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need some help tuning flathead 6 in a 55 plymouth
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HerbertsNatural
Posted 2015-08-21 9:53 PM (#487726)
Subject: need some help tuning flathead 6 in a 55 plymouth


Member

Posts: 35
25
Location: Yakima, WA
Hey all,

I've had my car for 6 months now. barely been able to drive it, if its not one thing it has always been another.

Currently I've replaced or fixed: charging system, wiring, plugs, wires, cap/rotor, points, condenser, rebuilt carb, adjusted timing, R&R'd vacuum advance.

I'm thinking at this point the car needs someone more proficient to tune the thing. It idles great at -2* timing but when I rev the thing up it'll start sputtering and sometimes backfire. Its a 3 on the tree and shifting from 2nd to 3rd gear is happening at 20-25mph lugging the engine down too far in my opinion to be very drivable. If i try to go faster in 2nd gear it will sputter and not rev up and backfire on occassion.
I checked my timing again, and vacuum advance is now working.

The only problems that I can see is that the timing seems to jump around a little (according to my timing light) at an idle when warmed up.

Is there something I am overlooking?
Anyone in central washington willing to lend a hand?

I'm trying to save some money and not take it to a shop, I've got a bad habit of overspending when it goes to a shop.

I feel that I'm not getting anywhere with this car and the other engine I have (chevy) that DOESNT BELONG IN THIS CAR is starting to look too appealing if I cannot get this thing figured out.

Thanks.

Edited by HerbertsNatural 2015-08-21 9:55 PM
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GaryS
Posted 2015-08-22 7:52 AM (#487738 - in reply to #487726)
Subject: Re: need some help tuning flathead 6 in a 55 plymouth



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Posts: 1207
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Location: Ponder, TX
I don't see a timing chain on your list. If it's sloppy or jumped a tooth, no amount of tuning will cure the problem. It's been about fifty years since I changed one on a flathead six, but I don't recall it being too difficult.
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58coupe
Posted 2015-08-22 10:36 AM (#487742 - in reply to #487726)
Subject: Re: need some help tuning flathead 6 in a 55 plymouth



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Location: Alaska
You might also change the coil, but first double check that it is wired properly. You don't mention but is it still 6 volt with positive ground? The wires may have been hooked up wrong on the coil sometime in the past and IIRC, the wire from the ignition switch should be on the negative side. If it is wrong it will run poorly.
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Polybun
Posted 2015-08-29 10:00 AM (#488278 - in reply to #487726)
Subject: Re: need some help tuning flathead 6 in a 55 plymouth



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point bounce maybe? Usually if they run ok at low speed but spit and sputter at high speeds that's dicked up points.

A friend of mine has one of those engines that was freshly rebuilt but then water froze in it and split the block wide open. I'll see if he'll rob the timing set off of it. I'll be able to save you a few bucks if you want to try that swap.

The other thing that comes to mind is valve float. It's possible with the age of the engine that the valve springs are just that worn out. I had this happen on a '64 dodge polara about 15 years ago. The valve springs were just so loose that she wouldn't turn faster than 3000rpm without floating valves! That entire engine was just wore out though. Seriously, only held 25psi oil pressure at 3000rpm and about 5 psi at idle.
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57plymouth
Posted 2015-08-31 6:41 AM (#488391 - in reply to #487726)
Subject: Re: need some help tuning flathead 6 in a 55 plymouth



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Posts: 3577
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Location: Blythewood, SC
Double check the coil polarity.

Did you replace the ignition parts with good parts or the sketchy parts from somewhere like Advance? I've had bad luck with cheap points in particular. They burn pretty quick. Napa has better ones, but they still only last a year or two.

Did you happen to replace the wire from the coil to the distributor? If so, the original was a resistor wire. I've replaced that wire with regular wire and burned points before. If the wire is original and in good condition use it. If not, be sure to add a ballast resistor in line to cut voltage to the points. Another lesson learned the hard way.
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HerbertsNatural
Posted 2015-09-08 9:36 PM (#489273 - in reply to #487726)
Subject: Re: need some help tuning flathead 6 in a 55 plymouth


Member

Posts: 35
25
Location: Yakima, WA
so the car is a 55 but I switched it over to 12v negative ground and when I did that I bought a new coil that was a 12v coil. It is wired from my ignition switch to the + terminal of the coil, and then from the - coil terminal to the distributor. I have no resistor inline and I'm sure the coil says it is 12v rated right on it, will have to look.

I had it running fine for a few days drove it on the freeway and she loved to get revved up and go 70mph. But then all of a sudden it started acting like it had no fuel even when my gas tank was full. So I opened up the carb to take a peek and it was a mess, extremely dirty, so I rebuilt it.
I put her all back together and it still wouldnt run right. So i looked inside the distributor next and found a burnt up points. So i replaced the points, gapped at 0.20 inch, and then set the timing according to the owners manual (*2 BTDC) and now itll start up and idle beautifully but just doesnt wanna rev.

I got some tips to check my intake manifold vacuum as I rev it, and also to set the timing at 10* BTDC. Also to check fuel flow going to the engine.

Im not so sure that the timing chain jumped a tooth or a valve is sticking because i did drive the vehicle several times before this all happened. But I don't know honestly something could have happened between then and now.
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jimntempe
Posted 2015-09-08 10:24 PM (#489277 - in reply to #487726)
Subject: Re: need some help tuning flathead 6 in a 55 plymouth



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Location: Arizona
If the timing jumped a tooth or valves are sticking you should see some indication of that on the vacuum readings. Assuming the timing is set correctly I would expect it to have at about 18 inches of steady vacuum at idle it things are as they should be. If you have low or jumpy vacuum you would need to start looking for reasons. Did you check for a plugged exhaust system as someone else has mentioned? Also, I'm not sure but I think most coils are labeled "12v" even the ones that are supposed to have a ballast resistor so they really run at 9 volt once the car is started. It could be you have fried the coil by running it at 12 volts. It kind of sounds like that may be the case because you said the points were burnt up. 12v to the points will burn them up, it adds a lot of extra current. If you can't find anything else to throw parts at I'd start with a new coil and a ballast resistor if, as you say, it was running good for a while.
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HerbertsNatural
Posted 2015-09-14 9:04 PM (#489660 - in reply to #487726)
Subject: Re: need some help tuning flathead 6 in a 55 plymouth


Member

Posts: 35
25
Location: Yakima, WA
Good thinking I'm toying with it right now. I have a ballast resistor I can throw on it and order in new points and a coil tomorrow they are quick easy and cheap to swap.
Also considering some sea foam to try and unstick a valve if that is the case.

I set my timing at 10* btdc didn't seem to help much.
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57plymouth
Posted 2015-09-17 6:21 AM (#489878 - in reply to #487726)
Subject: Re: need some help tuning flathead 6 in a 55 plymouth



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Posts: 3577
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Location: Blythewood, SC
You have burned the points. You must have a resistor in line between the coil and the points. I know it isn't there originally, but you must have a resistor in line between the coil and the points.
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jimntempe
Posted 2015-09-17 10:47 PM (#489928 - in reply to #487726)
Subject: Re: need some help tuning flathead 6 in a 55 plymouth



Expert

Posts: 2312
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Location: Arizona
I saw another thread that is the same car right? You said the vacuum was around 10". That's way too low. Go back to basics, pull a plug, find TDC and set the timing to whatever the factory calls for based on where the real TDC is. See if that changes the vacuum readings, assuming it will still run. You might want to do a compression test too. You might even disconnect the exhaust pipe from the manifold just to make sure a plugged something in the exhaust isn't your problem.
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