360 issues-need help!

-
D

davezinn

Active Member
Joined
Jan 5, 2006
Messages
42
Reaction score
2
Location
Triangle, Virginia
i just got a '71 Dart with a 360 in it. the engine is supposed to be recently built. it has 10:1 pistons. weiand intake with a carter 750, crane 302h cam, mp electronic ignition with new accel super coil and super stock wires, hedman headers and some other stuff i'm sure i forgot. the trans doesnt seem to have much of a stall converter in it, if at all. the rear is the 8 1/4 with some sort of posi and 3:90 gears. the problem i have is when you nail the throttle from a dead stop or when in motion the car mis-fires badly. some throttle positions are okay and when it doesnt miss it runs like a bat out of hell. it also does not want to power brake, but if you torque it against the converter and then let off the brake and nail it it spins the tires hard and gets pretty sideways. then as the rpm's get up the car again will start to miss. i want to get rid of this problem , but i'm not sure where to start looking or what maybe the issue. any help would be greatly appreciated.
dave
 
So is this engine miss at lets say midrange or high RPM. Try to explain a little clearer at what RPM it's happening and is at WOT.
 
the missing seems to be at mid-range rpm's, but sometimes it happens too at higher rpm, 3500 and up. i did happen to notice that the vacuum advance is not hooked up on the distributor. there does not seem to be a vacuum line loose though that should be there. if this could be the issue where should the vacuum hose run from to the vacuum advance? i am bothered by the lack of torque, which i am assuming is because of the cam, which i think is all wrong for this car. am i wrong on this?
 
Sounds like tuning issue(s). Take a compression reading from it. I agree than cam may too large,but it shouldnt misfire. Is the firing order right? check cylinders 5 and 7 especially. what is the current timing curve?
 
i havent checked the timing yet, i just got a timing light the other day. what is the base timing for a stock 360? i havent done any of this stuff in like 12 years , so i'm a little rusty!
 
sounds like the old carter has a pretty good dead spot in it. a good starting point would be replacing or rebuilding that carb you could also check the timing
 
You dont have a stock 360, so the factory specs means nothing at this point. Start with initial at around 12°, aim for a total of 35-37° all in by 2800. If it's a stock distributor (other than MP) you will need to recurve it to get that. I'd get a timing tape too, unless you light has the dial advance function.
 
hey man check to make sure the accerator pump is set to the correct hole. Also definately get the vac. advance hooked up. If it isnt hooked up then the timing wont advance correctly as you are dumping fuel to her, causing it to trip over itself. Typically it is hooked up to one of the small vacuum tubes at the front of the carb at the base. They are usually to either side of the large tube in the center.
I had to adjust my accerator pump and then adjust the timing and air fuel mixture. Like it was said earlier sounds like you may just have a bunch of little contributers to a bigger issue.

:blob:
 
This may seem like a no brainer, but make sure your plugs are good. Nearly 30 years ago, I had a friend working on a pickup he had recently bought. It was an early 50's Ford that had a 292 V8 swapped into it. He and another friend (both of which, along with me, had been through vocational school training as auto mechanics) had decided that the reason the truck ran so crappy was because the timing chain & gears were shot. They pulled it apart & the timing setup was like new. They put it back together & then called me when they could't get the distributor back in correctly. After I straightened them out on that, they told me about how the timing set was in such good shape & they couldn't figure out what the problem was. I pulled the plugs & the side electrodes were about gone. :banghead: They drug me out to an unheated garage in the middle of winter for this! :violent1:

Sometimes it's easy to overlook the small stuff. :lol:

They didn't hear the last of it from me for a long time!



:burnout:
 
Several things come to mind.. High secondary resistance in a wire or plug, carbon tracking in cap or rotor.... as far as timing goes.... as much as it will take and still start hot then figure how much over the top you are at speed and shorten the curve to the neighborhood of 38 degrees. You do this by shortening the slots the advance weights slide in. As far as vacuum advance ...this is just for part throttle cruise economy and should be connected to ported vacuum for mopar use. Total timing at part throttle cruise should not exceed 45 degrees on stock engines even less on hi comp units if used at all.
 
Sounds like a lean carb mixture, accel pump, and or timing advance curve problem to me. Check the basics and lets us know where its sitting.
 
thank you for the help guys, maybe this weekend i will have the chance to check alot of the stuff mentioned and get this all figured out. i blew the collector gasket the other day, so that will get replaced too. is it possible that the 750 is too big for this engine combo? i have a stupid question concerning torque converters as well. the one i have in there currently is supposed to be a 2000 stall unit. the recommended converter for the Crane 302h cam is a 3000-3500 stall. how would this work with my current combination? would it really help to have this high of a stall? i drive this car around for fun and to work sometimes. hopefully i will be taking to the track for some fun next spring, but it will be a mainly street driven car for fun.
 
Does it only break up or miss when you are getting on it or at light loads as well? If at heavy throttle only, possibly fuel related, but likely ignition. If it breaks up at all throttle settings, almost certainly ignition. Remember, 90% of "fuel related" problems are ignition related.

I would start by doing a thorough tune up including new plugs, cap and rotor (buy a good ones like Blue Streak or Accel), PCV valve, and fuel filter. Hook up your vacuum advance to the timed vacuum port on the carb; on an AFB, AVS or Edelbrock this is the port to the right on the front of the carb. If you look carefully this port will be slightly higher up on the carb than the port on the left. Note where yout timing is at BEFORE you touch anything, and in fact I wouldnt monkey with it yet (assuming its set to about 10-12 degrees initial advance at idle). After each new part drive the car, better? If not, try new plug wires next especially if the existing ones say "supression core". (Accel Super Stock wires are basically OEM grade stuff at best, especially the non-spiral wound ones) No need to spend the megabucks on a set of Taylors just yet, a $25 set of parts house specials will work fine for troubleshooting. Also make sure the coil is bolted down securely and the primary wires are on tight, correct polarity, and in good condition.

Next, and only after all of the above would I start screwing with the carb. Clean, rebuild etc... Pay close attention to the float level (where it is set now and where it should be). If you have a fuel related problem, that would be the first place I would look. Keep an eye out for hackery (modifications) made by the previous owner, as thats enough cam to cause some people to start making carb mods (for better or worse). Also, are you sure its a 750? AFB or AVS? Whats the carb number (located on lower right corner)? A 750 is fine for your combo, but most factory AFB's were a lot closer to 600.

In any event locate and "repair" the problem before you "tune" or you will just chase your tail. Avoid "shotgun maintenance" and make one change at a time otherwise you will never know what was wrong. A higher stall speed will help your combo; less pull against brakes at lights, better launch, etc...
 
You must log in or register to reply here.
-

Back
Top