New (to me!) '77 CB400F - US model

[mattsz]

Regarding the clutch...

It seemed to work fine three years ago when I rode it last, but now it's become extremely difficult to pull.  I won't hazard a numerical guess about the actual force required, but it's not safe to ride in this condition.  It can be fully pulled, and it does return on its own, albeit a bit sluggishly.

Aside from the obvious possibility of a binding cable, what else could be the trouble?

Might this be expected of a bike that's been sitting for a couple of years?  In other words, should I be thinking about solving this problem before I try running it (whenever that turns out to be)?  Or might it sort itself out with some oil circulation and exercise?

[Bryanj]

Almost certainly cable and as a hint DO NOT oil an original cable as the onner is rubber coated and the outer nylon lined, oil tends to "swell" both and make the cable tight. Aftermarket cables may dispense with one or both of the linings and be safe to oil but i dont comment on that!!

[mattsz]

Almost certainly cable and as a hint DO NOT oil an original cable as the onner is rubber coated and the outer nylon lined, oil tends to "swell" both and make the cable tight. Aftermarket cables may dispense with one or both of the linings and be safe to oil but i dont comment on that!!

Thanks for all you helpful advice bryanj!

[mattsz]

I took a look at the fuel tank today.  The interior looks to be pretty rust-free, but I can't see in very far... and I hear some fine particles rolling around inside when I twirl the tank about.

I removed the petcock and the fuel filter tube stayed in the tank, the gasket sealing it to the petcock was a bit chowdered.  I made it worse pulling it out of the petcock nut.  I was able to drag the filter out, revealing rust in the petcock mounting "tube."  Still can't see inside the tank, though, to try to get a sense of what's going on in there.  Pics below - the fine rusty-dusty particles fell from the filter when I tapped it on the table...

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I don't know if the petcock innards are in working condition... body is riveted, is there any hope of refurbishing this one, or should I just spring for a new one?

[Bryanj]

What size is the tread on the tank, if 18mm i can help you.

[mattsz]

What size is the tread on the tank, if 18mm i can help you.

Not sure... just measure across the outlet exterior?  I do know that the nut holding it on takes a 19mm wrench.

Help in what way?  We are on different continents... aren't we?

[Bryanj]

Measure the diameter of the spigot, i have a pattern, new, 18mm petcock complete with strainer and seals, if it fits you can have it for post cost.

[mattsz]

Measure the diameter of the spigot, i have a pattern, new, 18mm petcock complete with strainer and seals, if it fits you can have it for post cost.

I think the '77 bikes have a different petcock than the earlier models... anyway, I measured across the threaded fuel tank outlet (see second pic a few posts back) - its outer diameter is 13.95mm, inner diameter 8.72mm... does this help?

[Bryanj]

Sorry that means the one i have wont fit mate, try looking for 14mm petcock on fleabay.

[mattsz]

Sorry that means the one i have wont fit mate, try looking for 14mm petcock on fleabay.

Thanks anyway!

Is my one no good, then?  The filter tube can't be reinstalled and the gasket renewed?

[Bryanj]

If you can get them yes but frequently nowadays you can only find the complete petcock.

[mattsz]

David Silver's US site sells just the strainer and o-ring, as well as the whole petcock:

https://www.davidsilverspares.com/CB400F-SUPER-SPORT-1977-USA/part_163258/

Interestingly, though, his UK site only lists the complete unit.

Does anyone know how this thing is supposed to install?  Does the strainer just insert flush into the tank opening, then the o-ring drops into the petcock fitting and you just tighten it up?  That's how I found mine, except the o-ring was wedged beneath the big retaining nut.  Could be it just forced its way in there over time?

EDIT: DSS lists two different "genuine" parts at two different prices.  Huh.  One of them has a good photo showing the inside of the retaining nut:



I'm guessing that o-ring isn't meant to retain that strainer, if it was it would probably restrict flow to the reserve opening.  But it does look a bit like the strainer is meant to stay attached to the petcock, which mine clearly didn't...

Or, do you drop the strainer over the tube, then slide the o-ring over the strainer, so that the open end of the strainer is held captive by the o-ring down inside the retaining nut?

EDIT x2: That pic doesn't show the strainer... so I'm still not sure how it's supposed to go...

[Bryanj]

Just recently done a cbx 550 so i can definitively tell you that if you do not want a leak the strainer pushes into the petcock then you fit the washer/O ring before fitting the assembly to the tank

[Nurse Julie]

Yep, same as the 400/4 then Bryan.

[mattsz]

I'm sorry guys, but I'm just not clear on how this thing is supposed to be configured.

When I removed the petcock, the o-ring was stuck beneath the threads of the retaining nut, and the strainer remained tightly stuck in the tank opening, perfectly flush with it.  It was a tight fit between the little collar on the open end (which is how the gasket is supposed to hold it in place?) and the tank outlet.

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I needed a sharp 90º pick tool to reach in and hook it and drag it out.  As far as I know, the petcock was working and not leaking, but it sounds like that is not the correct arrangement?

Now this photo shows the how the strainer lies in relation to the reserve opening when the petcock is on its side; it fits loosely enough on the inner tube that it doesn't block the reserve opening:

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But if the gasket is properly round with an opening right in the middle, holding the strainer down against the petcock body, I would expect the strainer to remain centered, with the collar blocking the reserve opening:

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But this is the correct arrangement?