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Stromburgs..rich or lean?  Rating:  Rating
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 Posted: 05-04-2008 05:59 pm
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Frank Schwartz
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My son Mark, says he is convinced his carbs are too rich. Says it will now start the moment he touches the key switch...no cranking or choking needed.  Last year we replaced the needles with new ones and balanced the carbs and set the needles as per factory instructions.  Started with some choke.  Things have apparently changed.  My question is..how does one tell if the carbs are rich or lean and how does one know what is the "correct " setting?  I can borrow a colortune gadget if this is the only way.  Never used one, but can follow instructions.
Regards to all,
Frank Schwartz

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 Posted: 05-05-2008 12:32 pm
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Brett Gibson JH5 20497
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Frank, best way of telling if it's to rich is look at the spark plugs, plus if it backfires after you shut the engine down, a few seconds after, definately to rich, unburned gas in the exhaust. As for choke, sometimes I would need to use mine other times not, so dont worry to much on that score.

Brett.

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 Posted: 05-05-2008 09:44 pm
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Frank Schwartz
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Thanks,  Brett...I thought I had them set right, but my son, Mark, is a bit paranoid, and inasmuch as he has overtightened the rubber gasket on the lower valve cover and now has leakage, he is convinced the engine is running too rich...since he no longer has to choke the engine to start it. However, he is on a 1000 mile trip down to Florida and thereabouts and is driving it daily, it probably does not need to be choked during this
period.   I will borrow a ColorTune anyhow and check it when he gets back....

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 Posted: 05-06-2008 11:17 am
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Brett Gibson JH5 20497
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Frank, I tried a colortune once, and was not impressed with the results, I tried full rich to the leanest and it barely showed a differance, worked great on my lawn mower though.

If you really must have a go at them (stroms), try leaning up a half turn at a time, remebering the original setting, and see what that does for you.

Cheers. Brett.

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 Posted: 05-06-2008 04:29 pm
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edward_davis
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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!

Edward

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