# 52 8N develops popcorn miss



## chris scott

Now that I have my Ford 3910 running, wife says I need to sell my 52 8N. I bought it in 2017, put new valves & guides in it, pertronix ignition + another $1500 in parts. It has run flawlessly since restoration - 16 hours on the new proofmeter. Had it sold, and it's getting revenge by suddenly developing a "popcorn" sounding miss. I'm stumped.

Here's what I've done so far in the last two weeks:

Replaced Plugs

Replaced coil

Replaced wires with resistor type per pertronix recommendation.

Blew propane around intake manifold to check for leaks - no change.

Checked compression (perfect)

Checked valve clearance (it's correct at 15 thou)

Re-adjusted carb mixture.

Rocked distributor timing through it's range (still misses)
Misses at both high and low rpm. Misses when cold or warmed up.
Pics here: http://scott-inc.com/ford8n/

Signed, stumped.


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## chris scott

This is not my tractor, but the miss sounds exactly like this:


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## chris scott

That guy fixed his miss by re-sealing the exhaust manifold clamp to the tailpipe. Done. Sealant is drying, will check it tomorrow.


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## deerhide

Check for loose connections or mountings, paint that could make a connection or insulation, the coil, coil wire, rotor button, dirt under distributor cap or it cracked(try putting the old one back on)and plug wires that might be touching or loose.


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## chris scott

Thanks! Yep I thought of that. That's why I replaced the coil, wires, plugs, and went over the pertronix installation again, cleaning all and re-dressing wires. The cap has 16 hours on it , is clean, and looks brand new.


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## chris scott

Re-clamped and sealed the manifold / tailpipe joint, still have the popcorn miss.

I'm thinking that it must either be the pertronix ignition, or something weird with the valves ( even though valves & guides were replaced 16 engine hours ago). I guess that I should swap back to a points & cap ignition to see what happens. But I through away the baseplate and points thinking I wouldn't need them.


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## deerhide

chris scott said:


> Re-clamped and sealed the manifold / tailpipe joint, still have the popcorn miss.
> 
> I'm thinking that it must either be the pertronix ignition, or something weird with the valves ( even though valves & guides were replaced 16 engine hours ago). I guess that I should swap back to a points & cap ignition to see what happens. But I through away the baseplate and points thinking I wouldn't need them.


_I can't figure out why this thing is printing like this...Whatever. 
How would sealing the exhaust joint affect how the tractor works? I used a 'late 8n' like yours, logging for years with no exhaust pipe at all.
I'm suspicious of the pertronix system it's probably higher volts, make sure there isn't a spark jump. Have it running in the pitch dark and look good!_


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## chris scott

I would not have thought that the exhaust would cause it either, but if you look in the comments of the video I linked to, where his 8N had the same miss as mine, he said fixing that joint cured it. So I tried it.

I did the "dollar bill" test at the exhaust, and there is no reversal to vacuum when it misses. If any thing, the pressure increases during the miss.

I once had an engine miss at mid rpm - was very hard to find that the last rebuilder had put in a valve spring that had smaller gauge wire, causing valve float, or bounce. But this miss is at all rpm, and it's not like "morning sickness" with a sticky valve - it happens at all temperatures. I'm leaning to an ignition problem. Partly because I don't want to pull the head again.


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## deerhide

You have a really nice looking place. Park the 8n on the front lawn, take the battery cables off and let the kids play on it. They will all turn into old tractor addicts and when you tell them they can't drive it because there is something wrong, maybe one of them has a Grandad who will come and fix it! I'm grasping at straws for advise.........


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## chris scott

Last night I ran it in pitch dark to see any possible high voltage arcing. Saw none. Although they're just 2 years old, my next try will be to replace the distributor cap and rotor. If that doesn't get it, I'm installing the standard points and capacitor in place of the pertronix.


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## chris scott

Replaced dist. cap and rotor. Same miss.


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## pogobill

Are all your plug wires alright? I replaced my wires, but used the wrong ones. Also I had one that seemed to ground out against the engine and caused the miss in the engine.


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## chris scott

Replaced coil, wires, plugs, rotor, dist cap, fuel, compression and valve clearances normal.


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## FredM

condenser ??.

why do you think your problem is electrical ?, when you have what you think is electrical, will be in fact a fuel problem, and when you think you have a fuel problem, it will be electrical and that is fact, they go hand in hand and you have to decipher which is which .

