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Mysterious substance in Stromberg float chamber.


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At last I have managed to make a start on the rebuild on the Vitesse's carbs at the weekend. 


I started with the back carb and began by cleaning it externally before stripping it down. Removing it from the manifold gave me some indication of what I would find inside, no gaskets had been used either side of the insulator just copious amounts of RTV that had spread into the insulator, carb and manifold bores.


It was surprising therefore to find that on the outside it was actually quite clean, needing only a quick blast with Xylene based cleaner and a gentle brushing to have it looking respectable. Inside the float chamber was however quite a different story.


First of all the float height was miles out, possibly to compensate for the missing O ring in the jet holder perhaps? But most puzzling was the presence of a layer about 1/4" thick of red dust not unlike talcum powder in both feel and appearance. It was easily removed by turning the bowl upside down and then brushing the bottom of the bowl with Xylene.


At first I thought this was rust but nothing in the bowl showed any sign of rusting, the fuel pipes are copper, the tank appears to have been replaced and the in-line filter is clean and full of clean fuel. More significantly the mystery powder dissolved completely in the Xylene, turning it slightly pink so not rust then.


After a lot of thought the only thing I can think of is that it is the residue from a stabilising fuel additive after the fuel has evaporated, I should perhaps add here that I left the card for a couple of days after I had taken it off the manifold for just that reason.


As that carb is now rebuilt with new jet, needle, diaphragm, inlet valve and a full complement of O rings this weekend I shall repeat this procedure with the front one. If I find more red powder I'll photograph and post it. If I don't find any in that carb then the mystery deepens.


Any ideas?

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No gentlemen it is definitely not rust. In a previous life (some 40 years ago) I was a laboratory chemist and I know what raw metallic oxides look like. This was red as is Pillar Box Red not rust brown and was a fine homogeneous powder that dissolved in Xylene.


I suspect it is from some sort of additive, although I only use Castrol Valve Master very sparingly, but until I find the same substance in the other carb I won't commit to that.


Odd that it dissolved in Xylene but apparently not in petrol and that makes me wonder if it could be some sort of coating applied to protect the bowl in storage. I'll know more tomorrow when I start work on the second carb.

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I had some fuel line problems and eventually dyno-roded them with strimmer cord, what came out was thick pink sludge. This was old fuel and I wonder if this had been left to evaporate whether I would have got your pink powder?


There again I used a fuel adaptive for a while. I took a plug out to check the mixture, hoping for biscuit colour, but prepared for black. The plug was pink! A good reason not to use additive!

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How interesting!


 A  bright red powder 1/4 inch deep

that is  soluble in xylene?


rust? ( ie red rust  that is iron(111) oxide  Fe2O3 ) - like in  Colin's picture?

No = wouldn't be soluble in  Xylene.



No= seems unlikely- This would  have to have been be a very, very concentrated solution to leave an evapourated  residue 1/4"inch deep in a small float chamber and the possibly of some one putting neat additive into the float chamber seems a bit unlikely,even if this would produce so much  residue.If the same concentration was in the tank this would represent a huge amount of additiive and  then,unless it was cleared the filter at least would show some evidence.


The clue, I suspect, seems to be the missing gaskets and O ring


I venture that , in the past ,someone  has used sealants rather "ad lib" in lieu of gaskets  etc around the carbs  -and not  the newish silicone based   stuff but some  nice smelling, old fashioned stuff  like Hermetite or silmilar ( these often using solvents such as xylene  or toluene)   which partially  dissolved in the petrol in the  float chamber,  engine spluttered to a halt fairly  soon afterwards and the residue dried and degraded.


Or there again, it could be....

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All good ideas and today a friend who is a paint sprayer suggested it could be red oxide primer used inside the tank.


However this afternoon I stripped the front carb and no residue at all in the bowl, very confusing as it looks as if this carb has not been apart in an even longer time than the back one. 


It was also missing the same O ring but did have all the gaskets intact. 


Overall I am leaning towards Red Hermetite as the culprit but they must have used a whole tube of the stuff.


Anyway both Strombergs are now fully cleaned and rebuilt so tomorrow and Sunday will be installation and tuning days. Long time since I've had to set up anything other than 45 DCOE Webers so this should be fun,

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So both carbs are back on the manifold and the engine starts and runs beautifully although slightly rich as weather and other commitments prevented me from setting the balance and mixture as yet.


What I did do was pump some fuel through the lines into a jam jar and got clean petrol with no trace of any odd colour, so I removed both float bowls and found them full of again clean uncontaminated petrol.


Whatever my mystery contaminant was it isn't there now, so my last line of attack will be to borrow a bore scope and check the inside of the tank. If that is in good order then I'm afraid this will be another of the Universe's great questions.

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Hi Pete, thanks for the offer of your scope but I already had one from a friend. So I looked into the tank and no red oxide or rust in there, it actually looks new.


No idea at all what that powder was or where it came from but its not there now and the carbs are balanced and tuned so all good.


To treat myself I've replaced the points with a Lumenition Optronic set up driving the MSD system. Awesome, I think the spark could jump start a corpse but the timing is so much more accurate now I need to advance it up a little. More to do next weekend.



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  • 1 month later...

Solved it!!!!


Well in truth not me but a friend in the trade told me the answer as soon as I mentioned this. 


The clue should have been the colour, it is the residue left when a chunk of gasket gets dropped into the bowl during a rebuild. At first it gets saturated with fuel and sinks to the bottom but then over a long time the binding resins dissolve until only compressed gasket material remains when the bowl is removed or left without fuel and then you get red powder.


Apparently quite frequently found in pre-war carbs.

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