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Stromberg 150 CD carb question


Jedi Warrior
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I have a 70 GT6+ with Stromberg carbs. I have the shop manual for the car but it is a bit fuzzy to me when it comes to the carbs.

I am burning rich and I have the floats adjusted correctly and the needs are all the way down to the lean mark. I use to have a manual for these carbs but can't find it anymore and I remember something about a screw on the side of the car opposite side of the idle screw that also effected something. I just don't remember what that screen does anymore. (I think this is in the bypass assembly )

I also noticed at the back, bottom of one of the carbs is a brass pipe (it looks like a vacuum line should go here), it has a hole right behind the butterfly (throttle disc) that it connects to. Should this be plugged or connected to a vacuum line. I have the vacuum advance attached to the other carb on the top pipe.

Do any of you have some good instructions on this carb and what adjustments can be make and what are the presets.

I will do some checking tonight to make sure I don't have any air leaks as well around the manifold, or in the carb.


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Hi Tom.

I'd get other input before hauling off and doing anything on just my input here, but the bypass assemble on our carbs is often ripped and can contribute to poor running. It looks like this;


The brass pipe on the front bottom of the carb near the intake manifold usually is connected to a vacuum line, but I'm not sure how the GT6 is supposed to be set up.

These carbs are all fairly similar, and the accepted reference materials is the Buckeye Triumph rebuilding guide;



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I should have added that I recently rebuild my 175CD carbs with a lot of help, patience and coaching from the folks here and especially Poolboy. It isn't hard, the results are great, and once you get comfortable with it I found it fun to do.

I have an augment to the Buckeye guide specifically on the bypass reassembly so let me know if you'd like to see it.


Jedi Warrior
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You have the right picture. Now I just need to figure out the how to adjust it and also what the extra vacuum connection is for.


Great Pumpkin - R.I.P
The bypass valve shouldn't be able to cause rich mixture tho, only fast idle or possibly lean mixture. I'd be more suspicious of the cold start valve (if present on your carbs).

The brass pipe sounds like a vacuum retard port. If so, it should either be plumbed to the retard side of the vacuum module on the distributor, or capped off.

The first thing to check of course is the rubber diaphragm. Even a pinhole leak can upset the mixture, so stretch it a bit with your fingers and look all over.

I would also be suspicious of the floats (which sometimes aren't compatible with the ethanol being added to our gas these days), and the fuel pressure. There have been several stories lately of replacement fuel pumps putting out too much pressure.

You might also double-check the float bowl vents. There were several different configurations, but I think your carbs would have a simple port on the side, that should be open to the atmosphere through either the air filter or the carbon canister.
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