SU Carb leaking like Crazy!

[Mobjak]

Hi all,

I just recently cleaned and renewed all the seals/washers on my SU H1 carb and the motor runs, but the carb leaks fuel!

I found a web page that suggested that I had to soak the cork washer in oil for a couple of days before I assemble. I had not done that, so I ordered a new washer and started the soaking.

I just put the carb back together and the cork washer for the jet locking nut compressed down very nicely. I adjusted the jet adjusting nut just a couple of turns to give me as much adjustment as possible. The car started up and ran nicely. To my horror, fuel was streaming from the bottom of the carb.

Specifically, fuel was running down the lower jet bearing at a fast rate. I shut down the engine and got out the buckets.

I tried to tighten the jet adjusting nut, but it still leaks when the fuel pump is turned on.

Am I missing something about the jet bearing assembly? Should I be looking else where for my problem, like the float bowl? Should that much fuel be at the jet? I did replace the copper washers as part of the complete rebuild kit.

Any suggestions would be greatly appreciated.

TIA, Mike

[newagetraveller]

Firstly check that the float in the float chamber is not leaking. Take it out and shake it to make sure that there is no petrol inside it.
Secondly, when the petrol in the float chamber reaches a certain level the float should rise up and operate the float lever which closes a small valve in the top of the float chamber. This prevents too much petrol from entering the chamber via the pipe coming from the petrol pump. If the top of the float chamber is removed you can check the valve by blowing into the tube in the top of the chamber and seeing if pushing the float lever up prevents air coming through.
Thirdly the float lever should be set to the correct clearance which is done using a 5/16 inch drill for the 948cc carb. and may be different for yours. Unless this has been disturbed it is best left alone.

[Willie]

Lo, I have always had trouble from the float chamber needle and
seating on SU carbs, which seem to leak if the car has been off
the road for some time,even though they didn't leak when parked
up. If it is the needle you will easily see the petrol coming out of
the top of the float chamber. The other favourite place is the
small tube running from the bottom of the float bowl to the jet,if
you have that type of SU. I assume you have a good drawing
of the asssembly? if not I could e-mail one to you
Willie

[Willie]

Further to the above.....with the pump on but engine not running
you should lift the carb piston so that you can see where the needle
enters the jet. There should be no petrol issuing from there. If there
is then either the float needle is not sealing or the level at which it
cuts off the flow is too high.
Willie

[Mobjak]

Thanks for the tips Newagetraveller and Willie,

here is where I am at the moment. Fuel still drips out of the bottom of the carb when running.

The float is water(fuel) tight. It has no fuel in it, and it rides up and down the shaft with no resistance.

The float needle setting was a little off, and I used a slightly larger 15/32 rather than a 7/16 drill bit to set it, but I figured that would be close enough for testing purposes... I hoped. I will procure a 7/16 bit tomorrow to make the final adjustment.

This is what I did, and what I thought might fix it.

I removed the suction chamber and piston/needle assembly.
I loosened the Jet locking nut and positioned the lower jet bearing in the middle of the jet bearing drilling in the carb body.
I then installed the piston/needle assembly and made sure it moved freely.
Next I tightened the jet locking nut(after removing the piston/needle assemlby) while visually locating the upper jet bearing in the same position prior to tighting.
I reassembled the carb and turned on the ignition switch. The fuel pump ran and filled the bowl.
No leakage at the bowl or the lower jet bearing.
When I started the engine, the fuel started to leak from the lower jet bearing within seconds.

ACK!

After writing the last sentence, I looked at the "SU carburater tuning tips and techniques" manual, and I noticed that it says the lower jet bearing washer is brass!!!! I think the one I installed is copper#@#%^
Could I have installed the wrong washer.....

Has anyone done a recent rebuild and used copper instead of brass?

This is where the fuel is leaking from, so I suppose that I should confirm the washer before I go any further. It was a rather simple rebuild kit, with no directions or lables as far as parts go.

Well, back to the garage, if anyone thinks of anything, or sees something that i should be doing, chime in.

TIA, Mobjak

[newagetraveller]

As far as I can see the only difference between switching the ignition on and having the engine running is that in the second case the butterfly valve opens slightly and the piston assembly moves up by a small amount.

I would be interested to know if you get a petrol leak with the ingition switched on (but the engine not running) if you raise the piston assembly manually. If you get the same leak when you do this, does the petrol appear to be coming from the top of the jet? This would seem to suggest that the problem is with the valve in the top of the float chamber not closing properly.

As copper is softer then brass then provided the copper washer has the same dimensions as the brass one that it replaced I would not expect it to make any difference.

[Mobjak]

Ok, more testing....

I turned on the ignition and let the fuel pump run until it stopped.

No fuel leak.

I moved the piston assembly up and there was no sign of fuel.
The lower jet bearing was not leaking.
I observed this for 5 minutes and kept checking, no fuel leak.

I was feeling lucky, started the engine.
Looked under the hood, fuel was leaking from the bottom of the jet assembly. I checked needle/piston assembly and no visible signs of fuel, but still a steady drip at the external jet assembly.

I did notice that there is a certain amount of movement in the lower jet bearing, even with the locking nut tight. Should this be?

I have just checked and it looks like a real rebuild kit might be what I require, not just a gasket/washer renewal kit. That might be my next step.

