Carb info please

[pfenlon]

I have a pair of fixed jet Stromberg carbs on my 250, I note that the carbs each have a small tube, see pic.

Is it required to be used in the UK? for I imagine it was an emissions fitment for the USA.

 

any help appreciated.

[harlequin]

That is the vacuum supply to the by-pass valve. The idea is that on over run (high vacuum) it opens the valve which puts a spurt of air around the butterflies to prevent popping in the exhaust. Most people blank the valve off, to do that undo the 3 slot head screws which will remove the valve then make a solid gasket for the valve and replace.

As you don't have the vacuum supply connected your valve is not operating but there is a diaphragm in the valve which can split, when that happens you have an air leak so it's best to blank them off.

You can tell when the diaphragm has split because engine breaking is reduced.

George 

[harlequin]

I notice that you have what looks like a US TR6 inlet manifold which is a wide port type, I think all TR250s had a narrow port head so it is worth checking that the ports align.

George 

[Kenrow]

The Vacuum Retard System should run through the two carbs attached at the tube you are pointing to. What have you done with the fitting in the middle of the intake manifold which the brake servo nipple screws through? In the end the tube hoses will end up at the Distributor Vacuum Retard.

https://trf.zeni.net/TR6bluebook/28.php#navbar (Part AT4)

You might want to check with the TR 6 crowd as it looks like your target setup might be in line with the 1970 TR 6.  The 70 TR 6 bypass valve does not have the tube you are pointing at, and it might just be a case of plugging the tube in each carb.

https://trf.zeni.net/TR6bluebook/32.php#navbar

https://trf.zeni.net/TR6bluebook/52.php#navbar

Edited September 22, 2022 by Kenrow
added info

[pfenlon]

1 hour ago, harlequin said:

I notice that you have what looks like a US TR6 inlet manifold which is a wide port type, I think all TR250s had a narrow port head so it is worth checking that the ports align.

George 

I changed the Head for a TR6 one so they line up, but tanks for the info, Peter.

 

1 hour ago, Kenrow said:

The Vacuum Retard System should run through the two carbs attached at the tube you are pointing to. What have you done with the fitting in the middle of the intake manifold which the brake servo nipple screws through? In the end the tube hoses will end up at the Distributor Vacuum Retard.

https://trf.zeni.net/TR6bluebook/28.php#navbar (Part AT4)

You might want to check with the TR 6 crowd as it looks like your target setup might be in line with the 1970 TR 6.  The 70 TR 6 bypass valve does not have the tube you are pointing at, and it might just be a case of plugging the tube in each carb.

https://trf.zeni.net/TR6bluebook/32.php#navbar

https://trf.zeni.net/TR6bluebook/52.php#navbar

Cheers Ken, I have only one vacuum unit on the distributor having removed the second one, but again, thank you for the information.