239 / 2gc idle issues

A

Austincarnut

Junior Member
This is a long story about why this even happened but here's my dilema: I have a 239 mated to a mercomatic medium case trans w/ 2gc carburetor, mallory dual point. I cannot seem to get it to idle low enough and strong enough to handle transmission engagement. Could the torque converter stall speed / rotating mass be an issue? I figure with the difference of 16 cubic inches vs the merc's 255, It should be able to handle this.
 
Believe the idle speed spec. for the automatic is 485 RPM.
Mine is happy with 500-550 RPM.
What is your idle RPM?
Engine displacement has nothing to do with it.
 
Last edited:
My way of thinking is that there is not enough mass / inertia to maintain idle speed properly. I cannot get my idle speed much below 700 or so. Are you running a mercomatic? what is your idle speed in gear? thank you for responding...
 
1. Are you running a stock cam? A performance cam will exaggerate this problem.



2. Is the timing set at approx 4 degrees at idle speed?


3. Does the engine try to die when put in gear or is it just too harsh a shift into gear?


4. Do the idle mixture screws have any effect when turned out or in?



Terry
 
Austincarnut said:
My way of thinking is that there is not enough mass / inertia to maintain idle speed properly. I cannot get my idle speed much below 700 or so. Are you running a mercomatic? what is your idle speed in gear? thank you for responding...
Click to expand...
My Merc-O-Matic has the same idle speed in or out of gear.
Don't over think the mass/inertia thing, get the RPM down to the appox. 500 range then see what happens.
 
The mix screws will stall the engine, Where they are now, they are too fat. the cam is stock for the '53 ford sedan the engine came out of. the transmission is '51 merc. the 2gc was built for this in mind. maybe timing is a tad retarded @ 2* BTDC
 
Ok. Something's not right in the tuning if a lower idle can't be achieved. Maybe a vacuum leak (although rich running doesn't point to that) or maybe an idle circuit problem in the Rochester. That carb should work fine. I'm running a small base 2GC on my Merc and it'll idle at 400 if I want.

How does your engine sound when trying to run lower than 700 rpm? May get a clue from that...


Terry
 
Austincarnut said:
The mix screws will stall the engine, Where they are now, they are too fat. the cam is stock for the '53 ford sedan the engine came out of. the transmission is '51 merc. the 2gc was built for this in mind. maybe timing is a tad retarded @ 2* BTDC
Click to expand...
You say you are running a 2gc.
If you are using a Merc. manifold to mount it that had a divorced choke.
There is a vacuum port/hole that has to be plugged where the old choke mounted.
 

Attachments

  • plug.jpg
    plug.jpg
    382.3 KB · Views: 10
Last edited:
51 MERC-CT said:
You say you are running a 2gc.
If you are using a Merc. manifold to mount it that had a divorced choke.
There is a vacuum port/hole that has to be plugged where the old choke mounted.
Click to expand...

Ok, I have it worked out. I didn't mention the engine is a fresh rebuild. Ran it about 4 hrs and progressively lowered the idle, I believe the engine was built very tight and would not cooperate until it was bedded in. It will now idle correctly. Thank you all for your help.
 
You must log in or register to reply here.
Back
Top