The 350 Crate Engine in Carl Arentz’s 1964 Chevelle Has Severe Driveability Issues. We’re Gonna Fix It.
The Combo

Carl Arentz bought his 1964 Chevelle two years ago, well used but running. “I’m well aware that it’s an old dog that should have been put down,” he says, “but I can’t bear to see these cars go to the junk pile.” He’s been restifying it ever since. Upgrading and refreshing the car’s tired drivetrain, he had the car’s M22 Muncie four-speed rebuilt, installed a new clutch, and swapped out the car’s weary small-block for a mild GM 350 crate motor. The end goal was a reliable cruiser.

The Problem
But the new engine never ran right. Several different mechanics unsuccessfully tried to tune it, trying different size carbs and messing with the ignition advance. Nothing really seemed to help. When Arentz’s latest carb—GM’s recommended 670-cfm Holley Street Avenger “spec unit”—still didn’t cure the problem, Arentz turned to HOT ROD.

His main complaint: “The car won’t cruise at a steady speed. If you try to keep a constant speed it surges; when you decelerate, it bucks as if you’re coming to a stop in Third gear and forget to push in the clutch. It’s better going uphill then downhill. I’ve tried it at all speeds from 50 to 80 mph and in all gears. It lessens at higher rpm, but it’s still there. Whenever I’m accelerating at full throttle, it feels good.”
The Diagnosis

We sent the Chevelle to Rollings Automotive, one of our go-to SoCal shops. Owner Norm Rollings, nephew Mark Rollings, and the rest of his crew can fix just about everything. Norm knows the 350/290hp crate motors well, remarking, “We’ve had some issues with them. The 290hp package with its fairly mild cam ground with a 114-degree LSA [lobe separation angle] should produce good vacuum—but it doesn’t, probably because of the engine’s low 8:1 compression ratio and an intake lobe that’s also ground straight up at 114 degrees, not advanced like many typical street cams. These motors can have only 12 inches of vacuum [at idle], which I consider low for a daily street driver.
“We started by looking at the carb, engine vacuum, and ignition timing, with everything set the way the car was received. Overall, the engine ran rough: I can put my hand on the fender and tell what the car’s doing. Grandpa used to put a water glass on the fender and watch it shake.” Major issues included a stuck choke, way over-advanced ignition timing, and a carb idle circuit that had never been properly adjusted. Later, Norm and Mark fixed an off-idle lean stumble, and dealt with slightly high coolant temperature.

A] Adjust choke
B] Verify TDC location; set timing
C] Fix/adjust vacuum advance
D] Adjust/dial-in carb
E] Proper brake booster hose
F] Reroute heater hoses
G] Gut thermostat
H] Install PCV return hose
The Fix: Choke

After verifying it was getting a full 12 volts, Mark adjusted the electric choke’s settings. The main culprit turned out to be a fast-idle speed screw turned in so far it prevented the choke from fully releasing, but the choke cover was also adjusted too rich for mild Southern California. Norm explains, “This is common with factory-set chokes. They’re set to work in a worse-case winter climate. Just about everywhere else—but especially here in Southern California—you must change the choke’s baseline settings. Ice-cold we like to see 1,500 to 1,800 rpm on the highest step [of the three-step choke cam], dropping to 1,200 on the first ‘kick’, then down to 1,000 on the final step. It should fully release within the first 30 to 60 seconds of running.”


The Fix: Timing

There was way too much lead: 23-degrees of base timing plus 27-degrees of centrifugal advance yielded 50 degrees on the balancer at rpm. The HEI distributor’s vacuum advance was hooked to a manifold vacuum source; it should have been high at idle, but was actually near zero. Its fully 30 degrees did finally came in late and by 2,800 rpm total advance under low load climbed as high as 80 degrees!


A closer look revealed a screw internally plugging the vacuum advance hose; eventually, some vacuum was able to worm its way around the threads as rpm rose. Ultimately, the base timing was dialed back to 10 degrees BTDC, the as-received 23 degrees of centrifugal advance was not changed, and the distributor’s adjustable vacuum advance unit was adjusted to reduce full vacuum advance to 14 degrees using a new, unrestricted hose. The final sum: 33 degrees total base plus centrifugal, climbing to 47 degrees at cruise with a fully engaged vacuum advance (see table).


