I took my truck for a drive on Saturday, I knew the engine was tired but I was cruising at 50Mph and suddenly the power died off, I had a 3ft flame countinuous out both exhausts and things sounded bad. I backed the throttle off, things came back to normal and I drove it home without further incident but I have now lost considerable oil pressure, compression and a now have a severely shagged out set of mufflers (they were old and rusty but now, well....).
I assume the Holley must have had a temporary fail on the powervalve or something stupid like that but it seems my engine rebuild is now upon me, what mods are good to improve a 318's economy (cam, valves etc?) and it it practical to multipoint fuel inject this thing (Magnum top end?)
The BEST way to improve the mileage on your engine would be to dump the Holley carb and put on a good Carter AVS or AFB. I know that's going to cause a flame war given the the Holley has spent millions on the auto mags trying to convince everyone that it's the best carburetor company but I've run dozens of both brands on every Mopar engine from the 273 to the 426 Hemi and the Carter carbs ALWAYS out-performed the Holley 4 bbls. For example. I bought my 383 Challenger with a 750(?) cfm Holley on it. but it hardly ran when cold, the transmission didn't shift properly and it only got 7 -8 MPG even after it was warmed up. Holley at that time had the fuel inlet on the wrong side, no provision for the kickdown linkage, and no way to connect to the in-the-manifold choke. Holleys' mechnical secondaries also don't work well on Mopar engines. Carbs with properly adjusted vacuum secondaries work MUCH better! I pulled off the Holly and put on a 750 CFM Carter AVS off of a 440 and the choke now fit and worked, the transmission worked properly since the kick down linkage could now be hooked up AND I started getting 15 MPG (as long as I keep my foot out of it!) I bought that car in 1978 and I still have it and it still has the same carb on it! The ONLY Holleys that I run on my Mopar engines are the factory 3 x 2 bbls on my Six Pak motors.
But it sounds like you need to find out what happened first. I'd start by pulling all the spark plugs and checking them for anything unusual in an attempt to find which cylinder(s) had the problem. Even if it's a carburetor problem, you'll probably see signs of flooding, excess fuel or something on the plugs. If it is a carb problem you can follow the intake manifold runners back to the carburetor barrel(s) that's causing the problem. I'd also run a compression tests on all cylinders to be sure that you haven't blown a piston or a valve.
If you're thinking of Fuel Injection, check out the MegaSquirt system. It's an enthusiast designed FI controller that's completely programmable and you can use many different types of injectors and sensors with it. FI usually won't get significantly better mileage or performance over a GOOD carburetor system but it does stay tuned longer and does have better cold start characteristics and is more easily adjusted since everything is controlled electronically.
My thoughts (non-brand specific) run more like a dropped valve or timing issue. I would think a carb dumping fuel would give you lots of black smoke and rough running (rich to very rich). Fire out the exhaust would only occur if the exhaust system were hot enough to combust the unburnt fuel, which from recollection of the old days didn't happen all that often. Being that you say things got better when you backed out of it, I'd suspect a timing issue, that was opening an exhaust valve early. This leads to the cam, distributor, vac advance and other timing related things. I do agree with the previous poster that this will require some detective work, you might not have a big problem now, but let it go and you soon will.
Thanks for the advice guys, the problem is already bad so I will just reco the engine and go right throught it tip to tail. The distributor is something I'll look closely at as the mechanical side of the timing seems ok but once I have it stripped down I will know more. The Megasquirt system is something I'll definently look at plus I'll look at the possibility of finding magnum parts or a complete engine locally and I'll post pics as I go along, the timing of the fault is a bit of a pisser though but we'll find what we need and the Dodge is just going to have to go off the road until further notice.
I can use the Jeep, yes but it dosen't have the same feel on the road and I suspect it would get a little upset about 1 ton of generators, welding gear and tooling sitting in the back that the Dodge usually has lurking in it, although, maybe it's worth a try to fit it all in??
my 2 cents on carbs is different. I run a "B" engine (400 cu in) in my 71 dart. I found in the past that if you runa stock..ish engine a carter avs or afb is fine. They work good and give resonable fuel mileage. IN my case tuough with the heavy cam and the high stall converter the 750 carter won't cut it. It does not deliver enough fuel on the 4 bbl side. runs really crispy on the primary side. Did some rejetting etc.... did not work. Put on a Holley, 750 double pump and wow! It comes alive. No hesistation and oodles of power. I know in my past Holley has 2 bit me, they always seem to need to be tweeked but for heavy cam cars and trucks Holley deliver the goods. (I raced my Dart for 3 years and did lots of playing.) High lift cam, 4500 stall converter 391 gears, for me this was the best setup for me. I found out from tuning another car that had the holley 4 barrel throttle body injection, that it was slow to repond. A carb is instant when you hit it, but EFI is not instant. Just had a 1/2 sec or so pause before it would go. Takes time for a computer to adjsut to radical throttle changes. ..... just me 2 cents.
Your problem does indeed sound like a timing issues, most likely ignition timing. Severely retarded ignition timing can cause un-burnt and burning fuel to enter the exhaust system. The symptoms you describe are severe, but possible. I had it happen with a Corvette I owned that had the Hooker side pipes on it. The engine was running like crap and I was trouble shooting it in the driveway at night. Flames were blasting out the pipes as I got on and off the throttle. Turned out to be the distributor was loose and had turned.
I've had good luck with most carb brands. I drag raced (Fords) a lot back in the late 70's early 80's and had great luck with Holley's in that app. On the street . . . . Not so much. Holleys are great at delivering mixture at WOT. I find that they can require constant tuning for optimum street performance.
Carter AFB, great street carb, not bad at the strip either (ran two on a 289 with good results). The Thermo-Quad never really caught on in my circle. I tried one once on a 383 and it sounded great, but didn't perform that well. However, I never really learned to tune one.
Now for the two odd balls. . . . . .
Best all around street/strip carb for a small block? Autolite 4100. Simple to tune, super responsive, super reliable and super efficient. Of course, it's only rated at 480CFM in most forms. However they were made in 620 CFM for BB Mercs.
Next . . . everyone's carb to hate.
The much maligned Rochester QuadraJet. IF. . . . IF you could tune one to your particular engine build, it'll run rings around all others. and get way better economy. The key is being able to tune one. Not an easy task. Fortunately I knew one of the guys that designed it, (yes, I grew up in Rochester NY). Imagine the contempt from my Ford buddies when I lifted the hood on my 67 Mustang to reveal a GM "Quadra-Junk"! (Never-mind that Ford used them on the 70-71 429 CobraJet). You could bring home 15-18 mpg on a BB with one, and still kick everyone's a$$ when push came to shove.
My built 289 4spd Mustang would get 25mpg at 60mph with 4:11 gears on the Q-Jet. Much less when I got into it. A Holley 780 was lucky to get 12 mpg in on the same engine.
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