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H Type Carburetors BN2 M version Leaking Fuel At Jet Bearing Area

Martinld123

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screenshot.2139.jpgMy H type Carb M version is leaking fuel at Jet bearing area. This "M" carb is only about three years old that I bought new from Moss. Too soon for three year old new carb to be leaking fuel I think. I had rebuilt my old M carbs so I can do it but hoping for a shortcut instead of pulling carb, air-box, etc, off engine. If it is the cork sealing ring I think I can do work in place? I have an older unused cork sealing ring soaking in oil right now. That has to be problem area, right?<br>
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Another note: I lose oil in this (new) dash pot also. Unrelated I am sure. On <u>my old M carbs</u> I bought Moss <u>no leak rubber replacement Gland washer</u> at top of jet bearing area. Seemed like a great idea until I realized it caused choke to stick. Ended up putting cork gland washer back in. Anyone else had any experiences like this? Looks like this cork washer needs to be replaced also.<br>
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Update: I am lost. It seems to be leaking fuel worse than ever after replacing two jet corks and one bottom ring sealing cork. Maybe I should not have soaked bottom sealing cork in oil over night? Leak has an oil color to the fuel smell. Dash pot? I think I will install new bottom ring cork dry and see if that might do it. If that is not it I will have to remove carb and look for a hair line crack in case. Any other ideas? Marty<br>
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Final Update: I was in shock when removing the carburetor to see the quality of workmanship on my brand new pair of 100M carbs made in UK ordered though Moss, order #370-738. The pictures tell it all. The crack in the casting is unrelated as far as I can tell to fuel leak but just another example of the workmanship. It looks like they missed the final machine step in thumbnail photo below but even so how could you not see this when assembling the carbs? I spent the better part of a day removing their rough machine work with 800 grit sandpaper on a sheet of glass. I did not take the other carb off car since it was not leaking petrol. I should have. I think they are made in pairs. Moss is closed now because of Wuhan Flu but will contact them when open again but do not blame them for the problems. Marty
 

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I think the only way to do it would be to attack from underneath, but I don't know if that's even possible. I think these seals--either rubber or cork--are going to leak sooner or later; maybe why SU went to diaphragm-type HDs?

Did you grease the seals? I don't know if it's called-for, but it seems logical. FWIW, the HSes on my M weep a little fuel, but not so much I'm concerned (yet).
 

BLU_HLY

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In place of the cork gland washer I installed white Teflon O-rings TEF010 from the O-Ring store. Use 2 rings for each cork ring. Smooth and fuel tight
 

Dandare

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Before doing anything too drastic it may be an idea to try nipping up what SU call the jet locking screw(s).

This is actually a large hex under the base of the carb which holds the whole jet assembly tight. It has a large cork ring (originally) which may have shrunk a little. A bit awkward to get a spanner on with the linkage in place but should be do-able.

Danny
 
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Martinld123

Martinld123

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Before doing anything too drastic it may be an idea to try nipping up what SU call the jet locking screw(s).

This is actually a large hex under the base of the carb which holds the whole jet assembly tight. It has a large cork ring (originally) which may have shrunk a little. A bit awkward to get a spanner on with the linkage in place but should be do-able.

Danny
M carb cork sealing ring.jpg

Danny did this shrink a little, lol? Brand new "M" carb from Moss delivered from England about three years ago. This is how it came from the manufacturer. I think instead of putting in oil over night they just cut dry cork in half to fit! Who would do work like this? Marty
 

Dandare

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Marty that is bizarre, looks like it is 47 years old.

I would definitely check the seals on the jets as well...both carbs.

Danny
 
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Martinld123

Martinld123

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Update: I am lost. It seems to be leaking fuel worse than ever after replacing two jet corks and one bottom ring sealing cork. Maybe I should not have soaked bottom sealing cork in oil over night? Leak has an oil color to the fuel smell. Dash pot? I think I will install new bottom ring cork dry and see if that might do it. If that is not it I will have to remove carb and look for a hair line crack in case. Any other ideas?

When bottom ring is tight I can still tap side of jet and take it off of center for jet needle. That seems wrong to me. Marty
 

Dandare

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Marty, this may come down to quality of parts.

If the new sealing cork you show in the picture a couple of posts back is the one you are installing, then it looks a bit cheap & nasty to me. The good cork ones are made from a sort of (what I call) neoprene cork. You can see this material in a lot of flat sheet type gasket material.

Danny
 
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I'm (just guessing) that pre-oiling cork gaskets may not be appropriate in this case. My dad rebuilt a pair of M carbs, and I'm pretty sure he didn't pre-oil anything, and I get a little bit of seepage from the bottom of the carbs but not enough to worry about. The gaskets should swell a little when gas gets to them. Soaking/pre-oiling is correct for 'Oilite-type' bronze bushings, and I've never heard of anybody having any luck soaking cork in oil (doesn't mean it hasn't happened, of course)
 

Dandare

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I have found that the neoprene cork type don't really need soaking but it was apparently the thing to do with the originals.

Danny
 

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steveg

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The workmanship is sub-standard. Wonder if these UK-sourced carbs come from Burlen. Maybe we can find out from Moss when they're open again.

Danny - Is there an outfit in Australia which also makes SU carbs?
 

Dandare

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Steve & Bob,

The originator of Midel, the late Bill Bressington, did have some connection with the SU company years back and I'm reasonably certain they did make components for Burlen at one time. I think at least they made certain needle profiles that weren't covered by Burlen.

I always believed they made their own cork bits as you could buy them (and the brass/copper bits) in bulk instead of buying a lot of unnecessary gasket packs.

I don't know that they made the more modern carburetors but there used to be a pair of huge old racing jobs they had made up on a shelf behind the counter.

They are run by a son now and, although I haven't dealt with them for quite a few years, I have seen a few negative remarks creeping in about their rebuild work...which is a shame if true.

Edit. Going back to Martin's (OP) original problem I meant to mention a couple of points.

1/ With regard to the big cork seal at the top (jet locking) I find it best to actually tighten this up first to seat and compress the cork and then slack it off to do the jet centreing and then when you then re-tighten it it should be nicely seated.

2/ I have heard that some of the new jets around are less than smooth and might benefit from a bit of linishing lest they destroy a new seal immediately!

Danny
 

LarryK

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This 10% ethonal doesn't help either. Only way I try to beat the leaks, is drain carbs after a drive.
 
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