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Su Carb Fuel Leek


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Hi My son and I have only been members since last September. We bought a 1969 TR3A last year.

Noticing a petrol leek just below the jet nut and spring, I bought service kits from Rimmers. Carefully following instructions in an SU handbook fitted the gaskets.

The leak is now worse. What have I done wrong please. Any suggestions.

I notice on one of the carbs the ring above the jet lock nut containing the cork seal is loose even though the nut is done up tight.

 

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Hi, from my experience that doesnt sound right. That metal ring that holds the cork washer should be tight. Can you feel petrol coming from here or is it just at the bottom of the jet and dripping? Have you soaked the two cork washers that fit on the jet saft in oil prior to fitting? I think they are meant to be soaked in oil for 24hrs before fitting. There is some discussion on the net about changing these cork seals for PTFE seals. I tried that and they leaked slightly so went back to Cork. I have swapped the big cork washer at the bottom to a modern rubber one but personally I never had much problem with that seal. 

   I'm struggling to think why the bottom nut would be tight before you got enough pressure on the cork seal and washer to stop it spinning. 

Neil

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21 minutes ago, Chipperman52 said:

Hi Petrol is dripping from the bottom of the jets and probably from the large nut as well, the fact that the nut won't compress the cork seal suggests the cork seal isn't big enough. Soaking in oil for 24 hours was done as instructed. Frustrating as car runs a treat!!

Or if could suggest that the internal parts are longer than they should be which makes the nut go tight before the cork is squashed. I'm trying to think how that could be. It might be worth taking everything out again and checking it's all in the right order. But I'm struggling to explain why this would lead to this. 

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Which SU ‘s do you have ?

the HS6 with the tube feed to the jet

or

the H6 with all the choke mechanism and levers on the bottom. ?

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I have also wrestled with this problem for years. I did manage to find some Viton  o rings which replaced the cork seals. Recently on the forum someone fitted some fibre washers instead of the very thin copper washers and cured his leaks.  Burlen ,the SU Carb co. also sell a kit with new parts and Viton seals but you have to buy and replaced the whole thing. It is not cheap but will cut out years of opening the bonnet and worrying about petrol near the exhaust. Burlen products are top quality.

good luck

Richard & B.

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3 hours ago, Chipperman52 said:

If I take the copper washers off the top bearing the nut tightens. 
I have put a fibre washer on the left carb and the nut tightens. See picture. 
still leaks from the bottom of the jet. 
 

I was thinking that taking the copper washer from the top may give you enough to tighten. The carb on the left looks like the bottom nut is on further than mine (I use the rubber O seal like you have on mine and they dont go so tight). When I've had issues it's mainly the seals on the jet that leak. 

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When I rebuilt I found this Website very useful - 

https://thosbryant.wordpress.com/2014/03/01/su-carburetor-rebuild-h-4/

I have HS6 carbs as well but its the same principle as in the link. I did get some PTFE seals (Teflon) but I found the leaked slightly. I haven't tried Viton and may give that a go at some point but the cork is working for me at present. 

Neil

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1 hour ago, Chipperman52 said:

PS. Shame car not drivable as weather is perfect at the moment !!

Having just taken mine for a quick 30 mile spin I would agree but it is a bit brass monkeys around the ears with the top down and no sidescreens.  I know, wear a better hat.

Rgds Ian

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We are still in lock down folks so essential travel only. 
 

but yes if you so wish that essential travel can be in your classic. 
 

sorry to be the big bad covid policeman - but that’s my job.

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20 hours ago, Chipperman52 said:

Many have recommended the Viton washers which I have ordered which seems to be the way forward. 
I’ll let you know how I get on when they arrive. Cheers for now Guys. Thanks

I've actually ordered some Viton washers after reading others have used them. Ordered 50 of them for around £4.50 so I'll see how I get on myself. My concern would be around the friction and if the jet would return fully up when the choke goes back in. Presently have cork washers fitted and working fine. 

I'm some time off trialling as I have the gearbox out at present and I'm thinking the engine is out next to work on the rear Crank seal and general bottom end check (kind of obvious to do if the crank has to come off).

Neil

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A few comments:

1. Lots of luck with the Viton.  They don't work.  Well, they might seal the leak, but they have too much friction, and the jet won't return.

2. PTFE (Teflon) does work, but you need to install two of them in place of each original cork jet seal.  And, of course, the two dished washers must be installed the proper way around.

3. Neil's problem (with leaking Teflon seals) is not the usual outcome.  I've installed thousands of the Teflon o-rings, and although there have been a few leakers, all of them were due to some sort of fixable problem, sometimes a mistake of my own, never the PTFE o-rings themselves.  I suggest he try again, and if there is a leak, look for the source of the problem, and not give up until he finds it, because it will be fixable.  And, once properly fixed, those PTFE o-rings will not fail in your lifetime.  The holes in the sides of the jet should be chamfered with a file to remove the sharp edges so they don't cut the PTFE seals as they slide over the holes.

