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MG Midget and Sprite Technical - Help with 1 1/8 carbs

I had the carbs of the Frog at the weekend with the intention of stopping the leaks at the float chambers. When I had then carbs on the bench I discovered the rear jet lever was stuck fast so had to get it all apart to free it up.

So after taking the jet assembly to pieces for the first time in my life, I got it all back together on the car tonight and ran it up. Of course everything was fine apart from a leak from the rear jet assembly! What do I need to do?

Is it most likely that the whole thing need tightening up to compress the cork washers (presumably that will make them fatter and may seal against the rod) or have I over tightened them and damaged them?

I counted the turns of the jet locking nut when it came off, but with the new cork washers in the mechanism then I presume that won’t be the same? I guess it is the same for the jet adjuster nut too – if the length of the assembly is longer due to the new washers then the adjuster will need to be reset too.

Can anyone explain how tight/loose I should be doing these nuts up and/or point me in the direction of a reference book or web resource to explain what I need to do?

The carbs are standard HIs.
Mark '59 Frog

two thoughts for you, don't know how well they will help though:

1) for cork washers, the torque spec would be "tight enough to stop leaks, but not so tight that they are crushed completely". Wishy-washy, I know, but if you have to tighten beyond "compression" and getting into "crushing", then take it back apart and look for another cause of your leak.


2) the last time I worked on Bugeye SUs, I thought I had a jet leak only to find out that it was in fact a stuck float bowl valve (old gasoline), and the overflow (fuel pump pushing raw gas out the top) ran down and only seemed to be dripping from the jet. I sure didn't expect that, because the float bowls have their own overflow drain tubes, but there you go.


Norm
Norm Kerr

Mark -
Hope you have a book or other instructions.
There are three leak paths possible.

1) Out the bottom of the jet where the U shaped steel saddle for the linkage is. This is held to the jet proper with a screw, and sometimes they are loose. Loctite is the cure. Rare but possible.

2) Along the jet past the cork seals.
The cork seals need to be soaked in oil for a few hours, which softens them up, prevents breakage and leaks.
The assembly is top bearing, seal, internally chamfered washer - chamfer to seal, spring, lower chamfered washer - chamfer to seal, lower bearing, and the jet passing upward through all that. The spring must have enough force to compress the seals in the chamfered jet bearings and the chamfered washers. Frequently the springs are weak or rusty; some are bronze, some are steel. If correct,the upper bearing will almost come off the jet when you hold it in your hand, before installation. New jets frequently have ridges, burrs, and generally bad machining which causes leaks; examine carefully and rectify. Some people replace the seals with two teflon O-rings (two rings for each seal), but I've never found it necessary.

3)Around the whole jet assembly bypassing the seals.
The assembly is clamped by the big retaining nut on the bottom; if any parts are missing it won't work.
Assembly is wide copper flat washer, top bearing, bottom bearing, narrow copper ring washer, jet retaining nut with large internally chamfered washer and big cork seal which also needs to be soaked in oil. The whole jet assembly 2) fits inside this stuff. It is very common to find either of the copper washers missing, which means there is an internal fuel leak as well as the external one you can see. The big nut gets tightened dead tight, which clamps the entire assembly in the carb body. The length of the correct assembly is such that the hole depth in the carb is just right. The big cork washer will be well compressed, but the large chamfered washer will not quite touch the carb body. This final tightening is also what locates the jet central with the needle, so the last half turn is the last thing you do when assembling the carb, after you've fitted the piton and vacuum chamber

Ideally all the copper washers get renewed each time they are disturbed, but they usually work all right a couple of times. The very narrow one sealing the lower jet bearing to the retaining nut is most subject to damage on reuse.

Note that the vac chambers are not necessarily perfectly concentric, so mark them as to which side faces out when centralising the jet. The eccentricity can be useful as a final tweak once you get the jet reasonably close, be sure to mark the final position.
Also, soaking all the fibre washers in oil along with the cork ones makes it much easier to keep the lines and float bowl banjos from leaking.

FRM
FR Millmore

Mark,

If you still have trouble I can scan and mail you info from an old manual I have (Monday earliest when back at work - no scanner at home)
Leave a mail address on the board.

Richard.
richard boobier

I wonder if this link will work for a carb manual

http://www.spridget-tech.com/service_manual/Section-D.pdf
Robert (Bob) Midget Turbo

Good try Bob but no cigar - link was for HS2's, Not H1's as on Froggies.

R.
richard boobier

Mark you have mail

hope it helps
bill sdgpm

Evening guys.

Bill you have mail back, thanks for that. That will go well with the small diagram in the srvice kit! It's so small I have to wear my glasses rather than my contacts so I can lift the glasses up to read!

FRM I think you have highlighted my error! I have a new shiny washer left in the overhaul kit and I think that on taking apart and putting back together again for the second time I have missed the copper washer out that sits between the jet bearing and the locking washer. I will be out there in the morning to see what is what.

So tight enough but not too tight! That is always the case on these damned cars :)

As always a quick and helpful response from all, thanks. Spridget guys are the best!

Mark
Mark '59 Frog

Yep,

These guys are great!

Glad I found this forum...they've helped me a bunch over the past 8 months.

Dave
Dave Rhine ('78 1500)

Mark,

If its any help, in the shed I've got some cork/brass/rubber overhaul bits for 'H' carbs - may be from 30/40 years ago !
I will stick them in an envelope and post to you if you drop me an address.

rdboobierATbtinternetDOTcom

Hope Bill's instructions did the trick.

Richard
richard boobier

Update. Yesterday I was not successful and had to go out, but this morning the job has been done successfully. The locking washer was leaking so that is nice and tight now and the jet adjuster nut is back on the three and a flat turns it came off with. No petrol leaking and the main jet rod goes up and down smoothly and the choke spring pulls it right back n position too.

A nice even idle, at about 800 to 900 rpm, and about to risk a drive to see my parents before lunch. Thanks for the assistance guys, when you do a job for the first time your help is invaluable.

Richard thanks for the offer, but the service kit I had has done the job. If you are still keen to get rid of the bits I will drop you an e-mail.

Cheers

Mark
Mark '59 Frog

yeehah!

glad of that Mark
bill sdgpm

This thread was discussed between 12/02/2010 and 14/02/2010

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