Gents, I've got a '68 Wagoneer with a Buick 350 from the factory; the engine has been replaced with the same from a '72 Le Sabre, but with a 4-barrel intake and Quadrajet. It is driving me nuts - I wonder if you could give me an idea of what's up with it. Started some time ago - sputtering every now and then, and sometimes backfiring through the carb. At first, it would go away when the engine got warmed up; now it's always there, to the point that anything other than slightest and smoothest gas application causes backfire through the carb. What I've done so far to address this... - mechanical fuel pump replaced with an electric - plenty of fuel coming out of it. - carb - Quadrajet - taken off, top taken off it, jets cleaned up, new accelerator pump and gasket installed. There was a little fine sediment in the bowl, but nothing seemed too bad. Filter replaced just in case. - ignition: MSD6 running off points; I've reverted to points-only today to make sure it isn't an ignition problem. Seems to be okay. - spark plugs: pulled out three at random - squeaky clean. Before it all started happening - it used to diesel a bit after ignition-off; the anti-diesel solenoid is dead, so the throttle stop has to be a bit above the butterfies-fully-closed position. There was a hint of a flat spot, about where the secondaries should've been kicking in. Otherwise - no detonation, and very smooth. Any suggestions?
How's your timing? Have you checked your valve train? I have had backfiring problems thru the carb. when one of those 2 needed addressing.
hi John, timing seems to be near perfect - about 6 deg BTDC, rock steady; the only thing I can judge the valvetrain is by vacuum reading - 20-21 inHg steady at idle. It is the very first engine in my life pulling that much vacuum. It feels like if I were _very_ gentle with the gas pedal, pressing it slowly and gradually, it would work great. If I pressed it a bit more aggressively (not even stepped on it, just increased the rate), it would pop through the carb. The obvious thing - accelerator pump - is and was working okay. I've replaced the plunger, just in case.
How many miles are on the engine? Sounds like you have carboned valves or carbon build up on pistons causing pre-ignition? Is the engine burning oil? Does not sound like your ignition. Did you remove the plugs and verify conditin (fouling, carbon build up, porcelin discoloration, bad/worn electrodes)? How about wires? New or old? You don't have a fuel problem. You have an pre-spark or spark problem(firing late/early)
ok, a little update. Got a new coil on my way home last night, at least, to eliminate coil intermittent failure, and put it in. Could not check much - I made a mistake of buying a stock coil, and running it off MSD6A box caused arcing from the center electrode to both low-voltage terminals. The feeling was the same - sputtering under light load. Will get a 12V coil tonight - any suggestions on what to tell the parts counter guy? (Year/Make/Model?) How many miles on the engine? Absolutely unknown. The engine came from a '72 Le Sabre, and seemed to be in top condition. It does not run rich, and did not seem to have run rich in its past life, so I am not sure about the carbon build-up. It does not burn oil, except for a little blue cloud upon cold start-up. I've pulled three plugs within the easiest reach - they seemed to be in absolutely top condition (very lightly beige insulators, nearly white) after about 5-7kmi since I put this engine in. Wires are less than a year or ~10-12kmi old. Don't remember brand, but nothing fancy - stock replacement set. I may buy a generic MSD V8 set tonight and replace them all - is there any less expensive but decently performing alternative? I don't necessarily need low-resistance wires with MSD ignition box.
Problem solved. It was nearly as dumb as it gets - which I suspected from the beginning. After it dawned on me which year/make/model to specify at the parts counter to get a 12V, low turn ratio ignition coil (FYI: 1989 Land Rover Range Rover), I got my coil and went to work on the jeep. Replaced the coil. Okay, no more sparks flying everywhere. Pulled the driver's side spark plugs. All in excellent condition. Checked the compression - 155 to 170 psi in all cylinders. As I pulled the wires from the plugs, one completely separated from the terminal - so, since I had a set of Autolite wires sitting around, I decided to replace them all. As soon as I replaced 4 wires on the driver's side, miss and backfire was gone!!! It was a classic case of 5-7 crossfire. As silly as it may sound, the "old" wires were not even a year-old; those were, I believe, Borg Warner 7mm stock replacement issue. Never again! So... with about $100 in the hole, I have now an electric fuel pump, cleaned Quadrajet with a few parts replaced "just in case," brand new proper ignition coil that is not likely to kill the MSD box again, a brand new set of wires (with a seemingly-better terminal crimping job and thicker insulation) and nicely-running Buick 350. Thanks all for your input, p.s. if you ever were to do away with a mechanical fuel pump, the block-off plate is labelled for a big-block Chevy.
What does that mean???o No: "12V, low turn ratio ignition coil " Do they make a high turn ratio coil. Makes sport cars turn n spark better? Ok I am not being a smart:moonu: but just wonder what that means or is? :beer :beer
Sorry for not having replied earlier - was out of reach of nearly anything. Most coils have turn ratio between 70 and 130; the higher is the turn ratio, the higher voltage one can expect at the coil's output. Higher number of turns in the secondary winding of the coil mean two things - higher voltage output, and higher coil resistance. Higher voltage will only help in high-compression engines, but ONLY in conjunction with higher-grade ignition wires with thicker insulation, fatter spark plug boots, and larger distributor cap. Case in point - jeep people with AMC engines replace stock Motorcraft distributor cap with a much larger Ford cap. Otherwise, higher voltage will lead to arcing everywhere possible - in my case, from coil's high-tension electrode down to low-voltage terminals, and cross-firing between two spark plug wires. Low primary winding count also has a number of consequences: higher output voltage of the coil (see above), and lower resistance and inductance of the primary winding. Lower inductance of the coil allows it to produce spark up to higher RPM, but makes it less efficient at low RPM (unless electronic multi-spark ignition like MSD6+ or Jacobs is used). Lower resistance of the primary winding puts more stress on points or stock electronic ignition (also, units like MSD5 or Pertronix). The combination of the above factors in an MSD Blaster coil killed my MSD-6A box - mind it, these two units were supposed to work with each other! I am happy that I caught the arcing this time, before it had a chance to fry the ignition box again. Now, coil voltage: most round-can ignition coils were designed for vehicles with point ignition, or simple stock electronic ignition. The design stems from ages of 6V electrical system; the newer 12V electricals were used to the advantage of easier starting: the coil was provided with full 12V during starting, and after the engine is started, the coil is fed through a resistor limiting the voltage to something between 6 and 10V. A 6V coil will have lower primary winding turn count, and higher turn ratio. It would have been okay with stock wiring (with limiting resistor), but no more with MSD-6A box.