5. Back to the OP (Chipperman52) and the loose conical ring above the gland nut:  Sounds to me as if the cork ring itself is too thin.  I always toss those in the trash and replace them with a 1/8" X 3/4" ID ("Dash 210") Buna-N o-ring.  That should do the trick.

6.  Don't even think about tossing that copper washer above the upper jet bearing.  It's absolutely necessary for two reasons:

a. It seals the jet bearing so that fuel doesn't leak around it and past the jet orifice, upsetting the air/fuel mixture.  Leakage here will not come out the bottom of the jet where it would be visible, but it could make it difficult (or impossible) to get the proper air/fuel mixture.

b. It must be present (and of the proper thickness) to lock the whole jet bearing assembly in place so that the jet adjustment nut can be turned without also turning the male-threaded jet bearing itself.  "Proper thickness" is 1/32nd inch (0.031") no more and no less.  Many repair kits come with a much thinner (typically 1/64th inch) copper washer.  That should be either thrown in the trash, or if necessary, doubled up to get the proper 1/32" thickness.  Replacing that 1/32" copper washer with fiber is, well, just plain silly.  Don't do it.  (Even if that copper washer did leak a smidgen, you'd never know it by examination of the bottom of the jet.  Any leakage would be upward, into the throat of the carburetor.  Small amounts of leakage past that copper washer, if it should occur (unlikely), would not be enough to upset the air/fuel mixture.  So... there's just no reason to ever even think of using a fiber washer there.)

7. In answer to Neil's comment:

"I'm struggling to think why the bottom nut would be tight before you got enough pressure on the cork seal and washer to stop it spinning."

It's not the pressure on the cork seal that prevents that male-threaded piece from turning; rather, it's that 1/32" copper washer that keeps the thing in place and prevents both turning and leakage.  It's also quite possible for the cork seal (or Buna-N o-ring) to be "wicked tight" and the upper jet bearing to be loose and leaky, particularly if that 1/32" copper washer is missing or if it's been replaced by a 1/64" copper washer.  But again, I must clarify, any leakage past that copper washer and upper jet bearing would be upward, into the throat of the carburetor, and would never be visible at the lower end of the jet.

8. Sometimes fuel leaks past the screw that holds the yoke onto the bottom of the jet.  Such leaks can be fixed with Loctite.

9. Frankly, I don't know why everyone doesn't just give up on cork jet seals and move on to the far superior Teflon.  There is now a far better material than cork, so why Burlen, Moss, and everyone else, just doesn't enter the modern age and toss the cork in the dustbin of history is beyond me.

Tom Bryant

 

 

Edited by Tom Bryant
Added Items 8 and 9.
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4 hours ago, Tom Bryant said:

A few comments:

1. Lots of luck with the Viton.  They don't work.  Well, they might seal the leak, but they have too much friction, and the jet won't return.

2. PTFE (Teflon) does work, but you need to install two of them in place of each original cork jet seal.  And, of course, the two dished washers must be installed the proper way around.

3. Neil's problem (with leaking Teflon seals) is not the usual outcome.  I've installed thousands of the Teflon o-rings, and although there have been a few leakers, all of them were due to some sort of fixable problem, sometimes a mistake of my own, never the PTFE o-rings themselves.  I suggest he try again, and if there is a leak, look for the source of the problem, and not give up until he finds it, because it will be fixable.  And, once properly fixed, those PTFE o-rings will not fail in your lifetime.  The holes in the sides of the jet should be chamfered with a file to remove the sharp edges so they don't cut the PTFE seals as they slide over the holes.

5. Back to the OP (Chipperman52) and the loose conical ring above the gland nut:  Sounds to me as if the cork ring itself is too thin.  I always toss those in the trash and replace them with a 1/8" X 3/4" ID ("Dash 210") Buna-N o-ring.  That should do the trick.

6.  Don't even think about tossing that copper washer above the upper jet bearing.  It's absolutely necessary for two reasons:

a. It seals the jet bearing so that fuel doesn't leak around it and past the jet orifice, upsetting the air/fuel mixture.  Leakage here will not come out the bottom of the jet where it would be visible, but it could make it difficult (or impossible) to get the proper air/fuel mixture.

b. It must be present (and of the proper thickness) to lock the whole jet bearing assembly in place so that the jet adjustment nut can be turned without also turning the male-threaded jet bearing itself.  "Proper thickness" is 1/32nd inch (0.031") no more and no less.  Many repair kits come with a much thinner (typically 1/64th inch) copper washer.  That should be either thrown in the trash, or if necessary, doubled up to get the proper 1/32" thickness.  Replacing that 1/32" copper washer with fiber is, well, just plain silly.  Don't do it.  (Even if that copper washer did leak a smidgen, you'd never know it by examination of the bottom of the jet.  Any leakage would be upward, into the throat of the carburetor.  Small amounts of leakage past that copper washer, if it should occur (unlikely), would not be enough to upset the air/fuel mixture.  So... there's just no reason to ever even think of using a fiber washer there.)