Any help, as always would be appreciated.

thanks, mike

[Willie]

NO, there should not be play in the jet bearing, that is your problem
I did ask if you had a good schematic of the assembly?? If not I will
e mail you one if you wish? Incidentally,the bottom jet bearing washer is
brass.....the top one is copper.
Willie

[Mobjak]

Thanks Willie, yes I would like a copy of the carb schematic.&nbsp; You can never have too much documentation.<BR><BR>My next step is to order a new washer and maybe the lower jet bearing.... should I replace the whole jet assembly?<BR><BR>TIA, Mobjak

[Mobjak]

The diagnosis continues....

Ok, I have removed the carb again.
I disassembled the jet bearing assembly and examined the installation. The parts all appear to be installed in correct order. I still have all the old washers and the old lower jet bearing washer is copper and the same dimensions as the new one.

Now, I have noticed that one side of the lower jet bearing washer has a sharp edge to it, just like the old one. Should this sharp/cupped edge face the brass surface of the lower jet bearing or the steel face of the locking nut?

Examination of the entire assembly noted that the jet had very little if any play an moved smoothly through the bearing gland washers with no issues. The movment that I noted, was the entire jet bearing assembly and after reading the documentation, that should be able to move while the locking nut is loose, but should be tight, once the locking nut is secure.

I may not be achieving that last item. When completely reassembled, the last time, I could move the entire jet bearing assembly. I plan on reassembling the carb tonight and hope to find that all will be secure.

If anyone can answer my question about which direction the sharp edge of the washer that would be great.

TIA, Mike

[newagetraveller]

This website has a diagram of the carburettor.

http://www.auto-part.com/auto/shop/Display.asp?page=9

Is it of any help in reassembling yours?
If not can you indicate which washers are the problem.

[Mobjak]

The saga continues...

Newagetraveller,

it is part #40 on the H2 diagram.


Well, I have disassembled and reassembled this carburator so many times now, I might need a whole new gasket set just due to wear and tear!!!

But, let me post my results...

I am using the Brooklands SU book and followed their directions to the 'T'.

I tightened the locking nut as tight as I could get it without stripping the carb body drilling....

The leak continued. I will attempt one last change. I plan to remove the carb tonight and reverse the position of the lower jet bearing washer. I figured I had a 50/50 chance of getting it right.

I do have a question... Do I need to, should I, soak the jet bearing locking nut cork washer in oil again, before I reassemble?

Well, wish me luck...

[newagetraveller]

Milder weather has finally enabled me to find an old H2 carb and have a look at it.
Inside the carb are:
42 cork washer
43 brass washer
44 gland spring
43 brass washer
42 cork washer
As far as I can see the two brass washers (43) are both dished and the dishing is facing away from the spring (44) and towards the two cork washers (42). The effect of this dishing should be that when you tighten the locking nut up the dishing on the brass washers squeezes the cork washers against the jet and thereby prevents petrol from leaking through the gland. Is this of any help?

[Mobjak]

Newagetraveller,

I don't believe the gland assembly is leaking. Here is a drawing that shows the lower jet bearing washer just below the jet bearing (bottom half) as the culprit.



Whoooaaa... I will reduce the size of the pic....

I have not had time to flip that washer over... work, cold, snow.... maybe this weekend!

TIA

[Mobjak]

Well... it took a long time, but the leaking carb has been fixed. (Fixed back in July, after sporadic time to work on Roland)

The local car club had a technical session on rebuilding SU carbs on an MG and during the session I confirmed that my technique was good, but I found that the kit I was using, had very few parts.

The shop owner/president of the club was using a kit from Joe Curto from New York. The kit had a lot more parts than the one I purchased. I got on the phone the next week with Joe and ordered a new kit for my carb.

Many more parts were replaced in this kit, it did cost about twice as much, but it worked like a charm. A new Jet, needle, flowjet etc seemed to take care of my problems.

The engine now runs very good, I can actually turn the jet adjusting nut and it makes a difference.

Thank you all for your help.

I hope to start back working on Roland in the next few months...

[MMDream]

Hello,

I have the same trouble on my double carb "SU H2"

I know it isn't Minor, but MG TD it still cousin!

My carburator leaking, then I order a new gasket (Cooper & cork)

After that the Jet still leak. In fact it flees at the bearring Jet. and the engine can start but it's really too rich.

Next step:

New order with new gasket, needle (standard and weak), Jet, Grose Jet (needle and seat replace by ball)
I check the fuel level (sorry not sure of English name) (9.5mm for H2 on MG TD)

No leak
I start the engine it still rich but little bit better

But when I pull the choke it's not leak but gasoline is flowing through the bearring Jet (view at the spring JET)

After so many build rebuilt & reassembly again I do not know what to do anymore!

In conclusion: The engine start but really too rich (same with weak needl, but still really better with that one)
The bearing jet still weak same after change the gasket (cooper) and spring to be on it at the right pressure
I can't pull choke or the SU throw up gas.

if any body have idea...

Cheers

[MMDream]

I now change almost every things:

needle - Jet - bearring jet - cooper seal - cork gasket - all spring - nut of bearring jet...

But still leak.

[Declan_Burns]

MM,
There are Teflon carb seals available for the MG TD- a chap called Thomas Bryant sells them
Thomas Bryant <thosbryant at gmail dot com>
Here's a link to a long discussion on the MG T Series BBS Forum about the same problems you are having.
http://www.mg-cars.info/mgtd-mgtf1500-b ... 725660.htm

Regards
Declan

[MMDream]

Thank so much for the link.

I'll use the next times because I just solved my problem.

In fact I change WZX1593 from Moss, Bearring Jet kit.

i think the plate parts of bearring by pressing the seal (cooper really thin) it probably little scratch

Now just need to finish the setting.

Thank for your helps.

Cheers