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PostPosted: Wed Aug 29, 2018 8:29 pm 
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TBI Slant 6

Joined: Mon Jun 15, 2015 1:58 pm
Posts: 149
Location: So Cal
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Well the engine is not missing, but seems like a cylinder is not firing randomly. Worse at low rpms (like when stopped at a light). I can feel it miss, and sometimes if I accelerate I can feel that something is not firing but then it catches on and feels fine.

this is 66 dart sedan 270, engine rebuilt a few years ago, running a slant 225. Converted to HEI, electronic dizzy, recurved. Alternator checks out, converted over to the square back. Using magnecore wires, iridium plugs, standard cap and rotor . voltage reg., barely 1 year old, maybe 15oo miles on it.
Converted to Super Six setup with carter 2bbl. rebuilt.

no vacuum issues. Lashed, timed, mixture set. So how do I trouble shoot this miss. Never backfires. just a puff miss. sometimes in succession, sometimes every few seconds. Stops missing if I rev high, and if I give it a solid stomp.

help.

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66 dodge dart 270, 225ci, 3.7l, L6


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PostPosted: Wed Aug 29, 2018 8:42 pm 
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Joined: Mon Mar 31, 2003 1:04 pm
Posts: 7401
Location: Oregon
Car Model: 2023 Eichman Digger?
When they rebuilt it, they may have installed a cam that needs non-standard lash settings.

Hot, running, loosen the lash up unitl the valve clatters, take a measurement. close it down until it misses. Measure. Set it in the middle. Check all of them until you find a happy place for your engine and adjust your tune to your cam.

CJ

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PostPosted: Wed Aug 29, 2018 8:59 pm 
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Turbo Slant 6
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Joined: Mon Jan 25, 2010 11:29 pm
Posts: 672
Location: Seattle, WA
Car Model: 75 Dart SE (2),75 Swinger, 74 Dart Sport,91 Ram RV
My 2 cents: Pull the spark plugs to see if one is shorted out? Drive it on the highway at 50 mph or higher for 45 minutes, then pull the plugs to find the dirty cylinder? Spark plugs are cheap, so change out the whole set just to see the results. (You needed a spare good set anyway.) Could be an ignition wire breaking down or shorting through the insulation: inspect for grease / oil contamination, and wipe-down the length of the wires with lacquer thinner or some solvent. Check for ignition wires strapped too tight together and jumping between wires? Look inside the distributor cap for defects/ contamination/ corrosion on the posts/ arcing tracks. My experience with daily drivers is that what you described is "usually" ignition caused, but there's always the chance that it is a sticking valve. Ignition is easier to fix, 'cuz I'm lazy, and a firm believer in the K.I.S.S principle.

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"Louise", a 1976 Dart Custom project, (now sadly reverted to being just an "organ donor" to our other project Darts.)


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PostPosted: Wed Aug 29, 2018 10:08 pm 
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4 BBL ''Hyper-Pak''
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Joined: Mon Aug 27, 2018 7:49 pm
Posts: 27
Location: Southern Illinois
Car Model: 1973 pymouth scamp 225
When was the last time that a thorough tune up was done? Especially decarboning the cylinders. Im wondering if a piece of carbon is causing a secondary spark inside a cylinder. Since you say it is worse at low rpm you could try pulling one spark plug at a time while at idle to try and narrow it down to one cylinder or maybe discover that it s random through all cylinders (would indicate ignition hardware; module, coil, plug wires, etc). If it is just one cylinder try swapping in a new plug and a good wire.

Also make sure the inside of the distributor cap is clean of carbon tracking and the rotor tip and posts arent burnt. Make sure carb mixture is set right. Just spit-balling but thats my suggestions.

-Josh

(Guess I should read all the replies before I post! Basically what Louise said, sorry!)


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PostPosted: Thu Aug 30, 2018 2:27 pm 
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TBI Slant 6

Joined: Mon Jun 15, 2015 1:58 pm
Posts: 149
Location: So Cal
Car Model:
Hey thanks for the tips. To clarify, when I had the engine rebuilt (bored .60 over), they kept the same Cam, but just had it ground down.

I dont know what decarboning means? I pulled the plugs today, all looked good, not rich. I did notice each plug has carbon at the base where the threads begin.? And I do get lots of black carbon coming out of the tailpipe, leave a nice black sooty mess on my driveway.

I regapped them, to 35, as they were about 40.

I then hooked timing light to each wire, and they all give a steady stream of light, and when I hear a stumble in the engine the light does not change, it keeps flashing normal. So I have to assume wires, ecoil, dizzy , cap, rotor all are doing their jobs. So then it could be a bad plug? or something about too lean?? does anyone remember which way I turn the screws to richen the Carter 2BBL carb. super six version. thanks guys, will do a better test drive tonight and see if changing the gap made any difference. And to correct, I have the NGKVpower, not Iridium.

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66 dodge dart 270, 225ci, 3.7l, L6


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PostPosted: Thu Aug 30, 2018 3:14 pm 
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Joined: Mon Oct 21, 2002 11:08 am
Posts: 16451
Location: Blacksburg, VA
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If you get black carbon out the tailpipe, then idle mixture sounds like a probably culprit. Turn the idle mixture screws in to go leaner.