I haven't commented earlier because I am not familiar with your carby, the only updraught carbies I have dealt with, are an updraught on my father's 1934 B4 Ford tourer in the 40's and 50's and a TE20 and a MF35 tractor from the 60's till the 80's,-- but tell me does this have a high speed mixture screw beside having an idle mixture screw,-- I reckon your problem is fuel based, if your carby has the high speed mixture screw, have you tried running the engine on "high idle" and either screwing the mixture screw out or in about 1/4 turn either way? to see if this changes things.

Another thing is you are now into your winter, so you may have a little moisture in your fuel, have you thought of placing a tin or bowl under the float chamber drain plug and draining the fuel so you can check for moisture?.

a carby running lean will also carry on like yours is doing.


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## chris scott

Thanks, Fred,
Two years ago when I restored the tractor I bought a new carb, and used a glass spark plug to set mixture - blue or yellow burn. I had to change jets to have adjustability into the rich zone, but got it set properly - it is a MS carb, and has run very smooth. A week ago I swung the mixture screws one way or the other, at idle and high rpm. I could get it to really lose power, but nothing would cure the popcorn. 4? days ago I completely drained the tank through the carb drain, and put very fresh gas in. No luck. I have not changed points because there are none with the pertronix ignition, but have a baseplate, points and capacitor or order to eliminate that as an issue. If that's not it, I'm thinking it must be a weak valve spring - valves and guides were new 2 years ago, and now the new proofmeter shows 16 hours. What do you think?


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## FredM

Well Chris !!, you seem to be covering all of the bases and I don't know what you have left to check, have you tried running the engine and removing a HT lead from a plug one at a time and progressing through all 4 plugs to see which cylinder/s is/are missing ?.

I suppose a valve spring could have weakened if made over the pond, but if they are genuine, I doubt this very much, and at 16 hours, and I guess you would have worked out that the miss/pop will be on the exhaust valve side of things.

Apart from the weak valve spring, the only other thing is the Petronix ignition kit, many years ago an Auto electrician told me "a electronic ignition will either work or it wont", and I have gone with that statement ever since, it is a shame you threw the old base plate away, but that is the way of things, I have done the same and wished I hadn't.

When you get your new base plate, points and condenser, hopefully this may fix your problem.


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## chris scott

Update:

Warmed up engine. It popcorn misses.
Killed engine.

removed #1 plug lead
restart and run about 1300 rpm
Does not popcorn miss.

Repeated for each of the four cylinders.
Does not popcorn miss.

Reconnected all plug wires. Run at 1300 rpm.
It popcorn misses.

I would not have believed it possible unless I witnessed it.


Someone suggested that it really is still missing but I can't notice it. I don't think so, as it runs pretty smoothly on just 3 of 4, and when standing behind the tractor listening to the exhaust, the popcorn miss is plainly audible or not.


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## FredM

could the exhaust system be resonating ??.


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## chris scott

I don't know. On a tip from a youtube guy who has the same tractor and the same sounding miss, I did reseal and re-clamp the manifold to to muffler joint. No change. The exhaust is plain stock, and was new 16 engine hours ago.


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## flattop

chris scott said:


> I don't know. On a tip from a youtube guy who has the same tractor and the same sounding miss, I did reseal and re-clamp the manifold to to muffler joint. No change. The exhaust is plain stock, and was new 16 engine hours ago.


Check the runout on the distributer shaft, there should be no side play, also look at the lobes where the points would run. Had an old 8n that the lobes were worn so bad that it would not open the points all the time or trigger the pertronics ignition


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## Sojourner

try adding some Lead additive just in case a valve is sticking. I listened to the video. I'm hard of hearing, but I didn't hear the popcorn miss you're talking about.


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## chris scott

How much runout is normal?


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## chris scott

On the advice of a friend, I swapped out the exhaust pipe with 4 feet of tube. Same popcorn.
I removed the manifold cleaned the surfaces, put back with new gaskets and permatex copper sealant. Same popcorn.


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## FredM

Hey Chris !! have you ever thought of trying a vacuum gauge on the inlet manifold ?, these were magic on the older engine, I found a chart of the different readings but wasn't able to save to my desktop, I will keep trying though.

As soon as I get this, I will attach to your post.


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## FredM

https://www.autoequipment.com.au/vacuumgauge/vac1.htm

This is an automated chart which comes in two parts, to check the second part click on the triangle icon at the bottom and the same to return to the first page.


