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Spark plug confusion
#1
FLMan Jamie Losee
Palm City, FL, USA   USA
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1976 MG Midget 1500 "Lucy"
Hi, first post- been reading a ton. I have a new to me 76 that’s been de-bumpered, de-emissioned, electronic ignition, Weber DGV. She was running rough, lots of pops when pushing hard through 2nd and 3rd. I pulled the plugs thinking it would help me see how my mix was and found 1 and 4 were black, 2 and 3 perfectly clean. New plugs (properly gapped), wires, and same issue. What’s causing this??


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Re: Spark plug confusion
#2
Watauga Avatar
Watauga William B
Richmond, IN, USA   USA
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1974 MG MGB
Jamie, Is your Vacuum Advance set up correctly? Using the correct ported or manifold vacuum for that distributor and advance part number? The leaner running center plugs is another issue with the Weber carburetor?

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Re: Spark plug confusion
#3
PeterC Avatar
PeterC Platinum Member Peter Caldwell
Madison Wisconsin, USA   USA
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1931 Morris Minor Saloon "Cammy OHC"
1960 Land Rover Series II
1962 MG Midget MkI
1963 Volkswagen Karmann Ghia    & more
Check you've got your firing order correct.


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Re: Spark plug confusion
#4
FLMan Jamie Losee
Palm City, FL, USA   USA
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1976 MG Midget 1500 "Lucy"
Pretty sure I’m good on firing order and the vacuum advance looks good. The ignition and distributor were both replaced by the PO when he went electronic


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Re: Spark plug confusion
#5
refisk Rick Fisk
Frankenmuth, MI, USA   USA
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That distributor has vaccum retard, not advance. The entire reason for it to be there is emissions control. Disconnect the hose at the carb and plug the port. Then set your timing to 10 BTDC. It will run much better.

In reply to # 4786594 by FLMan Pretty sure I’m good on firing order and the vacuum advance looks good. The ignition and distributor were both replaced by the PO when he went electronic

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  JAMADOR, FLMan, and oleanderjoe thanked refisk for this post
Re: Spark plug confusion
#6
PeterC Avatar
PeterC Platinum Member Peter Caldwell
Madison Wisconsin, USA   USA
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1931 Morris Minor Saloon "Cammy OHC"
1960 Land Rover Series II
1962 MG Midget MkI
1963 Volkswagen Karmann Ghia    & more
Yep. see that now. Couldn't tell in first pic.


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Re: Spark plug confusion
#7
B-racer Avatar
B-racer Jeff Schlemmer
Shakopee, MN, USA   USA
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1950 Willys Jeep Pickup "Ratrod"
1964 Land Rover Series IIA
1971 MG MGB
Actually, that's vacuum advance. In a Pertronix distributor.


jeff@advanceddistributors.com

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Re: Spark plug confusion
#8
refisk Rick Fisk
Frankenmuth, MI, USA   USA
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Coulda fooled me. I don't use them electronic gizmos. smiling smiley

So why do the two middle plugs look like they're waaaay to hot?

In reply to # 4786640 by B-racer Actually, that's vacuum advance. In a Pertronix distributor.



Edited 1 time(s). Last edit at 2024-04-18 12:54 PM by refisk.

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Re: Spark plug confusion
#9
pbcjr Avatar
pbcjr peter cantamessa
east brunswick, NJ, USA   USA
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1971 MG Midget MkIII
How does the inside of the distributor cap look?
Any carbon tracking between cylinders 1 and 4?


In 1974 when I was 18, I passed on buying a running and driving 1966 E-Type coupe for $1,500, which is what they were selling for at the time.
Fifty years later, I'm still kicking myself...

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Re: Spark plug confusion
#10
FLMan Jamie Losee
Palm City, FL, USA   USA
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1976 MG Midget 1500 "Lucy"
I haven’t actually pulled the cap yet. I know I should have. I’ll take a look tomorrow

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Re: Spark plug confusion
#11
FLMan Jamie Losee
Palm City, FL, USA   USA
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1976 MG Midget 1500 "Lucy"
I pulled the cap. There is a little bit of a deposit in the contacts but it looks equal on all 4.


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Re: Spark plug confusion
#12
Wellkevi01 Avatar
Wellkevi01 Gold Member Kevin Wells
Midland, MI, USA   USA
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1978 MG Midget MkIV
I don't have any experience with the Webber DGV, but I've done some googling. From the things I've found, it looks like the Weber is a dual barrel and the intake manifold runs are nearly completely partitioned from the cylinder head up to the carb. This leads me to think that either the outside barrel that corresponds with cylinders 1 & 4 is running rich, or the inside barrel that corresponds with cylinders 2 & 3 is running lean. I can see that the intake does allow for all cylinders to pull from both barrels(aka it's not partitioned all the way to the base of the carb), but if the mixture is off far enough, that might not be enough space to give the air/fuel supplied by both barrels enough time to properly mix.

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Re: Spark plug confusion
#13
JAMADOR Avatar
JAMADOR John Amador
Spring, TX, USA   USA
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1975 MG Midget 1500 "Midge"
In reply to # 4787011 by Wellkevi01 I don't have any experience with the Webber DGV, but I've done some googling. From the things I've found, it looks like the Weber is a dual barrel and the intake manifold runs are nearly completely partitioned from the cylinder head up to the carb. This leads me to think that either the outside barrel that corresponds with cylinders 1 & 4 is running rich, or the inside barrel that corresponds with cylinders 2 & 3 is running lean. I can see that the intake does allow for all cylinders to pull from both barrels(aka it's not partitioned all the way to the base of the carb), but if the mixture is off far enough, that might not be enough space to give the air/fuel supplied by both barrels enough time to properly mix.

DGV is a progressive 32/36, and they're positioned perpendicular to the pistons
Intake runners seem pretty equal length


1975 MG Midget 1500 - Midge
Work in Progress

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Re: Spark plug confusion
#14
inverse121 Avatar
inverse121 Gold Member Chris K
East Central, NY, USA   USA
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1963 Austin-Healey Sprite
1976 MG Midget 1500
Have you checked for an intake leak? In particular the lower center footballs?

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Re: Spark plug confusion
#15
FLMan Jamie Losee
Palm City, FL, USA   USA
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1976 MG Midget 1500 "Lucy"
Ok you’ve lost me. I’m pretty mechanically inclined but I’m lacking knowledge. How do I do that/what am I looking for?

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