Topic: CB350F bench syncing questions.

[superthegoose]

Are there any specific FAQ or walkthrough instructions on bench syncing a CB350F? Is it done from the engine side with the butterfly valves or the airbox side using the throttle slides? A lot of the "How To's" that I've read or watched use the screws on the bottom to adjust the butterflies, but I've seen the adjuster screws/slides used, as well, and that makes more sense to me. Which carb is used as a guide, #2? Or does it matter? Input appreciated. Thanks.

[robvangulik]

Those butterflies are your choke, when turning the throttle you lift the slides directly.

[iron_worker]

Synchronizing your choke butterflies is not a bad idea either but synchronization of your throttle slides is what will give you the dead smooth idle (assuming everything else is up to par).

IW

[superthegoose]

Okay - that's what I thought. Why are there so many tutorials on bench syncing where the butterflies are adjusted in lieu of the slides? Just different specs on different bikes? Also, is there a "sweet spot" where the butterflies should be adjusted to on this bike, by way of the screws that adjust them?

[superthegoose]

Thanks, guys. Is there a specific method to adjusting the choke butterflies? Is one valve only adjusted by the idle screw?
Also, with the slides there is a screw that adjusts each one.. Is there one particular one that should be adjusted and used as a reference? Or just go over them all a few times until they're all on point?

[robvangulik]

You don't really sync the chokes, you just make sure that if one is closed they ALL are closed.

What probably confuses you is the manuals you've seen for CV carbs, with those you sync the butterflies. Not applicable with your cb350.....

[iron_worker]

You don't really sync the chokes, you just make sure that if one is closed they ALL are closed.

Which is more or less what I would call a bench sync... 

What probably confuses you is the manuals you've seen for CV carbs, with those you sync the butterflies. Not applicable with your cb350.....

I think we have a winner.  I would have never thought of that.

Manual slide carbs you adjust the slide height which gives equal vacuum on each carb which should then draw equal amounts of fuel and thus create equal amounts of power on each cylinder to give a smoothe idle.

CV carbs (or vacuum operated slides) you would adjust the throttle butterflies to give equal vacuum on each carb which would, in turn, raise all the neeldes to the same height, which would then allow equal amounts of fuel to each cylinder --> thus smooth idle.

All the 69-78 bikes had manual slide carbs.

IW

[superthegoose]

Got it. Thanks, again, fellas. Makes a lot of sense.

The CV vs. manual slide has been the one thing that's thrown me off the most about rebuilding these carbs. Most of the research I did dealt with CV carbs and I didn't totally acknowledge the distinction until I had them mostly torn apart.

[robvangulik]

Which is more or less what I would call a bench sync... 

More or less, but much easier, if all but one or two close, loosen the ones that don't , push them shut and fasten....not really syncing in my humble opinion

[lucky]

Okay - that's what I thought. Why are there so many tutorials on bench syncing where the butterflies are adjusted in lieu of the slides? Just different specs on different bikes? Also, is there a "sweet spot" where the butterflies should be adjusted to on this bike, by way of the screws that adjust them?

Forget all that nonsense about "butterflies".

Just make sure they close all the way.
If they are choke butterflies just make sure they are all opening at the same time.
They do not usually need to be synced and many times no adjustment provided.

There is no "sweet spot" nonsense.

[superthegoose]

Okay.

Idiot check: slide cutaways facing choke side, correct? Using the little notches in the slide bottoms on the engine slide as a reference point for syncing.

Also, what's the consensus on the idle adjustment screw? Should this be used in the syncing process or opened/closed all the way?

[robvangulik]

Idiot check: correct.
Just set idle so that the bike runs well enough to vacuüm sync it properly.....

