BobnJeep
02-22-2005, 10:04 AM
Did the top end rebuild a while back and can't get it to stop backfiring through the 4 barrel. So this is the advice I got from someone on FSJworld:
EEEEWWWwwwwwwww. A-heh....."Advance the cam at installation"....That's not a nice thing to say. You, or whoever cammed the puppy, should have timed it according to the new timing gear set. I'd go for strait up timing if you are choosing to redo it. All you do when you altar your Cam/ Crank timing is move your power to the torque or HP side of the curve, it really shouldn't miss! The firing order is easy to check- 1,8,4,3,6,5,7,2. Clock-wise distributor rotor rotation. Your cylinders are numbered from the front spark plug going to the rear- 1,3,5,7 on the driver side, and 2,4,6,8 on the passenger side starting at the front spark plug.
So- First thing to check is the wiring order, OR- pull all of your spark plug wires, get the engine to top dead center indicated by the damper and timing cover and pull the number one spark plug and have someone hand rotate the crank from the front damper nut untill your timing mark on the damper is at TDC on the timing cover and you can stick a wire into the spark plug hole and fell the piston at the top of the cylinder. The wire should stick down into the spark plug hole 1.5" from the top of the spark plug hole to the top of the piston at TDC. NOW you can be at TDC compression stroke OR for the exhaust stroke. So pull the distributor cap and make sure your rotor is pointing to the front of the PS pump and not to the coil. If its pointed at the coil or towards the passenger side and rear of the engine, its 180 degrees off. So rotate the crank one more full rotation and you should be pretty damn close. Now that you have confirmed the crank is roughly at TDC compression and the dizzy would be in the firing position for no. 1 cyl (front driver side) You put the cap back on the distributor and start with the shortest plug wire- go to number one cylender, then work your way around the cap, finishing with cylender 2, the front passenger side cylender. Now REcheck by tracing the wires, I think you can get heat resistant labels for labelling your wires, if you want to, Now you will want to try starting the rig. If it back fires but will not start, its possible you could be still 180 out if you forgot a step. But usually it won't do crap if your timing is set up to spark right at TDC, so advance the distributor buy turning the base in the timin cover a bit at a time, You will want to advance the timing, so rotate the base counter clockwise.
You'll probably end up with about 10 BTDC to start. then advance it until it idles real smooth, adjusting your idle speed down so it should run 800 rpm with 10 to 15 degrees advance. DO NOT CONNECT the VACUUM ADVANCE! this will screw everything up! Adjust your carb mixture screws also so you get a nice clean idle and about 16" of manifold vacuum.
If none of this is relevant.....let me know, I'll delete it and try something else. I hope this works for you. If its just the spark and carb need adjusting, that's about the luckiest you can get! If nothing you do helps or when you try to time it and the timing mark "jumps" around but is flashing every time, you have a worn out timing set.....get ready to make a mess, you need to replace it and possibly the cam- check back. Good luck!
One thing you could try, if you can get the vehicle running, put the timing gun on all 8 spark plug wires (seperatly of course) and make sure they are all firing, Obviously you can't check them in reference on the damper/timing marks, but just make sure they all flash at a regular rate when the engine is running. This rules out bad plugs and bad wires as your "missing" problem. You could also have flat cam lobes or bad lifters....or....well, I'll stop there before it gets to expensive.
So I took the advice and checked to see if the wires are right, and they are. It looks like to me that the cam is 180 degrees off. Is my next step to re-install the cam?
EEEEWWWwwwwwwww. A-heh....."Advance the cam at installation"....That's not a nice thing to say. You, or whoever cammed the puppy, should have timed it according to the new timing gear set. I'd go for strait up timing if you are choosing to redo it. All you do when you altar your Cam/ Crank timing is move your power to the torque or HP side of the curve, it really shouldn't miss! The firing order is easy to check- 1,8,4,3,6,5,7,2. Clock-wise distributor rotor rotation. Your cylinders are numbered from the front spark plug going to the rear- 1,3,5,7 on the driver side, and 2,4,6,8 on the passenger side starting at the front spark plug.
So- First thing to check is the wiring order, OR- pull all of your spark plug wires, get the engine to top dead center indicated by the damper and timing cover and pull the number one spark plug and have someone hand rotate the crank from the front damper nut untill your timing mark on the damper is at TDC on the timing cover and you can stick a wire into the spark plug hole and fell the piston at the top of the cylinder. The wire should stick down into the spark plug hole 1.5" from the top of the spark plug hole to the top of the piston at TDC. NOW you can be at TDC compression stroke OR for the exhaust stroke. So pull the distributor cap and make sure your rotor is pointing to the front of the PS pump and not to the coil. If its pointed at the coil or towards the passenger side and rear of the engine, its 180 degrees off. So rotate the crank one more full rotation and you should be pretty damn close. Now that you have confirmed the crank is roughly at TDC compression and the dizzy would be in the firing position for no. 1 cyl (front driver side) You put the cap back on the distributor and start with the shortest plug wire- go to number one cylender, then work your way around the cap, finishing with cylender 2, the front passenger side cylender. Now REcheck by tracing the wires, I think you can get heat resistant labels for labelling your wires, if you want to, Now you will want to try starting the rig. If it back fires but will not start, its possible you could be still 180 out if you forgot a step. But usually it won't do crap if your timing is set up to spark right at TDC, so advance the distributor buy turning the base in the timin cover a bit at a time, You will want to advance the timing, so rotate the base counter clockwise.
You'll probably end up with about 10 BTDC to start. then advance it until it idles real smooth, adjusting your idle speed down so it should run 800 rpm with 10 to 15 degrees advance. DO NOT CONNECT the VACUUM ADVANCE! this will screw everything up! Adjust your carb mixture screws also so you get a nice clean idle and about 16" of manifold vacuum.
If none of this is relevant.....let me know, I'll delete it and try something else. I hope this works for you. If its just the spark and carb need adjusting, that's about the luckiest you can get! If nothing you do helps or when you try to time it and the timing mark "jumps" around but is flashing every time, you have a worn out timing set.....get ready to make a mess, you need to replace it and possibly the cam- check back. Good luck!
One thing you could try, if you can get the vehicle running, put the timing gun on all 8 spark plug wires (seperatly of course) and make sure they are all firing, Obviously you can't check them in reference on the damper/timing marks, but just make sure they all flash at a regular rate when the engine is running. This rules out bad plugs and bad wires as your "missing" problem. You could also have flat cam lobes or bad lifters....or....well, I'll stop there before it gets to expensive.
So I took the advice and checked to see if the wires are right, and they are. It looks like to me that the cam is 180 degrees off. Is my next step to re-install the cam?