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High HCs at one exhaust- Where to start?

G Guest
Hi Jack ...need help.

Went to get motor smogged in Arizona and failed miserably. High HCs. I put it
on an exhaust gas analyzer, and found the
driver's side header at 1200PPM!!! Right bank
is 300PPM. That was as good as I could get it, despite adjusting timing and mixture screws. I have a brand new Holley Avenger 670, one year old plugs with 300 miles, new wires as well. Performer intake. Mild crane cam and roller rockers. The left valve train area has a slight tick from time to time. Perhasps valve adjustment needed? Also get
popping through exhaust when down shifting or taking out of gear at moderate RPM. Ocassionally get a backfire at startup, even with brand new carb. (this carb has backfire protection) Overall, the performance is generally poor on this 5000 mile motor. Something is wrong. Thought the new carb would fix it.

What should I check? Plugs, wires, valve springs?

Advise appreciated.
Thanks, Tom

Thanks, Tom
Original Post

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M mikep01 (Guest)
i must say it sound that you hav a miss on the drivers side. well how does it show on the ignition scope? how is compression? just because an engine cranks over smooth dosent mean it cant have a low cylinder. i have been bitten by that one once already. did it fail at idle, idle 3500 rpm or is it the asm test??
mike
S Steve3075 (Guest)
Just a thought: I had a problem with my engine just not running right. After checking plug wires, coil wire, timing, carb, possible vacuum leaks, etc., it turned out to be a spark plug with an almost invisible crack in the porcelain. Guess the current was jumping through this "hole" in the insulation.

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J Jim (Guest)
Have you checked compression or done a leak down test? I have just had the heads worked on because of a leaking exhaust valve.
The symptoms were a backfire through the carb when accelerating from about 1800 to 2000 RPM and some popping out the exhaust at idle. At first the backfire only occured on an autocross course, but later would happen anytime I tried half throttle acceleration.
I have no idea how the emissions were since my car is a 72 model and doesn't require testing in Atlanta.
TC Thomas Curb (Guest)
For all those that are helping...thanks.
A little more info. HCs are failing only at idle. I will do a compression check on
Saturday (in two days). Since the performer
manifold shares a common plenum, I do not think it is the carb, otherwise the right
exhuast would also measure high. I suspect
something with valve train. I do have new
plugs and wires. Suppose one could be faulty.
I do not have a scope to check overall firing curves. Will compresion check help
diagnose burned valve, bad spring, or out of adjustment lash?

Thanks, Tom
M mikep01 (Guest)
doing a compressin ckeck will help aid in finding a valvetrain problem. is it a mechanical or hydraulic cam? what are the cam specs? what kind of plugs? i run motorcraft af42c in my clevland. dont use bosch(=junk) if there campions and they have been fouled once replace them. there should be idealy no more than 10 percent difference between the highest and lowest cylinder. check all 8 cylinders.

let us know

mike
TC Thomas Curb (Guest)
Did compression check...150,150,160, 170.

Plugs all look good. Found a potential problem...PCV plumbing appears to be
installed backwards. Not sure it matters.

The passenger side valve cover filler cap
connects (unrestricted ) to the
aircleaner. The drivers side goes trough a PCV valve then to the carb base. Is this
correct?
S Steve3075 (Guest)
One question: When you replaced the wires, did you replace the wire from the coil to the distributor? Worn coil wires have caused 2 panteras I know of to run as if they were "missing". Don't think this could cause the lopsided emissions, but who knows...?

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TC Thomas Curb (Guest)
Mike P,

Yes I have a performer. Tried to adjust the idle mixture to pass, but could not get a low reading on the left header. Right bank
was fine. Perhaps the PCV plumbing is faulty, and is sending too
much recirculation to the carb and it is being fed to the left bank, causing high HCs? Thoughts?

Tom
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