Dynaflash8

41 Buick Roadmaster fouling plugs 1 & 2 - HELP

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Posted (edited)

The car is a 1941 Buick Series 70 Roadmster, 59K miles.  We have installed a new carburetor, new AC-46 spark plugs and done a compression check (all good).  Spark plug wires are almost new, custom made by a man on ebay.  Distributor recently rebuilt with all new guts during professional restoration.  Put your foot into it and it runs like a scalded Ape.  Starts good.  Has a new accelorator pump into NOS carb, and no more faltering.  What it does have, and mechanic is stumped, is a slight miss, like a vibration, running along easy around 35-40 mph, and plugs 1 & 2 are fouling so you can see it starting with only few miles (already wet).  It was previously sooting up all the plugs with AC-48 spark plugs and old carburetor.  I ordered another set of new wires and another new distributor cap today from Bob's just for a looksee if that is the problem, but with little hope that will solve the problem  Do any of you Buick or otherwise mechanical genious' have any ideas. 

Edited 2 minutes ago by Dynaflash8 (see edit history)
Edited by Dynaflash8 (see edit history)

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Hmmm, that's a strange one. Since it's just one and two fouling, it probably isn't something universal like coil or points and 47s are a step hotter than stock so fouling shouldn't be a problem. Maybe swap out plug wires and see if it improves? Do your new plug wires have exposed ends instead of boots? I've had cars with spark plug covers that touched the exposed ends of the wires and ground out the plug for a misfire. I'd bet $5 that it's related to the wires, new or not.

 

I'm assuming that you've double-checked the gaps but is it possible that the plugs themselves are defective? Maybe move those two plugs to #3 and #4 and see if the fouling stays put or follows them.

 

How are plugs 7 & 8? The outer barrel on the carburetor(s) feeds 1,2, 7, and 8, but since it's so far away from 7 & 8 they may not be getting the same amount of fuel. Could the outer barrel of the front carb be a little rich? You mention that the carb is NOS, even though it's "new" it may still have issues.

 

Leaky valve guides? Is there any oil burning (blue smoke) visible out back? Unlikely since it's specific to 1 and 2, but maybe.

 

Really reaching, is it a head gasket? Are you sure it's oil and not coolant? Very unlikely, but maybe?

 

More simple troubleshooting will get us closer, I'm sure. It'll be something easy but weird.

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An easy way to look for cross sparking is to run the engine in a dark garage or at night.  If there is high voltage arcing it gets quite obvious when no ambient light is present.  I’ve used this method many times over the years to find high voltage ignition leaks.

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On 5/8/2020 at 7:51 PM, Matt Harwood said:

Hmmm, that's a strange one. Since it's just one and two fouling, it probably isn't something universal like coil or points and 47s are a step hotter than stock so fouling shouldn't be a problem. Maybe swap out plug wires and see if it improves? Do your new plug wires have exposed ends instead of boots? I've had cars with spark plug covers that touched the exposed ends of the wires and ground out the plug for a misfire. I'd bet $5 that it's related to the wires, new or not.

 

I'm assuming that you've double-checked the gaps but is it possible that the plugs themselves are defective? Maybe move those two plugs to #3 and #4 and see if the fouling stays put or follows them.

 

How are plugs 7 & 8? The outer barrel on the carburetor(s) feeds 1,2, 7, and 8, but since it's so far away from 7 & 8 they may not be getting the same amount of fuel. Could the outer barrel of the front carb be a little rich? You mention that the carb is NOS, even though it's "new" it may still have issues.

 

Leaky valve guides? Is there any oil burning (blue smoke) visible out back? Unlikely since it's specific to 1 and 2, but maybe.

 

Really reaching, is it a head gasket? Are you sure it's oil and not coolant? Very unlikely, but maybe?

 

More simple troubleshooting will get us closer, I'm sure. It'll be something easy but weird.

Matt:  The mechanic says it is gas in the two plugs.  I just read that 1 & 2 and 7 & 8 are somehow connected in the carburetor.  This carb had been in the box for many years.  All he did was put a new accelerator up into it.  Car runs good at high speed, develops a small miss between 30-40 that almost feels like a vibration.  No, no blue smoke.  What would you do about the outer barrel on the front carb being a little rich? Not coolant.  I wondered if it was oil, but the mechanic says gas (or maybe a mixture of gas and oil?)  I took them a rebuilt Doub Seybold distributor today.  Plug wires are solid core and custom built by a man on the internet who sells them, but I also ordered another new set from Bob's on Friday, but they just shipped them 2-day ---today.   I did take him two new plugs Friday, but they stayed away from my car today.  It's really tough around here.  This is a two man shop with a knowledgeable owner who spends more time answering the phone or working on his Corvette that doing the heavy lifting on the modern cars...phone rings constantly and the owner works on a lot of foreign cars. The mechanic is one of those stolid and solid guys who's been through the wars, and he knows his stuff,  but not sure he's had to tackle many dual carb setups.  I judge him to be about 55.  He's really good but scratching his head on this one I think.  Going into this, the car would run good, and then suddenly start starving for gas...or, that's how it felt...like a vapor lock situation.  Personally, I think it is something wrong with that new carburetor.

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On 5/9/2020 at 9:01 AM, TerryB said:

An easy way to look for cross sparking is to run the engine in a dark garage or at night.  If there is high voltage arcing it gets quite obvious when no ambient light is present.  I’ve used this method many times over the years to find high voltage ignition leaks.

I suggested that.  The mechanic had to reinstall a faulty transmission in some foreign car Saturday night.  It would have been a perfect time to try that.  I think it has something to do with that front port on the carburetor as Matt Harwood suggested.  I still have two kits.  I'm going to suggest (and I really have to be tactful about that too) that they overhaul the NOS carburetor in its entirety, but I suspect they may install the rebuilt distributor first.  The mechanic doesn't take well to suggestion from a non-mechanic dummy like me. 🙂

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Posted (edited)

Dyna,

Just an idle question re your '41.

Do you have your spark plug cover on ?

Is it screwed down tight ?

Could be that your 1 and 2 plugs are grounding on the cover.

if so, take it off and start her up, let her idle and ground each plug with a screw driver, and see if the idle changes.

You said you are running AC 46's.

You know that they come in different heights.

Ask me how I know.

If they are the new ones, they will ground out on the cover.

I use the OLD C-49's in my '40 LTD as we mostly putt around town, and they are noticeably shorter.

 

Mike in Colorado

Edited by FLYER15015 (see edit history)

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I finally got my 41 Buick Roadmaster back today.....said to be repaired.  It was by most people's perception, VERY expensive.  But, I think I had to pay for some on job training time.  In the end they installed a rebuilt distributor and wires that I had in my garage (a Doug Seybold rebuid I hadn't used after having it done), and then they took the NOS front carburetor apart (finally) and discovered a port was blocked by some gunk that had grown in there over the last 75 years or so.  Many more things were done along the way that didn't fix the problem.  This town in Florida is truly a vast wasteland for old cars and old car work.  As a result of this AACA line, I did receive one message from a volunteer mechanic in Clearwater, but my repair was completed today after three weeks.  Keep in mind, my car had to be worked on among all of the modern cars that clog this garage every day making it a very popular shop in this town.

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