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Old 11-19-2012, 05:47 PM   #16
SloMo228
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Joined: Sep 2012
Location: SE Michigan
Oddometer: 1,519
Nice project, I really like how it's coming out. I always feel a little bad about chopping up old bikes, too, but I also always chop up my bikes. I guess my justification is that just about every bike I've owned, I saved from a scrapyard, so at least they're still on the road.
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Old 11-19-2012, 06:09 PM   #17
Kt-88
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Location: SLC area, Utah
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The front mounts are all wrong. The sprocket alignment is even more all wrong. The pegs and pipes and brakes are incredibly wrong.


So, yes, it should be amazing.
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Old 11-30-2012, 06:31 PM   #18
TheRadBaron OP
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Skid plate

I was kind of going back and forth on whether I wanted to mess with putting a skid plate on the bike. On one hand, I wanted one because they're practical and I plan to ride this bike offroad when the opportunity presents itself. Also, they're period correct and they look the business on a scrambler. However, I still have a good bit of metalworking and fabricating to do and I have sort of a love/hate relationship with metalwork. I have to be in the right mood to enjoy it and do a good job.
While looking through the parts for sale section here I learned that Honda actually offered an optional skid plate for the CB/CL350. That would be perfect since it would be a bolt-on affair, but I've also learned that they're really rare and the only ones that I've been able to locate are NOS units and quite expensive. I looked through my stack of random skid plates but didn't find one that would work without serious mods. Just tonight I was cleaning out an area of my shop when I came across one that wasn't in the stack where it should be. Turns out that it's almost a perfect fit! It's made of steel plate that's a good bit thicker than what I'm used to. You could crash into a boulder with this thing and not dent it. I have no idea what it's from originally, but the front mounts line up perfectly with the lower front engine mounts, and the curvature of the plate matches the frame rails perfectly. I'll have to fabricate the rear mounts, but they'll be very simple. I'll just weld some mounting points onto the rod between the foot pegs and bolt it up.
I can't post a picture right now because I guess I watched too many heavy metal videos on Youtube and exceeded my maximum bandwidth for the month. Sheesh. When my internet gets back up to speed I'll post a picture. It would be nice to know what it came on, too.
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Old 06-10-2013, 08:17 AM   #19
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Well, it's been a long time since I posted on this thread but I'm making progress again. I didn't do much motorcycle wrenching this winter at all, but now that spring is going I've been right back at it. Here's the bike as it sits right now.


