17080212 to 17085213 Conversion

[HeavyChevy]

81 Chevrolet 3/4 ton 454 Very mild RV cam (208/218 @ .050") stock intake and exhaust manifolds.
Problem is, When I rebuilt the original Carb (17080212) I discovered a hole in the casting allowing fuel to leak out of te bowl into the intake.  So I have another complete carb (17085213) I changed all the calibration over to the new carb, but I'm still using the original throttle plate (bushed and in good condition).  So, I know there is a difference in the bypass air orifice from the hot air carb throttle body to the electric choke throttle body.  The results are: the engine runs great except at idle, where it loads up very rich.  Idle mixture screws have no effect (runs same with them lightly seated).  If I remember correctly, the hot air choke throttle body (17080212) had idle bypass orifices in the .090" range, whereas the electric (17085213) had approx. .054"  If I open the port up to the .090, wont this compound the rich idle situation?  Am I missing something?  I transferred the entire calibration from the 17080212 to the 17085213 with the exception of the throttle body.  Should I go ahead and rebuild the throttle body and use it also?
Any help would be great.  Book is awesome.  Love the forum.

Thanks, Lane

[429bbf]

no your thinking backwards. the idle bypass air will give it more air at idle and should lean out the stumble. hth

[HeavyChevy]

ok, understood. But I'm running the large bypass throttle body.  Same throttle body the original calibration was used with.  The only current difference from the original setup is I have converted to an electric choke.

[429bbf]

gotcha my first thing id look at the gaskets and the holes in both base plates . i seen different holes on some of them base plates. its almost like you plugged off the hole to the idle bypass in the baseplate.

[von]

Yes make sure the base plate is correct for the main body and gasket. I've seen quite a few that are mismatched, especially with parts store "remans". I've been able to make most of them work with some drilling, grinding, epoxy, and mods to the gasket but it sometimes can be a lot of work. GM made countless variations which means the mismatch passages often don't match up. Usually vacuum and/or idle air bypass.

[HeavyChevy]

Thanks for the replies.  Ill pull it back off and see what I can come up with.  Will update with findings.

Lane

[HeavyChevy]

ok, Pulled carb, checked baseplate gasket.  All holes seem to be aligned correctly. 
Runs good above idle.
Idle is rich smelling, Idle mix screws have no effect (even closed)
removing vac cap (leak) stabilizes idle
So...do I need to add more air?
or restrict fuel?
MAB = .052
Idle tube = .036
Idle restriction Orifice (I call it CRO Channel restriction Orifice) = .046
Bypass Air = .100

No nozzle drip, hot restart is good, just too rich on idle
I'm thinking I have plenty of idle air, so I'm considering restricting fuel?  Best way to accomplish this?
Ideas?

Thanks, Lane

[429bbf]

have you tried taking the springs off the idle screws?

[HeavyChevy]

No, I have not, but They are still stock size. .062"
Thinking towards opening up my MAB?  Opinions? Ideas?

[429bbf]

not sure if that will help the problem. what size are your idle air bleeds?