[Spridgets] Runs great, but terrible mileage - Weber 40 for sale

[David Riker]

DCOE carburetors are designed for power at high rpm, think of them like 351 
Cleveland ford heads.  Huge ports= high volume@ high rpm, but at low rpm the 
air velocity is too slow.   At low velocity,  fuel droplets atomize poorly, 
and aren't able to burn as efficiently.  Improperly tuned, DCOE's will make 
an engine feel like it bogs down at low rpm.  They can be tuned to run 
smoothly at low rpm, and the stumble can be tuned out of them, but they 
still really aren't meant for low rpm applications and will consume about 
30% more fuel than a good SU.  The real benifits are that they are 1) set 
and forget... once dialed in, they NEVER go out of tune, 2) quicker throttle 
response... you get a real accellerator pump which shoots raw fuel into the 
airstream when you mash the pedal, 3) they look real cool... 4) they sound 
real cool too...

Adding a ported vacuum feed for your vacuum advance system isn't all that 
difficult. I drilled a hole adjacent to the front throttle plate, so that at 
idle, the hole is on the aircleaner side of the throttle plate and no vacuum 
signal is present, but as soon as you roll into the throttle, the throttle 
plate swings open past the hole, and a vacuum signal occurs.  I used 
alumiweld glue to glue a small piece of metal tube into the hole, and hooked 
a vacuum line to it.  I had to try 3 variations on location, testing with a 
vacuum gauge and a hose that reached into the driving compartment and watch 
how the vacuum signal responded before I set on a location that yielded 
vacuum under light throttle and cruising conditions, but none at idle.  With 
a lopy cam and high lift rockers, any vacuum signal at idle makes the timing 
at idle jump all over the place.

Part of my less than optimum fuel economy can also be attributed to the cam 
and high lift rockers.  The engine doesn't even start to sing until above 
about 2500 rpm, but from 3k to 6k it is a whole lot of fun.
David R.


----- Original Message ----- 
From: "David Ramsey" <dwramsey at att.net>
To: <WeslakeMonza1330 at aol.com>
Cc: <spridgets at autox.team.net>
Sent: Friday, September 17, 2010 1:34 AM
Subject: Re: [Spridgets] Runs great, but terrible mileage - Weber 40 for 
sale


> Just because you have a Weber DCOE, why wouldn't you have a vacuum 
> advance?
> It is very easy to set them up for it.
> Crash
>
> Any Weber DCOE is only heavy on fuel because you don't have distributor
> vacuum advance for when you are driving slowly or because you tend not to
> accelerate or drive slowly anymore anyway.
>
> It's foot to the floor work - usually lots of acceleration rather than
> having the car flat out that drops the fuel consumption.
>
> Regards
>
> Weslake-Monza 1330
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