What a great write up! Can I ask a quick question on the float adjustment? It's meant to be 7mm closed 15 mm open on the 26. Do the same float measurements apply for the 28 as well? I can't find a 126 Haynes manual just now...

8mm and 16mm for the 28 if I remember correctly George. If I remember I'll double check tonight when I have access to the manual

Yes, Damian (Paolo66) is correct--8mm and 16mm. I have a Haynes 126 workshop manual--if it will help you, I can copy the relevant pages and post them to you. Also, as Chris (Bambino) mentioned, check that the little alloy washer that the needle-valve sits on is in place. Lastly, remove the float and give it a shake--if there is ANY fuel in it, bin it and buy a new one. The floats are known (suffered it myself) to 'gain' very small cracks in them. The petrol, over a period of time, will slowly seep into the float which will prevent it doing its job properly--it just sinks! Once the fuel is in the float, it is practically impossible to get it out, hence the requirement to replace it.

My 26 IMB is leaking. It collects around the drip plate on the bottom. If heat is on in the car I can smell the gas. I already changed the gaskets and seals last year. Any other ideas? Should I just buy a complete rebuild kit?
Great write up by the way!

Morning Labman;
Check the carb as per all the advice on this subject (float, float level, needle-valve etc.) plus, check that the top cover of the carb is level and has not warped, although if your carb is leaking as bad as you say it is, too high a fuel level would be the most likely cause--definitely check the float.

the hobbler said:

Morning Labman;
Check the carb as per all the advice on this subject (float, float level, needle-valve etc.) plus, check that the top cover of the carb is level and has not warped, although if your carb is leaking as bad as you say it is, too high a fuel level would be the most likely cause--definitely check the float.

Click to expand...

I was thinking the top cover might be warped. Fuel seems to be weeping out of the seams and it is screwed down tightly. I changed this gasket but didn't think to see if it is warped. If so, can it be fixed? Do I have to get a new cover or a whole new carb?

The 26imb is very prone to the bottom flange and the top cover warping. The 28imb is a little more robust but can suffer similar problems. I use my large 5" jaw vice with suitable bits of packing to press the carb parts back into shape. The problems are generally caused by over tightening of the screws and mounting nuts.

Toshi 975 said:

The 26imb is very prone to the bottom flange and the top cover warping. The 28imb is a little more robust but can suffer similar problems. I use my large 5" jaw vice with suitable bits of packing to press the carb parts back into shape. The problems are generally caused by over tightening of the screws and mounting nuts.

Click to expand...

I will try this. If it doesn't work I guess it's time for a new carb

Another option, to confirm if it is the top of the carb that is warped is to fit another gasket---top is then refitted with 2 in place. You may have to 'tweak' the float level a fraction (to 6.25m), but trying this initially means that you won't have to resort to using the 5" vice --yet!

Toshi 975 said:

The 26imb is very prone to the bottom flange and the top cover warping. The 28imb is a little more robust but can suffer similar problems. I use my large 5" jaw vice with suitable bits of packing to press the carb parts back into shape. The problems are generally caused by over tightening of the screws and mounting nuts.

Click to expand...

Well my top cover is definitely warped as can be seen in the picture. I'm worried about putting it in a press as its made of pot metal I believe? How would you recommend I do it?




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The picture looks fairly typical of what I have come across on a number of the carbs. I had already straightened a few bottom mounting flanges by that time so I was pretty confident that there was a degree of flexibility in the metal alloy . I removed all the parts from the top cover then with parallel bars across the holes on the underside to give clearance for the float chamber pivot mount I applied pressure in my vice. Just like the bottom flange I found it impossible to get it totally straight with the amount of pressure I was happy to apply so I did a little more work holding the cover in my vice and giving it a few taps with a small mallet.

Toshi 975 said:

The picture looks fairly typical of what I have come across on a number of the carbs. I had already straightened a few bottom mounting flanges by that time so I was pretty confident that there was a degree of flexibility in the metal alloy . I removed all the parts from the top cover then with parallel bars across the holes on the underside to give clearance for the float chamber pivot mount I applied pressure in my vice. Just like the bottom flange I found it impossible to get it totally straight with the amount of pressure I was happy to apply so I did a little more work holding the cover in my vice and giving it a few taps with a small mallet.

Click to expand...

OK. I see what you mean. I will give this a try. I ordered another gasket kit so if this doesn't work then maybe I will double up on the gasket that goes in there. One of the two should work. I'm looking forward to there being no more gas smell!

I was just thinking...won't gasket sealant help with this? Seems much easier.

I also had this problem, but not quite as bad. I used a flat file to remove the high spots until it laid flat

Franko500 said:

I also had this problem, but not quite as bad. I used a flat file to remove the high spots until it laid flat

Click to expand...

You can also place fine sandpaper on a sheet of glass and rub the surfaces on it until They are flat

Do NOT under any circumstances use gasket sealer--there is a real risk, due to the thinness of the bowl wall and the proximity to jets, that as you tighten down the top of the carb onto the main body that bits of sealer will be squeezed out and enter the jets and (fine) passages in the carb--then you really will have running problems!

the hobbler said:

Do NOT under any circumstances use gasket sealer--there is a real risk, due to the thinness of the bowl wall and the proximity to jets, that as you tighten down the top of the carb onto the main body that bits of sealer will be squeezed out and enter the jets and (fine) passages in the carb--then you really will have running problems!

Click to expand...

Agreed. I thought this and won't be using gasket sealer. I would have used it just around the outer edge of the gasket and not internally, but I still don't know where that sealer may go once I tighten it down.
I tried using a file but it really didn't do much. It's hard to get a good amount of material off this way as there are a lot of obstructions in the way. I think the double gasket will be my best best. If this doesn't work then I guess I will just buy a new carb unless I can think of a better way to get that top plate flat.
I still don't see how I can get it into a vise and straighten it out.

First of all, find yourself a 2nd pair of hands (girlfriend, wife, sprogs etc) and a selection of small pieces of hard timber (soft woods tend to crush too easily). By putting pieces of timber on both sides of the top in places that will allow you to bend AGAINST the bow, you can VERY GENTLY straighten out the top--BUT BEWARE--it is made of what is colloquially known as '**** alloy',
it is not very strong. Proceed very carefully--you might still need to buy another carb, but at least you will have done all you can to retain the original.

the hobbler said:

First of all, find yourself a 2nd pair of hands (girlfriend, wife, sprogs etc) and a selection of small pieces of hard timber (soft woods tend to crush too easily). By putting pieces of timber on both sides of the top in places that will allow you to bend AGAINST the bow, you can VERY GENTLY straighten out the top--BUT BEWARE--it is made of what is colloquially known as '**** alloy',
it is not very strong. Proceed very carefully--you might still need to buy another carb, but at least you will have done all you can to retain the original.

Click to expand...

Ok. I'm assuming then put it in the vise and hope for the best.

I did add a second gasket and that seems to take up the gap rather nicely. See picture below. Should I just be happy with this fix?




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Bad warp at base of carb. I'm thinking I should just get a new one now. How can this be fixed?




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