what happened???

Sorry I'm not disagreeing just trying to helpout with what i've experienced that's all. That's what were all here for.

 

Getting back to the original problem, first post, and dist problem. The breaker plate should move about 6-8* (dist) times 2 for crank degree which would be 12-16*. The heavy spring in the vacuum can will make it hard to move so watch for this. The ported vacuum from the carb will not be there at idle so the dist will not be advancing at idle. With the cap removed, you should be able to grab the rotor and rotate it about an inch +/- (outside radius) clock wise and spring back when you let go of it. This should be the case every time you twist the rotor. This is what advances the cam lobes at the points to give you the needed advance. You can suck on the vacuum tube going to the vac-advance and watch the breaker plate move.

 

sorry I was out so long, had car troubles. My vac advance is hooked up to the manifold and not ported, I have read many many places that this engine should be on manifold and that it was set on manifold from the factory. From what I understand, ported didnt show up until the 70's. I can twist the rotor and it moves as you stated. When I suck on the vac line I get nothing (except a head rush), I am going to make sure it's not hanging up on anything and probably buy a new can.

 

I replaced the vac advance can and got the same thing. it is hooked up to manifold vac, I unhooked the hose from the can to see if the carb was pulling vac, and it is actually "blowing" air out not pulling vac. The ported vac on the carb is pulling vac but not the manifold port, Why in the world would this happen? if anything, I thought the ported pulls no vac at idle and the manifold does. My idle mixture screws are acting up as well. The passenger side seems ok, the engine will stall if you screw it all the way in. The drivers side seems messed up, if you screw it all the way in it affects the engine but will not stall. idle fluctuates and few hundred degrees at idle as well. Idle used to be steady and motor ran good before I got on it at WOT. Any ideas? It seems to drive ok as long as you are increasing rpms, if you try to cruise steady at pretty much any speed it has a stumble/miss kind of thing going on for about one second then picks up and smooths out.

 

I don't claim to be an engine expert but I do not think there should be any positive pressure port or manifold. Do you think that you might have popped a head gasket on the wot run?

 

I dont think so, but im not sure. engine temp is the same at 185ish, no oil in the coolant or visa versa, what are some ways to tell? I am going to double check tomorrow evening to make sure it had positive presure coming from it. I am no engine whiz, but not a total dummy either and I have know idea how this could happen if it is indeed blowing air instead of pulling it. Could a carb malfunction cause this? I will post more confirmed information tomorrow night. thanks for your replies

 

Maybe a broken intake valve? With each upward stroke of the piston, air would be pushed into the manifold causing a positive pressure. A compression check could tell you a lot.

Just thinking out loud...

 

So, I didnt get to spend a lot of time on the jeep tonight but did look it over and the manifold vac port at the bottom of the carb is spitting air out and not pulling vacuum. The ported vac source on the side of the carb IS pulling vac, not real strong vac but it is pulling. It has always been hooked up to the manifold vac port and the timing degrees would rise when I pluged in the vac hose. Checked my oil and it still looks new, checked antifreeze and it looks fine. There are no noises, pinging, knocking. Any ideas?

 

Your ported vacuum is low because your manifold is being pressurized (blowing air) which is not good. I believe you are needing a compression test as stated above.

 

GREAT! I will check with a friend and see if he has a compression gauge I can use, as I don't have one. So what would that mean? Did I blow the motor? I just put like 500 dollars into it for cam, chain, rods, lifters. I have somewhere to start now.. it may be a few day before I can test it but I will post what I find out. thanks for your help

 

Did you check the valve clearance when installing the new cam? Valves don't like touching pistons...

 

Just to make sure I’ve got this right, you say it doesn’t idle right but pulls fine when given a load? And by “fine” I mean no misses, fires cleanly on all cylinders? But then off throttle is where you feel it starts missing?
This all started after cooling off from a big heat cycle?
Then after looking into it you found a vacuum port that is blowing air?
I tend to doubt it’s a broken valve spring or bent valve because it would run like *** everywhere not just off throttle.
Dunno, this is a head scratcher but a compression test would be worthwhile, if for no other reason than to eliminate an issue inside the cylinder.

 

He’s working with a Gen I 327 SBC HO with the Camel Back heads.
His cam lift is below .500” valve lift so unless he’s running huge dome pistons, and since he’s also running pump gas I doubt it, or the valve train is way out of time there shouldn’t be a valve clearance issue. Not saying it isn’t the case here but I’ve been through a few of these engines now and never had a problem with it as long as valve lift isn’t any crazier than about .500-.550”.

 

Well, by fine I mean it feels fine. It is hard to hear the motor over the fenderwell headers to muffler exhaust, but it feels pretty smooth with acceleration. If you lightly accelerate it will miss, on a fairly heavy accel it feels ok. If you rev it up at an idle, it may sputter for a sec then revs to the moon smoothly. Im wondering if it in the carb?(same carb that I was told needs replaced) most of the time I give it gas it has a sputter then smooths out and gos. Yes, this all started after a hard run, and it was running so good before that. Noticed it the next morning when I was going to drive it for the day. The ported vac port on the side of the carb is pulling small amount of vac, but the manifold port on the base plate on the front of carb is blowing air not pulling vac. I have tried adjusting the carb and that helped some, but the drivers side idle screw didnt seem to have much affect on it. Gas fumes are bad, and it is using a ton of gas. I am basicly driving it with no vac advance to the dist right now until I get this figured out. Oh, and the timing is still set a 12* btdc.
I am going to borrow a gauge for the compression test just to check it out. Thanks for all your help

 

Driver's side induction air leak. Do a propane enrichment test around gaskets and manifold runners to see if idle suddenly smooths out.

 

Holley DP carb right?
I don’t know nearly enough about them to comment.
Patrick had a good point right off the bat, when I’m lost on an issue like this I try to just get back to the basics. Points, reset dwell, if not outright replacing them it doesn’t hurt to pull your spark plugs to have a look at how things are burning. Since you suddenly have gas fumes permeating and its guzzling gas I wouldn’t be surprised if you didn’t just foul a spark plug.

 

Problem here is that a fouled plug won't pump pressure in a vacuum chamber. A broken valve spring that won't close an intake valve all the way will.

 

Yes, it is a holley 650 DP. I have the carb off already to look it over, but I will do all the above suggestions. pull valve covers and look for broken valve springs, do the propane or starting fluid around gaskets, pull the plugs as soon as I get it back on. Walt got me thinking about something with his suggestion that a broken valve spring would allow presure in the vac chamber. The air coming out of the carbs vac port seems to be in phase with the sound of the exhaust rhythem. Is it esay to see a broken spring or do I need to look very closely? I am going to borrow a compression gauge also as soon as I get over to my friends to get it, Probably going to be a few days though, but I will do the above over the weekend first.
You guys dont know how much I appreciate your help, I dont know much about how all the internals of an enginge work together, or how x causes x to do y. thanks

 

Agreed, and that is confusing.
But I've been through a couple of broken valve springs myself and never had one that would clear up and fire all cylinders once off idle. In fact my experience is quite the opposit, I could actually get it to run decent at an idle but as soon as given a load it would run like trash.

 

Checking valve springs: I'd look at each one closely by bumping the engine around just like when lashing the valves in. In other words start with #1 cylinder exhaust valve and bump the motor around until the #1 intake valve goes full lift then starts sitting back down. This ensures the cam lobe is pointed away from the #1 exhaust lifter. For the #1 intake valve, bump the motor around until the #1 exhaust valve just starts to lift, for the same reason. Do this with each cylinder to inspect the valve spring at its tallest height.