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## chris scott

Recently, I converted back to points & condenser. Same problem. I guess to check vacuum, I would need to drill & tap a hole in the center of the manifold? Then, I guess if the gauge goes crazy when it pops, I've got a floating valve issue?


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## deerhide

Drop the exhaust pipe so the exhaust is coming right out of the manifold. That will narrow down where the 'popcorn miss', isn't!


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## chris scott

deerhide said:


> Drop the exhaust pipe so the exhaust is coming right out of the manifold. That will narrow down where the 'popcorn miss', isn't!


I did take the exhaust pipe off and substituted a 3 foot bent pipe without muffler. No change, so I took the manifold off, cleaned everything up, (didn't look that bad) and put back with new gasket and Permatex ultra copper sealant. No change in popcorn.


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## chris scott

Well, it still does it. Not all the time. My neighbor said most of them (early Fords) do it.

I'm wondering if it could be from not using leaded gas. About 20 engine hours ago I installed new valves & guides, and lapped the seats. Compression is fine on all cylinders. I wonder if I should buy some "100 low lead" (has more lead than car gas used to) from the airport and run it on that for a while. I have heard that valve stems may get sticky without any lead.


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## Joe.S.AK

Well, a popcorn miss sounds to be electrical connections loose or bad somewhere. I had the same symptom and it was the brand new coil. The Stainless Steel inside contact (not the spring) in the front, that contacts the distributor cap below was not good. That curved Stainless Steel strip wasn't making a good contact so a *little* creative bending, scraping the slight pitting in the Stainless steel contact strip and light sanding of the distrib cap contact (followed with a tiny bit of Dielectric grease just on those contact points) fixed the problem.
- Joe -







0


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## Garylou

For what it's worth, I have a 49 8n and finally had to replace the exhaust as the various bandaids
finally got to me. After I put on a tailpipe and muffler combo bought on the internet, my tractor started making a sound very similar to yours shortly thereafter. Still does. I did nothing else but replace the exhaust. Just a thought...maybe disconnect your exhaust and see if it still "pops"? Might be your new exhaust.


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## Joe.S.AK

Might also be a change in back pressure from the 'similar but not exact' new exhaust system, too. If you try removing the exhaust system that, in itself, changes back pressure.

Of course, spending some time around idling big Harleys will make the teenie, weenie popping seem to be just gentle purring.

OH, maybe substituting spark plugs, one at a time, would help remove a random plug wire short or intermittent short in a plug. Inside of the distrib cap squeeky clean? I've had carbon trails ("Lightning Bolts") create intermittent internal shorts for just one plug before.

- Joe -


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## Joe.S.AK

Chris,

Any good news?

- Joe -


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## chris scott

Well, before it got cold, I tried a few more things - and now I've tried just about everything that seems possible. When it warms a bit I'm going to buy some aviation 100LL gas (which has tons of lead) and run it a bunch on that. It just about has to be intermittent valve sticking.


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## Joe.S.AK

Chris,

I spent 5 years refueling aircraft of all types from 747s through home built ones and from that hands-on experience I actually know something about Aircraft fuel designations - including "Avgas" 100LL.

100LL is a designation of two primary characteristics in this fuel - simply 100 from it's Octane level (the same Octane rating as on gas station pumps) and the lead content ---Low Lead--- . NOT high lead but rather LOW lead compounds directly affecting the octane. Read paragraph 5 here: EPA Takes Final Step in Phaseout of Leaded Gasoline | About EPA | US EPA

If you think that the valves are sticking, REALLY think that, then either you or someone else is just going to have to pull the head and check them out. If they're sticking it could be old, bad fuel used in the past, poorly adjusted carb in the past or even something like a damaged push rod or even a poorly seating valve. 

Hoping that pouring something in the gas tank is your answer (if it is a sticking valve or such) is a bit over hopeful. I find it helpful to work from a position of specific knowlede instead of just hope.

All the best to you.

