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

[mattsz]

It did an excited wee because it was going home. 😂

It was better off where it was - now it's relegated to a corner of an unheated garage.  But at least it will get some attention...

[mattsz]

I have a question regarding the individual choke plate adjustments.  There's some lash in the system, so when the choke is in the closed (for cold starts) position, the #1 plate is completely closed, and each successive plate remains a little more open than the last.  When I open the choke fully (running position), each plate is mostly open, but a little less than its neighbor to the left.  This is how they came to me (click on photo to zoom in):


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I've been messing with the adjustments - I can't seem to get all the plates to be open and closed the same amount.  Is it better to set them so they all close perfectly together, but end up in slightly different positions when open (per above photo)?  Or better to set them so they all open exactly the same amount, but don't all quite completely close with choke?

[taysidedragon]

I'm no carburation expert, but I would set them all equal when fully open. That's where they run for most of the time, choke only on for a short time.
Where is the lash in the system, strange they are not moving together?

[mattsz]

I'm no carburation expert, but I would set them all equal when fully open. That's where they run for most of the time, choke only on for a short time.

Thanks!  I was thinking the same...

Where is the lash in the system, strange they are not moving together?

I'll show you, let me get a photo...

[Laverda Dave]

Mine are the same on both 400/4's. The lash or lack of adjustment appears to be in the choke linkage assembly on each carb (the flat blade screw with the locknut). If you get no.1 carb choke closed you loose a bit on no. 2 and it subsequently gets worse on no.3 and no.4. Your 4th carb looks particularly bad though, do you have any adjustment left?

[mattsz]

The choke lever turns the choke plate shaft on carb 1.  There's an adjustable linkage between the shafts of carbs 1 & 2.  Another adjustable linkage between the shafts of carbs 2 & 3, and another between 3 & 4.  See photo:


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Each of the linkages on my rack were adjusted with a little gap between the set screw and stop.  So, choke 1 plate had to rotate a bit before choke 2 plate began to do the same.  Choke 2 plate had to rotate a bit before choke 3 plate began to move.  And so on - by the time choke 1 plate was fully open, choke 4 plate had a ways to go - as seen in the photo a couple of posts back.

I don't know if mine are normal, or if there's something wrong with the mechanism, but I can't adjust them so they all open together as a unit and close together as a unit, ending up in the same positions at each extreme of travel.  Hence my question about which choice is the better one.

Having changed the adjustment for equal open position, you can see the above photo also kind of shows how, when the choke is closed, even though the #1 choke plate is fully closed, each successive choke plate remains open a bit more than its neighbor to the left.

Here's a pic of the readjusted plates in the open position - all the same (compare to the photo a couple posts back)...


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[Bryanj]

I am probably wrong but i thought there was a spring in each adjuster

[mattsz]

I am probably wrong but i thought there was a spring in each adjuster

Each choke plate shaft has a spring forcing it closed.  Tightening each adjustment screw pushes the plate "open."  I think...  I just did it a couple of hours ago, and I've already forgotten... 

[mattsz]

Some observations...

All four float bowl o-rings were glued securely in place with plenty of some sort of goop.  Will have to clean them all off...

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#4 float bowl has a mismatched screw - bigger head, and shorter thread which is somewhat stripped at the end (although the pic doesn't really show it).  The proper screws seem to work in all four positions (carb body thread isn't damaged), so I'll get a correct replacement...

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[mattsz]

While we're playing with 400 carbs, I have another choke operation question.

There's a cam-driven linkage which appears to tie the choke to the throttle.  As mine is currently adjusted, when the choke is open (normal operation), there is a gap between the choke lever linkage and the adjustable set screw on the throttle mechanism:

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When the choke is closed, the cam shifts the linkage slightly - in theory, I suppose, to push on the adjustment screw and open the throttle a bit:

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Mine is currently adjusted so when the choke is closed, the linkage just touches the adjustment screw - but it doesn't actually open the throttle at all.  Is it supposed to open the throttle?  My copy of the service manual doesn't mention it...

[mattsz]

I've spent a good long while reading through carb cleaning posts - not finding anything definite: I'm hoping to clean all the carb bits I've removed from inside the float bowls - I haven't split the carb rack or opened the top covers.  What's the best way to do this?  Any particular solvents better than others?  I have carb cleaner spray, and some cans of solvents, including mineral spirits (paint thinner), lacquer thinner, acetone, kerosene (paraffin for you blokes?), even alcohol.  I could buy a gallon-can of liquid carb dip, but it's not cheap.

I wasn't planning on any kind of major soak for the four attached carb bodies, but I'll need to clean the undersides of the carbs and all the passages (spray for that, I guess)...

[taysidedragon]

Carb cleaner spray and use of an old toothbrush cleans up the carb bodies ok.

To clean all the passages and jets it's best to use an ultrasonic cleaner. Check passages are clear afterwards with air jet can (computer type) or carb cleaner spray. No prodding with wire!

[mattsz]

Carb cleaner spray and use of an old toothbrush cleans up the carb bodies ok.

To clean all the passages and jets it's best to use an ultrasonic cleaner. Check passages are clear afterwards with air jet can (computer type) or carb cleaner spray. No prodding with wire!

Thanks!  Not even thin copper wire?  This seems a fairly common procedure.

[mattsz]

While we're playing with 400 carbs, I have another choke operation question.

There's a cam-driven linkage which appears to tie the choke to the throttle... 

Never mind... I found this on page 7 of the factory manual:

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Clearly mine is not correctly adjusted.

Even with my carbs sitting on the bench, I'm not sure I can reach that adjustment with any tools I currently have.  I certainly can't imagine being able to do it with everything assembled on the bike... must be possible, though...

[Laverda Dave]

Looking at your re-adjusted carbs with the chokes open is about right.  As Taysidedragon mentions, they are normally open 95% of the time so that is where you want the adjustment to count.  As an aside, when I start my bike on full choke I have to open the choke a fair amount once the engine has started otherwise it races up to 3000RPM.