I started going through the engine and tuning things up and have ran into an issue I'm stuck at. Flushed the coolant, changed the oil and put new plugs in as soon as I got it home. It has a holly 600 carb so I did my research on how to set that up the right way. Adjusted the electric choke, check air/fuel mixture, checked float and still had back fire through the carb at times, mostly start up and low idle. The HEI coil went bad so I replaced it with the original distributor with points, added the coil and regulator but still have issue with it back firing and running at low idle. At high idle it is fine but once I put it in gear and the idle drops and it has a stumble. I drove it down the road about 200 yards to see how the trans would shift, shifts fine but has trouble going up the hill in front of my house. The next thing I am going to do is pull the valve covers and check to make sure that the valve train is working properly (possible stuck valve?) but wanted to see what you all thought before that. Also, valve cover gasket recommendations would be greatly appreciated, cork, rubber or blended. Thanks in advance folks.
Jeremy

With no idea what year, or how many miles are on your 318, we are just guessing.
Backfire at idle with a stumble, and low power could all be caused by a vacuum leak. A 600 Holley on a 318 means at least the intake has been changed, and 600 Holley's are known to have warped cab bases. Start by looking for a vacuum leak. Base of the carb, throttle shaft bushings, intake to head gaskets.

Maybe it just needs a new carb.

No where am I reading where your ignition timing is set. Its not unheard of to have the balanced slip on high mileage 318s, try bumping the ignition timing up a bit and see if that helps. Sometimes a little extra ingition timing helps a lot, and sometimes it doesn't make any difference or it may even make it worse, but its something easy to try.

The next thing for a high mileage 318 could be a loose timing chain, it may need a new timing chain and gears. Gene

It is a 79 engine but I am not sure of the mileage on it. It does have an aftermarket intake and headers as well, I'm not sure if the cam was changed but it does sound like it. I checked all the vacuum lines and then checked the carb and entire base of the intake for leaks as well but I couldn't notice any difference in the idle while doing that (carb cleaner while it was running). I haven't gotten a timing light on it yet but I put the old distrubutor on it and adjust the timing back and forth until it was in the middle of impacting the way the engine ran. I will get the timing set and then check the timing chain. With not knowing what the engine has had done to it or the condition of the internal workings I am considering pulling it anyways. I wanted to wait a bit longer before doing that but it may get shifted up higher on the list. Thanks Gene,
Jeremy

You made a good start. Get that timing checked soon, and then I would try and do a compression/leak down test. Wonder if you COULD have a burnt valve on older engine like this.

I checked the compression and have 145-150 for 7 cylinders and 135 for one. I also pulled the valve covers off and turned the engine manually to make sure all the valves were opening and closing but who knows what the valves look like in there. I am pulling the front end apart this weekend to check the timing chain and then reset the timing to see if that helps. If not I will pull the engine and just start at the top and work my way through it. When I changed the plugs you could tell the engine hadn't been taken care of in a while either. I've been doing some price checking and if its anything major i think it is 360 time for old blue.

Try a new cap and rotor, wires, and set the timing.

Not much of an update but I finally got the front end taken apart so I could see the timing chain. It has about an inch of play in the chain and you can see from the first picture it even looks kind of loose, at least to me. A quick 118 bucks at summit and I have everything I need, plus a set of valve cover gaskets, to get it back together and hopefully running. I am going this week to look at a 91 Dakota to start a frame swap so the money i'm spending now could be a waste but it would be nice to have her running while I prep the frame for the swap at least. I'll keep a track of the project and post a thread when I'm done. One of these days I'll figure out how to get the pictures to load up right. They are normal on my computer but rotate when I upload them.

That chain slop is most likely not cause of popping, but change it out as long as you're in there.

I agree, depends on where the initial timing is set. mileage on plugs/cap/wires/rotor either way that is a lot of slop and I am sure it floats around with a light on it. I bet it has chain slap noise also. slop lets the timing move from advance to retard or vise versa under load and deceleration under load and float when at idle. could be enough slop stacking up to get a sweet spot for the popping with poor tuning.

either way it needs replaced. cant TUNE out a mechanical failure no matter how you try.


FYI- install chain dot to dot (cam at 6 o'clock crank at 12 o'clock) and rotor pointing at #6 on cap.

then turn crank 1 full turn for both dots at 12 o'clock and rotor pointing at #1 on cap.

this keeps it from being 180* out after a cam/chain replacement.

I would be looking to see if the cam lobes are worn down and out of specs to see if it dying a slow death.

I got the timing chain installed and everything put back together. I had just put new plugs in before I got to the timing chain and today I put a new cap, rotor and plug wires on it. That stopped it from back firing through the carb the way it was but didn't completely get her running the way I wanted.The idle is still pretty high to get it to actually run smooth, around 1700 rpm at 30 before top dead center. I couldn't get it to idle much lower that that, lowest was probably around 1300 and 20 before tdc, but will stall once put in gear. Tere is still a vacuum problem because it will idle low and then raise slightly on it's own and when I put a gauge on it the vacuum bounced around. The only other thing I can think is I have an issue with one of my valves not seating or closing properly. That is my next step is pulling the heads and giving then a look on the other side to see what shape the valves are in but I am going to give it a few days to see if I'm missing something that one of you might catch. I'm not sure how many miles are on the engine and if the valves are bad and needs the heads redone I'm not sure if its worth the money to rebuild them compared to building a 360 to replace it. Thanks in advance guys.

I was having some major difficulty getting my 318 to run properly.

What I finally found was a major carbon buildup under the intake manifold. I scraped and cleaned that out and it ran properly after that. It was restricting the exhaust flow.

The heat crossover being plugged will for the most part cause cold weather drive ability and the choke not to open.

I am assuming the timing set at 30 degrees and 20 degrees respectably is set at 2500-3000 rpm and not an initial timing setting. If your trying to set it at that much of an advance for the timing at an "idle" setting, that could be part of your issue.

I'm also not understanding how you can't get the idle below 1,000 unless you have a big cam. I have to think your throttle blades are not fully closing, or you have a bad vacuum leak, maybe at the throttle bushings. Can you shift the throttle arm forwards and backwards a little when the motor is off? I didn't look, what carb is on the motor?

I went back and read and I see you have a 600 Holley carb. The 1st thing I would do is pull the carb and set a straight edge across the bottom (the surface that bolts to the motor) and make sure the corners where the carb bolts to the intake are not pulled down. There should be no gap between the straight edge and the bottom of the carb when the straight edge when its placed corner to opposite corner across the carb, or even across the same side of the carb. Any air gap can be a vacuum leak, even with a new base gasket. Back in the day, a lot of the Holley carbs were run with the thick ply cardboard gaskets and then the 4 corner bolts were cranked down warping the carb base. extreme tightening even resulted in cracking or breaking the ears off. The problem carbs are the ones that had the corners pulled down but didn't crack or break. They would suck air under the base, and even between the base and the carb body, even with the bolts tight. I've seen a few guys that were lucky enough to file or grind them flat, but not many were that lucky. I think once they were pulled, they just kept pulling a little more every time. Gene

Confirm your firing order, very easy to cross a wire/cylinder when installing plugs/wires, and costs nothing but your time to check...

This^ If you are going to pull the heads,do a leak down test after you pull the covers and rockers.It is easier to diagnose a bad valve or cylinder with air before disassembly .It gives you a direction to look for any issues that may not have been otherwise visually noticeable.