- Joe -


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## chris scott

Joe.S.AK said:


> Chris,
> 
> I spent 5 years refueling aircraft of all types from 747s through home built ones and from that hands-on experience I actually know something about Aircraft fuel designations - including "Avgas" 100LL.
> 
> 100LL is a designation of two primary characteristics in this fuel - simply 100 from it's Octane level (the same Octane rating as on gas station pumps) and the lead content ---Low Lead--- . NOT high lead but rather LOW lead compounds directly affecting the octane. Read paragraph 5 here: EPA Takes Final Step in Phaseout of Leaded Gasoline | About EPA | US EPA
> 
> If you think that the valves are sticking, REALLY think that, then either you or someone else is just going to have to pull the head and check them out. If they're sticking it could be old, bad fuel used in the past, poorly adjusted carb in the past or even something like a damaged push rod or even a poorly seating valve.
> 
> Hoping that pouring something in the gas tank is your answer (if it is a sticking valve or such) is a bit over hopeful. I find it helpful to work from a position of specific knowlede instead of just hope.
> 
> All the best to you.
> 
> - Joe -


Have they changed 100LL in the last 20 years? Used to be that it actually had lots of lead and when you pulled the plugs it would adhere to the elements - had to regularly sandblast them.
You're right that it's best to have real evidence, but I've done everything short of pulling the head off. I did a valve job (new parts and lapped) 18 engine hours ago, and the compression remains perfect on all four cylinders.


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## Joe.S.AK

Chris,

I'm not (ABSOLUTELY NOT) an organic chemist, but as I understand it, Tetraethyl Lead was added to gasoline, starting in the 20s, to raise octane - and from that change knocking was reduced / eliminated in the engines of the day. It was added in diminishing amounts up until the mid 90s when it was completely phased out. That is why the gasoline at the pumps in the 50s was labeled as "Tetra Ethylene Added", then it went to "Low Lead" and now, today, is called "Lead-Free" (and now replaced with Ethanol Alcohol, giving us the catchy name "BIO FUEL"). 

I think the talking point here is the quantity of lead and the resulting lead deposits after burning. What, how, why and other specifics concerning the lead deposits are all a bit beyond me. In the past things I've heard all sorts of things about TEL's effects on engines but, ahhh, all that was 'unconfirmed' at best. There _was_ a consistent rumor that the lead deposits somehow had something to do with the valves seating (or alternately, burning) - but ... blah, blah, blah ... I don't know much beyond just gossip.

Just as a question - do you use gasohol or non-ethanol gas in your '52 N? Gasohol that sits in seasonal storage scrubs water from the air migration in/out of the fuel tanks every day. I know it's sort-a grasping at straws, but even though early engine designers and engineers ALMOST decided to run those new Internal Combustion Engines on alcohol (instead of that new fangled gasoline) it finally was decided to run them on gasoline only. That's the way "things" stood in '52 and then up until the politicians got their unknowing hands into the works and screwed things up. Here is something just to know on "Good for You - *NOT!*" additives: MTBE controversy - Wikipedia

*One other thought* - in re-reading and thinking about your first and latest posts, you had mentioned that 16 - 18 hours ago you (or someone else) put in (among other things) new valves and guides. 16 - 18 hours of normal use COULD have been just enough time for those valves to have 'worn-in' and maybe, could, possibly should be re-checked anyway. Just a guess, but that's pretty much the minimum time interval for a break-in period and good 'go back and check' interval on those new valves. Good compression after a rebuild is a good thing to have but going back and checking for OMGs comes in there as well. As a bare minimum I (the only person I can speak for) would throw a compression check to see if the numbers have stayed about the same as right after the rebuild.

Anyone else have some thoughts? Better thoughts than mine, at least?

- Joe -


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## chris scott

I started this thread 12/19 and have tried many things to effect a cure. Well, I FINALLY found it - I used an oscilloscope to look at the points side of the coil, and could see that every now and then the pulses were irregular. The points looked good, so I suspected that the grounding of the points mounting plate was intermittent. I ran a ground wire to the points hold-down screw, and voila! problem cured.


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## FredM

AT last Chris!!👍


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## Joe.S.AK

Well done Chris!!!


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## 8n_guy

chris scott: The ground wire from the points hold down screw goes where, through the distributor housing directly back to the battery ground cable screw? I have the same intermittent miss. I ran a temporary wire from the distributor housing back to the battery ground strap and it did not affect the intermittent miss.


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## fuddy1952

If it's like a car points distributor, and I assume it's similar, the points mounting plate has a bare braided wire cable from plate to housing. Distributor is grounded to block by hold down clamp. Block grounded to frame by another cable, battery ground cable to frame.

Sent from my SM-S205DL using Tapatalk


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