Lou

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PostPosted: Thu Aug 30, 2018 3:21 pm 
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Supercharged

Joined: Thu May 12, 2005 11:50 pm
Posts: 6291
Location: So California
Car Model: 64 Plymouth Valiant
https://www.physicsforums.com/threads/d ... ct.793344/

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64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

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PostPosted: Thu Aug 30, 2018 4:52 pm 
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4 BBL ''Hyper-Pak''
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Joined: Mon Aug 27, 2018 7:49 pm
Posts: 27
Location: Southern Illinois
Car Model: 1973 pymouth scamp 225
If you haven’t already done so, get the three books recommended by SlantSixDan. You can look in the FAQ section in the engine forum and there is a link called ‘Dan’s links’. Tons of great information also the book recommendations are there. The FSM is an absolute must!! Decarboning is discussed in the peterson book as “probably the most important part of a tune up”. Read the above link from emsvitil. Basically water or a solvent is used to loosen accumulated carbon in the cylinders, tops of pistons and valve faces. Have new spark plugs ready because afterwards the could be badly fouled depending on the amount of carbon in the cylinders. Also do it outside because it will smoke from the tailpipe to high heaven! You can use google/youtube to get a better idea of the process. I know at least one member here runs water injection with good results. Good luck!

Do you do a lot of idling or more open road driving? Do you get a few puffs or more of blue smoke from the tailpipe at cold startup? Soot from the tailpipe indicates a rich mixture. IIRC carbs by nature tend to run leaner at idle and richer at higher rpms.

-Josh


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PostPosted: Thu Aug 30, 2018 5:32 pm 
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4 BBL ''Hyper-Pak''
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Joined: Mon Aug 27, 2018 7:49 pm
Posts: 27
Location: Southern Illinois
Car Model: 1973 pymouth scamp 225
In your initial post yes said it was converted to hei with magnacore wire. Your plugs should be gapped at .045. Also the Hei module really needs to see full line voltage (ballast bypassed) like what is suggested in the hei retrofit topic. In my case my original ignition run wires werent up to the task(excessive drop, still need to clean the ign cylinder contacts) A couple of hours is all it took to run a relay with the orignial wire to trigger the relay.

Again just spitballing.

-Josh


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PostPosted: Thu Aug 30, 2018 7:42 pm 
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TBI Slant 6

Joined: Mon Jun 15, 2015 1:58 pm
Posts: 149
Location: So Cal
Car Model:
Thanks so much for all your ideas and link.
I did get those 3 books back when I bought this car.
Also I have already put the ignition on a relay, along with relays for headlights and also relays for the HEI.

The gap is tricky. Seems the bigger the gap, the worse combustion I get.

I do mostly short trips, but a few times a week I do drive to work and back which is a 20 mile roundtrip, usually never going faster than 55.

Putting water into the intake sounds like fake news, but I did look at the videos. I might be more agreeable to some sort of solvent, I will have to investigate. After tonight's drive, I will check under the hood for arcs, then in the morning I will see if I can lean it out a little more. though won't that give me more opportunity for misses? I put about 1500 miles a year on this beast. and i have new sparkplugs coming.

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66 dodge dart 270, 225ci, 3.7l, L6


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PostPosted: Thu Aug 30, 2018 10:06 pm 
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Turbo Slant 6
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Joined: Mon Jan 25, 2010 11:29 pm
Posts: 672
Location: Seattle, WA
Car Model: 75 Dart SE (2),75 Swinger, 74 Dart Sport,91 Ram RV
"The gap is tricky. Seems the bigger the gap, the worse combustion I get. "
Sounds like a weak ignition module. Possibly breaking down?
Anyone...?

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"Louise", a 1976 Dart Custom project, (now sadly reverted to being just an "organ donor" to our other project Darts.)


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PostPosted: Fri Aug 31, 2018 7:07 am 
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Joined: Mon Mar 31, 2003 1:04 pm
Posts: 7401
Location: Oregon
Car Model: 2023 Eichman Digger?
Gapping iridium plugs you say?

CJ

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PostPosted: Fri Aug 31, 2018 10:50 am 
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Joined: Thu Oct 17, 2002 7:27 pm
Posts: 14119
Location: Park Forest, Illinoisy
Car Model: 68 Valiant
Throw the iridium plugs away and put some standard plugs in. Also, make sure the float and power valve are adjusted correctly.

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PostPosted: Sat Sep 01, 2018 8:30 am 
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TBI Slant 6

Joined: Mon Jun 15, 2015 1:58 pm
Posts: 149
Location: So Cal
Car Model:
Wanted to correct my original post, I do not have Iridiums, instead I have the NGKVPower plugs.

Also upon closer examination, I did find one rubber plug on the carb. that had cracked and could have been giving a very tiny vacuum leak. So I replaced the cap too.
It is not missing like before. Though I am still going to try to lean it out and see if that makes any difference. and for fun I have a new set of plugs, that I am going to gap at 45 and swap them in and see what happens. Thanks for all of your help guys. I love this old site. Just slants, all the time.

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66 dodge dart 270, 225ci, 3.7l, L6


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PostPosted: Mon Sep 03, 2018 8:12 pm 
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4 BBL ''Hyper-Pak''
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Joined: Mon Aug 27, 2018 7:49 pm
Posts: 27
Location: Southern Illinois
Car Model: 1973 pymouth scamp 225
Good deal finding the vacuum leak. Is the miss completely gone? Im no expert but i wouldnt think changing the plug gaps would make a huge difference when there is a vacuum leak. In other words if the vac leak caused the miss wouldnt it miss regardless of the plug gaps? Does your hei module get bot to the touch?

Either way, glad you found the issue and it was an easy fix!

-Josh


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