Interesting Stromberg problem

Talk about the E-Type Series 3
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jagwit
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Joined: Thu Oct 18, 2012 6:52 am
Location: Pretoria
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#1 Interesting Stromberg problem

Post by jagwit » Wed Sep 02, 2020 6:23 pm

V12 RH front carb does not flow fuel via transparent pipe to rear carb even when choke (enrichment valve) is fully activated.

Problem was found to be the outer valve housing that had bent due to overtightening of the two screws holding it to the carb body.

This resulted in air rather than fuel being sucked into the valve past the gasket, between the outer housing and the sandwich plate, rather than fuel.

Sanding the outer cover on a flat surface was enough to get a good seal of the gasket and thus a fully operational enrichment valve.
Best Regards
Philip
Jag: 72 E-type V12, 80 XJS (Megasquirt + 5sp manual O/D)
Jensen: 74 Interceptor (EFI by Megasquirt + O/D 4sp auto)
Chev: 59 Apache std, 70 C10 (350V8, 700R4)

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PeterCrespin
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#2 Re: Interesting Stromberg problem

Post by PeterCrespin » Thu Sep 03, 2020 12:04 am

Mazak zinc alloys make great castings but do not stand up well to overtightening, especially with thickish gaskets. Being soft, however, they are easy to sand flat. Two-ear flanges like old bike carburettors were notorious for this when tightened onto insulating spacers. The irony was/is that by tightening too hard trying to avoid a leak, people caused them... That's why Jaguar used an triangular recessed o-ring to seal the heater valve to the pipe and bulkhead, not a flange gasket.
1E75339 UberLynx D-Type; 1R27190 70 FHC; 1E78478; 2001 Vanden Plas

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42south
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#3 Re: Interesting Stromberg problem

Post by 42south » Fri Sep 04, 2020 2:14 am

Hi Philip,
Thanks for posting this, my car has the same issue.
I was going to check that the choke plate was in the correct orientation. Is this what you term as the enrichment valve?
Now I have another thing to check, would spraying some inert gas around the valve with the engine running demonstrate a change in engine rpm, thus proving the problem? I’m a little hesitant to spray volatile stuff around there with the engine running.
Mark
Mark Brown
1971 S3 Etype
Son: when I grow up, I want to be a pilot
Dad: You’ll have to choose.

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jagwit
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#4 Re: Interesting Stromberg problem

Post by jagwit » Fri Sep 04, 2020 2:27 pm

42south wrote:
Fri Sep 04, 2020 2:14 am
Hi Philip,
Thanks for posting this, my car has the same issue.
I was going to check that the choke plate was in the correct orientation. Is this what you term as the enrichment valve?
Now I have another thing to check, would spraying some inert gas around the valve with the engine running demonstrate a change in engine rpm, thus proving the problem? I’m a little hesitant to spray volatile stuff around there with the engine running.
Mark
Choke and enrichment valve is the same thing yes. In case of the Stromberg its more correct to refer to the enrichment valve as this is exactly what it is. (But the end result is the same as a "choke" - richer mixture for cold starting purposes)

I doubt very much that spraying a gas near the valve will show you anything because fuel (and air) is sucked INTO the valve when operating correctly, and also the amount of air being sucked in is VERY little. Note: some air is sucked into the valve through a dedicated hole in the outer cover (and even smaller holes in plate with the "C-groove" inside). This is where the bubbles in the pipe liking the two carbs come from. HOWEVER!!! Air is meant to be sucked into the hole provided for this purpose, NOT via the housing perimeter because it is warped.
Best Regards
Philip
Jag: 72 E-type V12, 80 XJS (Megasquirt + 5sp manual O/D)
Jensen: 74 Interceptor (EFI by Megasquirt + O/D 4sp auto)
Chev: 59 Apache std, 70 C10 (350V8, 700R4)

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