TR4/4A TR4 Zenith-Stromberg CD175 tuning question

[eschneider]

i don't see these very often in the shop. To be clear, this is the variant with the bar choke - no stinkin' cold start valve, water choke, altitude compensator, or emissions. Actually kinda likable critters without all that stuff..... (And surprisingly, it looks like the TR4 is the only application that uses the 1-3/4" in simple form)

So the question:

I'm used to SU's - the mixture adjustment is fairly (cough) precise - couple flats too high and the lift pin causes an RPM stumble, couple of flats too low and the RPM rises.

Seems the stromberg margin betweent the 2 extremes is at least a couple of full turns (12 "flats") -- so from experimentation and checking plugs, I've been adjusting them up I get the lean stumble, then back down 1/4 turn.

Happened to be working on one today, and thought I'd prod the experts for their insight and experience.

 

[TR4]

I assume you balanced both carbs first so they are sucking the same amount of air? Your method of getting them to go lean and then backing out 1/4 turn will be close enough to see how they perform on the road. Drive maybe 40 miles and pull the plugs to see if they are black, white or a nice toasty brown.

 

[trrdster2000]

You are going to be real close, like Phil said. It's a bit tricky to get the clamps tightened without movement. Push down on the idle screws as you tighten them up. Always liked them myself and found they were a little quicker off the mark than the SU. I have a set for the TR6, but ran across the triple Weber's for it and haven't done either as it's just too hot except in the morning. I know I'm getting sorry in my old age.

Wayne

 

[eschneider]

Thanks guys-

So it sounds like Strombergs are just a little fussier on tuning mixture than the SU's.... It's not just me.....?

Yes, I balanced the carbs, set the timing, checked for vacuum leaks. Really, my question is general - I'm not having a specific problem, just seeking knowledge.

 

[SkinnedKnuckles]

I never liked the old "lift the air valve" method. I go by plug readings.