Twin H idle speed

dave11

Been focussing on carburator issues on my 52 308 lately. 

Got the engine to run and idle nicely, however the idle speed is a bit higher than I would like.

The intake manifold has been milled for flatness at the engine block mounting surface, with new Best brand gaskets. Replaced all the carb to intake mounting gaskets. The carburetor throttle shafts seem to have little play or wear if any.

I have set up the carbs with a unisync. Still in order to get the idle speed down I have to back the idle stop screws off untill they are not touching, then turn them in untill they are just touching. The idle screws are adjusted to best lean setting. Engine vacuum is 19 ( at 800 ft elevation ) Adjusted ignition timing for maximum advance using 91 octane fuel. 

To restate,..the engine runs great , but the idle speed is a bit higher than I would like. My thinking is the intake must be getting air from somewhere?

Spraying the intake manifold gasket surfaces or the carb area (when the engine is idling) with fuel does nothing to increase the idle speed.

Just wondering if this is normal with a twin H set up?

Dave Eddie

50ClubCoupe

I'm running a twin H on my 262 and I'm able to get my idle down to 550 rpm.  I did the same process as you described above however I backed my timing advance down by 2" Hg from the max vacuum.  

Uncle Josh

I may have had an anomaly, but I had to back both mixture screws off to 3 1/2 turns to get it to idle smooth.

dave11

Ken,

I don't use a timing light much, rather I run high octane fuel then keep advancing the timing untill the engine "Pings" then back it off slightly untill it doesn't ping. If the timing is  advanced too far it will kick back on the starter.

I have also used a vacuum gauge,....advance the timing to get the highest vacuum reading then retard the timing untill I get about 2" of vacuum drop.

Not the most technical method I know but my engine runs so much better with lots of ignition advance.

I'll check the timing tonight with a light just for information sake.

Dave

dave11

Turns out the ignition timing is 8 degs BTDC