General Tech Tuning an engine with a vacuum gauge

[70herald]

Quick question. Since I feel like playing around, I just ordered a vacuum gauge to tune the herald.

I have the Stromberg CD150 carb - non- emissions version. Can I use the vacuum output to the dizzy vac advance or is this affected by the throttle?

My manifold doesn't have a vac port but of course I could drill and add a port if needed (but for obvious reasons would prefer not to do so.

 

[NutmegCT]

Do you feel vacuum at the vacuum advance when the engine is idling? Some carbs use "ported vacuum" and some not. I'm pretty sure you can't use a vacuum port which is only "open" to vacuum when the throttle is open.

Edit: another way to tell - is the carb vacuum port above, or below, the throttle butterfly?

Tom

 

[dklawson]

As above. For tuning you want manifold vacuum, not ported vacuum.

 

[TR3driver]

I agree. And I'm fairly certain the Herald uses ported vacuum for the advance. There were a few "emissions" engines that didn't but all non-emissions Triumphs used ported AFAIK. But you'll know quickly enough when you hook the gauge up and the reading at idle is ridiculously low.

 

[Andrew Mace]

You might want to get one of these adaptors: https://www.speedograph-richfield.com/html/vacuum_pipelines.html

It's much easier than drilling and tapping the manifold for a fitting and, since it's after the carburetor, gives you the vacuum you need for gauge readings.

 

[70herald]

OK, I just found a worn out carb in the junk pile and I see how the vacuum would be blocked by the butterfly valve, so that clearly won't work.
Andy that adapter makes much more sense than drilling the manifold and I think I have a few spacers just waiting to be drilled into.