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TR6 My '74 TR6 Zenith Stromberg Carbs Float Bowls Leaking Gas

TR6Dan

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I am not sure what the problem is (why I am here). I have swapped by float bowls which have plastic plugs for late 70s bowls from MGB with no plugs; thought the float bowl plugs and new O-rings might be leaking along with leaking gas past the gaskets; the latter which to me sounds like the bowls are filled with gas all the way to the top ( I would think they should only fill to about 1/2 full). Thought it might be the needle valves allowing the bowls to fill to the top; so replaced them with GROSE-JETs, checked and adjusted the float height above the carb surface for the correct ht. (about 16-17mm); they both are still leaking gas past the gaskets. Please help me with what the problem could be.

Thanks,
Dan
 

poolboy

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What are you using for a fuel pump ?
And don't discard the plunger type needle valves....Grose jets tend to leak more often than needle valves.
 
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TR6Dan

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I am using a mechanical pump from Moss Motors. Installed about 2 years ago; car has run fine since replaced.

I still have the plunger type valves replaced with Grose jets; leaked and filled bowls with both. If they are working properly; shouldn't the bowl not fill to the top but about 1/2 way up?
 

poolboy

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I don't know about the "1/2 way up" part, but at 17 mm the floats should put enough pressure on the needle valve to shut off the fuel when the proper level is reached.
You could check the floats for bouyancy and have a look at the float pivot bracket...but to have both carbs over flowing would be unusual in those scenario.



ZS carb floats 002.jpgMICHAEL SPANO  more 001.jpg
 
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TR6Dan

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I measured the float level at 17 mm per the manual and adjusted to fit that. Floats looked fine and did not seem to contain gas and pivoted fine. If the valves are working correctly I would think the bowls would not be full; and the bowls must be full to have gas leaking at the gaskets. Have done the same thing with both the old and new valves. Not sure what to do now.
 

poolboy

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If all that checks out...fuel pressure, float bouyancy, float height, float brackets, proper gasket installation, needle valves working.... then the only other thing I can think of is excessive air pressure within the float chamber...What
do you have connected to the float chamber vent nipples ...the 'red' ones ?
ARV Vent 001.jpg
 

poolboy

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Since it's simple to do, unplug that hose from the Carbon Canister and see if the leak stops....I don't see why it would matter but just try it.
 

Sarastro

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Sorry, I'm not familiar with the ZS carbs used on the TR6, but I am familiar with the TR4A ones. Still, here's what I found:

The O-rings used on the jet assembly, which seal between the assembly and the float bowl, are not really sized right; I suspect they are the closest modern size to something now NLA. I think they probably work when there is minimal wear of the surfaces against which the O-rings seat, but in our 50+ year old carbs, sometimes not. I replaced mine with slightly larger O-rings.

It wasn't clear to me where your leak is coming from. If fuel is coming from the jet assembly, this might be your problem.

See http://tr4a.nonlintec.com/external/#fuel_system for my experience; scroll down to "A Tale of Two O Rings"
 
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