misfire, running rich or junk it?

[pontiacratrod]

well, after a couple months of screwing around i finally pulled all the emissions crap off my 86 1/2 ton gmc sub. put a mid 70's dizzy and q-jet. replaced exhaust to delete cat etc etc etc. new carb, plugs, wires, cap, rotor and coil. drove it for the first time today and here are my problems.....
if you stand within a mile of this thing you will pass out from the exhaust fumes. i dont see any smoke, but it smells like it is running horribly rich. its got a misfire that keeps a rhythm and is worse at low rpms. looks like blowby or exhaust coming out of heat riser (its not loud like an exhaust leak should be though). if i keep it in overdrive and try to drive it falls flat on its face, rpm drops and it seems like it floods and almost dies. it will only run moderately ok if i keep it in drive. it runs the best if you beat the crap out of it and rev it up. ive got the timing set at about 6 or 7 degrees. any help would be appreciated......

 

[southernspeed]

Start from the beginning again with a tune up. Check all your plug gaps. Check the leads are ok and in the right order. Check dizzy cap and rotor are ok. Even though you've 'just done all that', do it again to double check. varify that your TDC mark is actually at TDC on #1 .Check that your mech advance is working by gently twisting the rotor and letting it spring back. Run the truck with the vac advance disco'd and plugged from the manifold source and set initial timing to 8* BTDC. Reconnect vac advance and if you have a dial back timing light, verify that your timing at idle has now moved to around 20* BTDC. If you don't have a dialback light, you can see with the strobe on the marker that the balancer timing mark is now several inches to the left of the marker tab. If it's not, check that your vacuum source is manifold takeoff, not timed port.
Once all that is good you can start tuning your carb. Check float level first before messing with jets etc.

 

[imiceman44]

Start from the beginning again with a tune up. Check all your plug gaps. Check the leads are ok and in the right order. Check dizzy cap and rotor are ok. Even though you've 'just done all that', do it again to double check. varify that your TDC mark is actually at TDC on #1 .Check that your mech advance is working by gently twisting the rotor and letting it spring back. Run the truck with the vac advance disco'd and plugged from the manifold source and set initial timing to 8* BTDC. Reconnect vac advance and if you have a dial back timing light, verify that your timing at idle has now moved to around 20* BTDC. If you don't have a dialback light, you can see with the strobe on the marker that the balancer timing mark is now several inches to the left of the marker tab. If it's not, check that your vacuum source is manifold takeoff, not timed port.
Once all that is good you can start tuning your carb. Check float level first before messing with jets etc.

What he said.
Mine turns out to be the carb, it was getting a slight miss at idle and barely noticeable while driving, failed smog badly too, now it is fine.
I did have all new plugs, wires dizzy cap and everytihng was perfect except it had the miss, Carb was a rebuilt out of the box too but the adjustments on it weren't great.

 

[Hogback Fabrication]

Checking all of the stuff above is a really good idea but I'd put my money on carb. Its possible that the float sank, its possible there's crap in the carb and its possible the carb came from a significantly different engine than yours.

If the ignition side looks good, rebuild the carb and see what happens. Clean it REALLY well, blow out all the passages with compressed air and replace the float. If that doesn't fix it, you may need to change metering rods and jets.

 

[southernspeed]

Yeah it may well be the carb but you ALWAYS do the carb last 'cause any ignition/engine problems affect the vacuum on the carb and how fuel it'll flow.
One thing I didn't mention above is valve lash, when was that last chacked? Any noisey lifters?

 

[MrArmyAnt]

Not to hijack a thread, but i have the ac delco 44 spark plugs, what i always use. Is gapping them that important?

 

[southernspeed]

Not to hijack a thread, but i have the ac delco 44 spark plugs, what i always use. Is gapping them that important?

Yep, a small gap will effectively advance your timingbecause the spark jumps sooner but you'll also get a smaller spark. A wider gap retards it slightly but with a powerful ignition system you'll get a much stronger spark.
.005" eitherway won't make a lot of difference but .010" or .015" will.

 

[MrArmyAnt]

Mihgt be my problem i listed in another thread. hopefully its something else though, those damn headers make pulling plugs a pain.