And how would that differ from bank to bank? Some 79's have a vacuum
operated heat riser. I'd see if it's stuck. Some 79's have a leaking
Qudrajet carb, but that would show in both banks if it has the original
Generaly when you have a backfire through carb is cause by a lean
condition. A stuck heatriser on one side could cause this problem
because even if mixture is rich it will be lean relative to cylnder
because old mixture will not escape properly and mess up incoming
I swapped out the carb last night, backfire through carb stopped, still
has a strong oder of gas comming out of the right tail pipe. It's still
not firing on all 8.
New top end, true dubble roller timing chain and gears, freshly
rebuilt 1.94 heads, new cam, new lifters new cast iron intake manifold
2500 miles ago, no vacume leaks through out system... its all bypassed
ATM for trouble shooting ..
Al, It misses so badly at idle the truck dies as soon as I take my foot
off the throtle, i cant even put it in gear.
yes, i changed the plugs and tested the wires, swapped out the whole
distributer with a known good working one, new cap & roter. did
compression test, all are even
Big Al wrote:
Look for a big vacum leak too. Also, you cannot realy test wires with
a ohm meter because it will not show hi voltage leakage potentail from
insulation break down. If they are more than a few years old here,
replace them regardless of ohm reading.
I understand what you are saying but it is sometimes possible with a
leak to load up sometimes really bad because low manifold pressure
will cause power valve on carb to enrichen mixture. Replace wiring and
cap if it has not been done aready and recheck firing order and engine
timing (you want about 4BTDC as a starting point). You might hook up a
vacum gage if you have access to one too and what type/heatrange plugs
did you install?
Totally false. The power valve has NOTHING to do with the idle circuit. He
smells gas because it's misfiring and pushing raw fuel out the tail pipe.
Stick with the ignition system. You said you replaced the distributor, did
you use the old cap or rotor? Rotor failures are common on that vintage GM
vehicle. Don't ignore the cap either. Best test for the wires is to move
them with the engine running and see if the idle changes. Or, if you get
shocked. Know anyone with an ignition scope? That would really help. One
thing NOT to do with that vintage HEI. If you pull the plug wires with the
engine running, like to see if a cylinder is missing, it will kill the coil,
rotor or cap. Don't do it. Don't use solid core plug wires either.
No the totally false part is your lack of understanding of how a carb
works because if the power volve is open due to low manifold vacum or
high absolute pressure it will dump extra raw fuel and cause engine to
load up, even at a idle. This may not be the cause but it is one of
the possibilties involved here. Excessive fuel pressure can overwhelm
float seat and dump raw fuel too. Point is there is a lot of varibles
involved not just a few as you suggest. If he has a Qudrajet they are
well known for floats saturating with gas with age causing mixture to
go rich and flood engine and cause it to load up too. Lots of
possiblities here and you need to go down the checklist.
changed plugs, wires, cap, roter high energy coil, pickup coil, the
replaced carb, we got it hitting on all 8 at idle now so that's a
pluss but its loading up while ideling in gear, all the tune-up parts
are new. the carb and dist are off of a known well running rig.
i spayed carb cleaner around the whole base of the carb and around the
fractory cast iron intake manifold and blocked every single vacume hose
but the vacume advance, I've been searching for vacume leaks for 3
on the road test its backfiring through the carb at wide open throtle
and has no nut sacks
I'm really greatfull for all this help you guys, dont give up on me,
I'm making progress
Big Al wrote:
Good. Did you check the heat riser like I asked in the beginning of all
this? Is it overheating or running hot? Or does it smell hot after you drive
it? Did you check to see if the balancer moved? Find TDC in number one or
six cylinder. Just use a pencil and turn the crank with a socket on crank
nut. Make sure the timing mark is on zero when it hits rock over. By any
chance is this a 400?
YES. it is running hot...
Is the heat rizer a little vacume opperated jobber with a hunk of
linkage that closes a flap on the ex manifold? I wiggled it, it's not
suck, when I put a vacume pump on the vacume opperated jobber it
moves.... wire it open for now? how do i test it?
timeing is set at 8 before TDC (by the book)
Big Al wrote:
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.