A few days ago, after running a fuel pressure gauge, I noticed the motor started really
being sour at low rpm and right off idle.

In checking today I found that the o-ring for the drivers side idle screw had broken and
the idle mixture screw was bottomed against the seat. But, the one thing it was doing better,
was idling and the plugs on the drivers side really looked pretty good.
(as opposed to them normally looking pretty dark if they have a lot of idle or low rpm time on them.).

So, that told me I should consider trying to lean the idle fuel restriction (the idle screws are right at about 1turn out).

I pulled the front metering block and the idle feed restriction holes are over .002" larger than indicated in the Book by SA designs
on Demon carbs (and on the web page below). The book says they should be .038" and they are .040" (.0415" with a digital caliper). I checked with a pin drill set (used for drilling out welding tips).

Most of the other orifice sizes are also over by about .001.

The model is a
2563010DR
on http://www.demoncarbs.com/demon/30.aspx

Anybody had experience with how close these should be to spec??
Anybody ever used something other than pin drill bits to check hole size?

I went back and tripple checked everything and it appears that my new ebay special digital caliper is about .001 higher than the old dial pos iv been using for 3years. So, the holes are closer, but still a minimum of .001" over and .002" over for the idle fuel restriction.

 

A couple thousands is a pretty acceptable tolerance. I think you're over thinking things a but. Getting the idle mix where you want it isn't hard, no drilling involved. Fix the broken seal, and lean the mix screws out a hair.

 

the screws even at <1 turn really did not make too much differnce. i would have thought these tolerances (especially ones that .001 can make a significant difference in the end result) would have been tighter.

Its always had the age old symtpom of the idle going slower and slower after you sit at a light for a bit.. tale-tell sign of plugs loading up.

 

Does it still run if you close the screws?

 

the thing it used to do when the fronts were <3/4 was just about die when i would turn or stop rapidly.

 

Install the tap in air bleeds that come with it..fixed my rich idle on my Demon instantly.Start with he primary side only..stillrich intall the secondaries also.I have all 4 installed in mine.Also helped with a small off idle flat spot..crisp and clean now.