Inner cylinders rich, outer cylinders lean??

[MalcolmV8]

Hey guys,

A buddy of mine has a really nice 1970 Charger he's spent the last 2 years building and finally has it running. It has a 493 big block, 440 bored and stroked.

Anyhow it has a dual plane intake with a 950 carb. I think it's a dominator but I forget now (to many cars we worked on yesterday).

The issue is the inner two cylinders on each side of the motor are rich (black wet plugs) and the outer two are so lean the headers are glowing red (white plugs). He richen'd up the mixture to where the headers don't glow any more but those center two cylinders are probably just dumping gas. In the last 3 days he's used up $170 gas playing around in that thing. His speedo is not working yet so we don't have exact numbers but based on him cruising with us and gas consumption we've worked out he's around 4 or 5 mpg. Owch.

His car is wicked fast though. We weighed it last night and it's 3840 lbs and from a 40 roll he'll hang with my Cobra. I only pull about a car on him.

So my question is wtf with the difference in cylinders? His engine builder (in Minnesota and we're in Kansas City) says it's his carb. I don't see how. I say something with the intake manifold. His intake manifold is ported, wonder if that has anything to do with it?

I'll sms him quick for exact carb/intake but any ideas? Not sure how to fix this one.

[MalcolmV8]

His carb is a Quick Fuel 950 q series. Indy dual plane intake ported out.

[v8ranger]

Hmmm.... I agree with you, Im thinking that its an intake problem... It sounds like the center is "sucking" more than the rest. Could be because of the size of the intake holes. I would change the intake to maybe even the stock one, just to see what it does then... But I would say its an intake problem.. Maybe even ported wrong. Maybe the center ports are bigger than the outers??? Maybe??....

[Chris]

If the intake was in stock form, I would have a hard time wrapping my head around that as the problem. It is a dual plane, that means the right side feeds the right outer corners and the left inner two, the left side then feeds the left outer corners and the right inner two. There's nothing in common with the four affected cylinders. However the porting may have thrown everything off balance.

Now having said that, I remember back when I has in school one of my Hot Rod instructors told us of a similar situation on a chevy 350. He had a 750 Holley but I don't remember what intake(that was many moons and many beers ago), he swapped the 750 for something bigger and problem was solved. He said that the 750 wasn't enough for his engine combo and since the center four cylinders had a more direct line to the carb, they had priority over the outer cylinders. I don't know how much I believe any "stories" those instructors told because allot of them were just crap. Just thought I'd throw this in too.

This sure is a stumper, please let us know when you guys get it figured out. It'll be nice to know for future reference.

[MalcolmV8]

I never thought of the carb been to small and not been able to feed the outer cylinders. It's just so odd that they would be starving to the point of the headers glowing and the inner ones so rich the plugs are black and wet.

I wonder if the center cylinder runners just got ported so excessively compare to the outer two? That seems like that would do it.

Unfortunately he doesn't have a stock intake or carb to swap on there and play around. He has to buy parts.

[plowboy34]

since the intake has been ported that could change many things. Was it done by him or by a professional. I'm with Chris that if this was a stock or unported intake it would be hard to wrap my thoughts around it. I would have to start with the intake if it was me. I have seen many problems come from porting done by people who think they know what they are doing. Since it is equal problems on both sides I just believe it is an airflow problem.

[MalcolmV8]

He didn't port it himself. He had it ported by his engine builder but I'm starting to wonder about how good this guy is. My buddies swear by him but this is the same guy who built another buddy of mine's 496 in his Camaro that I was asking you guys about the timing locked out at 30 some degrees and how his would just foul plugs like crazy. He ended up just selling that 496 car. We never did get it running right.

[Chris]

Yea, something don't seem right about that engine builder. For him to have built two separate engines that both have problems. There's just something going on there.

[plowboy34]

I wondered if it was same guy, I remember you said he was from Minnesota. Something definitely ain't jiving with this guy.

[MalcolmV8]

I'd agree but for some reason my friends think this guy is so gifted with big blocks they rent trucks and drive from KC to Minnesota to have him build their engines. He's not cheap either. They've each spent around $10k on their motors. All high dollar stuff though, forged internals etc.

To me it seems ridiculous cause he's so far away he can't offer any support when they get back to KC and stuff doesn't work right. Then it seems I get stuck trying to fix their stuff lol

[v8ranger]

Just for **** and giggles, did you check the compression and see if they are all pretty even?? I know it may seam stupid. But if the center cylinders have allot more compression, don't you think that would cause them to get more gas too?? I also know that on my boat's engine it has a divider plate on the center two cylinders inside the intake manifold so that the center two cylinders don't get to much gas sense they are the closest to the carb. But that's an inline Chevy 6 cylinder from the late 70's early 80's.... Sometimes its the stupid stuff that stumps us the most.... lol...

[Chris]

I think V8ranger has hit the nail dead square on the head, knocking the ball out of the park, getting a hole in one on a par 30. A carb intake has grooves in the plentum portion under the carb. These grooves cause turbulence in the plentum. This turbulence causes the air/fuel to mix there by equily distributing among the cylinders. While a fuel injected engine wants no intake turbulence, a carb engine requires this turbulence. With out it, the fuel will pool at the bottom of the intake under the carb. It will then pour into the center four cylinders, leaving mostly air to enter the outer cylinders.

Pull the carb off and check the intake plentum for those grooves. If it's smooth, there's your problem.

[plowboy34]

I just have to say if the guy ported those grooves out of the intake they need to find someone else to build there engines... I have been racking my brain trying to figure out what he could possibly have done to that intake but never even thought about that possibility but I would definitely check that out. As I said before I have seen MANY problems from a port job by someone who doesn't know what they are doing.

[Chris]

I agree, porting a carb intake is never a good idea.

[MalcolmV8]

Chris, your explanation about grooves on the inside of the intake manifold make perfect sense. I've not dealt with carbs much so I didn't know that. Excellent piece of information there. I passed on to my buddy and we'll see if he pulls the carb and takes a look.