[TR] Gas Mileage

Randall tr3driver at ca.rr.com
Tue Oct 14 13:34:04 MDT 2008


> I've tried 
> backing off the fuel mixture, but that tends to result in 
> harder starting

Are you using the choke when starting ?

> and slower response. 

What kind of oil do you have in the dashpots ?  SU or ZS carbs ?

> I *DO* have dark sooty exhaust in the tail pipes though! 

Not conclusive that the mixture is always too rich, but certainly evidence
that it was too rich at some point.  Once it's sooted up though, you have to
get it really hot to burn off that soot.  Used to be different, with the
exhaust depositing a fine layer of white lead oxide all the time, but
unleaded fuel doesn't do that.

Car engines do actually run better (make more power) with the mixture rather
rich; which is why the carbs are supposed to go rich when you first open the
throttle and at higher flow rates.  But best fuel economy is achieved with
the mixture on the lean side.

> Rebuilt carbs

Which needles ?  Using the 'rich' needles did terrible things to the fuel
economy on my TR3A.

Have you checked for things like dragging brakes, wheel misalignment, etc. ?
Do the vacuum and centrifugal advance mechanisms both work ?  How's the
ignition timing ?

If all else fails, I'd double-check the valve timing.  I also would not want
to run the valves tighter than specified for the cam you have (BTW, which
cam do you have ?) ... better to listen to a little clatter than have to
tear the engine back down to replace burned valves, IMO.

Randall


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