Anybody else really hate the factory CB350 Twin carbs?

S

sclay115

Been Around the Block
It's probably just me. But I can't get them dialed in worth a damn. They seem to work well for a bit, then without any warning, it presents itself again. Little background on the bike:

Internally stock engine(rebuilt)
Pods
Mac 2-1 with no baffles( ;D)
New-ish iridium plugs
New wires
Factory coils(ew)
New points/condenser



I almost feel like it could be an ignition problem. But I'm not sure. As it seems very intermittent, and I can usually get it running pretty swell by simply resetting the carbs back to zero(all the screws in, then back to factory specs). I have re-jetted it. I'm on 110 mains and 70 secondaries. Perhaps a bit to rich on both? It seemed to be running wicked lean before(the headpipes were bluing), so I figured I'd bump it up. Just a bit stressful, hurricane season here in Central Florida means I have to really plan my rides, and when she isn't running right, well. It sucks. All I want is wide open throttle and the symphony of that exhaust(or lack there of). The mixture screws are at about 1 turn out, and if I know my stuff(which I probably don't), where the screw is located on these carbs, turning out is more fuel, and in, obviously, less fuel, yea? I have some Mikunis on my XS650(roundslides), and it's before the plate, which in turn regulates the air, not the fuel, or so I think. Anyways, lemme know if you guys can shoot some help my way.

P.S. Pictures for good measure! :D

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Steve
 
This might be a dumb question but where is the battery? this might be why you cant dial it in right.. or not. I dont know what im talking about.
 
Fuel Screws are located on the engine side of the carb, think of it like a faucet; Turn clockwise to reduce (lean) the amount of fuel, CCW to add more (richen) fuel. The air screw are locted on the inlet side of the carb; turn the screw CW to reduce (richen) the amount of air, CCW to increase (lean) the amount. Does this make sense? It's not really fair to hate a set of carbs that were designed to work with an airbox and baffled exhaust ;)
 
The battery is in the tray under the seat. That would be exceptionally difficult to get it tuned without one.

But yea, I understand they were 'designed' to work with the airbox and a full exhaust, but hey, where is the fun in that?
 
Try resetting the carbs so it runs right, then mark the position of the mixture screws with a Sharpie or nail polish or even just a small nick on the carb body to see if the screws are backing out or changing position while you're riding. If it is that's the answer and a drop of blue locktite or white glue should keep it in position. Ignition maybe but you said it clears up after you reset the mixture screws, odd. Does it do this during the ride or after when it cools down? I'm just thinking out loud here.

Terry Monday
J'ville, Fl.
 
The tank is rust free? The petcock thoroughly clean? Even the slightest dent in fuel flow can make it feel like the engine is missing and all sorts of weird stuff.

How's the timing? Checked with a strobe light?
 
Timing is money, checked it with a light, with the side cover off, one of the first things I looked into. Take is clean, I might take that petcock off though and verify there is nothing in it, can't hurt right? And I'll check and see about those screws. That might be a logical cause..
 
I was just fighting two weeks worth of headaches with the bike missing and running like crap. Turned out the petcock had a plugged hole. Runs great with gas. Who woulda thunk?
 
What exact symptoms are you having?
I love your CB by the way, the color scheme looks wicked! The only thing your bike is missing is clip ons!
 
tobiism said:
What exact symptoms are you having?
I love your CB by the way, the color scheme looks wicked! The only thing your bike is missing is clip ons!
Click to expand...

Well it goes like this. Things will be fine(keep in mind this is a first kick engine here), and then after about 15-20 minutes, if you are on a level grade, it'll start to miss, ever so slightly, and only occasionally. Eventually need to slow down, and then accelerating it will be like the power just dropped out, and will spit and backfire like nobody's business. It won't do this at idle, and it won't do this if it isn't under any load. I really think it might be the fuel screws backing out, I can't believe I didn't think of it before, but I do recall the one on the right side cylinder never being where I left it, mischievous thing...

