425 bad stumble rich, timing? distributor?

wheelshop · #1 (**permalink**) 03-16-08, 04:59 PM

I put a 425 from a 77 deville into my 37 chev truck, new carb, new plugs,cap,rotor,wires.....still stumbles when you try to accelerate esp under load.....could it be the pickup? module? coil? I have plugged the egr hole with a plate, could that do it?....Haven't checked fuel pressure, but the floats are holding...any suggestions...it also smells very rich.....600cfm edelbrock carb, but it was exactly the same with the quadrajet..... Thanks, Jay

wheelshop · #2 (**permalink**) 03-16-08, 05:34 PM

Ive read conflicting timing info....I have it set at 23 degrees initial without vacuum as one book had said, but now Ive seen it to be 10 degrees at 1400rpm..does anyone know what the proper timing is supposed to be?

djcwardog · #3 (**permalink**) 03-17-08, 05:58 PM

If this is a stocker, then you have the same motor as mine when I started out - exactly...

Re: the plate on intake with 425 EGR valve removed. I have one as spare parts in my garage and I'll look when I can but you want to be sure that a simple plate actually blocks the exhaust gas flow at that part of the intake. If there is a plunger that actually seats INSIDE the top hole (presuambly into a second hole down inside the manifold) then you have basically set the intake up to receive exhaust gases full-time and that would not be so great... If, on the other hand, it is designed that the plunger operates up in the valve itself, then you may just see two small holes in the intake and be OK with your plate - but then you'd need to look elsewhere...

Be sure your carb is sealed up to the intake with a fresh gasket. The stock Rochester was set up to run really lean - but mine is a good carb. If you return to the stock carb, then consider upping the jets a size or two - but your "rich" complaints would only get worse that way...

Also, I assume that you installed the distributor correctly indexed for #1 to fire near TDC and the rotor pointing to the #1 wire on your cap. So, recheck your plug wire routing...

Try setting total centrifugal advance at 36 degrees. Do this by pulling off the vacuum timing (hose running to the can) and then check engine wih timing light to confirm that all timing comes in at or before 2500. Then set your light for 36, run the engine at 2500 and set timing to read on the ZERO mark. Your light will factor in the 36 degrees for you - slick! I got rid of much of my stinky (rich) exhaust smell after I did this. With the vacuum can reattached to a vacuum source (run that direct from the intake and skip that smogger 4-port tube on the front of the engine) you will see another 25 or 30 degrees of timing. My engine seems to be working OK even with all of that. I recently swapped cams for an MTS#3 torque cam and this was part of my dialing it all in.