7. In answer to Neil's comment:

"I'm struggling to think why the bottom nut would be tight before you got enough pressure on the cork seal and washer to stop it spinning."

It's not the pressure on the cork seal that prevents that male-threaded piece from turning; rather, it's that 1/32" copper washer that keeps the thing in place and prevents both turning and leakage.  It's also quite possible for the cork seal (or Buna-N o-ring) to be "wicked tight" and the upper jet bearing to be loose and leaky, particularly if that 1/32" copper washer is missing or if it's been replaced by a 1/64" copper washer.  But again, I must clarify, any leakage past that copper washer and upper jet bearing would be upward, into the throat of the carburetor, and would never be visible at the lower end of the jet.

8. Sometimes fuel leaks past the screw that holds the yoke onto the bottom of the jet.  Such leaks can be fixed with Loctite.

9. Frankly, I don't know why everyone doesn't just give up on cork jet seals and move on to the far superior Teflon.  There is now a far better material than cork, so why Burlen, Moss, and everyone else, just doesn't enter the modern age and toss the cork in the dustbin of history is beyond me.

Tom Bryant

 

 

Thanks Tom, I may have to revisit the teflon option. I have 50 of those washers as well :). In fairness it was only one carb than leaked and it wasn't dripping, I could just feel the wetness by touch. I certainly had not appreciated there was a thickness to the copper washer (I've no idea the thickness of the ones in mine). Holes on the jet are chamfered and was straightforward to do.

   I'd never thought of fuel leaking through the yoke at the bottom of the jet. I'm not sure if mine have screws holding them in, from memory they looked like rounded rivet heads (not sure of the right terminology, traditional rivets). I'm the proud owner of 4 good jets so have options here as well but will check the ones presently off the car. 

 I must admit I was hopeful of the Teflon seals. When I fitted them in the rebuild and tuned the car I had the best mixture I had seen on It in all my years of ownership. It was really the first time I was able to get it lean enough AND still have the ability to make even leaner. Previously it was at the edge of adjustment and slightly rich. I didn't mind it being slightly rich but was never comfortable I had no adjustment left. It was just wet at the bottom of the jet. 

   Will experiment again once its all back together 

Neil

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  • 3 weeks later...
On 3/1/2021 at 11:08 AM, Tom Bryant said:

A few comments:

1. Lots of luck with the Viton.  They don't work.  Well, they might seal the leak, but they have too much friction, and the jet won't return.

2. PTFE (Teflon) does work, but you need to install two of them in place of each original cork jet seal.  And, of course, the two dished washers must be installed the proper way around.

3. Neil's problem (with leaking Teflon seals) is not the usual outcome.  I've installed thousands of the Teflon o-rings, and although there have been a few leakers, all of them were due to some sort of fixable problem, sometimes a mistake of my own, never the PTFE o-rings themselves.  I suggest he try again, and if there is a leak, look for the source of the problem, and not give up until he finds it, because it will be fixable.  And, once properly fixed, those PTFE o-rings will not fail in your lifetime.  The holes in the sides of the jet should be chamfered with a file to remove the sharp edges so they don't cut the PTFE seals as they slide over the holes.

5. Back to the OP (Chipperman52) and the loose conical ring above the gland nut:  Sounds to me as if the cork ring itself is too thin.  I always toss those in the trash and replace them with a 1/8" X 3/4" ID ("Dash 210") Buna-N o-ring.  That should do the trick.

6.  Don't even think about tossing that copper washer above the upper jet bearing.  It's absolutely necessary for two reasons:

a. It seals the jet bearing so that fuel doesn't leak around it and past the jet orifice, upsetting the air/fuel mixture.  Leakage here will not come out the bottom of the jet where it would be visible, but it could make it difficult (or impossible) to get the proper air/fuel mixture.

b. It must be present (and of the proper thickness) to lock the whole jet bearing assembly in place so that the jet adjustment nut can be turned without also turning the male-threaded jet bearing itself.  "Proper thickness" is 1/32nd inch (0.031") no more and no less.  Many repair kits come with a much thinner (typically 1/64th inch) copper washer.  That should be either thrown in the trash, or if necessary, doubled up to get the proper 1/32" thickness.  Replacing that 1/32" copper washer with fiber is, well, just plain silly.  Don't do it.  (Even if that copper washer did leak a smidgen, you'd never know it by examination of the bottom of the jet.  Any leakage would be upward, into the throat of the carburetor.  Small amounts of leakage past that copper washer, if it should occur (unlikely), would not be enough to upset the air/fuel mixture.  So... there's just no reason to ever even think of using a fiber washer there.)