[superthegoose]

So I bench synced the carbs with a 1/16" drill bit. Got everything back on the bike (the air box/boots were a bit of a "female dog in heat" and the clamps are a bit bent up/boots look like they need to be re-adhered but I'll deal with that later - it did all go on eventually). Started it up after a few kicks. Coughed a bit but came to life. It did dump some fuel out of one of the overflows AT FIRST, but it ran pretty well and seemed FAST compared to before. I only had time to ride it around the lot before work, but I told my buddy he could take it for a short ride to see how it felt. He said it ran pretty great, but still stumbled a bit or "lacked pep" off idle or in low rpms. He set he took it to 80mph.

I had initially set the pilot screws to 2 turns out, as per the Clymer's manual, but after reading posts on here a bit more I set them to 1.5 turns out to see how it felt the next day. It started up with a couple of kicks and I rode it home and it felt pretty good. Stalled once off idle at a light but started right back up electric (starter worked when I got it but now starter clutch seems to only work intermittently when bike has been running a bit). I went for a ride with my girlfriend yesterday and it seemed like it was misfiring on one cylinder by the end and it was back to losing power going up steep hills, at one point a loud pop and a surge.

I haven't done or gotten a vacuum sync yet, simply because I don't own a manometer. I'm hoping to have that done ASAP. Would this noticeably improve things? Should I set the pilot screws in more (I've read 7/8 turn on this forum, I just assumed I'd make adjustments in increments when needed)? There have been no more leaks since initial startup after rebuild.

Another thing I noticed was the breather hose that's routed from the engine seems to have a constant stream of whitish smoke. I wouldn't call it heavy, but it's steady. I put my finger by it yesterday and there was some oil residue, but oil is not pouring or spraying out or anything. It may have always done this, but I never noticed this breather until I was reassembling the bike. I'm not even sure how to route it, so it's hanging off the side of the frame now.

One last thing I'll point out is that when putting in the needle jet in the #2 carb, the clip was slightly bent. I straightened as much as I could, however there was some slight play left in that particular needle once clipped into the slide, whereas the others had none. This doesn't seem like it'd be an issue to me, I just figured I'd mention it just in case.

[flybox1]

BREATHER Vapor - nothing to worry about.  since the 350F did not have the breather filter and recirculation system other bikes had, you can put a filter on the end of it.  it will decrease the more you ride.

a vac sync really quiets the 350F down....assuming you have all the other stuff done, first.
(valve adjustment, timing, cam chain, etc)

[superthegoose]

I noticed that the diagrams for some other bikes show the breather on a recirculation system. I'm glad the vapor isn't really an issue.

I do plan on getting a vacuum sync as soon as I can.
I haven't done any of the other stuff mentioned, as this is my first time doing any work on a bike and my problems had seemed fuel related. If digging deeper is necessary, it may have to wait until the winter when I can really figure all that stuff out. Cam chain makes a rattling noise that's sometimes noticeable, but not hugely. The guy that initially cleaned my carbs before I decided to rebuild them myself said that he tried to troubleshoot the noise, but couldn't figure out how to get it to stop. Not sure what he did to troubleshoot it, if anything.

Any input as to why it would misfire and lose power uphill/under load?

[superthegoose]

Maybe I should also mention that the PO put 4-4 straight pipes with heat wrap on this bike. No headers. I don't know how else to describe them, the pipe almost look like headers themselves. Just pipes curved to position. Kinda #$%*ty. Planning on getting a new exhaust setup when I can.

[flybox1]

it could be a number of things...
you really need to start knocking out the items on the 3000mi scheduled maintenance, otherwise you're chasing a symptom while not knowing everything else is in order.

did you press out the emulsion tubes hiding under your main jets when you cleaned your carbs?


ahh....aftermarket hack jobs.  with those pipes, jetting will be needed.  did you note what size jets were in there?
stock is 35pilots/75mains

[iron_worker]

Yes, agreed on above. Non-stock exhaust means that non-stock jetting can be expected.