I'm going to try and put some miles on it today, she what she does. Looks like we are clear from the storms now, so time to get some two wheeling in.

And I did think about clips. But honestly, until I get the other bike on the road(XS650), there is no way in hell I'm tearing this thing apart again, too much fun to ride when it's running right. I think you all know what I mean.

Thanks for the suggestions! I'll report back with what I find.

Steve

P.S. Thanks for the comment tobiism. I dig the scheme too. Little scary at first seeing that frame color by itself, wasn't sure how it'd look...
 
These are just a couple of things I thought of. Your coil could be going bad, and only showing signs after its warmed up. I've seen this happen before.
I've had bad gas caps cause that situation as well. When they don't vent, fuel won't flow out of the tank very well. Try riding around with the gas cap off and see if it continues.
Usually those adjusting screws don't just back out by themselves.
Good luck!
 
Sounds like coils going bad to me too. Also, something to check is your spark advancer. It might be a little gummy with dirt and stuff and heating up and sticking on you. Take it out,check to make sure the weights and springs move well, clean it and lube with white grease.
 
Holy coils...

So, I read somewhere you can use these Bosch Blue coils, made for air cooled VW's, on basically any 12v ignition system. And I've seen one CB350 twin running them, but not in person, and no real details. Well, lemme tell ya, you can. They aren't particularly cheap(36 a piece), and they aren't really hidden(I will get pictures tomorrow), but good lord, what a world of difference. It's amazing what happens when I replace something that is almost 40 years old with something brand new. And couple that with the 7mm automotive wires(using the NGK caps), and well, the bike sounds different, it feels different, and it feels BETTER. Took a quick ride tonight to see if it's ready for the work ride tomorrow, and it's go time.

Like I said I'll get the pictures, but lets just say they are VERY exposed, and they look the business. Do they match a thing on the bike? Nope, but I think that's what is fun. Bright blue coils with bright yellow wires, right up front. They are nearly as tall as the carbs.

Thanks for all the guidance guys. And for anybody reading this, it's real easy to overlook the coils, I replaced every damn piece of the system, points, caps, wires, plugs, condenser, wiring for all those, and well, like I said, these pieces are damn near 40 years old, and yea, they wear out, I think if you're still running them, they've put in their time, invest in some proper coils. Pictures tomorrow when it's daylight outside.

Steve
 
Pictures! Keep in mind the other 'tab' of the brackets hasn't been removed yet(it's in the works) this was a temporary but solid mounting setup to make sure these puppies weren't going to melt my face off. Enjoy!

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And for the non observant, yup the ignition switch has been moved, it's new home right below my shweet catch can(lots of these fueled this project in the wee hours of the night):

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Steve
 
Right on man, I'm glad you got it running!
I about had sticker shock a couple of months ago when I bought a new blue coil for my VW. I remember when they were $12 a piece!
 
Any details on how you hooked them up? My brother has a couple of them laying around from his VW bus rebuild he is working on. Any pics with the tank off and how they are wired? Thanks in advance.

-Jon
 
neubs said:
Any details on how you hooked them up? My brother has a couple of them laying around from his VW bus rebuild he is working on. Any pics with the tank off and how they are wired? Thanks in advance.

-Jon
Click to expand...


+1, please.
 
Oh yea sorry guys, lost track of this one. It's really pretty easy to hook em up. There is a positive terminal, and a negative one on the coils. Well, you can probably see where this is going, but hook up the switch 12 volts to the positive terminal. And then the negative terminal goes to the wire for the corresponding cylinder coming out of the points/condenser. It's really super simple, since it's just like your factory coils, just...bigger and meaner. Any other questions?

Steve
 
That's what I thought, but I wanted to be clear. Where did you get them and do you have a part number? There seem to be several different "blue 12v" coils available.

thanks again,
s
 
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