engine backfire and popping in the headers

[neilbyrd]

I'm back again, to recap on what happened before the engine lost power and backfired at altitude. Plugs were black and wet. I rejetted the truck avenger carb on the 302 down 2 sizes and readjusted the bowl level. It ran better but was still popping in the headers so I jetted down 1 more size and now I have detonation. Here is the problem I have detonation and still have poppng and backfiring sometimes. On the way up the bee canyon it was having slight detonation so when I got to the first platue I turned around to go back down, as soon as I turned around and started driving it started backfiring and popping. I was wondering if the problem could be the spark plugs. They are motorcraft partshouse plugs, they are not indexed so the electrodes are pointing all over the place. I am wondering if the spark is somehow being hidden by the electrode and not igniting the fuel. Would going to a multi spark type plug help my problem (like e3). This is getting fustrating and keeping me from wheeling any help would be greatly appriciated.

[Lumpy Grits]

What is your timing set to?
How much is your total advance?
Do you have a vac. gauge?
Do you know how to read/use a vac. gauge?
What temp is your t/stat?
Respectfully,
LG

[6spdYJ]

One oddball question - LG wisely asked your thermostat temperature. Do you have a thermostat? Some people errantly take them out when trying to drop temperatures. What this causes is the coolant blasting through the radiator before it can be cooled off by the airflow.

[Jeeperator]

LG is right need to start at square one. You might have other issues and this info is pretty important.Especially total timing. Forget multi electrode type spark plugs they are crap and just a gimmick good ol fashion motocraft are just fine but knowing the heat range kinda helps too. If they are to hot that can cause preignition or detonation too. Once those plugs turn black and sooty you need to change them. When you jet you usually go up or down 2 sizes at a time so if its a 76 and you want to lean it a bit you need to go to a 74 and then a 72. So what did you start with and where are you now. Does that carb have power valves. If so you can put power valve plugs in and it will decrease your jetting about 2-4 sizes IIRC.

[neilbyrd]

The carb is a holley truck avenger, it started with 57 jets I changed them to 55 first and then today I changed them to 54. The timing I can't tell what it is because the harmonic balancer has no timing mark, I cleaned it real good and looked everywhere with a flash light and no mark. Tomarrow I will be going to get a vacuum gauge and see if I can get the timing better with that. As for the thermostat it is a 160 degree. I know the engine is old and in need of a rebuild but I should be able to get a little time out of it to have a little fun before I take the Jeep down again. I just finished a 3 year build and I want to enjoy it a bit.

[aw12345]

You can always find top dead center on cyl number1 and then make some timing marks on the dampner and on the timing cover if need be. Vacuum gauge is a good thing to use on it. Helps spotting flat cam, busted push rod, or rocker etc. When you figured it misfired and ran to rich did it puff black smoke? Seems to me it is something in the ignition department. Vacuum gauge will tell ya of the mechanicals are still reasonably up to snuff. If it runs on all 8 cyls, doesn't have bad blowby, then there is no reason for it to not run decent and make acceptable power

[Russ Chung]

...It ran better but was still popping in the headers so I jetted down 1 more size and now I have detonation...

Probably need to go back up 1 size.

...Here is the problem I have detonation and still have popping and backfiring sometimes. On the way up the bee canyon it was having slight detonation so when I got to the first plateau I turned around to go back down, as soon as I turned around and started driving it started backfiring and popping...

First, I want to make sure I understand the terms you are using to describe what is happening. By "detonation" I believe you mean the engine "knocks" and/or "pings", because "detonation" is usually silent. The most common cause of knocking or pinging is low octane gas, but in this case, I don't think it is the gas. It is probably the timing, especially since you said in the previous post that you can't find the timing mark on the harmonic balancer. By "backfiring" and "popping" I understand that the fuel/air mixture is burning in the exhaust manifold and that it is NOT burning in the intake manifold and backfiring through the carburetor. This could be caused by a number of things, but knowing the recent history of your adjustments, I would suggest that you go back up one size in the jetting, and retard the ignition timing "a little".

...I was wondering if the problem could be the spark plugs. They are motorcraft partshouse plugs, they are not indexed so the electrodes are pointing all over the place. I am wondering if the spark is somehow being hidden by the electrode and not igniting the fuel. Would going to a multi spark type plug help my problem (like e3)...

