Tuning for a mopar 318

[Cliff Ruggles]

In most cases being open between both sides will not effect light throttle performance, but I've seen it impact full throttle performance (stumble/hesitation/bog) when going quickly to full throttle.

I don't have any good suggestions at this point.  Those are NOT lean carburetors, they use small MAB's and primary POE.

You might want to try blocking off or removing the primary POE system to see if it's not actually a rich condition rather than lean.  The POE adds a LOT of fuel at light part throttle when throttle angle is increases slightly, and maybe the engine doesn't like it?.....Cliff

[toocheaptosmoke]

I agree, it seems like even with 68 main jets it is still on the rich side everywhere except for the lean spot.  I will look into the POE, at this point I will try anything, haha.

Another thing I thought of is just trying an entirely different carb.  I have a Q-jet in a box somebody gave me a while back, most of the parts seem to be present, I think I should be able to piece it back together.  It is number 17080212, if you think it's a decent setup worth trying we might build it up and see what it does.   Thanks.

[toocheaptosmoke]

Turned out the extra 17080212 carb I had was a bit worse than anticipated, so I didn't bother with it.

 

A little while back I grabbed another complete carb from the local swap meet, #17056208.  The new carb's air horn was slightly warped, so I tried to flatten it just a little and ended up cracking it slightly in between the primaries.    Lesson learned, that's why sanding is recommended...  But we did get it flat.  Also found the APT screw threads were a bit stripped down at the bottom, but it can still be adjusted some.  Throttle shafts are also worn, in general the carb was a lot worse for wear than it looked.   I threw it together with leftover bits and pieces I had, figured nothing to lose at that point.  Wouldn't you know it, the lean spot stumble I've been fighting disappeared instantly with the new carb, and the A/F ratio is a LOT more consistent than it ever was with the old carb.  Just runs better in general.  Have some high idle issues I think are related to both the worn shaft area and sticking secondaries. 

 

I left the stock 76 (I think) jets and put the .044 rods in, along with the dark blue APT spring.  Managed 18.6 mpg on a 450 mile trip, and still could improve the cruise mix a bit.  Haven't made much progress with the secondaries yet, even with a high hanger, small rods, and 3/4 turn on the spring it still bogs out when they open. 

Now the problem is I need to either find another one of these carbs, or at least one similar enough that's worth rebuilding correctly.