearings, possibly new springs (?) and all the gaskets.  Who carries oversized pistons for the CB350?  Trying to keep the costs down as much as possible.  There's a set of .25 over pistons on eBay I might use.  Is it really bad enough I need to go to 4th over?

I am gonna eliminate the electric starter.  Don't see any use for it really.  I guess I still need a battery.  I'll just get the smallest one I can and hide it somewhere.  Gonna extend the swingarm, and maybe use CB750 front end and swingarm cause I've got a few laying around.

The carbs are trashed.  When I got it they had pinholes in the float bowls from water and fuel.  I rebuilt 'em and found new bowls, but they sat around on the bike and got set again and now they're full of that white crap from the decomposing potmetal.  I'm gonna scrap 'em this time.  Rebuilding them would probably cost more than rigging up a nice set of Mikuni's or something.  Any suggestions?

[johnny]

Wiring diagrams can be found here:
http://oldmanhonda.com/MC/WiringDiagrams/MCwiring.php

[JLeather]

Thanks for the wiring info.

Anyone know what different frontends swap on what frames?  I've got a couple CB750 frontends around.  How can I get CB750 forks onto a CB350 frame?  What about the 750 swingarm?

[HondaMan]

Ok,
  The bike is, as I recall, a '71.  Can't remember exactly, but it's certainly no earlier than '71.  I had the bike running a couple years back.  The tranny shifts fine, but then again I never really ran it to operating temps cause it had no tags.  The bike does definitely smoke from the right cylinder.  It probably needs to be bored.  I'm not lookin' for a ton of performance, just a fun little machine.  I'm keeping the frame light.  Is just a top end good?  Maybe oversized pistons, replace the cam bearings, possibly new springs (?) and all the gaskets.  Who carries oversized pistons for the CB350?  Trying to keep the costs down as much as possible.  There's a set of .25 over pistons on eBay I might use.  Is it really bad enough I need to go to 4th over?

I am gonna eliminate the electric starter.  Don't see any use for it really.  I guess I still need a battery.  I'll just get the smallest one I can and hide it somewhere.  Gonna extend the swingarm, and maybe use CB750 front end and swingarm cause I've got a few laying around.

The carbs are trashed.  When I got it they had pinholes in the float bowls from water and fuel.  I rebuilt 'em and found new bowls, but they sat around on the bike and got set again and now they're full of that white crap from the decomposing potmetal.  I'm gonna scrap 'em this time.  Rebuilding them would probably cost more than rigging up a nice set of Mikuni's or something.  Any suggestions?

The '71 will have the larger oil pump, so the bottom end will likely be fine, and for a long time. The cylinder: check for cracked rings (from over-revving, they love to rev), then for an oval (non-round) bore. The error is usually around.002"-.004", in an egg shape. While this will clean up in a single oversize, under hard-riding conditions it would continue to warp. With intermittent, non-touring/racing riding, it will probably last lots longer. IIRC, the '71 was whne the valves got better, too. Oh-and, if it has the oil-pressure-controlled camchain tensioner (no adjusting bolt), replace with the mechanical one instead. The oil-fed ones would let the camchain slap until it broke.

Carbs: the SL350 used Kehin slide carbs (24mm, I think?) for more low-end, less HP, for the offroaders. Using 28-30mm carbs yields good results, though. Almost any carbs will work, as the 325cc engine was oversquare and not real picky about carbs.

[Andoo]

I think you can run a cb750 tripple tree on a cb350 frame. I am also starting a cl350 bobber project.  There is a guy on e-bay selling "bolt on" hard tale frames.

[hahnda]

The CB350 and the CB750 have the same stem dimensions EXCEPT the CB750 is about an inch longer if I remember right. What you could do is cut a chunk out of the 750 stem to make it the correct length.

Cut the correct length out from somewhere in the middle. Find or machine a slug that will fit inside the hollow stem. Drill some holes in the stem for more weld locations. Put it all together and weld it up. Grind, sand, turn the welded area enough so that you can get the lower bearing past the welds.

[JLeather]

That sounds like what I'm tryin' to do.  I'll measure and make sure it's actually an inch.

BTW, I had seen the hardtails on eBay.  That's like 20 minutes from my house.  Save on shipping that way.  I just haven't decided if I'm going the hardtail route.  I kinda want some suspension.

[Z_Stingray]

Here is a basic chopper wiring diagram.  Hope it helps.

http://www.650motorcycles.com/ReadyKilo.html

[dusterdude]

I think you can run a cb750 tripple tree on a cb350 frame. I am also starting a cl350 bobber project.  There is a guy on e-bay selling "bolt on" hard tale frames.

would you have a link?

