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TR5/TR250 Bypass valve
- Thread starter mrw02536
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The brass pipe that attaches to the manifold vacuum has been soldered closed, in the left hand photo.
I also have another question about the gaskets that came with the diaphragm kit. I replaced the diaphragm and used one of the gaskets between the carb body and bypass valve, what are the extras for?
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Here’s a photo
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As I’ve said, as a project I purchased a set of cd-2 175 to rebuild. My 250 is in storage in Florida until I get there on December, when I’ll install the rebuilt ones. I dissembled the carbs completely and just waiting for parts to reassemble. I needed to replace the jet and adjustment screw as well as the throttle shaft and seals which were quite worn. The diaphragm in the bypass valve was brittle. Naturally all new gaskets and o-rings. Everything was cleaned in chemdip. The carbs are a slightly later version of what on my car, having adjustable needles and a plug in brass drain. Every else looks the same. This is my first and I wonder if there are any last minute things I should be aware of. I don’t no what to expect when I install them.
Now I’m confused. From the photo, vacuum from the photo gets to the carb through the small hole that fed by the brass tube that you suggest i cover with the gasket. What do I have wrong? It looks like the one on the right is the correct fit.
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poolboy
Yoda
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The type of TBV that was used on the TR250, the 69TR6 and the 74 TR6 is like the one you have..The sensing port for the vacuum that makes the TBV function is a hole down at the bottom of that nipple.
On the rest of the years the sensing port is internal and must remain open if you want the TBV to function,
BUT. the small hole gets covered in the 250, 69 and 74 versions
This 69 TR6 illustration is exactly the same as the TR250
I'd disable the thing entirely if I were you...make a substantial gasket,one capable of standing up to high manifold vacuum..in excess of 25 in-Hg during engine braking..a gasket that covers all but the 3 threaded screw holes that attach the TBV to the body of the carb.
On the rest of the years the sensing port is internal and must remain open if you want the TBV to function,
BUT. the small hole gets covered in the 250, 69 and 74 versions
This 69 TR6 illustration is exactly the same as the TR250
I'd disable the thing entirely if I were you...make a substantial gasket,one capable of standing up to high manifold vacuum..in excess of 25 in-Hg during engine braking..a gasket that covers all but the 3 threaded screw holes that attach the TBV to the body of the carb.
This is how I currently have it blocked.
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Could you explain your reasoning on why I should disable it with the rebuilt carbs?
Bypass Valve: The bypass valve provides a channel for air to flow around the throttle disk. A very high depression can exist in the intake manifold if the engine is operating at a high RPM with the throttle closed such as might occur when decelerating. Poor fuel combustion occurs in this situation giving increased exhaust emissions. This is frequently evidence by exhaust popping during deceleration. The bypass valve senses the high depression and allows some air to go around the throttle plate to reduce the depression to the desired level.
poolboy
Yoda
Offline
Right...the reason I disable it is because it's emission related only under those rare conditions that it opens.
Disabled, I don't have to bother with the procedure for getting it properly adjusted and the idle will never be affected by a bad adjustment or by the inevitable deterioration of the TBV's diaphragm
BUT if you have a 250 (or a 69) it's important to not only have the TBV properly adjusted but also the Vacuum Control Valve that's mounted and activated by the front carb which must be installed and also properly adjusted.
If you have all that and feel the need for the TBV to function when you use 'engine brake' then do not deactivate it.
Disabled, I don't have to bother with the procedure for getting it properly adjusted and the idle will never be affected by a bad adjustment or by the inevitable deterioration of the TBV's diaphragm
BUT if you have a 250 (or a 69) it's important to not only have the TBV properly adjusted but also the Vacuum Control Valve that's mounted and activated by the front carb which must be installed and also properly adjusted.
If you have all that and feel the need for the TBV to function when you use 'engine brake' then do not deactivate it.
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This is what i read:
Bypass Valve: The bypass valve provides a channel for air to flow around the throttle disk. A very high depression can exist in the intake manifold if the engine is operating at a high RPM with the throttle closed such as might occur when decelerating. Poor fuel combustion occurs in this situation giving increased exhaust emissions. This is frequently evidence by exhaust popping during deceleration. The bypass valve senses the high depression and allows some air to go around the throttle plate to reduce the depression to the desired level.
what is the downside if everything is working properly?
Bypass Valve: The bypass valve provides a channel for air to flow around the throttle disk. A very high depression can exist in the intake manifold if the engine is operating at a high RPM with the throttle closed such as might occur when decelerating. Poor fuel combustion occurs in this situation giving increased exhaust emissions. This is frequently evidence by exhaust popping during deceleration. The bypass valve senses the high depression and allows some air to go around the throttle plate to reduce the depression to the desired level.
what is the downside if everything is working properly?