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Su carb, jet sticking..


WIMPUS

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Hi,

Have a few trouble with my rear jet sticking when i used the choke.
it does stick around 2mm between the nut an the jet.

What to do about it or do i need another 'jet bearing kit' and maybe new jets ?  :o
Think it's also as old as the car itself !

Wim

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6797 wrote:


Well i know, could this be the problem ?  :-/

I do have another spare carb set i the shed, going to first try with another jet and then ... change the spring

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6797 wrote:
If you take the shaft off that links the 2 carb choke mechanisms together and the choke cable, you should see each jet snap back to the top  if you turn the choke cam and then let go. If not it's stuck or the springs are snapped/not working.


Soooo, if i get it right...

I best take the linkage off and each choke mechanism to see if it still sticks , right ?  :P (i'm a bit tired  ;D )

I was thinking of renewing the jet's (waxstat conversion then) and new jet bearing kit in the future, it's the only thing that isn't new on the carbs now !

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4526 wrote:


Well i know, could this be the problem ?  :-/

I do have another spare carb set i the shed, going to first try with another jet and then ... change the spring


Oh, so there is a spring is there  ;)

Before you pull it all apart
I presume you've tried lubricating all the moving parts of the linkage and carb bottom
On my 1500 once I removed the "lock washer" and pulled the little link bar out of the red bit, both my chokes moved back up freely. The red bits can turn a little causing things to not line up causing just a little too much friction which overcomes the springs


Quick edit
Has the wee return spring broken or "jumped " around on one of the carbs
Jet tubes don't just bend in normal use

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Well going to look at it tomorrow, already was thinking to remove the jet and lubricate it a bit better.
I sprayed some lubricant on all the linkages and pulled the choke and sprayed some on the shaft a bit more.
But seems to work this evening when i got back from eating at my aunt  :)

I don't think the jet shaft is bend, but just old.. the waxstats & jet bearing kit are 36years old and as the rest of the carbs where a bit worn .. :-/

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You could also try and check the cable moves freely, I've had many a cable "go stiff" on various motor bikes over the years caused by little frays on the inner cable catching on the outer
With luck from your last post, it's just gone dry so a good dose of lubricant may sort it out
Try some lithium spray grease if you can get it

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Wim, i'd be careful about which jet kits you get, cant remember where got mine from but it did say "SU spares" on the box.

i have huge problems getting the sodding control arm to fit, it kept jamming everywhere and was a right sod to fit, in the end i had to grind the blt head for the float chamber by about 1mm each side so the connecting rod would fit without being bent, if wasnt for my original ones pipes leaking i'd have sent them back as pain in the arse and removing them now and trying to reset the spring every time takes a while.  i know a lot of people rave about them so no idea why mine didnt fit very well but def would do it again.

rich

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1344 wrote:
You could also try and check the cable moves freely, I've had many a cable "go stiff" on various motor bikes over the years caused by little frays on the inner cable catching on the outer
With luck from your last post, it's just gone dry so a good dose of lubricant may sort it out
Try some lithium spray grease if you can get it


The choke cable is a solid steel one and i adjusted the choke now so when i push on the inside the sleeve at the carb come out of his secure thing (if that makes any sense !  >:( )
Was a try to get if off for sure  :P

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932 wrote:
Wim, i'd be careful about which jet kits you get, cant remember where got mine from but it did say "SU spares" on the box.

i have huge problems getting the sodding control arm to fit, it kept jamming everywhere and was a right sod to fit, in the end i had to grind the blt head for the float chamber by about 1mm each side so the connecting rod would fit without being bent, if wasnt for my original ones pipes leaking i'd have sent them back as pain in the arse and removing them now and trying to reset the spring every time takes a while.  i know a lot of people rave about them so no idea why mine didnt fit very well but def would do it again.

rich


The arms of the waxstat conversion you mean ?
I've heard about problems with the arms..
My waxstat jet's are actually converted to regular ones (penny/eurocent way, makes my car 8 eurocent more worth !  8))

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yep, the little metal bent wire bits that push the jet down when activate teh choke, why they werent designed to use the original ones which fit really easily i'll never know, and trying to fit the little return spring can be fun!!!!!

i'd stay as you are then and just try polishing them a bit to see if return any better, as well as fitting springs if not got them :)

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I had a look this morning, got the jet off and polished it, put some lubricant on it and tested it .
Seems to be still sticking 1mm or so ..

But noticed when i removed the jet on my spare waxstat carbs the little arm that moved the jet does jump up because of the tension of the spring ..
On my carb, nothing  :-/
maybe the springs can be worn...

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Hi Wim,

maybe it is just the bearing of the lost motion lever that is sticking.

Look at the canley diagram part no 36 a-e.
36c and 36d are small tubes. The inner one is slightly longer than the outer one.
If the inner one wears or is tightend to much, the whole system starts to stick.
You could try to leave the washer 36b out, or just loose the screw 36a a bit.

Harry

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2250 wrote:
Hi Wim,

maybe it is just the bearing of the lost motion lever that is sticking.

Look at the canley diagram part no 36 a-e.
36c and 36d are small tubes. The inner one is slightly longer than the outer one.
If the inner one wears or is tightend to much, the whole system starts to stick.
You could try to leave the washer 36b out, or just loose the screw 36a a bit.

Harry


Harry, it can be that also ! ::)
i really hope, now to just go back under the bonnet and have a look...

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Had a look if the bolt that holds everything together was to tight and no :/  (part no 36 on the canley diagram..)

And it's still sticking a bit  :-/

So..
I think i need to remove the offending carb and have a look on the workbench.
Otherwise wil try the change the choke mechanism with my other spare carb, choke works very well there and jets seems to go back very good.

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Move the throttle "pusher" (#30 I think in the diagram) out of the way - see if the choke/jet will then return properly (just make sure it's not the throttle that's jamming the choke)
Disconnect the jet from the choke mechanism and see if the choke spindle fully returns - that should tell you if the jet is jamming the choke mechanism of it the choke is keeping the jet too low (if you see what I mean)

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Well found another thing also..

So need to check it good, hope it wind stops so i can get busy (don't want another spitfire bonnet falling on my head  :o )


I had a look at my spare HS4 carbs from a dolly engine..
Seems they had problems also and solved it actually pretty clever !

Red mark shows where normally the springs it attached to and on my spare it was on the orange mark.
The jet seems to be closing very well, tested it with the spring at the red mark and seems to be not so good working..

So maybe a fix for my carbs on the spitfire ..
But i guess the spring could be just worn after all this time.

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1344 wrote:
So my original post about fitting a stronger spring wasn't far off the mark was it  ;D

Hope you sort it  :)


;D

tested it today by fitting the spring behind the orange thing on the pic and seems to be working very well now !
But i've mailed su carb (Burlen ) and Andrew Turner carbs for those springs.
only Rimmers seems to sell them  :-/

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4526 wrote:


;D

tested it today by fitting the spring behind the orange thing on the pic and seems to be working very well now !
But i've mailed su carb (Burlen ) and Andrew Turner carbs for those springs.
only Rimmers seems to sell them  :-/


After visiting Mr turner a couple of months ago, I think he should be able to sell you anything you need.

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