IW

[superthegoose]

I kind of started to figure the exhaust might be part of it. If I can track down some headers, is there a *close to stock* exhaust setup that I can put together without breaking the bank? I almost had my hands on some nice headers recently (missed the boat ) and was planning on ordering pipes from dimecity.

I didn't check the jet sizes I took OUT of the carbs, but I do still have them in plastic baggies and can check later if the size is listed on them(?). I used the K&L 350F rebuild kits and replaced everything save for one needle jet clip when the new one flung out of my hand into the abyss. Just used the old one which was kind of bent, but did the job. I had assumed all the old jets were stock, but I guess I could be wrong. The reason I got the rebuild kits was that the guy who had cleaned my carbs said I needed a new float needle and he advised going over all four carbs. I replaced everything in the kit simply to be consistent.

Before I rebuilt the carbs, I was getting fuel out of the overflow pretty consistently this season. So far, that problem seems to have been corrected save for immediately after putting the bike together and starting it. The sluggishness off idle and power loss uphill was going on before the carb rebuild and actually the main reason I started digging into the fuel system.

Ah, the emulsion tubes.. I feel kind of stupid, but I didn't take out all four of them. One of them FELL out when I took out the throttle slide and since the others were kind of locked into place, while this one slid in and out, I just left them alone. I thought I ought not mess with the others, for lack of knowledge. I do realize that the main jets keep them in place, I was just a little wary of messing with them at the time. However - I did a pretty thorough job with a carb cleaner spray, some q-tips, and a ton of compressed air in every hole I could find. It would definitely suck to have to rip 'em apart just to pull those tubes, but if I have to I have to, I guess.

[superthegoose]

What are the 3000mi scheduled maintenance items I may have missed?

It's got a new air filter, battery, plugs, plug caps, carbs rebuilt, tank lined, petcock rebuilt, fuel lines blown out, oil has been changed a couple of times, I put a new oil filter on last oil change, guy who cleaned my carbs also cleaned the points.

[flybox1]

be thorough on your carb clean or you'll be pulling them over and over.
the emulsion tubes take liquid fuel and air, and mix them really well on their way to the engine.
the tube itself has many tiny holes along its sides, and if any are clogged, this mixing process is less than ideal.

now, if the jets are still stock, and you have these open headers, you're lean = LACK OF FUEL
if the emulsion tubes are clogged = DECREASED FUEL SUPPLY
2 systems are causing a LEAN condition....i would assume this is why you have the accel issues you do.
this is supported by the fact that it ran BETTER when you turned IN the air screw (making it richer at idle)

OEM airbox and filter or pods?  whatcha got?

get the rest of your maintenance sorted.
you can use the headers, but jetting, and maybe intake will be needed if you stick with them.
MAC Performance makes a decent 350F exhaust for about 3 bills....check NICHECYCLE.com
minimal changes in jetting will be needed for the MAC

[flybox1]

What are the 3000mi scheduled maintenance items I may have missed?

It's got a new air filter, battery, plugs, plug caps, carbs rebuilt, tank lined, petcock rebuilt, fuel lines blown out, oil has been changed a couple of times, I put a new oil filter on last oil change, guy who cleaned my carbs also cleaned the points.

the biggies....
valve adjustment
points cleaning, gap set, timing and advance set
cam chain adjustment.
carb cleaning, oil, filter, plugs, air filter

...then, LAST....a vacuum sync of the carbs.


and did your guy just file the points and clean them, or did he gap them and set your timing and advance?

[flybox1]

pdf of your shop manual is here...
http://www.honda4fun.com/materiale-documentazione-tecnica/shop-manual
download all parts, and save them.

[superthegoose]

I'm going to go ahead and assume he just cleaned the points. Not certain, just my guess. I guess I'm gonna really have to go back and hit the book.

Is this all stuff I could reasonably do myself or should I just take it somewhere to have done? Mostly really talking valve adjustment and timing.

[superthegoose]

@flybox1 Thanks for the pdf and advice. Invaluable information is always appreciated.