Bad mechanics

I've been battling for quite some time getting the carb just right. I still have a choke issue but I'll tweak that this weekend.

I've fiddled and fiddled adjusted and tweaked that thing only to average 15-16 mpg. I bumped the timing to 12* btdc yet still the milage is low.

December 08 my mechanic attempted to make it pass the smog test and failed. Once I had the valves done it passed fine but was troubled with a hot carburator and fuel boilover issues.

Last April I drove it over 320 miles to the Fabulous Fords Forever show and was totally disappointed in the 18 mpg. I've been scratching my head ever since trying to solve the problem. So, yesterday evening I pulled the plugs only to discover they were gapped to .038" instead of the .048-.052". Boy was I pissed.

So, I regapped them properly and it sure does start even better than it did. What the heck were they thinking?

To make a long story longer do you all know what the function of the A.I.R system is? Well I'll tell you:

The A.I.R. system pumps air in to the exhaust manifold for two purposes. 1. It adds air to the exhaust to introduce more O2 to the exhaust thus reducing the percentage of NOX (nitrous oxides) in the exhaust and assists the catalytic converter in reducing HC (hydrocarbons). 2. It actually causes unburned fuel coming out of the cylinders (HC) in reburning in the exhaust manifold. The end result again is reduced HC in the exhaust. The exhaust gas in the manifold is pretty inert on older cars and all the HC just goes out the tailpipe. In an A.I.R equipped car the introduction of oxygen in to the exhaust manifold will actually cause ignition of the unburned fuel in the manifold. Somewhat of a "reburn" thus reducing the HC out the tailpipe.

So, with incorrectly gapped spark plugs there is less of a complete burn of the fuel in the cylinders thus more fire in the exhaust manifold causing the manifold to be much hotter than normal heating up the carburator to the point of boil over.

 

If a wider gap makes it happier (mine are at .050), and you change to higher output coil, without the A.I.R., you could get even better mileage? I know it takes more electrical jiuce for a big Accel coil, but that would overcome the wider plug gap resistance, say to .055? Yes?

 

Mine are now at .050. It's usually just right. I just go for the middle of the range. The rest of the week will tell the story.

I have to go ahead and hi-jack my own thread. It's raining cats and dogs here right now. We had a 20% chance of rain today. And the clean wagon is now all wet. Drat.:banghead3:

 

Rain, huh? That should give you better mileage, actually. The extra humid air helps increase the oxygen content in the cylinders. Water injection is used a lot in semi-trucks. Lots of DIY articles on it. Gives about a 10 to 15% improvement. Really.

 

That was interesting reading, TB...keep us posted. I can't remember ever having a car that the AIR wasn't removed.

 

Yup, the choke pulldown mechanism wasn't working. The nut of the linkage came loose. Starving for air, all better now. The poor engine had nothing but fuel. Speuwling (is this a word) smoke until the choke plate opened a bit.

I still have the old carb and the choke plate on that one has a hole in it that this carb doesn't have. I suppose it's to let more air in. The current plate will actually completely close the throat. Maybe I'll swap it.

 

Sounds like one of our Canadian cold carbie plates. The choke on mine stays closed for up to 20 minutes in -40F weather, but the car runs smooth, and idles like a fuel dragster at the lights. That little hole just makes sense. Funny the other one doesn't have one. IIRC, the holes were there to prevent carb icing. Warmer temps from below could keep the carb working.

 

Those holes are there to compensate for poor vacuum at idle. They get drilled in plates intended for use with high performance cams. And they are used to compensate for all the smog-related "tuning" applied to factory engines of the era.

 

Huh? I've heard water injection with semi's cause it helps lower intake air temperatures especially in turbo applications. How could humid air produce more oxygen? I guess you could be right with it getting better mileage cause the air is denser or it could atomize with the fuel better?...

 

So, problem solved on the carb boil-over issue?
The hind sight on that scenerio makes perfect sense.

 

I think so, no issues today and it runs much better.

 

i hate mechanics unless i find one thats actually good. like my VW guy. hes good. a few years ago i had taken my 77 Dodge Power Wagon to a "trusted" mechanic to redo a front axle Ujoint. when i got it back i had NO BRAKES! he told me "thats how we got it. its your problem." needless to say, that was the LAST time i ever went there or let any of my family or friends go there either. the funny part is i had just done teh brakes a month earlier and they had worked fine the day i took it to him. this truck WAS my daily at the time.

 

I know what you mean. This particular shop was "raved" about at work. You have to wonder if they can't even gap spark plugs correctly what else will they screw up. I should have checked them a long time ago. I wanted to let folks know that check the simple things yourself and not trust so easily.

It's all in the detail.

 

Better burn. Water/humidity has more H2O and combustion under pressure breaks it into both gasses as well as cleans the chamber. have a look:
http://journeytoforever.org/biofuel_library/ethanol_motherearth/me3.html

 

I must tell you it hasn't been better. Finally it runs properly. Mainly starts properly and doesn't have that annoying momentary miss anymore. Whew what a haul this has been.