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TR6 Stromberg Bypass Valves - Question

Sbardon

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I am currently chasing a poor vacuum issue, and along my path am into the bypass valves on the carbs.
1976 TR6 Vac retard.
I am a bit confused as the gasket that mounts the bypass valve to the carburetor has a section missing between the two ports?
I understand that:
There is a signal port (the tiny one), A port on the manifold side of the throttle plate, and a port on the Carb side of the plate. When the manifold depression exceeds the setting the valve floats and allows more air from the carb to the manifold side...

I seem to have old gaskets that have the bridge between the two larger ports, yet I also seem to have some without, which makes no sense to me as there would be a constant leak across this gap.

(In looking at the Moss Kit, it seems to provide both?)
Does anybody have any insight?
 

poolboy

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Depending upon what you see on the carb itself.
BypassValve6.jpg
If there is a channel between the inlet and outlet like this, use the gasket with the open space between the 2 holes.
Having said that you'll have less problems in time to come if you disable the TBV entirely.
And, btw, it's not just air that bypasses the throttle, it's whatever the mixture happens to be in that short interval of time that the TBV is forced to open.
 
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Sbardon

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Poolboy, thanks.
In the picture you provided, I see the gasket with the space, I don't see what you mean by the channel in between.
Both my carburator and bypass valves have flat surfaces.
Are you saying this means I should use the gasket that has material between the holes?
(would make sense to me)
And why or for what carbs would you want that channel(leak)?
 
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Sbardon

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Poolboy, thanks.
In the picture you provided, I see the gasket with the space, I don't see what you mean by the channel in between.
Both my carburator and bypass valves have flat surfaces.
Are you saying this means I should use the gasket that has material between the holes?
(would make sense to me)
And why or for what carbs would you want that channel(leak)?
 

poolboy

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See the channel or gap or whatever you want to call it between the hole to the mixing chamber and the hole to the manifold in that picture ?
If your carb has that then you'd use the gasket on the far left in this picture.
No channel then the gasket on the far right.
Carbs from a 250 or a 69 or a 74, the gasket in the middle.
TBV gaskets 002.jpg
I didn't design them, I just rebuild them....:crazyeyes:
 
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Sbardon

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Poolboy, thanks so much for your reply, I am afraid that old eyes and old phone mean I don't really see what you mean by the channel. In your picture it appears to me that there is a gasket in place, and the gasket is missing material between the holes.
The ones on my units were the ones on the left in your second picture(most likely not original). Wondering if they should be the ones on the right.
 

poolboy

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Apparently your eyes are better than mine because you're right, that is a gasket. I don't have a carb in my shop or in the scrap pile that has that channel to show...They are few and far inbetween

BypassValve6.jpg
 
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Sbardon

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Poolboy, thank you for your patience and insight. As both my Carborater and valve are flat, and I have the sensing... I should use the one on the right. Makes sense to me! Thanks.
It seems both my units had the wrong gasket. Have a variety of old gaskets, not the rights ones though, I will make new gaskets and try them out, and get some proper ones on order.
Thanks again. :smile:
 

steveg

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Poolboy, thank you for your patience and insight. As both my Carborater and valve are flat, and I have the sensing... I should use the one on the right. Makes sense to me! Thanks.
It seems both my units had the wrong gasket. Have a variety of old gaskets, not the rights ones though, I will make new gaskets and try them out, and get some proper ones on order.
Thanks again. :smile:

You might get away with Hylomar instead of a gasket, as it seems to be fuelproof. I've had it on my tank sender gasket for >10 years with no deterioration.
 

steveg

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...you'll have less problems in time to come if you disable the TBV entirely.

Poolboy - how do you disable the bypass valves?

Do you remove them and fit a home-made gasket or blanking plate?

I fitted my recurved BVU distributor and it was idling at 2500 rpm with the idle screws fully off! Both the bypass valve pipes were plugged. When I uncovered the rear one the idle went down to 1200 or so. Adjusting the bypass valves had no effect. Front valve:

screenshot.2436.jpg
 

poolboy

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I make a gasket that covers all the holes except for the 3 threaded holes for the screws that attach the TBV to the body of the carb...then if I leave the TBV guts in place I'll turn the adjustment screw fully counterclockwise. Just using the adjustment screw isn't what I consider permanent and sure as it will depend on the condition and integrity of the TBV diaphragm
I have some substantial gasket material that withstands the force of the vacuum which I use in my rebuilt carbs, but I have seen gaskets made from various metals, from brass to what looks like aluminum or 'tin'.
 

steveg

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....but I have seen gaskets made from various metals, from brass to what looks like aluminum or 'tin'.

Poolboy - thank you for the quick reply!

I've used household aluminum flashing in the past - easy to work; strong enough for blanking.

Edit: installed blanking plates made from alum flashing, sealed with hylomar. No problem setting idle at 1000. FWIW BVU recommends 1000 rpm idle (vs 800) to make cam last longer thru better lubrication.
 
Last edited:
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