Auto Service World
Feature   January 1, 2002   by Rick Cogbill a.k.a. Slim Shambles

A Breath of Fresh Air

Mona was a little short of breath when she dropped her car keys on the counter. Jeffery, her youngest, was washing the floor with water from the cooler, while Sabrina played "Old McDonald's Farm" for ...

Mona was a little short of breath when she dropped her car keys on the counter. Jeffery, her youngest, was washing the floor with water from the cooler, while Sabrina played “Old McDonald’s Farm” for her siblings on the horn outside.

“Gotta run, Slim,” she puffed. “Like I said on the phone, the van runs a bit rough in the morning, and surges when I’m going down the highway.” She headed for the door. “Oh yes,” she said. “It’s always been hard on fuel, but I think I’m using more gas than usual lately.” The taxi arrived at that moment and she herded the five kids into it. “We’ll be back when school’s out!” she hollered out the window as the taxi sped off.

“If I had a brood of wild kids like that, I’d be low on fuel, too,” observed Basil as he watched them drive away.

“Well, since you feel so sympathetic, why don’t you take a look at her van and see what the problem is?” I tossed the keys to him.

Beanie opened the bay door as Basil pulled the 1986 Dodge Caravan inside. The 2.6 Mitsubishi motor was not one of our favorites. The engine, prone to timing chain problems, was noisy and idling too fast.

“Before you get too far,” I said, “make sure the timing chain guides are okay. If this engine needs major work, it might not be worth it.”

Basil removed the valve cover and inspected the upper guide. “It’s in one piece, surprisingly enough,” he said. He checked the valve clearance, and found it within specs. “I wonder why the valve train is so noisy?”

“Look at how dirty and thin that oil is,” I said. “It looks diluted.”

Basil agreed, and put the valve cover back on. Starting the engine, he goosed the throttle a few times. “Hey,” hollered Beanie. “You’re smoking me out back here!” Clouds of black, sooty smoke filled the shop.

Obviously the van was running too rich, but the question was why. Basil spent the next few hours adjusting timing, idle mixtures, choke settings, replacing spark plugs and air filters-just about everything he could think of. Still the little van surged down the road at light throttle and produced major black smoke on acceleration. Yet it idled just fine.

By coffee time Basil was coming up empty. “I get the feeling that this van is starving for air,” he mused.

Tooner was losing at solitaire. “That reminds me of Ramblin’ Don and his gas-guzzling motorhome,” he grumped, debating whether to cheat or not.

“Move the Queen of Spades,” observed Basil. “Who’s Ramblin’ Don?”

“You were on vacation in Mexico at the time,” I explained. “Don’s motorhome ran great except on the hills, where it was starving for air due to a restricted air cleaner.” (*see SSGM March 2001 issue, “Postcards From the Edge”)

“Yeah,” put in The Bean. “It sure belched out the black smoke!”

“But I’ve run this van without the air cleaner on,” replied Basil, “and it still has a rich exhaust. So that can’t be it.”

I went out with Basil to take another look. “How about a flooded charcoal canister?” I grabbed the hoses from the canister and following them back to the carb. As I pinched off the large vapor hose, the engine suddenly quit.

“What did you do?” asked Basil.

I started the engine and pinched the hose again, and again the engine stalled.

We removed the hose from the port on the carb, which led into the bowl area. By plugging the port, the engine would stall every time.

“It’s like the float bowl is starving for air,” observed Basil. “Where’s the bowl vent?”

We checked out the diagrams and discovered that the bowl vent was controlled by an electric solenoid. Basil removed the solenoid cover. “Here’s the problem!” He held up the rubber diaphragm. It had been improperly installed, and a corner of it was folded over, allowing the control vacuum to bypass it.

“So the bowl vent port was always closed,” I said. “The only venting to the bowl was through the charcoal canister.”

“Right,” said Basil. “On acceleration, the carb would suck fuel-rich air out of the canister. That’s why the oil is so contaminated and the tailpipe so black.”

Once we fixed the bowl vent and changed the oil, Mom’s Taxi ran a lot quieter, and the surging was gone.

“Thanks, guys,” said Mona. “Do you think my mileage will improve?”

“Probably double,” said Basil.

Outside, the Horn Symphony was starting again.

Mona sighed. “If you could just find a way to siphon some of their energy into my gas tank, I think my mileage would triple.”

(If you’ve got a sticky solution you’d like to share with our readers, contact Slim at

About The Writer:

Rick Cogbill is a freelance writer living in the Okanagan valley of Southern British Columbia. A licensed technician with over 25 years in the automotive repair industry, including ten years as a shop owner, Cogbill creates his comic scenarios with Slim, Basil, Tooner, and The Bean out of actual case histories. “What you have just read is true,” drawls Slim Shambles. “Only the names have been changed to protect my hide!”

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