Engine experts ........ I got one for ya.

What would make an engine draw too much fuel?

Sounds like a simple question but here is what has led me to ask.

Vehicle: A sedan with a 1975 350/350 combo. 2 94’s on a Y adapter, lake headers and a Mallory unilite distributor.

What happened: The car was running fine, parked it. Next morning when I was driving it the exhaust sounded odd. The was a light popping sound that was not there before. The car has been on the road for a little over a year and has about 5000 miles on it. I was driving it around during the day and the popping got worse and I noticed a lot of black some out the headers and a very strong fuel smell. It starts right up and idles rough and pops out the exhaust at all rpms from both sides but more from the p***enger side. I figured I had a power valve problem.


What I have done:

I have rebuilt both carbs twice.

Switched to a single 2bl pulled from running car

Pulled the Mallory and put in a oe point distributor (about 6 times from same running car)

Tried 3 different coils

Disconnected the alternator and ran the car

Disconnected all the wiring and used a new ign switch

Removed the intake (I don’t see any cracks. ( stock cast iron 2bl)

Replaced the timing gears and chain

Replaced the cam and lifters (one lobe was a little round)

Dis***embled the heads and installed new valve seals (all valves look good)

Added a ground from block to frame.

Compression is 110 per hole

2 sets of spark plugs

Vacuum gauge reads about 15-16 lbs with a wiggle in it at idle and about 20 lbs

Hooked it up to my sun engine ****yzer and don’t see anything out of the ordinary

Tried different gas too.

I’m sure there is more I will post it if I remember.


What I still have: After 2 weeks and doing all of this **** the engine still runs the same. I must have missed something but what? The engine is drawing what appears to be a large amount of fuel from either carb setup. Plugs are black instantly and black smoke out the exhaust. The intake gaskets even look wet around the ports from fuel wicking out on them.

Any thoughts or wild *** guess would be appreciated at this point.

 

check your fuel pressure...those old carbs dont like much more that 2lbs. chevy mech pump will put out up to 7

 

I have a Holley regulator on it set at 3 lbs. It is not pushing fuel past the needle and seat.

 

110 per hole... is that a little low for a 350?

 

stuck or detached float? If you look closely at alot of old 94's you'll see little dents in the top of the housing where someone has been tapping on them to free the float.

 

Does the problem exist on all 8 cylinders, (plugs?) if not look for head problems. Bent valve, etc. you have changed everything that would cause the problem except for the heads. I would suspect they are the culprit. Damn that is hard to type when you are drunk!!

 

I had a car do similar stuff one time and the lead from the Ignition switch was almost burnt into inside the wire's insulation......turned out the switch was fried too.....LOW VOLTAGE is a source of weak fire/black plugs.....
I was reading your list and think maybe your suspect is one of the items that remained constant thru the repairs.....

 

Wingnutz: New chain, gears and cam/lifters.

choprodz: I did remove all the wiring from the engine and add and new ign switch with no change. I was thinking low voltage too.

7&7: Yea all cly are affected. All the valves looked good as well as the seats and It would be strange for both heads to suffer the same problem at the same time.

foolthrottle: I am running it with a single rodchester now and there is no change from the two 94's and it came off my dads 63 which is running.

49ratfink: I get 110 at every hole with one swing and I get about 125-130 with it hitting twice. The engine has about 80,000 rounds on it and had never been opened untill I just tore it apart.

 

oh...that's different. time to break out the digital volt meter. I had some hard starting troubles a while back.. fiddled with this, messed with that and nothing. so I put a pertronix in it. then it wouldn't start at all.

come to find out I had 12.?? volts going in and about 10 coming out of the original push ****on starter switch. put in a regular switch and I was done.

it doesn't take much of a drop to mess things up. maybe your "too much fuel" problem is not enough spark.

 

Since you've covered all the regular bases, it's either got to be something so simple it's been overlooked, or something thatis so unsusal that it's a one in a million thing.

PCV valve go screwy? You double and tripple checked the power valves?(probably not it is since the rochester does teh same thing) Cam go flat? damper slip causing your timing marks to be off? Mouse/squirel/armadillo crawl into the exhaust plugging it up? Someone dump diesel into your gas tank? What about water?

