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Do you want me to try and get you some cheap(er) choke plunger springs?

  • No, I think you're a tight arsed b*st*rd

    Votes: 0 0.0%

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skeptical old git
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Discussion Starter #1
in the unlikely event that any AT owner hasn't had their choke plunger sieze up (bad running at low revs, poor idle, poor fuel economy), have a quick look at this thread:
http://www.xrv.org.uk/phpBB2/viewtopic.php?t=4693

The replacement parts from Honda cost about 46 pounds per choke. But one possible problem is that the spring has corroded and is too weak to push the plunger back in. To get the OE spring costs 46 pounds as you have to buy the whole kit of parts!

Which is why my choke is now bodged with a biro spring...

I could investigate getting suitable springs from another supplier. I'm thinking it would be good to get a set of 6 springs - 2 springs as close as possible to the OE item; 2 springs about 20-25% stiffer; and 2 springs about 40-50% stiffer? The reasoning being that the OE spring is a bit feeble so a stronger one may help, and having a heavy action at the choke lever isn't exactly a big problem (though you might have to hold it on if the spring is really stiff).

Unit cost is going to fall dramatically if there's several people interested, as the minimum order is about 30 pounds. I'm happy to go with a concensus if others think my idea of 6 springs per person is daft, but buying 2 or 6 springs each isn't going to affect cost much, so if I organise it I'd want everyone to agree what we buy and everyone gets the same stuff, just to keep it simple.

If you're interested, please use the poll to vote yes, to save me counting responses in this thread!
 

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I hope it never happens, but I'm happy to go in on a job lot and they can hang around my garage looking useful.... :lol:

Thanks,

Ali
 

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3,086 Posts
Happy to pay a tenner and never use the choke so stiffness doesn't fuss me either.
 

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Premium Member
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The site can fund the minimum order if you want or stand guarantee if you don't get your minimum.
I'll happily take any excess and sell them on the site shop.
 

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skeptical old git
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Discussion Starter #5
DaveS said:
The site can fund the minimum order if you want or stand guarantee if you don't get your minimum.
I'll happily take any excess and sell them on the site shop.
Thanks Dave.

The minimum order works out at 26.44, so I think that will provide more springs than we need. If nobody minds, we could pass these on to you for the shop, proceeds going to support the site.

Incidentally, to get a match I need to measure the wire diameter, outside diameter of the spring, free length and compression rate. I have one spring purchased at vast expense from Honda to work from (using an old spring isn't going to work; we know they go soft, which is part of the problem).

Outside diameter and free length are easy. Wire diameter is hard (I don't have a micrometer(?)) but I can probably figure out which is the nearest thing that Springmaster stock - it doesn't need to be a perfect match.

The hardest thing is going to be spring rate. In principle it's easy - how much force is needed to compress the spring 1mm. In practice it's not such an easy thing to measure at home. I can compress it by 10mm by squashing it on the kitchen scales, but they're not going to be very accurate for such a small load!
 

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Complete Member
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Spring Rate is a function of the spring dimensions and material, but if you can accurately get the dimensions the material is unlikely to be that big a factor, don't forget the pitch and total number of coils when specifying.

If you can't get the wire dia measured accurately pm me and send me a spare spring and I'll get it miked up :D

To measure the spring rate, put the spring inside a clear tube and drop in lead shot of a known weight (weigh a bagfull and divide by number of pellets) and measure the difference, vernier height gauge is best (or the depth gauge fitted on vernier calipers.
 

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skeptical old git
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Discussion Starter #8
Dilbert said:
To measure the spring rate, put the spring inside a clear tube and drop in lead shot of a known weight (weigh a bagfull and divide by number of pellets) and measure the difference, vernier height gauge is best (or the depth gauge fitted on vernier calipers.
Excellent method!

Now I need some shot... have to eat a lot of pheasant :D
(Don't tell me there's another way to get lead shot. I don't want to know.)
 

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Just voted, I'd be very interested to have a set as spares for the day when my choke stops working.

I read in previous posts that the plastic fitting that holds in the spring often breaks on disassembly, does anyone have a picture of this? Does it have to be plastic or would a metal replacement work? If so maybe we could measure one and make a design to facilitate replacements being made (my dad is pretty handy with a lathe for example). Just a thought...
 

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Generalissimo Tea Boy
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Grader said:
Just voted, I'd be very interested to have a set as spares for the day when my choke stops working.

