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73 RRC overacelerated at low MSL


Carlucho
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Hey,

 

I need your help, I got 73 RRC  3.9-liter petrol with Stromberg carburetors.

 

Currently my house is at 1600 MSL (meters), so when I went to the beach (0 MSL) the last 3 times my RRC got accelerated until I returned home .

The distributor is calibrated to 9 degrees.

Do you know what may be happening?

 

Thank you in advance for your help.

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I suspect so. There's no altitude compensation on the Stromberg (or most carbs for that matter) so if you've got it right for where you live up high, it'll be rich down low. 

You've got relatively few options for easy adjustment and none that won't involve twiddling stuff with tools when you transition. How bad is it? 

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@FridgeFreezer maybe it's too rich, I don't know it properly because at 1600 MSL is working good at 850 RPM, but I supose that is rich for altitud reason. 

1 hour ago, lo-fi said:

I suspect so. There's no altitude compensation on the Stromberg (or most carbs for that matter) so if you've got it right for where you live up high, it'll be rich down low. 

You've got relatively few options for easy adjustment and none that won't involve twiddling stuff with tools when you transition. How bad is it? 

It's not that bad, maybe make some settings to keep it in an intermediate range.

 

1 hour ago, smallfry said:

Could it be a sign of a split or holed diaphragm ?

I replaced them already twice, also all carb gaskets as well once.

 

57 minutes ago, lo-fi said:

That shows up as runs terribly all the time. You usually get the opposite problem where its tuned for ~sea level  elevation and gets bad when going up high.

It's true, for that reason it was not common, I didn't know if I was lacking any knowledge about it.

 

Thank you for your help.

 

Any other idea?

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Ah, wait. You mean the engine is idling faster when at sea level? That's because for a given throttle opening, more air is entering because its denser. More air, more fuel, more power.

You could make some removable shims for the throttle stops. Just remove at low altitude and replace when you go back up. A piece of sheet brass cleverly cut, folded and soldered ought to do it. 

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