7. In answer to Neil's comment:

"I'm struggling to think why the bottom nut would be tight before you got enough pressure on the cork seal and washer to stop it spinning."

It's not the pressure on the cork seal that prevents that male-threaded piece from turning; rather, it's that 1/32" copper washer that keeps the thing in place and prevents both turning and leakage.  It's also quite possible for the cork seal (or Buna-N o-ring) to be "wicked tight" and the upper jet bearing to be loose and leaky, particularly if that 1/32" copper washer is missing or if it's been replaced by a 1/64" copper washer.  But again, I must clarify, any leakage past that copper washer and upper jet bearing would be upward, into the throat of the carburetor, and would never be visible at the lower end of the jet.

8. Sometimes fuel leaks past the screw that holds the yoke onto the bottom of the jet.  Such leaks can be fixed with Loctite.

9. Frankly, I don't know why everyone doesn't just give up on cork jet seals and move on to the far superior Teflon.  There is now a far better material than cork, so why Burlen, Moss, and everyone else, just doesn't enter the modern age and toss the cork in the dustbin of history is beyond me.

Tom Bryant

 

 

Very interesting read Tom. Learnt a lot.

Have fitted Viton rings, leaks gone but as you say, I think resistance is too great as choke now very stiff. 

You say fit double  PTFE (Teflon) but what size do you recommend ?

I also see Nitrile rings recommended?

Cheers

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Hi 

 I also have a fuel leak downwards from the jet on my Tr3a's front carb. The rear carb is leak free. Both carbs have four viton o rings on the jet and a larger Viton o ring on the gland nut.  To cure the leak and stop the male threaded piece from turning i had to fit a 0.055''  upper bearing washer. After reading Tom Bryant's detailed post i tried reducing the washer thickness to 0.032" but the problem reoccurred. Could my problem be that I have an incorrect thickness lower bearing washer.

Tom - can you please advise the correct thickness of the lower bearing washer. 

If the lower bearing washer is correct I intend stripping both jet assemblies and measuring everything to establish the difference.

Alan 

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My problem is now solved. The leaking front carb had been fitted, by a previous owner, with an incorrect upper bearing which was 0.1 inch less deep than spec. I then fitted 0.032 inch upper bearing washers as recommended by Tom and the leak is resolved. :)

Alan

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This does confuse me.

I also had leaks from same area on my 2, so spoke to burlen and found out about the updated viton kit since purchased sorted done.

Now why do suppliers continue to supply not fit for purpose cork seal kits ?

More important why are people trying to save pennies on multiple use of o rings and different washers when the correct kit is available . Quote:you have to buy the whole thing and it’s quite expensive, Bloody hell guys your talking about £25 k + cars and spending what £50 on item that keeps petrol away from your sparking electrics.

Al

 

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  • 1 month later...
On 3/17/2021 at 9:42 AM, Chipperman52 said:

Very interesting read Tom. Learnt a lot.

Have fitted Viton rings, leaks gone but as you say, I think resistance is too great as choke now very stiff. 

You say fit double  PTFE (Teflon) but what size do you recommend ?

I also see Nitrile rings recommended?

Cheers

Sorry to be so slow to respond; for some reason, I wasn't notified of your post and only stumbled upon it a few minutes ago.

The proper size of PTFE o-ring is "-010", 1/16" x 1/4" ID, available here (among many other sources):

https://www.theoringstore.com/store/index.php?main_page=product_info&cPath=367_93_96&products_id=4168

The Nitrile (Buna-N) o-rings for the top gland nut are "-210", available here:

https://www.theoringstore.com/store/index.php?main_page=product_info&cPath=367_23_25&products_id=1179

Tom

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On 3/23/2021 at 3:35 PM, Alanretired said:

Hi 

 I also have a fuel leak downwards from the jet on my Tr3a's front carb. The rear carb is leak free. Both carbs have four viton o rings on the jet and a larger Viton o ring on the gland nut.  To cure the leak and stop the male threaded piece from turning i had to fit a 0.055''  upper bearing washer. After reading Tom Bryant's detailed post i tried reducing the washer thickness to 0.032" but the problem reoccurred. Could my problem be that I have an incorrect thickness lower bearing washer.

Tom - can you please advise the correct thickness of the lower bearing washer. 

If the lower bearing washer is correct I intend stripping both jet assemblies and measuring everything to establish the difference.

Alan 

The correct thickness is 1/64" (0.016"), although I have seen some that were 1/32" (0.031") thick, which should work just fine.  These lower washers sometimes leak a bit.  When that happens, there's no need to replace them.  Simply apply a bit of anaerobic sealant and you're good to go.

Tom

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