V Minor Accelerator Pump Housing Leak

[Sir Paolo]

Gents,

Some advise, please - since rebuilding my engine (and carbs), I've noticed a very slightpetrol leak from around the accelerator housing gasket.

When I say minor, it is very minor - just enough to show as a thin line of petrol on a clean sheet of kitchen roll. 

I tried tightening the screws as much as I dare (no mean feet with carbs in situ), and petrol is still finding its way past the rubber gasket. Even without the fuel pump running.

I removed the carbs and re-cleaned all the mating surfaces to no avail. 

Question is, will this by any chance seal itself, or should I invest in new gaskets?

The difficulty is, I can't see what I done wrong to cause the leak in the first place (wish I'd left the old gaskets in place)

So I don't know what I'd achieve with new gaskets (I did buy a genuine Dellorto rebuild kit).   

Or could I use a little petrol resistant sealer such as Hylomar blue.

I'm obviously trying to effect a permanent repair, as we all know the carbs sit right above the dizzy and solenoid, so we need to keep the petrol away from the sparks!

Many thanks.

 

[andydclements]

I'd say re-seal it. When it comes to fuel leaks onto the dissy area there's no such thing as a minor one, they all could possibly lead to disaster.

Before attempting to guess what parts need replacing wrong, pull it apart and inspect it, you may find the cause is easily identified.

[Sir Paolo]

Thanks, Andy. I did remove the housing and nothing obvious was amiss. All surfaces were clean, and the gaskets weren't distorted in anyway. I re-cleaned the surfaces with 2000 grit W&D and petrol, but no change.

When you say 're-seal' are you suggesting using the Hylomar Blue?

[andydclements]

You could try that, I just meant whatever it takes to get it to seal.

[lguy]

Hi, don't use you car while you have the slightest leak from the accelerator diaphragm, I did, but luckily enough I always carry a number of fire extinguishers, so no lasting damage

The reason they are leaking is most lickley, where they have been fitted for so long, and now you have moved them they are not sitting in the same place

Order two new seals, fit and forget, no more worries.

You know it makes sence

Regards Len

[Sir Paolo]

Hi Len,

It does make sense, but my problem is that I fitted new seals as part of the Dellorto rebuild kit, and I can't work out why they're leaking.

The housings are clean, and the newly fitted rubber gaskets weren't distorted in anyway. The thing is, it's happening on both carbs.

If I knew why, I would buy new seals, but I don't. Which I why I'm thinking of trying Hylomar...................  

[jonwat]

You need to check the needle valve is sealing properly, if it's not the float chamber will fill with petrol & leak out of the gasket.

[Sir Paolo]

Thanks, John - how do I check that?

 

I fitted new viton tipped valves that came with the rebuild kit, and set the float levels (by bending the arms) accordingly.

 

I doesn't seem to be leaking out of the accelerator diaphragm, or the top cover gasket. Only (both) accelerator pump housings.

[lguy]

How's it going, all done? Where are you ? I'm in Chingford let me know two heads are better than one. Len

[Sir Paolo]

Hi Len, many thanks for your offer of help, but I think I may have found the problem.

It looks like a small trace of the old gasket was left on each of the mating surfaces. These remained despite my cleaning efforts.

I noticed this quite by chance as I ran a Stanley blade over the surfaces and was able to remove what must be remains of the old gasket, that are not visible to the naked eye.

There is a rib in the housing that must have been made shallower by the traces of gasket, reducing its effect and allowing fuel to leak past.

I've ordered some new gaskets, and l'll let you know what happens.

[lguy]

Well done, I've just put my car back together and it's always the last little bits that catch you out and take all the time, I've had those leak but you don't always see the fuel, have you got a fire extinguisher ? I only ask because with one you feel in control. Regards Len

[Sir Paolo]

Hmmm, unfortunately the new gaskets didn't cure the problem, but there is at least a little improvement.

Eurocarb have suggested I fill the floats via the pump and put carbs & m/f on bench to see if I can see a leak. Not holding out much hope as.I'm pretty sure I know anyway.

Still like you I've just put the engine back together, and it's not leaking from the headgasket or cam covers (yet).