[JLeather]

Bolt-on Hardtail

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=320194702427&ssPageName=STRK:MEWA:IT&ih=011

[JLeather]

Ok, my bad on the year, the neck says 12/72 for manufacture.  Got 'er stripped down pretty far last night.  Tank, seat, gauges, rear wheel, and a ton of stuff is off now.  BTW, if anyone needs some CB350 parts I don't need the stock stuff.  Man, this frame looks terrible.  The whole backbone is stamped with this crappy rib on top, and it's so cluttered where the seat is.  Is teh battery box welded in?  I couldn't get it out.  Swingarm is too small for the CB750 wheel I'm gonna be running.  I'm gonna try and squeeze a CB750 swingarm into it.  Anyone ever do that before?  Coupled with the wider/stouter CB750 frontend oughta make for a real nice stance.  I've got a set of CB750A alloy rims I'm respoking with SS spokes.  Ribbed GME tank and ribbed rear fender, etc.

I need to find oversized pistons for this bike.  Anyone know where I can get a pair, or if there are some stock pistons that would work.  What's the bore?  I've got an incomplete set of CB750 823 kit pistons if they'll work.  I think the CB350 is bigger than that, though.  Looks like I'm going to have to start the new backbone very near the neck to clean it up enough. Do I really need the top motor mount, or is it overkill?

[754]

Do you even look at it before you ask?? Take a 750 swingarm and walk over to your frame.. do you see  anything that may be an obstacle??

350;s vibrate a lot.. really a lot. Keep the motor mounts on. Adding a bunch of heavier fatter 750 stuff is not gonna make it any quicker. Just lace a 16 in on the back.

Did I mention that bike will vibrate ??.. more than you can imagine...

[JLeather]

754,
  I measured the opening for the 750 swingarm.  I didn't have one nearby, so I was running from memory.  I thought it seemed too small.  Prehaps I was wrong, I'll check tonight.

As for weight, the aluminum 750A rims, while being bigger, aren't heavier than the 350 rims.  Plus, the 750 frontend looks so much beefier on the bike.  I like the look.  And the brakes from the 750 are bigger.  I'm pretty big myself, and more brakes are always better IMP.  Actually, I've even got a 15" HD rim laced to a CB750 hub I had been running on my Amen before this.  That might look good too.

I haven't rode the bike in probably 6 years.  I don't remember how much it vibrated, but my buddy's got a Triumph and if it's anything like that piece I know what I'm in for...

Is the CB350 a 530 chain?  Do CB750 sprockets fit the output shaft of the bike?

[JLeather]

The carbs on mine were toast.  Pinholes in the float bowls and cracked diaphrams.  Nothing to use there.  What electronics do you need?  I've got all the stock coils, reg/rec, etc.  I've got the stock wiring harness.  A little rough, but I didn't cut anything.  Stock gauges.

I'm planning on doing a single-carb setup for it.  I need to bore the engine atleast one size to fix an oil-burning problem, and I'd like to go disc-brake rear.  With a 750 frontend I'm planning one of CycleX's fork-mounted speedos.  No signals and no electric starter means I can get by with the bare minimum of battery and wiring.  Small batt, DOHC honda reg/rec, and a couple toggle switches.  That's the extent of my electronics.  Might go hardtail, but I'd prefer some suspension if I can make it look cool.  I need forwards badly cause I'm tall and the bike ain't...

[JLeather]

I haven't found overbore pistons yet.  Hopefully someone will chime in with a source.

I'm gonna run the stock points with one of those chrome dual-output car-looking coils.  I think I can wire capacitors across the coil directly (haven't got that far yet).

I believe DOHC reg/recs will work on the 350.  I know you can wire them to a 750.  Got the diagram somewhere.  The 350 appears to use a similar system.  I hope I can, cause I won't need an electric box.  I'll just bolt the reg/rec somewhere outta the way.

Anyone know if the electric starter can be removed?  I figure I'll just need a blockoff plate or something to cover the hole it leaves behind.  Anyone done that before?

[JLeather]

Do you even look at it before you ask?? Take a 750 swingarm and walk over to your frame.. do you see  anything that may be an obstacle??

Well, I started cutting a bit to see if it could be done, and the answer is "not without too much work".  I thought I could cut the 750 swingarm into an H like the 350 is, and then re-bush it from the inside so it would pivot.  It's just not structurally sound and round enough in the middle to do it.  I'd have to basically make a totally new swingarm.  Guess it's gonna be a hardtail...

[Andoo]

Just got my Bolt-on/ weld-on frame off ebay. looks good! Quality stuff.

[JLeather]

I assume you got the one fro TriumphWizard?  I've been wondering where that bolt-on actually bolts to.

[JLeather]

That's kinda what I figured.  I looked at my frame, and compared it to the eBay "bolt-on" hardtail and it looked like the top actually bolts to the front part of the battery box.  I can't see anything else in that area that is vertical and flat to match the tabs on the hardtail.  I suppose I could extend it at the top and weld the tubes to the backbone, but as far as riding it I don't feel it's sturdy enough as a bolt-on.