The bike is running now and I've ridden it around a bit. It's running great and I haven't had any problems with the engine. The only thing that it really needs is the jetting sorted on the carbs. I've been having some difficulties with the jetting but I think I have it under control at this point. Those 1750 needle jets were so wrong that the bike wouldn't even get off idle, so I swapped in a set of primary-type P-0 jets and they're good enough to ride on. The 1750 jets don't even follow Mikuni's numbering model, so I'm not sure what they are. The real problem that I was having was that the bike was idling at 2,000 RPM even with the slides all the way down. It wasn't any of the usual stuff like no slack in the throttle cables or and air leak or anything. I'd never seen that happen before on VM carbs, but I had a hunch that it had something to do with the air bleed jet/orifice in the bellmouth of the carb. I think (though I'm not sure), that this jet/orifice is what supplies air to the idle circuit. So if the orifice was too big, the idle would be too fast. I'd never messed with this jet before, but I know that some carbs have a fixed orifice while others have removable jets. A popular modification on Yamaha 2-stroke twins is to drill out the fixed orifice and tap the hole to take the removable jets. I figured that I'd do this and experiment with smaller air jets until I got the idle slowed down enough. Well, I took off a carb and shined my flashlight into the orifice and discovered that some previous owner had drill the orifices out to about 2.5mm! For a point of reference, if you buy an off-the-shelf Mikuni VM28 the air jet is 0.5mm. I figure this has to be the cause of the high idle.
Those "Eureka!" moments when a mechanical mystery is suddenly solved and everything falls into place are one of the greatest and most rewarding moments of being a mechanic. Luckily, the holes weren't drilled too big for me to drill and tap for the 4mm x 0.70 thread. In hindsight, this is probably why I could NEVER get my old Yamaha R5 (350cc 2-stroke twin with RD350 read-valve cylinders) to run right with these carbs. I spent countless frustrating hours trying to make that machine run properly, until I finally managed to destroy a brand new top end before I got disgusted and gave up on that project (for the time being). That's really frustrating, but that's another story.
I have a bunch of new brass coming for the carbs that will hopefully get me pretty close. I did a lot of research and came up with what should be a good jetting baseline. It seems that most people who swap VMs onto their 350s use 30mm or 32mm carbs. I guess this is mainly because they fit into the stock intake manifolds, but they're really too big for a stock bike. Most of the jetting examples that I've found have been for the 30 or 32s, but I did find some clues for the VM28s. I don't mind buying multiple main/pilot/air jets since they're pretty cheap. Different needles isn't even so bad, but at about $15 each I want to avoid buying multiple sets or needle jets. Anyway, I'll be sure to post my final jetting numbers when I get it finalized.
I just finished recovering the seat yesterday. I tried a few new techniques on this one and I'm happy with the results. I used a can of 3M spray adhesive to glue the foam down to the seat pan in certain spots. This went a long way toward making everything more manageable as the cover was put on. I also stretched a t-shirt over the foam and secured it using the tabs in the seat pan, just like the cover. My foam wasn't in the best condition, so I figured that this might help hold everything together.
The seat cover is from an Ebay seller called gumtwo and I'm very happy with the quality. The cover was twice as expensive as some other covers available, but the quality is top notch. The last few seat covers that I've put on bikes were from less expensive sellers and I haven't been happy with the fit at all. This one fits and looks great. The chrome buttons came from http://www.siriusconinc.com and they're fine quality parts as well. There are lots of cheap, "arts & crafts"-quality, metal buttons being sold as seat buttons, but I think they'd be junk if you tried to use them.
I ended up using a throttle cable for a Yamaha Banshee 4-wheeler. It needs to be a TORS eliminator cable. TORS was some weird system that had different carb tops, so a standard Banshee cable won't work. The cable is designed for a thumb throttle, so I had to modify the throttle end of the cable a bit to make it work. I have a little solder pot that I made for making cables and it works pretty well. I wouldn't trust my cables for a front brake, but I've made a lot of throttle, clutch, and choke cables and they work great.
I also succeeded in finding a 12v conversion bulb for the old enduro headlight I'm using. It was originally a 6v bulb, and it's one of those bulbs that fits onto 3 little nubs and twists to lock. It happens to be the same bulb used on antique Harleys from the '40s and '50s. I've heard them called "bayonet" bulbs. Anyway, I figured that someone had to be making a 12v version of this bulb since a lot of old Harleys get converted to 12v systems. I ended up finding the bulbs at JP Cycles.
A few posts ago I mentioned that the CB rear brake pedal needed to have some metal cut off to clear the SL engine case. The part that I had to cut off was the part that the brake light switch attached to. Back when I used to ride this bike I hadn't been running a brake light switch from the front brake lever and just relied on the rear brake switch. I really liked the fact that there were no wires on the handlebars. Rather than try to design and fabricate a new way to activate the rear brake light switch, I decided just to swap and use just a front brake light switch. I had to put a few wires on the bars, but it's not a big deal.
There's a big classic motorcycle party here this weekend and I'm planning on taking this bike. There are a few CB350 enthusiasts that will be there and I want to show it off. Plus, I like parking it next to some insecure guy's late-model, "custom" Harley. I do it every chance I get and it really gets under their skin. I don't claim to understand their thought processes, but I can tell that it really effects their toughguy self image if there's a little Jap bike next to their "I custom paid for this", tribal ghost flame, tormented skull, iron cross shaped mirror, badass Haaawwwgg. It's even better when people look at the little Jap bike and ignore the Harley. This is an antique bike party, after all. You should see the indignity! What fun.
Even if my new jets don't show up yet, I'll be able ride it there and back.
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Old 12-17-2013, 10:43 AM   #20
outobie
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this thread is old but I thought I'd make a few comments on your carbs.

the CB350 CL350 motors had different heads than your SL350 motor. Mikuni VM30's work great on stock CB/CLs, VM32's are what we run on race prepped engines with cam, head work and big bore kits.

you're SL engine had smaller diameter intake heads (it was made to be a dirtbike so tuned for more low end torque) so VM28s are good for SL heads, Honda sent them with 27mm ID bore carbs

The SL head also uses smaller diameter intake grommets
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Old 12-17-2013, 03:03 PM   #21
TheRadBaron OP
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Thanks for the info. Just to clarify though, I still have a CB head on this motor. The head and cylinders are from the original '73 CB350 motor while the bottom end is SL. 30mm carbs will physically fit into the original CB intakes but I think they're still a bit bigger than optimum. I got the jetting sorted out and this bike runs beautifully with the VM28 carbs.
I'll update this thread soon with what I ended up with for jetting and where the project stands now. I kind of got sidetracked and forgot about it.
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