engine backfire and popping in the headers

[neilbyrd]

I have checked that the fan is pulling air in that is why I was wondering about the hot air blowing straight on the coil. As far as the cap it is new as is the radiator and it is working properly as I dont have a overheating problem per say more of symtoms at a certain temperture.

When I checked the voltage it was running for a few minutes idling in the driveway.

I took it out today on "THE HILL" I call it that because I cant make it without the jeep screwing up. I have the napa stock coil in it and it started acting up at 180 degrees. I turned around and headed back down and this time it ran bad almost all the way. Now I dont know what to do. Maybe a stick of tnt would be best at this point.

Steak dinner anyone?

[Jeeperator]

Whats the voltage on the positive side of the coil at about 2500-3000 rpm?

[6spdYJ]

I've seen a Plymouth 383 over-jetted to the point that the headers glowed red at idle. That motor got HOT and didn't run good at all. All the owner did was downsize his jets and life was good.

[aw12345]

I have checked that the fan is pulling air in that is why I was wondering about the hot air blowing straight on the coil. As far as the cap it is new as is the radiator and it is working properly as I dont have a overheating problem per say more of symtoms at a certain temperture.

When I checked the voltage it was running for a few minutes idling in the driveway.

I took it out today on "THE HILL" I call it that because I cant make it without the jeep screwing up. I have the napa stock coil in it and it started acting up at 180 degrees. I turned around and headed back down and this time it ran bad almost all the way. Now I dont know what to do. Maybe a stick of tnt would be best at this point.

Steak dinner anyone?

To the question if the coil is at fault, us e one of the cheap spark testers give it about 1/2" of gap and plug it into one of the sparkplug wires when it runs bad, rev it up and observe it for a good spark. Seems to me you do not want or cannot run it on the street, so take it out to the desert bring all your test tools and run it. I seriously doubt at this point you are suffering from electrical problems.
Not much in the mood to head all the way to Hemet. due to lack of time, but you are welcome to bring it over or take the thing out to IDTT, there will be plenty of us that would be willing to take a look at it there and get our hands dirty

[neilbyrd]

I am not sure of the voltage off idle I will check that in the morning.

I dont believe it is the carb because I have already been down that road when this first started. I have rejetted untill it started to detonate and then moved back up 1 size.

Art it is not that I dont want to drive it on the street it is just not acting up when I am on the street. When I am up the trail all I want to do is get down before I get stranded cause I am usually by myself. I would bring it to you but I have no trailer and top speed is 55 mph so it would take me about 3 days to get there.

Russ Chung is comming out to redeem the free steak voucher tomarrow morning so we will see if we can get it figured out hopefully I will have it on the trail soon.

[aw12345]

Cool deal, I hope the mystery gets resolved tomorrow, carb problems can be a lot more insidious than just jetting, some problems will only show up when hot and after a certain amount of driving

[Jeeperator]

Personally I think its ignition related. I have rebuilt installed and tuned a few holley style carbs in my day and they are pretty much full proof. Assuming he did check that the: jets are correct , choke isn't stuck closed, the air cleaner isn't pluged up, the floats are adjusted right & are not sticking open, air bleeds are not cloged or there are no power valves on that carb. There is no reason for it to all of sudden start dumping so much fuel for it not burn it in the combuston process and cause it to back fire and pop out the exaust. Unburnt fuel igniting in the exaust is the cause of a backfire. The ignition not firing at the right time or not at all (aka missing) is the cause of the unburnt fuel getting there. The only time it ran good was right after he installed the ballast resistor with a new set of points. Curtis made a good point earlier about the dizzy check for bearing slop on the distributer up down side to side. Pull it out and check the gear for excessive wear which could cause erractic timing fluctuations. Check those those points again make sure they aint burnt. I still think over 12 volts is too much for a points style ignition try another higher ohm rated ballast resistor. It is possible the charging system is over doing it? 14 volts is seems a bit high especially at idle.Whats it at 2500 rpm?

Edit: check the mechanical and vacuum advance too make sure its smooth and works good it should advance to ~34 degrees at 3000 rpm. If you havent put that timing tape on just put a mark on the balancer and timing cover and use a adjustable timing light to get an idea how much advance your getting.

If its the dizzy by any chance this might be a good cheap electronic hei replacement. http://cgi.ebay.com/FORD-289-302-5-0...item4cf5786b07

[neilbyrd]

IT IS FIXED! Russ came over today and we went through the ignition. Found some faint timing marks in the balancer and found tdc and applied timing tape to a location that we could see from under the jeep. It took 2 of us to time it but we have it to specs now. It was at 20 btc now it is at 6 btc. We also set the dwell instead of going off point gap now dwell is at 24. This jeep sound completely different now almost like a built big block. It runs cooler and has better throttle response.
I know you guys kept telling me to check the timing but I think I was just getting to fustrated over the last 3 months that I just couldn't see straight. I needed a fresh set of eyes and Russ Chung was that set of eyes.
Now hopefully I will finally be able to meet some of you guys out on the trail.

Once again thanks alot Russ you the man!
I think Russ is going to post some pics because some of you guys asked for pics of various things so he was snapping away.

[Russ Chung]

Here are pics of the right and left side of the carburetor showing the vacuum lines:

[Russ Chung]

The elusive timing marks on the harmonic balancer. This picture was taken after Neil cleaned the balancer with solvent and wire brushed it. Even though we found the timing marks, our view of the pointer was blocked by the water pump, so we installed the timing tape and used that instead.

[Russ Chung]

voltage at the ballast resistor with the engine running:



voltage at the coil with the engine running:



voltage at the coil with fan running:

[Russ Chung]

Test drive in town (1600' elevation). Neil adjusted the fan controller so that the fan would not start until the coolant temp reached 210º. We drove it around town and did the acceleration tests that Art suggested. The Jeep accelerated without missing, so Neil readjusted the fan controller to 180º and we took the Jeep up the trail.

[Russ Chung]

Pics taken on the trail:

At about 3000' elevation:



At about 4000' elevation:



At about 5000' elevation, where Neil declared VICTORY upon reaching Hwy 243:



We continued to Idyllwild (elevation 6000+) before returning to Hemet via Hwy 74.

P.S. The steak dinner was DELICIOUS!! Neil marinated a tri-tip roast all night, and slow cooked it in a smoker all afternoon while we worked on and test drove the Jeep.

[aw12345]

I am glad she is all fixed up, those darn fickle Jeeps. So it ended up being that the dwell and timing was way off.
Not things you look at to much these days, still it got mentioned several times, goes to show to check all the basics before going wild

[Jeeperator]

Cool! at first we assumed the timing was close thats why everybody thought it was the carb at first. Well ASSUME stands for an ASS out of U and ME lol. Damm 20 degress initial timing is definatly too much, probably come out to over 40 total after all the advance comes in. Timing should of been the first thing you should check on an older engine like that and it was definatly mentioned more than once at the begining. In the new computer controlled cars and trucks you cant really change it so why bother checking. As far as timing goes what was your total or did you guys check that?. I always tune for total timing to be about 34 degrees for best performance setting initial timing is just a starting point.