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Help needed rebuilding HS6 carbs

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Old Jun 29th, 2014, 22:22   #1
fishyboy
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Default Help needed rebuilding HS6 carbs

Hi all,
Rebuilt my HS6 carbs this weekend, but have come across two problems:-

1) I am having a problem getting one jet centered. I have followed the manual and removed the spring and adjustment nut and screwed the locking nut up. I then applied pressure to the piston and with the jet in its highest position tightened up the locking nut. However, once I fit everything back together and turn the adjustment nut down 21/2 turn the piston no longer drops freely.
Any ideas?

2) What keeps to fuel line in place at the bottom of the float bowl? Once I tighten up the brass I cant see how this stops the fuel line from popping out? Am I missing something?

Thanks
Phil
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Old Jun 29th, 2014, 22:27   #2
Derek UK
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Read Tom's write up here. He has posted on the forum. You should find it useful.

http://thosbryant.wordpress.com/2014...building-hs-6/
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Old Jun 29th, 2014, 22:45   #3
fishyboy
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Hi Derek
Picked up on this site a few weeks ago when you mentioned it, but doesn't really address my two questions.

As i did not replace the needles (they looked in good condition) that might be my next step. Perhaps one has got a little knock?

Phil
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Old Jun 29th, 2014, 23:20   #4
volvonic272
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Phil,
Not sure what the answer to question 1 is.
I think there should be a rubber o ring type seal, almost like a plumbing olive that seals when the nut is tightened . I had dolomite sprint with su carbs and they had the o ring seal, so I think it will be the same.

Dave
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Old Jun 29th, 2014, 23:39   #5
Ron Kwas
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Phil;

1. Jet centering is a tricky operation...assure the surfaces involved are clean...if you loosen the jet securing nut, does it unjam against metering needle?...you might try putting just one layer of the thinnest tape you can get (in my case high voltage Kapton tape), and wrapping it around the fat end of the conical needle, then trying again...after you tighten jet, remove the tape from metering needle and check for full travel...that extra thickness is just what might help with centering... keep trying, and don't get discouraged!

2. Not much stops the fuel-line from being pulled out...but it doesn't need to!... the rubber seal compresses around the line and seals...again, assure seal pocket in bowl is clean and trial fit seal (square cross-section!) into pocket (without line)to understand how it works (don't forget washer!): Nut compresses seal into this precision pocket and when it has expanded to the outside and contacted wall, it MUST expand to the inside sealing around line...yes it is easy to pull line out, but it never sees this kind of force...after all, it is held in place only 3 inches away. Pressure-wise, there is only the pressure of max two inch head of fuel also...so the seal does not really have a difficult job (only a mucho importante one!).

I hope that helps...I did make a detailed study of this seal not long ago, with a graphic and much more info, but haven't posted it yet...if you're still having difficulties with it, I'll try to expedite.

Cheers from Connecticut!
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Old Jun 30th, 2014, 06:11   #6
fishyboy
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Thanks guys,

Ron,
Great advice and try again tonight. Description of the fuel line fits will help.
Phil
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Old Jun 30th, 2014, 09:11   #7
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Check your needles for straightness.
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Old Jun 30th, 2014, 14:22   #8
Tom Bryant
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Quote:
Originally Posted by fishyboy View Post
Hi all,
Rebuilt my HS6 carbs this weekend, but have come across two problems:-

1) I am having a problem getting one jet centered. I have followed the manual and removed the spring and adjustment nut and screwed the locking nut up. I then applied pressure to the piston and with the jet in its highest position tightened up the locking nut. However, once I fit everything back together and turn the adjustment nut down 21/2 turn the piston no longer drops freely.
Any ideas?

2) What keeps to fuel line in place at the bottom of the float bowl? Once I tighten up the brass I cant see how this stops the fuel line from popping out? Am I missing something?

Thanks
Phil
1. I'm not quite sure what you mean by "applied pressure to the piston". The proper procedure would be to put the jet in its highest possible position, as you seem to have done, but leave the jet bearing nut a bit loose. Next wiggle the jet a bit to make sure the needle is centered. Then lift the piston about a half inch and drop it, making sure that the needle doesn't rub against the jet on the way down. Now tighten the jet bearing nut a little, and repeat the piston drop test. If still no drag, tighten the jet bearing nut "good and tight", and do the piston drop test again, just to make sure. If the needle doesn't bind with the jet all the way up, then there's no way it should bind with the adjustment nut turned down 2-1/2 turns.

If you just can't adjust the jet bearing so that the needle doesn't bind in the jet in its highest position, then you probably have either:
a. A defective jet or bearing.
b. A defective jet bearing seat (in the carburetor body), which is sometimes the result of the next item (c).
c. One of those gawd-awful jet bearing washers with little points on it that jab into the carburetor body and prevent the jet bearing from moving freely. If so, file the points off the washer so the jet bearing will be free to move to where it needs to be.
d. A bent needle, but that's unlikely, as you've undoubtedly already looked for that, and it would have to be bent a lot.

2. This one is easy. The jet tube is held in by the rubber o-ring seal. But make sure it's "good and tight". By that I mean as tight as you can reasonably get it. I see far too many come my way that were never properly tightened and the tube fell out. You gotta tighten that thing right up. Tight. There's really no way possible to over-tighten it. So, tighten it.

Last edited by Tom Bryant; Jun 30th, 2014 at 14:26.
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Old Jun 30th, 2014, 16:10   #9
fishyboy
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Tom
Great blog on rebuilding the HS6. I found it really useful.
Also great advice in you post and I shall have another go when I get home.

The "applying pressure" comes direct from the Burlen/SU website (http://sucarb.co.uk/technical-hs-typ...on-adjustments)
and I think is also mention in the book "SU Carburettors Tuning Tips and Techniques (Tips & Techniques) by R. M. Clarke". SU suggest gently pressing with a pencil inserted into the piston so that the piston is in proper contact with the bridge.

Having spoken with Burlen/SU it appears as though the two jets which come in the rebuild kit are specific to the front and rear carbs. The right hand jet/front carb has a yellow sleeve and the left jet/rear carb has a orange sleeve . However, they dont think this will make any significant difference if I have them the wrong way around. But I will check tonight.
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Old Jun 30th, 2014, 18:06   #10
Tom Bryant
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Quote:
Originally Posted by fishyboy View Post
Tom
Great blog on rebuilding the HS6. I found it really useful.
Also great advice in you post and I shall have another go when I get home.

The "applying pressure" comes direct from the Burlen/SU website (http://sucarb.co.uk/technical-hs-typ...on-adjustments)
and I think is also mention in the book "SU Carburettors Tuning Tips and Techniques (Tips & Techniques) by R. M. Clarke". SU suggest gently pressing with a pencil inserted into the piston so that the piston is in proper contact with the bridge.

Having spoken with Burlen/SU it appears as though the two jets which come in the rebuild kit are specific to the front and rear carbs. The right hand jet/front carb has a yellow sleeve and the left jet/rear carb has a orange sleeve . However, they dont think this will make any significant difference if I have them the wrong way around. But I will check tonight.
Sounds like bad advice to me. If the jet is properly centered, then the piston will be in proper contact with the bridge, but if you apply pressure to the piston, that could move it off-center, which would result in the jet being off-center. This could easily be where you went wrong. No pressure advised here.

As for the jets being installed on the wrong carbs, that is not possible with OEM-style jets, which is what Burlen sells. If you had tried to put them in the wrong carbs, you would have known it right away because you would not have been able to do so.

Tom
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