Is This A Problem With Air Gap Intakes Only?
Thread Starter
Melting Slicks
Joined: Apr 2009
Posts: 2,632
Likes: 112
From: Great Plains Iowa
Is This A Problem With Air Gap Intakes Only?
Two years ago I was returning home from a doctor's appointment 250 miles away when my front 4 spark plugs quit firing because of fouling. All of the gaps had widened to .055" (from their original .045") in about 10,000 miles. Then a few days ago when I was having choke problems the front 4 spark plugs fouled again. Both times the rear 4 spark plugs were as clean as when I had installed them so why are the front 4 ONLY fouling? Could it be a problem with Air Gap intakes?
Last edited by toobroketoretire; Dec 24, 2015 at 04:40 AM.
Le Mans Master
Joined: May 2006
Posts: 9,993
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From: League City Tx
I have an rpm air gap and I rarely foul plugs, and if I do, they are evenly fouled... Usually from race fuel...I've had this intake on for 18k miles..
You definitely have something else causing your issue, but it's not due to the "air gap".
If the choke is sticking, the primaries will be rich as hell, thus fouling the front cylinders as they tend to get a bit more flow from the primaries.
Could also be valve seals or sloppy ring seal, coincidentally all on the front cylinders, that's if the plugs are oil fouling.
You definitely have something else causing your issue, but it's not due to the "air gap".
If the choke is sticking, the primaries will be rich as hell, thus fouling the front cylinders as they tend to get a bit more flow from the primaries.
Could also be valve seals or sloppy ring seal, coincidentally all on the front cylinders, that's if the plugs are oil fouling.
Last edited by ajrothm; Dec 24, 2015 at 01:09 AM.
Thread Starter
Melting Slicks
Joined: Apr 2009
Posts: 2,632
Likes: 112
From: Great Plains Iowa
Several months ago another forum member had mentioned his front 4 spark plugs fouling and he also had an Air Gap intake. I'm wondering if the floor of the plenum might have a slight slant foreword which would allow gasoline to run into the front 4 cylinders.
Drifting
Joined: Oct 2005
Posts: 1,528
Likes: 148
From: East London/SW Essex UK
I have an Air Gap inlet on my 489, and yes, I do have one or two plugs foul-up occasionally even though I have MSD ignition (you would think the MSD would 'fire though' this?). My reasoning is the following. Cam, whilst not radical is a bit on the 'rumpity - rumpity' side at idle so will effectively need a richer idle mixture to run properly. Carb used is a Proform 950 cfm DP. The idle adjustment is very sensitive - difference between optimal setting and rich is just a fraction of a turn (despite optimising idle bleed jet sizes). Most of my initial driving (before getting out on main roads) is urban stop/start. So (for me) its really a combination of the above factors that create the occasional plug foulings.
Last edited by roscobbc; Dec 24, 2015 at 04:51 AM.
Instructor
Joined: Jul 2007
Posts: 115
Likes: 12
From: Philly Area NJ
I would think first towards carb tuning, then valvetrain, then perhaps towards cooling system. Might be interesting to take a lazer thermo and check the cyl head temp over top of each cyl, as well as the primary tube temps at operating temp. After that, do a compression and leakdown test.
Let us know what you find out!
Last edited by AW IR C3; Dec 24, 2015 at 05:01 AM.
Drifting
Joined: Mar 2011
Posts: 1,347
Likes: 121
From: Kernersville NC
I am running an air gap on a big block with no issues at all. I run a 195 degree thermostat and have only half of the baffle at top of the radiator to ensure cool air gets up around the air filter. The carb and air cleaner is actually cool when I shut down. Narrow down your variables by wiring your choke open for a while and see what happens to the plugs.
Last edited by flyeri; Dec 24, 2015 at 07:17 AM.
Burning Brakes
Joined: Oct 2008
Posts: 1,037
Likes: 14
From: Mobile Alabama
every carbureted intake has a slight slant forward.
I would think first towards carb tuning, then valvetrain, then perhaps towards cooling system. Might be interesting to take a lazer thermo and check the cyl head temp over top of each cyl, as well as the primary tube temps at operating temp. After that, do a compression and leakdown test.
Let us know what you find out!
I would think first towards carb tuning, then valvetrain, then perhaps towards cooling system. Might be interesting to take a lazer thermo and check the cyl head temp over top of each cyl, as well as the primary tube temps at operating temp. After that, do a compression and leakdown test.
Let us know what you find out!
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Le Mans Master
Joined: Dec 2006
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Likes: 1,028
Two years ago I was returning home from a doctor's appointment 250 miles away when my front 4 spark plugs quit firing because of fouling. All of the gaps had widened to .055" (from their original .045") in about 10,000 miles. Then a few days ago when I was having choke problems the front 4 spark plugs fouled again. Both times the rear 4 spark plugs were as clean as when I had installed them so why are the front 4 ONLY fouling? Could it be a problem with Air Gap intakes?
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
I was trying to think if I ever have had a fuel fouled plug that actually quit firing with my Air Gap manifolds. The only thing that I could come up with is I had a blown head gasket that put so much coolant in the a couple cylinders that the engine was misfiring. The other time a needle and seat failed open and the engine was flooding. Causing a misfire The plugs cleared up after replacing the needle and seat and I made it back home.
IMO air gap manifolds are a marketing scheme. I have a really nice thermal measuring gun. Did you know that aluminum is an excellent heat conductor? Did you know that A/F spends very little time from entering the plenum and into the head port. Very little time to significantly alter the temp of the incoming charge.
