I have a ’74 Duster with a 340 and a 727. My problem is that my lights flicker. The headlights, parking lights, and interior lights all flicker while the car is at idle. I do have a Purple Shaft cam, which makes it idle rough. I have replaced the alternator three times, along with the voltage regulator, headlight switch, dimmer switch, and voltage limiter. I have also replaced all the grounds, battery, battery cables, and checked all the wiring to no avail. Lights will brighten up when you speed the engine up. Any help would be appreciated.
Gilbert Tilghman - Via moparmuscle.com
Gilbert, I’ll bet if you put an analog voltmeter on any of the electrical circuits, you’ll find the voltage is not stable, but rather varying at idle. The stock charging system is deficient in several areas, and both the age of the electrical system, and the unstable idle from your big cam, exasperates the problem. The charging system is not able to keep up at idle, so it is probably undercharging the system, and with the choppy idle, the undercharge condition is not stable. Not only is the alternator marginal, but the wiring system in the charging circuit is barely adequate in stock form, and gets worse with time. All of the charging current goes through the bulkhead connector, and then through the Ammeter to the load side. As the connections get more resistance, you get poor charging performance and heat buildup that eventually burns up the wiring.
The best solution is an alternator and wiring upgrade. The simplest upgrade is to use an 87-amp alternator from a late-model M-Body application, which will bolt to your stock small block brackets, though some belt adjustability is lost. There are other alternator upgrades on the market, or you can fabricate your own to use the heavy duty Bosch or Denso alternators from a pre-Magnum truck application. Any of these alternators can be controlled by the stock style regulator. Upgrading the wiring can be done as simply as running the output (battery) terminal of the alternator directly to the battery lug of the starter relay and bypassing the OEM Ammeter wiring. You’ll then lose the factory Ammeter, so the common solution is to run an aftermarket voltmeter. Finally, optimize the electrical connections, especially at the bulkhead connectors by cleaning the terminals and making sure they are tight, and coating them with di-electric grease when hooking them back up.
I have a ’74 D100 short-bed truck with a 360 engine and 727 transmission. The engine features 10.0:1 compression pistons, a Comp XE268 cam, Edelbrock heads, Summit headers, and a Performer intake manifold topped with a OEM Carter Thermoquad from a 1974 440. The problem I have is the truck will bog off the line. I fully rebuilt the carb, and have worked on tuning it, but haven’t had any luck getting rid of the bog. If I really stomp on it, the engine will actually die right there on the road. I tightened the secondary air door a half a turn at a time, and it doesn’t seem to help. I went as far as five turns, and it is still bogging. I’m about to toss this Thermobog in the dumpster and get something else. Any ideas?
Frank Coin - Via email
Frank, the Thermoquad is a complicated carburetor, and is sensitive to many factors, all of which can make it bog. The first thing to do, is go through all of the adjustments step by step. Most guys will skip over many of the adjustments when rebuilding a carb, but you need to have every one of them dialed in. I would set the air door at two turns to start, but it is vital to make sure the air door open position, and the air door closed clearance on the pull-off are at specs. Make sure the pull off dashpot is plugged in to vacuum and the diaphragm is working, since the dashpot is critical to the secondary operation.
The next area to look at closely is the accelerator pump circuit. Make sure the pump is working properly, and that you are getting a good pump-shot as soon as the linkage is moved. If there is any lag here, you are going to have a bog. To work properly, the pump well has to be smooth, not pitted or corroded, the check valve at the bottom has to be good, the actuation spring has to be good, the check needle under the discharge nozzle has to seal perfectly, and the plunger height has to be at spec, or slightly higher. There are a lot of potential failure points here that can cause an inadequate pump shot and bog. If everything is perfect, you can enlarge the discharge tubes in the cluster to quicken the pump shot timing.
I have a ’65 Barracuda that is mostly original, and very tired in the motivation department. I would like to rebuild it with a little extra power without changing the original look. I’ve been looking at stroking with either a 360 crankshaft, or with one of Mopar’s forged crankshafts, but have not been able to find pistons that will fit. Can the 273 be bored from its 3.63-inches to the 318’s 3.91-inches, or does anyone make pistons that will fit a stroked 273? Also what do you feel would be a good cam? This motor has a four barrel Carter. What do you feel would be the best—and preferably cheapest way to make some decent power, while retaining the most stock components?
Dominic McGrane - Via moparmuscle.com
Dominic, you are not going to find any stroker pistons for the 273, but you can always have custom pistons made. The 273 will not bore out to 3.91-inches, and really there is no need to. If you want to up the cubes, a 318 engine block can be picked up dirt cheap, and there are stroker pistons for that engine at a reasonable cost. Such a swap would be the most cost effective approach.
If you want to stick with the 273, I would suggest just doing a basic rebuild on it with a mild cam and headers to improve the power. The stock 273 heads can be improved with a good valve job and basic porting. The heads are unique, and have a special intake bolt angle that differs from the more common later heads, as well as very small chamber required to maintain the compression ratio with such small cylinder volume.