So my non HAMB friendly mullet ride has a 66 327 in it with a holley single plane intake a edelbrock 600cfm and a hei. new plugs wires cap and rotor. full lengthg headers into 2.5" exhuast. pcv sytem and breathers. I have a few issues. but at first i want to let it be known that im not looking to change any major parts on this motor such as the intake/cam or carb. since this motor just has to last me a few more weeks till i replace it. so i dont want to sink a bunch of coin into it. Now here is the problem. i advance the timming a bit and i get really bad spark knock and a little bit more power. I set the timming back and i geta misfire under load onley and the car cant get out of its own way. ive had the idel air screws every wich way but out and it makes little diffrence other then throttle response. i pulled the cap today and made sure there were no burnt contacts on the cap or rotor and all looks good. It seems to run best with lots of advance like any other sbc ive had but this one loves to knock. its not even advanced enought to fight the starter so i know its not due to to much advance. Ive been able to run way more advance with other sbc and not get spark knock. Could the cam be wiped out? the timming chain trashed. im not looking for a huge tear down just something to help me figure this out and make it last a few more weeks. Firing order is right and all plugs and wires check out so i dont know what this misfire is about either. has any one else had this problem? and i checked it for va*** leaks and its good. Thanks Bryan
I'd say replace the rotor, cap, plugs, and maybe wires. But if you don't want to put any new parts in it, **** it, run it with a misfire.
those parts have like 400 miles on them. im willing to do simple things such as that but i dont want to tear into the intake or cam.
there was another thread earlier where we were all talking about "just cause it's new doesn't mean it's good." Maybe throw the old parts back on it to diagnose it? Or just buy the new rotor, cap, all that and try, maybe return them if it doesn't work. I mean, short of the cheap **** like that there isn't much you can do. Next guess would be a well worn out cam.
You can also pull the distributor and check the drive gear and bearings at both ends. If these wear, things get pretty sloppy and all of your issues could be seen.
Sounds like timing, check the distributor to see if the centrifical advance is free and if the vacuum advance is hooked up to manifold vacuum. Use a timing light and watch the marks to see if your getting any centrifical advance as you raise the engine rpm to like 3500 rpm.
Did this problem happen gradually, or suddenly, or did you just get the car running, or what? some history might help. Did you triple check the firing order? have you pulled the valve covers and made sure the rockers are all moving all the way?
If it only misfires underload first check the plug wires to make sure that they are not grounding to the header. It is best to do at night.I would also check the timing chain for slack. put a timming light on the balancer and rev the motor if it retards befor it advances it is bad. both of these will cause low power and misfire under load.
thanks for the ideas guys. it has been happing over time it just keeps loosing more power and ive never been able to advance it real far with out the knock. but the misfire just started the other day on the freeway. ive tripple checked the firing order and checked the wires about 10000 times for worn spots or any area that may be grounding out. and nothing! a while back the balancer fell off it and i had to get creative with getting it to stay on. but i dont see how that can affect it. im going to check the dizzy and the rockers cause im leaning towards a bad dizzy or a bad cam. hell i have a xtra hei i might throw in there to see.
Ha Ha...wonder if losing the balancer 75 times, overheating it and setting the carb on fire did anything to make it run any worse?! Like Gus said, check to make sure both the mechanical and the vacuum advance is working right without sticking or binding (do that trick I was telling you about with a Mity-Vac to check the vacuum chamber and it's linkage). That motor is cooked, though. Driving 15 miles on the freeway with the water pump at a stand-still didn't do it any good, and it was pretty beat before that. You could TRY another distributor, maybe another carb (original recipie instead of extra crispy!) and hopefully nurse it a long a LITTLE further...but that'll just be Band-Aiding it, as you know. (Although it also sounds like you may also have a vacuum leak causing a severe lean condition, especially under load. Dis-similar metals warp and do funny things when they get baked beyond the recommended temperature range...you got an aluminum carb and intake on a cast iron block and heads. Anything is possible at this point. Do a basic diagnostic check and find/isolate the problem(s) and go from there. You know...compression test, check for timing chain stretch, make sure all the cam lobes are still there and the rocker arms aren't too tight or too loose, ignition timing, vacuum leaks, fuel delivery, etc, etc, etc. How's the exhaust? Read the plugs, take it's temperature...the motor will tell ya what's wrong if you know how to ask it and listen to what it 'says' in return!)
Put a breaker bar on the crank nut and check back and forth for chain slack. Simple quick test to eliminate chain slack. Timing chain can cause problems checking things because it is always changing with the slack in the chain. also get some gauges on the thing and quit guessing. Fat Hack probably gave us more info than you did on the problems.
How old is the motor? Burning a little oil? If there is alot of carbon built up in the combustion chamber it could be causing a hot spot and pre-ignitioin. The earlier mentioned abuse.... er use didn't help either. Pull the plugs.... how much gunk is on them?
YEAH!! What he said! Anyways...the pickup coil in the bottom of the HEI is notorious for ****in things up. Sometimes all of a sudden and sometimes intermittent. The knock is most likely as hack said...warped components. Like it or not a manifold swap (even borrow one if ya gotta) might solve the problem. It still pains us to see a 327 "euthenised" tho.
you've got a minimum of 2 problems here. #1- if you adjust the carb to and fro, and nothing really happens, VAC*** is to blame-but it is inside the carb. you've either got a circut clogged, or completely blocked off. this would effect the overall vac*** the motor can produce. #2- check compression-but what you are looking for is not a "dead" hole-what you are trying to find is pressure differences from cylinder to cylinder. chances are pretty good you've got some pretty good ring leak going on. the effect that would have is lower compression-which lends to the spark knock. (not to mention that if the balancer has fallen off,it's probably slipped as well, so you aren't getting an accurate reading on the timing side,either) and are you sure your spark knock isn't an oil starvation knock? it's a small block,it happens...
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