Author Topic: 350f carb rebuild - step by steps  (Read 1775 times)

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Offline BraxtonJay

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350f carb rebuild - step by steps
« on: May 03, 2020, 03:56:15 PM »
Does anyone have easy resources on how to do a complete carb rebuild for a 72 cb350f? The only manuals I've found are terrible photocopied, and not very helpful. Tried finding videos as well, but nothing breaks it down step by step.

Any help is greatly appreciated! I just wanna get this bike up and running. Thanks!

Offline WhyNot2

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Re: 350f carb rebuild - step by steps
« Reply #1 on: May 03, 2020, 06:16:15 PM »
same boat here.
If it ain't raining, I'm riding.....~~{iii}?~~prost

If it sounds like I know what I'm talking about, it's because I cut and pasted from someone else.

Offline Bodi

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Re: 350f carb rebuild - step by steps
« Reply #2 on: May 03, 2020, 09:50:49 PM »
What does complete mean to you?
Taking the bodies off the rack is not usually necessary, but if you have leaks at the fuel junctions... 3 have to come off at least. The throttle rod assembly... not designed to come apart and it will be a real test of your skill to do that and get it together again.
Basically you open a case of canned worms by taking the bodies off, but that is possible. There are three main problems on reassembly: carb balancing, the idle secrew setup, and the choke throttle advance setup.
If you take apart the choke lever and linkages etc, do not lose the miniscule ball and spring for the choke lever detent.
If you want a basic renovation buy four Honda gasket sets and four Honda float valves. Get four food saver containers, mark them 1-4, and keep parts segregated.
Take each body apart as far as possible. The slides come out by removing the lift àrm bolt, the lift arm ball joint pulls out of the lift link socket: take care to study how it goes back in as it must go between two black parts... you don't have to take that bit apart for reassembly, a small pick wil let you open the gap and slip the ball in.
The needles are held in by the lift link, two small JIS screws then it rotates to come out. Note the clip position.
Be very gentle with the float pivot pins, the posts are delicate and you DON'T want to break any off. If jammed, some penetrating oil and a big of heat (carefully)  will free up most.
The black plastic floats will not be harmed by fuel, and can't leak. Careless handling can damage them, usually bent legs or damage at the pivot or tang.
The main jets just pull out after the retainer clip is removed. The needle jet / emulsion tube comes out the main jet hole, push in on the jet end in the throat with a wood stick.
Pilot jet screws in. Needle valve seat is held in by a screwed down clip.
Pilot adjuster screw may have a black cap to limit adjustment, that pulls off to reveal the actual screw. Remove the needle tip screws and their springs. First, screw them in to seat while counting turns, record that... probably around 1 1/2 turn. Check for o-rings stuck in the holes.
Avoid removing the choke plates if you can, their screws are staked. Screws should be replaced rather than reused. SS button head allen screws are available.
You need to clean out some air passages, these start from the outer throat. Carb cleaner spray should spurt out in the bowl when sprayed in the openings.
Carb spray should be safe for plastic and rubber parts, carb dip IS NOT.
Once all brass is out, clean the bodies. Carb cleaner spray and a toothbrush are good for the throat and exterior.
Clean the linkages and throttle rod mechanism as well as you can. Oil the rod bearings.
Clean the brass parts well. Carb dip is ok for them. Don't use hard wire to clean jet holes. Copper wire is ok to poke clean the cross holes in the main and pilot emulsion tubes.
Blow passages out with air, can or compressor.
Clean out the bowl drain passages. And in the drain screwsThe bowl gasket should be glued in. Clean the groove thoroughly, a soak in acetone and lacquer thinner should soften factory glue. I use "weatherstrip adhesive" but some swear by superglue.
Take many pics during disassembly, you will want to look at them during reassembly.
Assembly is done dry except for a film of oil on the slides.
The gasket kit has the bowl seal, top cover gasket, and a bunch of o-rings. There are 4 fuel tube o-rings in each, only used if you dismounted the bodies. The rest are for the main jet, pilot screw, drain screw, maybe something else.
Instaĺl the original brass parts. Replacement brass - other than genuine Keihin - is dubious at best. Install the slides. The cutouts must face the choke plates, no problem if parts were kept segregated but they can be mixed up and then installed backwards.
Set the float height to spec. The procedure is in the service manual. You don't need the tool, cut out some stiff paper to make one or use a small rule. Check you pics to make sure the floats are correct... they look pretty good upside down.
Once they are all together with lift mechanism connected the sync should be checked, the lift arm bolts allow some play even if nothing else was touched. If a slide or two look nuts - throat gap way off, check the lift ball is between the black parts. Pick one carb as "master" and do not adjust its sync screw. Adjust the other 3 so the throat openings match, this is your "bench sync".
Confirm that the idle screw has ok travel, loosening it should let the slides close almost entirely. Close the choke, slides should open a bit.

Offline carnivorous chicken

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Re: 350f carb rebuild - step by steps
« Reply #3 on: May 04, 2020, 07:27:15 AM »
Very thorough.

I just tore mine down because there were leaks at the o-rings at the junctions, pain in the ass. But it's not rocket science. One thing you did forget is to swear at the Honda engineers for making the rack so damn hard to remove and put back in the first place. Holding back to the airbox with ratchet straps helps, and moving them up and down to clear the boots helps. The other thing I'd add is to check the float level using the clear tube method before you remount the carbs. And get new fuel line on your carbs before you mount them.

I also replaced the float bowl screws with allen in order to make removal of the float bowl easier when the carbs are still on the bike.

Offline mattsz

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Re: 350f carb rebuild - step by steps
« Reply #4 on: May 09, 2020, 01:24:44 PM »
Clean the linkages and throttle rod mechanism as well as you can. Oil the rod bearings.

What are the rod bearings?  Are they accessible to oil if the carb bodies are not separated from the rack?

Quote
The bowl gasket should be glued in. Clean the groove thoroughly, a soak in acetone and lacquer thinner should soften factory glue. I use "weatherstrip adhesive" but some swear by superglue.

I've seen the "discussions" about gluing them in place - is this just to make them stay put while you mount the bowls, or is it required to get a proper long-lasting seal?

Offline Bodi

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Re: 350f carb rebuild - step by steps
« Reply #5 on: May 09, 2020, 05:09:23 PM »
The throttle shaft turns in the rack frame in some sort of a bearing, a drop of oil where the shaft goes in will give some lubrication.

The glue isn't 100% necessary, it keeps the 0-ring in the groove to make assembly easier and mashing a slipped-out section unlikely. I think all original carbs I've opened had that seal glued in, with a brown substance.

Offline mattsz

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Re: 350f carb rebuild - step by steps
« Reply #6 on: May 10, 2020, 03:12:25 AM »
The throttle shaft turns in the rack frame in some sort of a bearing, a drop of oil where the shaft goes in will give some lubrication.

The glue isn't 100% necessary, it keeps the 0-ring in the groove to make assembly easier and mashing a slipped-out section unlikely. I think all original carbs I've opened had that seal glued in, with a brown substance.

Thanks for the clarifications!

Glued in with a brown substance indeed...


Offline desertwash

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Re: 350f carb rebuild - step by steps
« Reply #7 on: May 31, 2020, 03:07:59 PM »
you tube Classic Octane "how to rebuild Honda Keihin CB350.
Does a great step by step video.