vapour lock or fuel evaporation?

[blue 464]

Ok, I have removed the carbs from the car.and removed the float chamber covers, hopefully from the pictures of the left carb which was flooding you can see that the 2 floats are not level. the setting at the highest point is correct at 17mm, but at the other end one is significantly lower than the other. the manual states they should be level. I have removed the needle valve, there was no muck in it and it seals when operated manually. Bear in mind these carbs were professionally refurbished 400 miles ago.

so question, is the difference in levels sufficient to cause the carb to flood? or should I look elsewhere?

as always thanks in advance for any answers, Derek

Image001.jpg Image002.jpgImage003.jpg

[V Mad]

so question, is the difference in levels sufficient to cause the carb to flood? or should I look elsewhere?

I think its the carbs that are at fault, especially if one is flooding and the other seems OK.

[V Mad]

Why did the Triumph designers put the filter under the bonnet and not in the boot?

They probably gave that job to the apprentice.

Why do many other manufacturers put them at the back near the pump?

[KOY 23]

Responding to post #32.
Not necessarily, due to high fuel pump pressure and hot fuel, the fuel will be at a much higher pressure than recommended 3psi. One float valve may pass fuel at a lower pressure than the other but will block fuel well in excess of normal fuel pressure. Hardly fair to blame the carbs when subjected to excess pressure.

What is max fuel pressure of float valves in your carbs, Chris?

[stag157.7]

I would like to make a few comments on the subject of strombergs
I do not usually mix forum matters with my business ventures
But I think it is relative in this thread
Firstly it is not just stags that suffer from carb flooding please Google other forums and similar issues are being discussed
on stags it is I can see only a very small percentage as a problem
I have reconditioned 476 sets now and know of less than 15 with problems
I recondition carbs for rimmers paddocks.robsport and stag classics who have reported no issues
Also bear in mind we are at the mercy of one supplier for the needle valves (burlin fuel) so no matter what supplier you purchase from they are all coming from the same place
I have personally purchased 250 needle valves so in the event of poor manufacture I will repace them
That being said the foremost problem lies with fuel pressure being too excessive and secondly dirt in the fuel lines
It only takes a small piece of fuel line debris on fitting to cause problems hence it is good practice to flush first
I have also fitted and tuned 15 sets and had no problems
This is think is true of Russ and stag classics
I am always available for help and assistance

Alan

[Stagsongas]

This is certainly an interesting subject. No-one has got wrong in these last two pages IMHO, it just needs a bit of pruning and a shuffle.

Kryten and many others have cars which don't suffer this problem, although they are running in the same air temperatures and are llikely to be using largely the same fuel. But I guess that's not to take a 'head in the sand' approach and then say it can't happen with other cars, because it clearly does. A clue to Kryten's good fortune might be in how he descriibes his ticking pump....Would that be the older, electric and points type pump that was designed for the purpose, one that delivers only 3psi or less?

That could be a clue. It has been said elsewhere that some replacement pumps deliver too much pressure already, and underbonnet heating, boosted even more by higher Summer air temps. could be putting the system (carb valves) over the edge.

VMad Chris is correct to say that the filter would be better in the boot, as it's purpose is to filter out debris from fuel put into the tank. That's where most 'crap' comes from. We should ask ourselves why much later designed modern cars have the fuel filter at the rear, very close to the tank. My guess is that is isn't about heating of the filter at all, it's about safety. In the case of and engine fire or impact damage, the last thing you want under a bonnet is a little flask full of petrol, it is better and safer to have it located at the rear where less ignition sources exist.

However, I think Chris is wrong in saying that a petrol fillter under the bonnet will cause more pressure rise in the system through underbonnet heating. The pipes have less petrol in them for sure, but they are subjected to the same amount of heat, The smaller amount of petrol in a pipe will increase system pressure more quickly than the larger amount of petrol in a filter subjected to the same amount of heat. This is only the same as a kettle with less water inside it coming to the boil more quickly than it would if it were full.

Alan makes a good point that all float valves come from the same source, and I guess there is the traditional engineering failure rate from new of around 2%. If failures rise above that percentage there may well be some other factor at work. Looking at Dereks' pictures, and taking into account that the reconditioner (whoever) knew his job well, I have to wonder if a float, when subjected to prolonged excess fuel pressure can actually end up with it's float valve actuator arm bent dowwards by the valve being forced off it seating, resulting in almost constant overfuelling in that carb. afterward?

We might question why BOTH float arms would not be bent in that case, but if one is bent, the excess system pressure would then be released. There will not be enough excess pressure remaining to bend a second arm.