I read in previous posts that the plastic fitting that holds in the spring often breaks on disassembly, does anyone have a picture of this? Does it have to be plastic or would a metal replacement work? If so maybe we could measure one and make a design to facilitate replacements being made (my dad is pretty handy with a lathe for example). Just a thought...
I have a CAD drawing of the plastic bit, need to dimension it up and get a pitch gauge for the threaded piece.

I can PDF it but don't know how to place that here.
 

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skeptical old git
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Discussion Starter #12
Grader said:
Does it have to be plastic or would a metal replacement work?
The only problem I could think of could be if it seized into the carb body, which would be a bit disasterous... I suppose that's one reason why it may be plastic?

What could be really useful I think would be a tool to undo the plastic bit without fumbling.

An ordinary 8mm (or is it 10mm?) spanner is just about OK, giving you 1/16th of a turn, but it is very hard to get access. I wonder of breakages are because it's hard to get the spanner on without exerting leverage (in the wrong direction) on the plastic bit?

In theory, something like an ordinary spanner with a 90 degree bend at the end - as close to the head as possible - should do the job?
 

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Generalissimo Tea Boy
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icenian said:
Grader said:
Does it have to be plastic or would a metal replacement work?
The only problem I could think of could be if it seized into the carb body, which would be a bit disasterous... I suppose that's one reason why it may be plastic?

What could be really useful I think would be a tool to undo the plastic bit without fumbling.

An ordinary 8mm (or is it 10mm?) spanner is just about OK, giving you 1/16th of a turn, but it is very hard to get access. I wonder of breakages are because it's hard to get the spanner on without exerting leverage (in the wrong direction) on the plastic bit?

In theory, something like an ordinary spanner with a 90 degree bend at the end - as close to the head as possible - should do the job?
You're right, it is mostly about the angle you apply pressure, but it's much more fragile when the plastics been warmed and cooled for a few years, it's a 46 quid disaster waiting to happen. My heart is going like a train when I undo the things and I would never do anyone elses in case I broke it.
 

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Just voted,Great idea, using a biro spring in the rear carb for the last year or so. and have a feeling trouble is just around the corner.


Eamonn.
 

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skeptical old git
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Discussion Starter #16
I haven't forgotten!

My approximate measurements:

free length 21mm
11 coils
wire dia. ~ 0.6mm
outside dia. 5.5mm
spring rate ~0.9N/mm

My cheap plastic vernier calipers aren't accurate probably, but should do for a "nearest match" from springmasters.

Spring rate measurement was probably poor. I compressed the spring by 10mm on some kitchen scales, which read 900g. So that's 90g for a 1mm compression. AFAIR from fizzicks many years ago, 1N is equivalent to 100g, so that's 0.9 N/mm.

Anyone with a spare spring like to post their own measurements?

I think we need a spring that is defintely no shorter in length; no smaller in diameter (it must fit around the base of the plunger) and not very much larger diameter (must fit within sleeve). Spring rate should be similar or higher.

Springmaster part nos. with reasonable match seem to be the following:


C-5503840, 6.0mm out dia, 0.61mm wire, 25mm length, 12.2 coils, 0.87N/mm

D11480, 5.63mm out dia, 0.63mm wire, 26mm length, 14.5 coils, 1.03 N/mm

C-5503990, 6.1mm out dia, 0.61mm wire, 22.23mm length, 10.0 coils, 1.04N/mm

C-5504440, 6.1mm out dia, 0.66mm wire, 22.23mm length, 11.0 coils, 1.31N/mm

There's no clear choice as I was naively hoping for, i.e. one very similar to OE, one a little stiffer, and one a lot stiffer. The first is a similar spring rate but 4mm longer; the last is nearly 50% stiffer but about the same length as OE.

Thoughts/opinions?

The list of possibilities is at: http://www.springmasters.com/compression-springs/61-66.html
 

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I had a quick look at the site, came up with these:

Similar to OEM:
C-66039802 0.61 wire dia / 6.10 OD / 20.62mm FL / 0.94N/mm

Slightly higher rate than OEM
C-6604430 0.66 wire dia / 6.10 OD / 20.62mm FL / 1.23N/mm

Considerably higher rate than OEM
C-6605420 0.74 wire dia / 6.10 OD / 20.62mm FL / 1.83N/mm

Not sure what the acceptable ranges for ID and OD but all the above have the correct free length.
 

