DeTomaso Mailing List: February 1997, Message #121
     



From: ingate@shiseis.com (Shane F. Ingate)

Subject: Re: 351C & sidefraft Webers

Date: Wed, 19 Feb 97 10:18:55 PST



All,

>         Using the downdraft IDA Webers on V8s are usually

> accompanied by horror stories of engine fires.

>         I've never heard such stories associated with the

> sidedraft DCOEs.  Is this something that DCOE owners are

> worried about?



Michael Porter sent me the following:



I haven't been (no fires after about fourteen years on a couple of

different engines).  But there is also something to consider with one

barrel per cylinder Webers--at certain rpms, probably varying with

engine type and camshaft, there can be reversion columns of air above

the carburetor--the column of air has sufficient momentum that it

literally rebounds compressively off the closed intake and heads the

other way.  When it does this, it takes fuel droplets with it. It's not

entirely uncommon to be able to see a mist of fuel droplets looking as

if they're dancing above the carburetor, at higher revs. But, this is

true of any type with one barrel per cylinder.  I suppose this might be

a cause of fires in the pits with the air cleaners off, but would be

unlikely at speed.



The other problem, which is a more likely cause of fires with the IDA,

rather than _some_ of the DCOEs, is that the IDA has no starting devices

on it.  No starters, and no strangler choke. They're pretty much a warm

weather carburetor.  If one uses the throttle a bit too much to prime

the engine when cold, there's plenty of raw fuel available in the

manifold for a backfire to light off--and nothing to limit flow of

burning fuel out of the carburetor if the throttle plate is partly open,

as it would be on a racing engine which might require an idle of 2-3000

rpm.  40DCOE 20s, 21s, 22s and 45DCOE 12s do have a starter which

richens mixture without opening the throttle at all.



Guess big cams and too many squirts of fuel on starting have more effect

on the chance for fire than the carburetor itself... have seen engine

fires in the pits with Holley double-pumpers on engines with fat cams,

too.

Cheers.









Shane Ingate in San Diego