Thanks, figured it wasn't enough for an exact answer but worth a try.

 

Actually, I admit to writing my response without a whole lot of thought, but you might find this interesting. Skip down to the section on Fault Finding and Diagnosis and then skip down again to the part on Dynamic Compression Ratio.

Compression ratio - Wikipedia, the free encyclopedia

I think I need to read it again myself... LOL

And I think there's a ton more info if you Google Dynamic Compression Ratio. I seem to remember I did find a Dyn CR calculator on line and I had to enter various cam info, but it never yielded what I was finding in practise, so I left it alone at that point.

 

Lol the wiki...guess I just skimmed over that last time I read it. I understand and know how to calculate SCR and DCR but never paid as much attention to the cylinder pressures. Good read. makes sense.

 

Ok guys this dang thing is still being a pain i have everthing timed right as far as i know and tried differnt combs on the edelbrock and it still is poping and conking out going up hills or just getting on the throttle fast so i dont know could i get some help please i love my 390 but if it keeps this up i am going to lay her to REST for a while

 

If you have your carb too lean, it will backfire through the carb when accelerating.

 

I've gone back and re-read the thread. It appears everything was fine until your tach started acting wonky and you replaced the distributor.

After that, timing appears to be the problem, which is understandable with the dist having to be replaced.

I'll mention a few things about timing, but first (and please don't be offended), but maybe you should check the ignition wires are all in the right order. If you get two mixed up, odd things can happen depending on which two got swapped.

I just find the wire to #1 plug, and then keep going around the dist cap, making sure each successive wire goes to the next plug in the firing order:

15426378

Now to clear up one little point. Bear was correct about timing when he said that when the exact timing requirement is unknown, forget about intial timing (the 8, 10, 12 or whatever you get at idle) and focus on having the maximum "mechanical" advance being around 36 deg BTDC.

Based on one of your comments, you actually adjusted the timing so that you got 36 deg max with the vacuum advance adjusted. That's not quite right. The timing can be higher than 36 when the engine is not under load and the vacuum advance is maxing out.

Temporarily disconnect the vacuum advance hose, and use your timing light to make sure you don't exceed 36 deg when the mech advance is used up.

If you have points, there's a fairly easy way to do this other than holding high rpms and watching the light.

With the engine off, rotate the crank until 36 deg on the balancer lines up with the block pointer. Doesn't matter which stroke you're on for this. Next pull the coil wire from the coil, and insert an old sparkplug wire. Put a sparkplug in the end and lay it on the block so it has a ground. Turn on the ignition. Now, with the dist cap off, rotate the rotor button fully CCW. The points should open and the spark plug should spark just as the rotor button comes to a stop at full advance.

If it doesn't, rotate the dist housing until it does. Make sure you don't accidently move to the next lobe on the dist. What I mean by this, is that when you're finished this adjustment, the rotor button should still point to either #1 terminal on the dist cap, or #6 dependant on which stroke you were on.

Next, hook everything back up, except for the vacuum advance hose. Start the engine and using your timing light, find out what the timing is at idle. You can then use that number as a reference for future timing... if the next step works out.

Connect the vacuum hose back up and go for a drive. Don't force the engine if it seems to fight you and not want to rev in case the vacuum advance puts the timing way over the edge, but chances are it won't, and worst case might be a bit of pinging under load.

BUT I can't CAUTION you enough. If the engine seems like it doesn't want to rev, your timing may be way to high and if you try to push the engine, you can break a piston. Ask me how I know....er, or maybe not.... Pinging is a much less serious version of this.

If it pings, you have the luxury of backing off the vacuum advance via adjustment. If you can't totally eliminate the ping, back your timing off 2 degrees at a time until it doesn't ping any more by rotating the distributor. (Use that timing number reference you wrote down and re-adjust for 2 degrees less).

Now if you've confirmed the ignition wires are connected up right, and have set the timing as described (or you're happy with the timing you currently have, which sounds close), and you still have a problem, then you may have the unlucky co-incidence of two simultaneous faults. So start with the easy things, such as checking the sparkplugs.

Other things would be ignition wires, dist cap (did you get a new one with the new dist?), and rotor button. Look for carbon tracking on inside of cap and top and bottom of rotor counter weight.

You might even want to check yoru fuel filter, but my experience with a plugged fuel filter is that the engine simply starts to lose power when going uphill. No pinging, banging, or other noises.

As far as the carb goes, your problems currently seem to be under load (when going up hills, etc.), and I don't think the idle circuit does a whole lot there. So that leaves the jetting, which isn't adjustable (unless you change jets). It workd before, so no need to change jets, but maybe clean them. And that brings up that if it is carb related, it's most likely dirt somewhere and the carb should be cleaned. And then there's the blown power valve (if your carb has one...I'm unfamiliar with it).

For now, I'd say get the idle mixture set right (peak manifold vac or rpms with mixture screws) , and then exhaust all other problems before tearing into the carb. You don't want to add a carb problem to what you have already, which can be quite easy to accidenlty introduce... well, easy for me to make a mistake with a carb, so I assume easy for all... LOL.

I wish I could help more, but troubleshooting over the internet isn't very easy. Video can help a lot, although we need to hear the engine too, and engine audio never seems to come out clear with these type of videos. But maybe you can try to take a 10 or 20 second video and post it.

Good Luck, and don't quite give up yet.

 

OK thank you for the write up i will take it to mind but some of you will think i am an idiot, but guess what i poped the dist cap off and turned the engine over to check the points and they were almost ready to be closed all the time way out of tolerance so fixed that and ran great didn't try and conk out going up hills but still had a ping only when i opened the secoundires up well changed the jet to the next step bigger/richer and still ping a bit well so i finally get smart and get the timing light out and shoot it which this amazes me how does my timing get clear up to 18 degrees initial? it was set perfect at ten last time i checked and after tight the set bolt for the dist was still set at ten so does any one have a idea of what would do that? (sorry i feel stupid guys i am just trying to learn i am 18 love my fe"s and trying to learn them lol) And why do my points slip and get out of tolerance any tricks of the trade to make them stay? the screws where all very tight.

 

Point gap too close/wide will affect the timing. Always check point gap, and set to spec before adjusting anything else igintion related.

 

And to think I thought I covered it all! Silly me. Oh well, maybe it'll help someone else who reads this thread some day.

Yes, Rogue_Wulff is right, a change in point gap affects timing.

Your points may have been like that since you bought the new distributor, or they may have been some intial rubbing block wear. Might want to check the felt in your new dist is lubricated. I just use a few drops of motor oil.

But regardless, you seem to be very close.

By the way, if you didn't have ping before all this mayhem and were using this carb all along, maybe it would be best to still focus on timing and assume the carb was fine the way it was.

Please continue to keep us informed. It will be interesting to see what your final solution is.

 

Argess, doesn't this all sound too familiar??? Remember back last month when I posted on this type of problem? After I went through a myriad of things and the problems seemed to keep cascading I gave up and took it to an old wrench turner. After I spent $300 with no resolution, he switched the vaccum to port and adjusted the timing, and carb settings and VOILA' she purrs like a lion now.

He told me that the timing was basically set to full advance at idle and the vaccum was hooked up wrong so that is why whenever I got into it hard it would bog, hick up, back fire and die. As long as I babied the throttle it was fine. Now, I can dump the pedal and she roars.

So I would try port vac and then adjust your timing and carb settings for starters.