I just gave my 70 Duster's 225 a valve job, rod bearings, timing chain, distributor (points--booooooo) and holley 1bbl. Can't get rid of some hicuping at idle to save my life. It acts like a mis-fire and is only heard through the exhaust, and only occurs at idle. What the crap is going on here? I work at a chivvy dealership and hate to pull in with the hot looking little duster sounding like crap--bad way to represent for the MoPar clan. Also has terrible vibration-could new bearings have thrown off the balance?

any help or ideas mucho helpful

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pfm

Was the engine removed from the car to do this work?
DD

yes

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pfm

yes, we removed motor and trans

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pfm

Misfire: Is the point gap and dwell set correctly? Is the vacuum advance hooked to ported (not manifold) vacuum? Plug gap set correctly? Idle mixture set correctly?

Vibration: rod bearings (properly installed) should not affect balance. Now if the RODS were swapped around and not put back in exactly the same positions, you could have a horrible imbalance. It could also be something as pedestrian as bad motor or transmission mounts. What kind of shape are the driveshaft U-joints in?

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I'll check the specs agian, but they were dead on when we first fired it. That's been about 10k miles ago. Doesn't seem to get any worse, and sometimes it runs smooth as silk. It does use more oil now, but could weak rings give me a misfire if the plugs all look good?

All mounts are new, as well as U-joints. I'm pretty sure we got all the rods back in the right holes. We did put another balancer off of a 68 dart on it though (anyone found new ones anywhere?) but it looked to be in a whole lot better shape than the original.

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pfm

A "rebuilt" (or "remanufactured") carburetor? If so, that's probably the source of your problem. See this thread.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I had a slight hiccup due to maladjusted valves. That would be an easy fix, at least.

Best of luck,

Joe

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Joe Hoppe

71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

64 Valiant Wagon 225 904 AT 3:23 8.75"

This does sound like a Valve problem. Although it is hard to diag something without hearing or seeing the results of the missfire. For it to come and go like you say does piont to a few things as being possible. The one being a Exhaust valve that is not sealing correctly. Maybe as it rotates it looses the seal & is why it is only part time missing. A compression or leak down test could help pin piont this. Also a Dizzy that is warn could give results like this.

When it is not missing is the vibration gone?


Also a lean condition can cause this, it could be from a vacume leak that is only effecting one cylinder and only leaks at certain temps. But a lean cylinder will kinda pop miss out the exhaust.


Valve ajustment is also possible and should be look at.


Jess