Cold air induction or alki added to the gasoline mix do change the air and manifold temp. Ice would form on my alki injected dragster intake on 90 degree days
My carbs don't have chokes because they always seemed to have problems, Both electric and thermal on aftermarket carbs So I went chokeless Vette 25 years ago.
Some people seem to not have the ability to learn new concepts
like the obvious stated above. Intakes have a forward angle to even out the rear tilt of the engine to keep the carb level
IMO air gap manifolds are a marketing scheme. I have a really nice thermal measuring gun. Did you know that aluminum is an excellent heat conductor? Did you know that A/F spends very little time from entering the plenum and into the head port. Very little time to significantly alter the temp of the incoming charge.
Cold air induction or alki added to the gasoline mix do change the air and manifold temp. Ice would form on my alki injected dragster intake on 90 degree days
My carbs don't have chokes because they always seemed to have problems, Both electric and thermal on aftermarket carbs So I went chokeless Vette 25 years ago.
Some people seem to not have the ability to learn new concepts
like the obvious stated above. Intakes have a forward angle to even out the rear tilt of the engine to keep the carb level
Le Mans Master
Joined: Oct 2010
Posts: 6,938
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From: melbourne florida
2023 C3 of the Year Finalist - Modified
I agree with fish's layer and Gkull, cold air intake cold manifold cold ambient temprature, could even be icing up. I don't run a choke the car runs fine, I admit I live in Florida but I used to live in northern Virginia.
The air gap does take a bit longer to warm up. Oh and I run a double pumper carb that some claim won't work on the street.
The air gap does take a bit longer to warm up. Oh and I run a double pumper carb that some claim won't work on the street.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
It was in the teens over night and won't make 30 for a high today and I can go right out and fire up my no choke carb.
I saw his other post about doing a really nice job of wrapping copper tubing around some exhaust pipe. When my choke way back was acting up a few times. The simple cure was to just remove all that junk.
The air gap has very little to do with how fast a motor warms up. The thermostat has a lot to do with it. I use a 195 deg. slant high flow.
Engines have the most ware when cold and starting without any oil pressure. So with your double pumper without a choke you give it two squirts with the gas pedal and then turn on the key. When it fires brink it right up to 2500 rpm and hold it there for 30 seconds or so and watch your temp gauge as it swings past 100 degrees. I don't even put it in gear till it is past 100.
It's a white Christmas here
I saw his other post about doing a really nice job of wrapping copper tubing around some exhaust pipe. When my choke way back was acting up a few times. The simple cure was to just remove all that junk.
The air gap has very little to do with how fast a motor warms up. The thermostat has a lot to do with it. I use a 195 deg. slant high flow.
Engines have the most ware when cold and starting without any oil pressure. So with your double pumper without a choke you give it two squirts with the gas pedal and then turn on the key. When it fires brink it right up to 2500 rpm and hold it there for 30 seconds or so and watch your temp gauge as it swings past 100 degrees. I don't even put it in gear till it is past 100.
It's a white Christmas here
Drifting
Joined: Oct 2005
Posts: 1,528
Likes: 148
From: East London/SW Essex UK
I agree with fish's layer and Gkull, cold air intake cold manifold cold ambient temprature, could even be icing up. I don't run a choke the car runs fine, I admit I live in Florida but I used to live in northern Virginia.
The air gap does take a bit longer to warm up. Oh and I run a double pumper carb that some claim won't work on the street.
The air gap does take a bit longer to warm up. Oh and I run a double pumper carb that some claim won't work on the street.
Safety Car
Joined: Apr 2006
Posts: 4,057
Likes: 421
From: BC
Two years ago I was returning home from a doctor's appointment 250 miles away when my front 4 spark plugs quit firing because of fouling. All of the gaps had widened to .055" (from their original .045") in about 10,000 miles. Then a few days ago when I was having choke problems the front 4 spark plugs fouled again. Both times the rear 4 spark plugs were as clean as when I had installed them so why are the front 4 ONLY fouling? Could it be a problem with Air Gap intakes?
Le Mans Master
Joined: Oct 2010
Posts: 6,938
Likes: 848
From: melbourne florida
2023 C3 of the Year Finalist - Modified
I think most of the perceived value of the air gap is air circulates more freely around the runners and plenum with the possibility of maintaining a cooler denser charge..
I think the design has some merit as air does flow through the engine compartment. I do think it takes longer to get the manifold up to temp.
I think the design has some merit as air does flow through the engine compartment. I do think it takes longer to get the manifold up to temp.
Burning Brakes
Joined: Oct 2008
Posts: 1,037
Likes: 14
From: Mobile Alabama
Thread Starter
Melting Slicks
Joined: Apr 2009
Posts: 2,632
Likes: 112
From: Great Plains Iowa
Its odd how the front 4 could be as blacker than black when the rear 4 could be whiter than white. You would think the rear 4 would at least show some darkening. You'd never guess they came out of the same engine.
Drifting
Joined: Oct 2005
Posts: 1,528
Likes: 148
From: East London/SW Essex UK
You could understand your issue if the Air Gap was a single plane manifold. Stagger jetting would then be a possible answer. As good as the Air Gap manifold may be there will still be a small degree of variation in fuel/air mix between cylinders - but minimal. Perhaps you need to look for something for more fundamental/mechanical within the engine. Are c/r's equalised on all cylinders? - I'd certainly use a temperature gun to log exhaust temperatures on each exhaust at varying revs, log the results and see if that gives any clues.