Triumph Repair: TR6 Stromberg 175 CD-2 SE Carbs, stop screws, stop screw

Question
I have a 1974 triumph, and I just had both of the carbs professionally rebuilt back east. I got them back and they did not run very well, bogging down any time I hit the gas and forcing me to use the choke to get any acceleration. I figured this was the usual, a lean mixture or not getting gas, and so I took them off my self and rebuilt them again, checking to make sure there were no clogs. When i put them back on the car, it ran about the same. When I placed my hand over the air intake, however, air was only being taken into one carb, and when I completely block the other it does not affect the engine at all. So I figure it is only running off of the one carb. My question is, taking into account that I have checked to make sure that both of the carbs are getting gas, that they are not clogged, that the mixture is correct, and that they have been rebuilt twice, do you have any additional ideas on what is keeping the second carb from running?

Answer
Hi Mitch,
It sounds like you didn't balance the two carbs correctly. Do this, disconnect the pinch bolts between the carbs so they operate independent of each other. Start the engine and hand operate the throttle of each carb one at a time to see if the engine will rev up operating on one carb only. If it does check the air going into each carb and on the one that no air is going into adjust the throttle stop screw until you are getting air into that one also. If the RPM is too high then lower the other one down a little. If you don't have a Unison gauge take a piece of hose like a vacuum hose and use it in one ear and put the other close to the intake to listen to the hissing noise of the air entering the carb.

By Adjusting the throttle stop screws to get the hiss to sound the same on each carb you can get close. If the RPM is too high or too low adjust each stop screw the same amount to get the RPM correct. Then recheck the sound of each carb's hiss. Soon you will arrive at a point where both sound the same and the RPM is correct. Now lock the pinch bolt on the throttle shaft so as to lock both throttles together.

Check that when you open the throttle linkage it opens both throttles at the same time and if not loosen it and adjust it to do so. Don't forget to put oil in the top pots under the caps. About a teaspoon in each.

The jets may or may not have been adjusted as that depends on each engine so a rebuilder can't set that. Only the installer can do that. Ignition timing MUST be set correctly first. Then the jets can be adjusted by removing the top cap and insert a 3mm Allen wrench down into the oil. Turn the screw to the right richens the mixture and left leans the mixture. You can NOT adjust the mixture until the throttles are set correctly as I outlined above.

Warm the engine up and lift the spring loaded pin under the side of the top flange. When you lift the front pin you are checking the rear carb (in spite of what you may have read) When you lift the front carb pin and the engine speeds up and stays fast, then the rear carb is too rich. If the engine dies then you either didn't get the throttles correct or the rear carb is too lean.

When you have them correct and lift a pin, the engine will slow down and sound like an old John Deer tractor.

Some Stromberg carbs had the adjusting screws blocked off with a plug so you could not adjust the jets. If you can't get the 3mm Allen wrench in then your adjusting screws are blocked.

Let me know how you do.
Howard