The number of electrodes and/or indexing aren't the problem, but there is a possibility that the heat range of your plugs may need to be changed. I don't think you've driven your Jeep enough to get a good reading on the plugs yet, so don't change them now. If they are too cold, there will be deposits on the spark plug. If they are too hot, the ceramic insulator will be worn.

[Jeeperator]

You can get a sticker with timing marks that goes on your harmonic balancer. Its called a timing tape. Like Art said find tdc with #1 cylinder put the timing tape where you can see it with a timing gun and mark TDC 0 degrees on the timing chain cover with a dot of paint or scratch or something. We need to know the timing before we move on. A good start on total advanced timing on a common v8 is ~34 degrees btdc. You must rev the engine around 2500-3000 rpm when setting this.

[neilbyrd]

I got a vacuum gauge today and got the vacuum to its highest reading and then retarded it about a half of an inch of vacuum, bought some e3 plugs and installed them. Upon starting the jeep it sounded alot better drove it about 5 miles on the street and then headed up the mountain. It was ok until I had the engine at about 210 for a while going up the long hill then it started popping in the headers again started loosing power when it was popping. I turned around and headed back down, as the engine started cooling on the trip down it started getting a bit better. As I was going down the temp stabilized at about 180. I am starting to think that the problem has something to do with the temp and how long it is there. It seem that everytime it is running bad I am either pulling a long hill or just finished pulling a long hill and it is at 210. I will see if I can find some of that timing tape that you guys are talking about and set the engine at tdc on the compression stroke before applying it.

[Lumpy Grits]

Sounds more like "vapor-lock" IMHO.
Is your fuel filter above the exhaust as it was OEM. If YES move it to the top of your valve cover.
Is the filter set with the return line at the top?
I get my stock carb(Carter BBD) CJ-7 above 210* all the time and have no issue at 9K'(asl).
You still MUST set the timing with a light to be sure. Till that is done you are just chasing-your-tail.
Respectfully,
LG

[6spdYJ]

Your best friend when setting timing without marks is an adjustable timing light. Once you get TDC established, mark it on the dampener and a corresponding mark on the timing chain cover. Set the dial on the timing light to 8 degrees advance and adjust the timing at idle until those marks line up. 8 degrees is a conservative figure for static timing and should be a safe starting point. However, Some of the '70's smog motors were as much as 6 degrees retard. It would be best to know the year and model the motor is from and look up the OEM specs.

[neilbyrd]

My fuel system and exhuast are nowhere each other, the fuel line is on the inside of the frame and the exhaust runs outside on both sides. The fuel filter is above the valve cover and there is no return line on the filter, it is a mechanical fuel pump. I am going to order the timing tape tomarrow. I was wondering though if it was timing wouldn't it do it all the time? The only time it is doing it is when I am going up a long steep hill in low range and the temp is at 210 for a while.

[aw12345]

Vapor lock and starving for fuel is not that hard to diagnose, let of the gas some and if the engine picks up and is running happy again you are not getting enough fuel under load. Seems to me it's more of a misfire, don't like that it's heating up either, you might want to dig into that also.

[neilbyrd]

Vapor lock and starving for fuel is not that hard to diagnose, let of the gas some and if the engine picks up and is running happy again you are not getting enough fuel under load. Seems to me it's more of a misfire, don't like that it's heating up either, you might want to dig into that also.

If it was vapor lock when it is popping and I give it more gas would it backfire? As far as the heating up I think the temp it is getting to is reasonable considering the hill I am climbing is steep and long. I just mentioned it because I am trying to give any and all information that I think might help someone help me.

[aw12345]

Lack of fuel it would just hold back, vapor lock when it's severe it will just quit and you will have a hell of a time getting it started. It's a stick shift right? Try this for the heck of it, works pretty good for doing a quick check of your ignition system.
Barely get it rolling in first gear then stick it in third and floor it, skipping second. You want to barely start the Jeep rolling then go to third gear and floor it to really get the engine chugging if it is backfiring you have an ignition problem. I.E. not enough secondary voltage to fire the plugs