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skeptical old git
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Discussion Starter #18
Grader said:
C-66039802 0.61 wire dia / 6.10 OD / 20.62mm FL / 0.94N/mm
[typo in part number? think this is C-6603980?]
C-6604430 0.66 wire dia / 6.10 OD / 20.62mm FL / 1.23N/mm
C-6605420 0.74 wire dia / 6.10 OD / 20.62mm FL / 1.83N/mm

Not sure what the acceptable ranges for ID and OD but all the above have the correct free length.
Thanks for looking, those are useful options. The OD (and feasibly ID) could be marginal - I should have given more in my post :oops:

The OD must be small enough to fit within the metal and plastic parts at the end of the cable. My (naff) vernier calipers suggest the inside diameter of these parts approx. 6.1mm, maybe slightly higher. So spring with OD 6.1mm may just be too tight; probably worth getting one or two options, but we need some smaller ones too I think.

It's hard to say how important the ID is without trying the springs. It must be reasonably firm on the base of the choke plunger - the plunger must not be able to slide up inside of the spring. So a small ID seems like a good plan - except that the choke cable and the nipple have to be able to pass through the spring, and the spring must fit around the narrower part of the plunger at its base.

The greatest ID we're considering here is 4.88mm (6.1mm OD, 0.61mm wire) which is 0.5mm oversize. I guess we'd get away with that, but I wouldn't want to push it any further..

Now the difficulty is finding a spring that's close to 5.5mm OD that isn't too weak; getting a high enough spring rate means having thick wire, but then the ID can get too low!

5.3mm OD springs are either too weak, or have thick wire that drops the ID down to 4.0mm (pretty sure this is too low)

5.63mm OD springs with wire that gives right rate have a good ID, but there's a jump from 18.5 to 26mm FL!

Above that and we're looking at 6.0mm and 6.1mm OD springs that risk being too wide :?

And finally, we probably need to worry about the length when it's fully compressed - this limits the amount of choke you can use. I think the OE spring could be fully compressed, which is 6.3mm. Most of the springs I found can be compressed that much - though I don't think the bike really needs full choke so probably we can forget this variable...

I'll summarise all this is a new post (as I doubt anyone read this far!)
 

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skeptical old git
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Discussion Starter #19
choices - I've marked this up as code to it should display as fixed width
(i.e. the columns should line up, so long as your browser window is wifde enough)

Honda OE measurements are approximate. OD = outside diameter, ID = inside diameter, FL = free length, CL = compressed length (is that the right abbreviation???). All dimenstions mm, rate N/mm.

Parts starting C-660 are stainless; others piano wire.

* indicates where there may be a problem, ** more so; note I don't think the compressed length matters too much as full travel of the choke lever isn't needed(???)

Code:
Part          wire     OD       ID       FL        CL       coils    rate     worthwhile?

Honda OE      0.6      5.5      4.4      21        6.3      11       0.9*

C-5503840     0.61     6.00**   4.78*    25.00     7.44*    12.2     0.87*    doubtful
C-6603980     0.61     6.10**   4.88**   20.62     5.73     9.4      0.94*    doubtful
D11480        0.63     5.63     4.37     26.00     9.14*    14.5     1.03     yes
C-5503990     0.61     6.10**   4.88**   22.23     6.10     10.0     1.04     maybe
C-6604430     0.66     6.10**   4.78*    20.62     6.60     10.0     1.23     maybe
C-5504440     0.66     6.10**   4.78*    22.23     7.26     11.0     1.31     yes
C-6605420     0.74     6.10**   4.62     20.62     7.92*    10.7     1.83     yes
I reckon there's 3 we should try, 3 more that may be helpful, and 2 that probably aren't worth it - but that's very personal judgement, please say what you think.

But bear in mind that these springs are probably cheap so buying 14 springs (2 each of all the above) may not even affect the price we pay!
 

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Icenian I've PMed you to see about sending you some plots (spring forces vs lengths for all the different options) for the different spring options.

Are you able to estimate the working lengths of the spring by measuring the parts? (max length and min length)

If I have understood the problem it is that the choke does not get stuck fully open but more in a part open condition. If this is the case we should try to select a spring that gives more force in this part of the movement (ie same rate but greater free lengh to give more preload)

Just some thoughts.


[took the liberty of inserting your graph - icenian]
 
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