View single post by edward_davis
 Posted: 05-06-2008 03:29 pm
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Joined: 07-06-2005
Location: Eugene, Oregon USA
Posts: 162
Frank,  Brett is right: the adjustment with the Stromberg is so small that you can't see any results with the colortune.  You'd have to actually change needles or jets to get any difference.  When I was riding with your son at Jensen East '07 es said y'all had changed the jets as well as the needles: or am I remembering wrong?  Anyway, if you put in larger jets, you would have to get different needles to make keep the system in balance. 

As I learned from Greg in an off-board discussion, the Strombergs were used because of a Federal desire to keep users from being able to do much to the fuel mixture in the engine.  Kind of like the way they keep the computer chips proprietary in the newest fuel-injected engines so hot rodders can't alter the fuel map for performance at home. 

To get any substantial change in mixture with a CD carburetor like the Stromberg, you have to go to a different needle profile: that's why the Dells are so good for folks with modified engines.  With Dells, you can go ahead and tweak the settings to get the "fuel map" exactly right for your new configuration.  With Strombergs, not so much.  I talked to an MGB racing team in NC that was using CD carbs because of regulations.  They were acutally filing down sections of the needles to change the richness in response to data from an oxygen sensor in the header.  Tha'ts a very, very analog version of the 'learning' fuel maps in the newest EFI cars.  If you can go with Dells instead of strombergs, you don't have to do all that.

So what I'm saying is, if you have a stock engine and new (correct) jets and needles, you should be able to get the richness right with the old "lift the plunger" test, as in the manual.  If the engine is modified for breathing better, you might end up needing to go to new needles, but (I think) it should be suffering from an extra-lean condition then.  If it's always too rich, you might be having problems moving air through the engine, and one obvious possibility is tight valves.  The shop manual insists that you shouldn't adjust the Strombergs until you have adjusted the valves.  In my own experience, the last time I adjusted my 'Bergs after rebuilding last year (on Mother's Day, no less: I will never hear the end of it!), I was not able to tune them out of being too rich, so I left them at the starting position recommended in the manual.  When I tore into the valves this spring (I almost have them done!  I swear!), I discovered that #1 intake was too tight and all of my exhaust valves were too tight.  I'm planning to return to the carb adjustment after Iget the head buttoned back up this week, to see if I can tune the mixture precisely now that the valves have the correct lash.

In the end, if Mark's 'Bergs won't adjust correctly, you might want to check the valve lash and also do a compression test.  Since the exhaust cam cover was tightened too much, you need to get in there anyway.  Tell him not to feel too bad about that cam cover, though: I've wrecked three rubber gaskets over three years trying to get the torque just right on that thing.

Hope this helps!