my 79 is bairly running, strong oder of gas comming from the right tail pipe (duel ex), black plugs on the same bank, back firing through carb, no backfire through tail pipe.... ignition issue or carb issue?
If all are black on one side, and ok on the other, timing chain? May have jumped a tooth or teeth are gone.
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 intake manifold.
Al
Yhea, but all four? Does the OP still have the heat riser on?
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 mixture.
----------------- TheSnoMan.com
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 ..SnoMan wrote:
Did you replace the plugs? Are the wires good? Does it miss at idle?
Al
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.
----------------- TheSnoMan.com
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?
----------------- TheSnoMan.com
High manifold pressure, not low.
low manifold vacum pressure or high absolute pressure.... it just depends on how you look at it.
----------------- TheSnoMan.com
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.
Al
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.
----------------- TheSnoMan.com
You're the last person to be chastising someone about how a carburetor works.
"low manifold vacum pressure"
Wow, you are really in a fog. I feel sorry for you.
Al
changed plugs, wires, cap, roter high energy coil, pickup coil, the whole distributer... 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 hours
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?
Al
What type of timming chain and gear did you install. Did the crank gear have three keyways. Bought a motor that the gear was put on with the wrong mark. Run like hell.
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