Taking all of these factors into account, and others not addressed here, I think it safe to rule out widespread problems with the Carb.s (either in orginal design or reconditioning) and the constituency of the fuel as major contributors.

What we can say is that heat is clearly a factor, and there is more of that around in Summer. More heat will cause higher system pressures when the engine is switched off and reports of hot starting probems certainly seem to increase at this time of year.

In conclusion, I'm happy to predict that most problems of this type can be cured by fitting a petrol supply pressure regulator, in which case the type of pump fitted is not as crucial,

OR

Only pumps delivering petrol at a pressure at (or lower than) the orginal specification should be fitted.

OR

Whatever type of preferred excess pressure device is fitted to return the excess fuel to the tank.


Regards

Steve

[KOY 23]

They probably gave that job to the apprentice.

Why do many other manufacturers put them at the back near the pump?

Do they? All the cars I have had for the last 20 odd years have had the main filter under the bonnet. All have had injection, so need super clean fuel.

[marshman]

Do they? All the cars I have had for the last 20 odd years have had the main filter under the bonnet. All have had injection, so need super clean fuel.

Cars I have experience of that don't have a fuel filter under the bonnet include: peugoet 106, citoen saxo, citroen ax, ford focus, vauxhall astra, bmw 320. Never had a "modern" petrol cars with one under the bonnet. All diesels I have experience of have them under the bonnet.

[V Mad]

the pump (from LD) has been on the car 2 years and there was never a problem with the old carbs.

I also have one of the LD pumps, and I dont think there is a problem with these (although we need to be aware that some others, like specific Facet types can put out way too much pressure).

I think the failure rate of reconditioned Strombergs is much too high even though some will try to deny it. If you are lucky enough to have a set which are 'correct' and working then thats fine. But I have not seen anything that has got to the bottom of the problem so far. It seems like most of the problems are due to flooding, which are probably due to faulty needle valves. But the so-called improved types of needle valve dont seem to be the panacea that we were led to believe.

Fitting regulators, and/or taking measures to reduce heat soak may alleviate the problem, but I think it just masks the real cause.

[Stagsongas]

The cars I specialise in all have the filter located virtually underneath the rear mounted tank. The pipes are plastic so they don't corrode internally.

[V Mad]

Alan makes a good point that all float valves come from the same source, and I guess there is the traditional engineering failure rate from new of around 2%.

If failures rise above that percentage there may well be some other factor at work.
Steve

I would be surprised if there arent some bad copies of float valves on the market. and failure rates can vary wildly due to many different factors (process, materials, handling and storage etc etc).

[stag157.7]

Thats a witch hunt comment
try and keep this this thread sensible and not turn it into a weber v stromberg debate or lets get the mods to close this thread
I do not comment on the weber problems nor do I wish to do so

throwing mud ,will not help other stag owners with problems whatever carb they choose to run


alan


we have been there many times

I also have one of the LD pumps, and I dont think there is a problem with these (although we need to be aware that some others, like specific Facet types can put out way too much pressure).

I think the failure rate of reconditioned Strombergs is much too high even though some will try to deny it. If you are lucky enough to have a set which are 'correct' and working then thats fine. But I have not seen anything that has got to the bottom of the problem so far. It seems like most of the problems are due to flooding, which are probably due to faulty needle valves. But the so-called improved types of needle valve dont seem to be the panacea that we were led to believe.

Fitting regulators, and/or taking measures to reduce heat soak may alleviate the problem, but I think it just masks the real cause.

[stag157.7]

I have requested that carl close this thread
as as usual v mad is determined to have a go at strombergs
wonder why!!!!!!!!!!!!!


alan

[KOY 23]

I also have one of the LD pumps, and I dont think there is a problem with these (although we need to be aware that some others, like specific Facet types can put out way too much pressure).

I think the failure rate of reconditioned Strombergs is much too high even though some will try to deny it. If you are lucky enough to have a set which are 'correct' and working then thats fine. But I have not seen anything that has got to the bottom of the problem so far. It seems like most of the problems are due to flooding, which are probably due to faulty needle valves. But the so-called improved types of needle valve dont seem to be the panacea that we were led to believe.

Fitting regulators, and/or taking measures to reduce heat soak may alleviate the problem, but I think it just masks the real cause.

Like fitting catch tanks to aftermarket carb conversions

Should a trader be criticising a fellow members competitive product?

[wilf]

One thing that I did spot is that the poster with flooding problems has no engine driven fan, just the Kenlowe. That will give rise to higher underbonnet temperatures in general, and exacerbate carb flooding issues due to heat soak, a point I have made in the past.

Apart from that it looks as though all valuable comment has run its course on this thread, and I am closing it to ensure it does not fall foul of the "competing commercial interests" issues.