And yes I do carry an extinguisher

[lguy]

Taking it all off is fine but I always use a big mirror with everything in place to look look and look again, and then take the carbs of when you have at least an idea what to do,

I'm a mechanic/mot tester, and the amount of times I get other "people" bring there car to me after they have striped it and put it back together and the problem is still there, diagnosis is the key

Regards Len

[molemot]

Get a piece of glass and put the mating surfaces on that...then you can look through the glass and see if you have any gaps or distortions. A small film of oil helps you to see.  If you have any minor problems, you can cure them by using wetordri paper on the glass and carefully rubbing the offending article on it in a circular pattern, cleaning and checking every so often.

 

Len is dead right... diagnosis rules...and NEVER, EVER, trust ANYONE ELSE'S diagnosis......that way you end up changing the LH wheel bearing when it's the RH one and similar daftness. Also, don't ever order parts or buy them before you have the duff bits in your hand....that way you won't end up with unwanted replacements for perfectly serviceable stuff.... 

Edited July 25, 2013 by molemot

[Sir Paolo]

Gents, agree 100%. Especially as no one other than me has seen the leak. My query was largely to see if anyone else had experienced similar and found out why.

Still it seems like a rare problem with no obvious (well to me at the moment) cause.

[lguy]

Hi again

It is only a carb, does it leak with just the pump running ? Is it just one carb ? If its one carb and you've replaced both gaskets you must be doing it right ! Faulty gasket ? You seem to know what your doing, and your getting the best advice from people who have "been there" where are you located ?

[Sir Paolo]

Hi Len, it's actually affecting both carbs, and leaks without the pump running. And as I say, it still leaks after new gaskets, and another clean of the mating surfaces (which seem flat enough).

I did notice a small leak from the top covers, but a tightening of bolts cured that, and it's definately not coming from anywhere else.

I spoke to Eurocarb, who are suggesting it may be float levels, but I'm not sure this is the issue as the accelerator pump reservoir fills up first, and long before the fuel level reaches the floats.

I've since bought a used housing and will see if that changes anything. I'll keep you informed (I'm in the Watford area).

[andydclements]

You can eliminate float housing by checking whether it leaks even if there's no supply pressure. If there's nothing pushing fuel in and there's not excessive fuel height then it's not float/ needle valve related.

[Sir Paolo]

Agreed, with or without the fuel pump running, there is no leakage from the auxiliary venturi's.

So I doubt float level is the problem.

If things don't change with the spare housing I've bought, it's time for some Hylomar.

Their tech chap seems to think it'll be OK, as they've tested it in long term exposure to petrol.

[Sir Paolo]

Gents, by way of another update, the damn leak is still there after trying the spare housing.

 

So, if another smoothing with W&D doesn't work, it's time for Hylomar!

[lguy]

Hi Paul

What are you going to do now ? Have you got any one close that can take a look ? Or should I come over and give my ideas ? Let me know I could be free on Saturday morning

Regards Len

[Sir Paolo]

Hi Len, just got my dizzy back from Aldon after a full refurb (good service, so recommend them should the need arise - the dizzy's lying flat can cause problems, so it's worth having them looked at), so was able to run the engine for a good while.

 

Interestingly enough, the leaks seemed if anything a little better. Whether or not that was to do with the heat I don't know.

 

What I do need to do is get some glass as John suggested, and after trying another housing, I'm sure the problem is at the mating surface on the carb body itself.

 

I've also bought some Hylomar, so I'll apply that, and see how that goes.

 

Really appreciate your offer of help , but we're away this week-end, so I won't be playing in my 'man cave'.

 

I'll keep you informed

 

Kind regards

Paul

[lguy]

No problem, do you think you may have swaped the two parts on to the opposite carbs? Just a thought ,

Regards Len

[Sir Paolo]

I don't think I mixed up the parts as I rebuilt the carbs one at a time.

Still it does look as though there has been an improvement since I last treated the carb body surfaces to a square rubbing down with W&d.

I'll give this another go and monitor it.

I keen to get this sorted as I want to get the car set up on a dyno after the rebuild

[lguy]

Dyno's are scary things, good luck