Ignition Timing Gremlin

[Jeep Craze]

Hello everyone, I am kinda new to this.....been surfing alot and reading everyone's problems and learning alot actually. Now I suppose It is time for me to ask my question. I am rebuilding a 1980 J 10 (hence the name) 360 4sp no a/c 2brl. carb. Now as everyone can imagine....I have depolutionized the **** thing. Headers dual exaust, problem I'm having now is seems like the ignition timing isn't working right. The advance that is. When I set my timing, vacum advance unhooked but plugged. I set it to 8before TDC. Like the spec tag says. when I advance the throttle slowlly......the timing mark does advance to about 15 @ 2000RPM. When I hook the vacum advance back up it as well advance the spark timing. Problem is when I dump the throttle It back fires out of the carb and If I hold it around 3000rpm it back fires alittle out of the exaust. if I advance the base timing, I can get rid of the exaust popping, but I still can't get rid of the intake backfire. If I slowly accelorate, it works fine. If I have it around 2000 rpm and unhook the vacum line it sounds like world war 3 out the exaust. Does it seem like it maY be the mechanical not holding or something. Or would a mis tuned carb cause this. I have rebuilt the carb and it isn't running rich(no smoke out the pipes). I don't know which way to turn jeepers, this one really has me stumped. I am starting to lose the jeep enthusiasm! Help from Pa. Thank you for your advice in advance. Craig

[steven79]

sounds like it is cross firering, did you replace the plug wires and cap & rotor? if so go back and double check your firing order.
or could be cam timing is off or jumped.

[Jeep Craze]

Thanx Steven A This is just something that started. I ran it in the morning and it ran great. Started it in the afternoon.....and it sounded horrible. if the cam timing is off by like one or two teeth would it make that drastic of a difference?

[Veepster]

whoa!!......time for my favorite saying.....when you hear hoofbeats think horses not zebras.......

cam timing skipping a tooth? possible bit very unlikely!.....

to check manual advance....remove dizzy cap and grab rotor and rotate it should move about 1/4 inch in one direction then return to original location...do it again, it should return to original location...if this occurs we can assume it is working...to check vac advance....check that it holds vacuum.....simple way to check: remove vacuum advance hose from vacuum source, with dizzy cap off suck on the tube you should see arm move in release vacuum arm should move out..now suck and put tongue over hole in tube......vacuum should hold...

if these 2 things work and you are sure there is no cross wiring, check your timing procedures.....Good Luck!!!

[Jeep Craze]

Thanx veepster,
I have checked everything w/ the distributer liek you said.....working just fine. Also I checked wiring fireing order that as well is fine. I did check the mechanical timing for the cam. Unless it jumped one tooth I would say that it is on. Do you think it has something to do w/ a crappy carb. I mean it was rebuilt however does that mean that it is right? Don't know. And I tried what another member said(set the initial timing at 14 BTDC and unhook the vacum advance and leave it off. That doesn't really work. By advanceing the base timing I can get rid of the popping out the exaust but I still have it out of the carburator. What should the base timing be without the polution and all the extra vacum parts. 8BTDC is what it is w/ all the parts from factory. Any commenst are greatly appreciated......Thanks Craig :confused:

[Veepster]

Ok lets back up...........did it ever work right? what did you do to the FSJ between when it worked right and now.......? let s think this through...I am quite sure something was inadvetantly cahnged that should not have been.....

could it be the carb? sure....

lets retrace your steps first and see if we can narrow it down....

[Jeep Craze]

Well, This is how it went. I ran it in the morning about 8am. Let it high idle for a few minutes......kicked it down.....Idled nice and smooth, accelerated PERFECTLY. Then shut it off.Left it sit till about 3pm. Started it again, To work on it some more. High idled for a few minutes, kicked it down.....ran great for about 5 minutes.Then it started chuggin like a locamotive. Black smoke bellowing out the pipes. No matter what I did to the air/fuel mixture screw, it didn't change anything....didn't even drop the RPM'S when they were turned all the way in. So I got a rebuild kit, rebuilt it. Now the RPM'S are affected by the screws...but still got popping and stuff. So today I got tired of it.....tired of just wondering if it was the carb. Bought a holley 650cfm, installed it....tuned it.......and heyruns great. The only problem I have now is that #4 cylinder on the header glows like a roamin candle.all the rest are fine. I am gonne post a new message asking about the glowing. I think I was after the wrong thing though when I had the poppin....guess it wasn't timing. Sorry......Craig

[Lindel]

On the glowing header, check and make sure that you don't have a valve stuck open, or closed on that cylinder. AFAIK, that's about all that'll cause that, especially if everything else is ok.