|
ChadS
11-28-2004 08:22:13
|
|
Re: Allan in NE-carb photo in reply to Paul Shuler, 11-24-2004 22:04:18
|
|
| |
Sure is a good looking engine! I think you have a combination of problems going on here. Been dyno tuning engines for years now,, Auto engines, and tractors, here is few things to ponder over in what I have learned on tuning an engine in... Basicly, it is all standard procedure, in order to diaginos the problem, you have to know a few important factors. Then, once you have the cause, the cure is simple. Youll fight it,, trust me you will, LOL! My honest opinion, the Edlebrock version of the AFB is the simplest carb to ever have! When they say, jet it, and forget it, they mean it. This is a full mechanical carb, should be no vacuum accesoires to run anything for the metering stems. Most carbs like this I have ever seen has the counterweight balance to open the metering stems inthe secondaries. It is a good system. But like most aftermarket carbs,, you cant just bolt em on, and run them, they have to be tuned for the engine. Hopefully your carb checks out, rebuild kits are simple, it is easier to tear em apart, and replace the parts as you go along, aint alot to em. But, to me, a backfire, and especially on acceleration, is not a fuel problem, it is ignition. If you have put in a cam, and you have an aftermarket intake, and carb, you picked up alot of different running factors that have changed VS a bone stock, cast iron, quadra jet factory set up. First off, you have picked up alot more volume in the intake, so it will need more fuel, check you plugs, they will tell you if you are getting enough gas to it. Hesitations caused from the carb, well, they should just hesitate, like you are running out of gas, not pop out the carb, or the exhaust. That is why I say its ignition. Here is a few reasons, engine backfire through the carb,,VACUUM LEAKS, an intake valve too tight, the distributor is worn and loose. Coil and electronics are shorting, or failing, spark plugs not at proper gap, timing not set for the rpm range needed for the torque curve. If the intake valves are too tight, itll pop through the carb only upon a lug of the engine, or sudden acceleration. Itll seal upon idle, no load, but you give it the gas, and take up more gaps in the parts, .001 can be the factor of the valve being too tight, or just right. Usually, I set them to when its running, I loosen them tillthe click, tighten it till the quit, then 1/8 of a turn more onthe nut. That, I have found works well, and does not collapse the lifters. Put a vaccum guage on it, see if it is a steady reading. That will tell you if you have a leaking valve, or a vacuum leak. If the igntion timing is set at stock settings, and you have installed a bigger cam, then you have to change the base timing too. That will cause it to pop out the carb, upon acceleration, the mechanical advance in the HEI, will activate, and over advance the timing, causing a pop out the carb at certain rpms, or acceleration. it activates the igntion too early is what I am trying to say,,,, I am not a fan of the Accel super coils and caps for the chevy. I tried to run one on a drag car, and it was junk! Kept shorting in the cap, shorting and burning the rotor carbon tips in the cap. I chased that ghost for a week! I thought since it was ACELL, it was good. Nope, not the case. It takes alot of grease to ensure the Accel system, not to short out in the cap, inside the cap where the coil sits. Grease is the only thing I found that kept it sealed under the cap. Spark plug gaps could be off a tad, if the coil is working, it has a hotter spark at the plugs,, so you can open the gaps up a bit, a combination of plug gap, and too early of igntion timing will cause preigniton. POP out the carb. Try setting the timing by ear, at 3500 rpms, then see how it acts, you want a solid tone out the exhuast, no little occasional puffs, or pops at idle, that is a sign of the timing too advanced. Hope this helps a bit, I have never ever seen an engine,, freshly rebuilt, to specs, that did not have to be retuned, and retorqued, and rechecked, to make it right. and when aftermarket parts are used likr the intake, carb and igntion you are using, it makes it tougher to find it. ChadS
|
|
|