Why wasn’t the centrifugal advance recurved? Norm explains, “On an HEI-style large-cap distributor, it’s hard to tune-in the centrifugal advance; the weights aren’t nearly as responsive as the mechanism on an old GM small-cap or the popular MSD distributor. [On an HEI], you’d also have to make your own stop or advance-limiting bushing.”
Why was the vacuum advance left hooked up to full-time manifold vacuum (a source below the carb’s throttle blades) and not connected to spark-ported vacuum (above the blades)? Rollings believes in old-school turning for an old-school basic carburetor. “We don’t believe in ported vacuum. If the centrifugal advance isn’t really quick, the car tends to be lazy on the bottom-end. Using manifold vacuum lets the carburetion work right now without major tweaking. With spark-ported vacuum, there’s little or no vacuum signal at idle, the opposite of manifold vacuum. To get a stable idle with no signal the carb’s primary throttle-blades will be open to about 12 degrees, at the end of the transition slot and starting to pull on the main circuit, resulting in idle-mixture screw adjustment problems. That requires much finer carburetor tuning.
“Using manifold vacuum with a basic carb on a mild hot rod delivers better idle circuit response in the transition mode as we accelerate. As manifold vacuum drops off idle, the centrifugal advance comes up to where there’s crossover between 1,200 to 2,500 rpm. The vacuum advance picks up and chases it. It’s an easy and quick fix anyone can do.”
The Fix: Stumble

Once the choke issues and ignition timing were resolved, Arentz’s gross problems were pretty much fixed. At this point, it was on to the usual carb adjustments and minor calibration enhancements. Initially, Mark set the float level, adjusted the idle mixture screws, and fine-tuned the curb idle-speed, but there remained what Norm describes as a residual slight “stumble” or hesitation at tip-in off idle. “This is a sign the primary side was a little lean. If there had been a tip-in ‘blubber,’ that would be a sign the carb was a little rich.”

Some would say a lean tip-in stumble calls for a larger accelerator-pump shooter. But Norm says the Chevelle’s 0.042-inch-id shooter was already on the large side. “On a typical small-block, if the carb has a 0.030-or-larger shooter, I take a look at the primary jets first. From my experience, most street 350 or 383 Chevys want about a No. 70 to No. 73 main jet. This carb had only No. 65 primary jets, so Mark replaced them with No. 73s. For an early street car, we prefer a slightly rich calibration. It makes for a very driveable package. Many older cars were marginal coolers on a hot day; a tad on the rich side helps keep the charge-temp cold and cylinder temps down: therefore, no detonation. In SoCal, there’s about 15 percent ethanol in our fuel—we need to protect ourselves.”

Norm also holds to traditional power-valve (PV) gospel: It should open below half the idle vacuum reading. “You want to keep off the PV around town,” he explains. “Make it up as needed in the jets.” This carb had a 6.5 PV, but idle vacuum was around 12 in-Hg. Playing it safe, nephew Mark installed a 5.0 PV. No vacuum-secondary diaphragm spring or jet changes were needed.

The Fix: Cooling
Arentz’s engine coolant temperatures were running slightly hot, 200 degrees or higher. “This is an old carbureted car; they want to run at 160–180 degrees,” Norm maintains. “We want to keep the cylinder and exhaust temps down to make everything live longer. We don’t want to burn up the oil, which runs about 40 degrees hotter than the coolant. Today’s fuels also run hotter. Old down-flow copper radiators begin to run into trouble if the temperature gets up to 210 to 220 degrees—they just can’t keep up.” In sunny SoCal, Norm’s fix was simple: Gut Arentz’s existing 180-degree thermostat. “We don’t want to remove it completely or water will flow too fast through the radiator. The remaining¹¹ thermostat rim serves as a slight flow restrictor.”

The Fix: Hoses
During the diagnostic and tuning process, Rollings’ crew observed several misrouted or incorrect engine-bay hoses. Sticklers for perfection, they also went the extra mile and corrected the observed hose faults.



The Results

The choke operates fine, the off-idle stumble is eliminated, and the car no longer bucks and surges. Coolant temperatures so far are holding at 180–185 degrees Fahrenheit without the need for any fancy fixes. Arentz says, “The car drives like a dream.”
Lessons Learned
“This is a way we’ve been successful on mild old street drivers. It’s a simple method anyone can duplicate.” — Norm Rollings, Rollings Automotive
Many roads lead to Rome, but these basic techniques can be copied by anyone with a mild motor and at least 12 inches of idle vacuum. “All you need is a vacuum gauge, a timing light, and a screwdriver,” Norm sums up.

Contacts
Fel-Pro (Federal-Mogul Corp.); Southfield, MI; 800.325.8886; FelPro-Only.com or FMe-cat.com
Gates Corp.; Denver, CO; 303.744.5651; Gates.com
Holley Performance Products; Bowling Green, KY; 800.HOLLEY1 (nearest dealer), 866.464.6553 (tech), or 270.782.2900 (general); Holley.com
RockAuto LLC; Madison, WI; RockAuto.com
Rollings Automotive Inc.; Mira Loma, CA; 951.361.3001; www.Facebook.com/RollingsAuto-2184804125077161/
Scott Drake (Drake Automotive Group Inc.); Henderson, NV; 800.999.0289 or 702.853.2060; DrakeAutomotiveGroup.com
Summit Racing Equipment; Akron, OH; 800.230.3030 (orders) or 330.630.0240 (tech); SummitRacing.com
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