rebuilding carbs

[exvalvesetdabbler]

I decided to have a go making the drain screws and had a practice run this morning. Here's what came out of the garage.
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The OEM screw is the tarnished one with screwdriver marks in the slot.

A little refining of methodology and it should be doable.  The first mistake was in cutting the screws slot and then facing off the screw. It caused the tool to jump a bit. Second was removing one thread too many closest to the screw head.

The 1 mm drill bit was a bit blunt after using it on fibre glass PCB material so I picked up a couple of new ones this morning.

Regards
Dave

[Johnny4428]

That looks just great Dave! Have you tried it in the carb float bowl?

[exvalvesetdabbler]

That looks just great Dave! Have you tried it in the carb float bowl?

Short answer  - doesn't fit

Long answer - the old knackered carbon steel die I  found lying around  is giving me an oversized thread.

This was a run through to make sure I had the necessary tooling and holders.  I'm sure with a decent die  and a regrind of the lathe tool to give a smoother finish on the underside of the screw head it will be ok.

Regards
Dave

[K2-K6]

Nice aesthetic in that though, which will make a good replacement when small issues, mentioned  above, are resolved.

Does anyone else find that you need a unusually large flat blade screwdriver to engage them properly, and not just twist them in middle of slot that leads to "camming" out along with that subsequent mushing of the slot  ?
Also need one with very good condition "grind" and flat end to let it engage fully and deep into slot.

[exvalvesetdabbler]

I have a big flat blade screwdriver intended for electricians that usually gives a snug fit.  The trick is not to overtighten them in the first place.

But you're right if some monkey uses a too small too thin driver the slots get chewed.

[Oddjob]

Were you aware that there is a Honda special tool for the clutch adjuster on the 500-4 Nige. The big slotted thing in the drive chain cover. Might also fit the drain screws, never tried it but seem to recall it’s a multi bladed tool

[K2-K6]

Were you aware that there is a Honda special tool for the clutch adjuster on the 500-4 Nige. The big slotted thing in the drive chain cover. Might also fit the drain screws, never tried it but seem to recall it’s a multi bladed tool

I was much more involved with the 750s Ken, and so not familiar with that tool. Sounds like it could be good for this though.

My own method is a great big woodworking screwdriver that my dad used to drive in big brass hinge screws by hand (before electric tools were invented    )not sure, but either Stanley or Marple brand, the type with see through yellow resin handles for properly leaning into the job in door hanging. 

[exvalvesetdabbler]

New m6x0.75 die arrived so on with making the drain screws. First job was making a jig for the through holes.

It screws onto the screw.
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Turn down a blank screw ready for threading. The undercut around the cross holes is 5 mm dia to match the root size of the thread in the float bowl.
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Add the thread and drill the through holes. I used my PCB drill for the cross holes using a 1mm bit. Important to get the length of the screw exact at this point.
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Saw of the screw and rough face off leaving a small pimple in the center. This is to center the slotting saw. The hole was slotted using a slotting saw mounted on a arbour and the screw mounted in a jig on the tool post. It does mean that the screw slot is slightly curved matching the diameter of the saw but it's not noticeable.
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Once slotted face off and polish. The screw is screwed into the holder to do the finishing cuts and something to hold onto while polishing.
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One issue that emerged was the female thread in the float bowl was slightly tapered, they hadn't gone all the way through with a straight tap so any over size on the screw length would tighten up before the head bottomed out on the recess on the float bowl.

Regards
Dave

[Johnny4428]

That’s a great job on these drain screws. Looks the business.

[exvalvesetdabbler]

Slowly getting around to final assembly and making a start on sorting through a pile of brass ware, in particular the needles and emulsion tubes.

All of the needles I could find all measure the same at the top near the circlip where the needle is parallel and not tapered.

Then  just dropping the needle into the tube and seeing how far it falls in.

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So top to bottom, all keihin needles
Good
Good
Good
Not so good
Really bad

With the good ones, the bottom groove lined up with the face of the oraface. Worn tubes allow the needle to drop in further. Swapping needles around makes no difference.

A lot of folk still maintain that original parts reused are a better option than Keyster replacements,  from experience, I don't agree with that unless you are paying attention to any possible wear on the inside of the tube at the top. It's not obvious just by looking at them. The needles seem ok though.  Ignore this and spend the next few months chasing rich running and sooty plugs.

I think wear to some extent depends on riding style, scratching around back lanes or urban traffic is probably going to impart more wear than constant throttle on a motorway.

Anyway, we have touched on this topic off an on, at least since I have been a member on here, so I thought about posting the evidence  for the next person that comes across this issue.


Regards
Dave

[DomP]

Hi Dave, thats in interesting way of doing it with the emulsion tubes, that my find the problem with my 550f rich running

[Oddjob]

I'm wondering why the bottom 2 needles only appear to have 3 grooves whereas the others have 5. The bottom needle point also doesn't look like a Keihin needle, too blunt and wide.

[exvalvesetdabbler]

I'm wondering why the bottom 2 needles only appear to have 3 grooves whereas the others have 5. The bottom needle point also doesn't look like a Keihin needle, too blunt and wide.

They have disappeared into the emulsion tube because the hole is enlarged.

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Regards
Dave

[exvalvesetdabbler]

I can't say this trick will work for all keihin but it does for the 400f

The two bad ones were responsible  for black plugs in 2010 when I rebuilt the carbs after they got gummed up while laid up for a couple of years.  At the time I replaced them with genuine parts and the problem went away. All other brass ware had already been replaced with  genuine honda bits, the tubes and needles weren't in the rebuild kit so you had to buy them as a separate needle set.

Regards
Dave

[K2-K6]

Good inspection and detail in appraisal.

Some interesting and relevant findings too.

Speculation on wear of emulsion tubes, I feel it is unusual in pure ability to "cut" or wear the emulsion tube with the needle as the periphery moves away from the needle with wear occurring, which in metal machining usually stops the cutting happening. Something clearly going on there, but a little of a mystery in trying to think exactly how it happens.

Certainly food for thought.

Wondering if there's any ovality to the wear or is it circular  ?  Could it even  be seen in that size though  ?