Ignition or Fuel?

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A-BOMB360 said:
that looks like an intake leak. just my nickle.
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Green Hornet, all of these idea are good ones but i'm with A-BOMB360

Get some carb spray, using short blasts, spray around the intake until you fine a place that raises the idle.

May sure that the spray is NOT getting in to the carb and giving you a false reading.
 
My oil leak problem before came from the lifter/cam valley. If that is where it is sucking air I wouldn't expect spraying around the outside of the intake mating surfaces to yield much results. But I will give it a try.
 
How about a lack of fuel pressure? Would that cause plugs to be uneven? Just a thought as I was working on her a little this evening and found the new fuel filter wouldn't stay full.
 
Anything can cause plugs to look bad. You know there are a few cylinders that are not burning well. You dont know why. The trick is to eliminate what you know or think you know. I like to do a basic "once over" on the visual side when I'm diagnosing and many times that is enough to get me pointed in the right direction. Reading what has been written is much harder to diagnose than having a breathing car in front of you...lol. So with a one-dimensional posting, you get every possibility tossed in. The only one that can reduce the possible issues is you because you've got the car there. It could be an intake leak but if the bolts go in by hand and the gasket is evenly crushed, i doubt it. It could be base issues with the carb's rebuilding...But if DS did the setup, again, I doubt it. It could be an electrical ignition issue. But it's only affecting a few cylinders so attention is turned to the parts that go to individual cylinders... But those sound like they should be ok. It could be internal engine issues, but they would normally combine oil with that unburnt fuel and/or the issue wouldnt clear up with rpm and/or the plugs would look a lot different. So what's left? The mechanic, yourself, who admittedly has limited experience and knowledge, and tuning issues. That's my thought process anyway. It doesnt really matter how you find what's wrong. So long as A. you find it , B. you fix it, and C. you end up happy. Right?
 
Green Hornet said:
I've been having a fair share of issues with a new 408 build in my Dart. There is a miss and pop out of the exhaust starting at around 1800 RPM and continues up around 3200 and tapers off some. I pull the spark plugs and find that plugs 1-2 look like brand new, 3-4 have a little carbon on them and the porcelain is light brown, 5-6 are black, and 7-8 look more similiar to 3-4. Ignition is all new MP electronic with chrome box and new MSD Blaster coil. The carb is a fresh rebuilt Thermoquad. Any help would certainly be appreciated. Thanks!
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I once had this problem with a gold MP ignition box. It misfired like yours is.
The problem stumped all of usfor quite a while.
Turns out that the ignition module was mounted too close to the coil.
The high energy pulses from the coil were interfering with the low voltage signal to the module from the coil. Apparently there is what is called a 6 to 1 rule.Move the coil one inch away from the module is equivalent to 6 ft away.

In other words try to move the coil and the chrome box further away from each other and see if that solves your problem.

Duane
 
Hey Duane,
I been a little busy so I haven't worked through all the other suggestions that were posted earlier. I will certainly give your idea a try. Right now the coil is mounted in the stock location close to center on the fire wall and the ignition box is mounted on the driver's side inner fender towards the firewall. Do you think they may be too close compared with the experience you were having? I will try it either way.
 
It looks a lil rich and the timing might might need to be advanced by the look of the tang.

If it vacuum leaks at the valley it'll definitely have oil in the runner and light smoke out that bank too.
 
Green Hornet said:
Hey Duane,
I been a little busy so I haven't worked through all the other suggestions that were posted earlier. I will certainly give your idea a try. Right now the coil is mounted in the stock location close to center on the fire wall and the ignition box is mounted on the driver's side inner fender towards the firewall. Do you think they may be too close compared with the experience you were having? I will try it either way.
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That does not sound too close. I had mine all mounted on a plate on the passenger side and it misfired.I had to move the coil away about a foot and she then ran fine.
 
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