 

I was thinking that too but have switched the entire ign system out several times. I'm ready to toss it in storage for the year and think on it over the winter!

 

Have you tried checking the fuel pressure with a different gage?

My first thought was that you had something jammed in the exhaust that wasn't letting the engine breathe, but that wouldn't affect both cylinder banks if you're running dual lakes pipe...

 

Just to be sure, you swapped out the coil for a known good one or two when you changed distributers, correct? I ***ume you've also visually checked to see that you have adiquate spark from each plug?

 

Well there is spark......is there any way to test the voltage at the plug?

 

check the wiring, not the components.

 

What wiring? I pulled all the wires from the ign switch and wired in a new switch. The only wire that remained constant was the battery cable. Keep the ideas coming.........

 

Sounds like you've checked all the obvious stuff. Have you changed the plugwires? Specifically the coil to dist. wire. Also in rare cases have seen aeration of the fuel caused by a small air bleed in the fuel line that feeds the fuel pump. That would be the line from the tank. (but this usually only causes a problem when the car is under load; but worth checking anyways) Just throwing out some oddball possibilities. Good luck, and please post the solution when you find it . It would be helpful for all of us.

 

My son and I just went thru a deal just like this with his '68 chevy pickup . Fresh 350 motor, single AFB that was working just great before the motor rebuild , GM HEI same deal ,new cap ,wires, plugs, everything new inside the motor , timing was right on but it would gas you when it fired , same symtoms , popping out the exhaust , wet plugs , voltage checked out OK at the plug in the cap , WTF ? Changed the carb to another , pulled the fuel pump to make sure it wasn't leaking internally, out of desperation we changed the cap, coil and rotor and module, Shazzzamm ! In a post mortem exam of the built in coil , we found a broken wire just where it entered the winding . Check the color of your spark at the plug should be bright blue and able to jump at least 3/4"-1" air gap to ground . If it's red it's dead.

 

hmmmm I have not changed the wire from the starter to the coil..... so I will give that one a try.

 

Try a new coil wire. If that don't do it, disconnect all the wiring to the ignition coil and hot wire it. If it cures the problem, its in the loom. Sounded like a bad condensor at first, but you say you swaped dizzy's right? Are you running a ballast resistor of any type? They usually work or not, but there is always a first. It sounds electrical to me, but I aint standin there. Good luck, Mike.

 

Maybe you ****ed up a big ol' hunk of salt at Bonneville! Ouch. Hope you get that figured out.

 

I was going to say vacuum leak, but it would have to be severe. I'm sure you'd notice it for what it was. Reason I think so, is that my exhaust starts getting really rich when I get a vacuum leak. Never had it soaking plugs, but it will make my eyes water, and it makes the idle go to hell. After reading the other post, i'm going to say weak voltage also, probably a conection between the components you've replaced.

 

This is Real Strange, i hope ya get it Figured out.

He uses a mallory Unilite so a Ballast Ressitor isnt an option.

 

Once, I had a vacuum mod. on a th350 leak. ****ed trans fluid and acted like it was running rich. fouled plugs FAST. only when I was checking vacuum with new plugs did I notice the red drips from the vacuum line.

 

Take the sbc out and put in a sbf. Done deal.

 

Why would he want to do something as *** backwards as that?

 

The engine/carb can't "draw too much fuel". The system draws fuel based on airflow more airflow more fuel/air. The carb. could be "draining" into the engine, look for fuel in oil.
If the plugs just wet out probably weak/ untimed spark.

 

I went and picked up a new coil and plugs. I have tested it with several used coils I have but who knows. I am going to by p*** the battry and wiring in the car and run it off another battery and ign switch. If that doesn't do it I got my hands on another intake and will slap that on to see if it does the trick.

 

"""""""What wiring? I pulled all the wires from the ign switch and wired in a new switch. The only wire that remained constant was the battery cable. Keep the ideas coming........."""""""

did you put a volt meter to any of them? many fuel problems are electrical. it doesn't take much of a drop to mess things up

a new switch will do no good if you only have 8 volts going in.

 

I do have 12+ going into the coil, with the ign on not running and running on the pos***ve side of the coil.

What should I have on the negitive side? or across the coils + & -.

I ***ume the - side of the coil will have zero untill the points shut then 12+?