Smokinnjokin
Well-Known Member
So, bottom line up front I just did a lot of work to my 360 and now it has a bad stumble/backfire/hesitation when I rev it up past cruise throttle positions. I am trying to figure out if it is a carb setting, or ignition problem. Car starts and idles beautifully, easy hot start after it has been sitting awhile, it just has a bad reaction when you stomp on the big pedal.
Here's the dirty details.
I have a smog 360 in my '67 sat that i just installed new lifters, timing chain set, edelbrock intake manifold, and swapped from points to HEI.
I installed the timing set exactly as old one came off, dots lined up both at 12" and used a tensioner. New eddy manifold has heat riser blocked. The carb, an edelbrock 1403, ran well with the previous combination of parts and had no issues. So the only thing that has changed the fuel/air demand on this engine is more accurate timing (stretched old chain) and an Edelbrock RPM intake with no heat crossover vs the old cast iron.
For the HEI system, I used a new OEM-style vac advance electronic dist. from R. Ehrenberg, he states it has a performance curve. I have the LX-301 ignition module mounted under distributor on the designed2drive plate, and I am using a standard ignition E-core coil. Ballast is bypassed. All the wiring is solder connections, heat shrinked. The ignition module is grounded to the block. My work is very clean, I am a former helicopter mechanic so I obsess over details. I checked continuity on all connections, all looks good. The cap is brass terminals, the wires are new 8mm and plugs look good and are gapped to 0.045". I double and triple-checked plug firing order.
Again, the car starts instantly and idles perfectly which seems to indicate all is well with ignition, but I don't want to rule it out just yet.
The carb is a 500 cfm eddy, again it worked perfect before this project started (about a month ago) and it sat on the workbench covered with a rag during that time. I have the correct pump seat/seal installed for mopars (blue? I forget which one but its good). Float height was set to factory settings a couple months ago, everything inside is clean and in good working order. Fuel in tank was seasoned with sta-bil before sitting for the month. Car has been in a garage the whole time. Clear fuel filter, I can see flow to engine.
Timing is set to 12deg BTDC with the vac advance unhooked and carb plugged. Car may want more advance but im not going to mess with that until I get the issue figured out. A couple degrees of fine tuning should not cause this bad of a throttle response.
When I apply throttle at lower settings, response is great and power is good. When i stomp on it, or get up to higher throttle settings slowly, it runs like crap and backfires.
So here's my troubleshooting theories:
1) somehow I did not install the chain perfectly lined up, mechanical timing is off. I put new chain on without turning anything in the motor, and the timing dots lined up exactly with a ruler. So this seems unlikely.
2) new intake manifold, ignition and chain were a radical enough difference to air/fuel demand that the carb needs jetting changes. Again, seems really unlikely.
3) carb has a plugged jet or passage or something? Has 2 fuel filters leading to it, and it sat in a clean garage covered up. Worked perfectly when removed. Seems unlikely.
4) Something is wrong with the ignition. High-speed miss or something. Arcing, grounding out? Again, my wiring job is solder connections, heat shrink, double and triple checked. And starting is super reliable. I ran it for over an hour today flushing the radiator too, engine was at operating temp for a long time (idling) with no issues whatsoever. So does not seem to be heat related.
I am going to run it tonight when it is pitch black and look for arcing, just to rule it out.
What do you guys think?
Here's the dirty details.
I have a smog 360 in my '67 sat that i just installed new lifters, timing chain set, edelbrock intake manifold, and swapped from points to HEI.
I installed the timing set exactly as old one came off, dots lined up both at 12" and used a tensioner. New eddy manifold has heat riser blocked. The carb, an edelbrock 1403, ran well with the previous combination of parts and had no issues. So the only thing that has changed the fuel/air demand on this engine is more accurate timing (stretched old chain) and an Edelbrock RPM intake with no heat crossover vs the old cast iron.
For the HEI system, I used a new OEM-style vac advance electronic dist. from R. Ehrenberg, he states it has a performance curve. I have the LX-301 ignition module mounted under distributor on the designed2drive plate, and I am using a standard ignition E-core coil. Ballast is bypassed. All the wiring is solder connections, heat shrinked. The ignition module is grounded to the block. My work is very clean, I am a former helicopter mechanic so I obsess over details. I checked continuity on all connections, all looks good. The cap is brass terminals, the wires are new 8mm and plugs look good and are gapped to 0.045". I double and triple-checked plug firing order.
Again, the car starts instantly and idles perfectly which seems to indicate all is well with ignition, but I don't want to rule it out just yet.
The carb is a 500 cfm eddy, again it worked perfect before this project started (about a month ago) and it sat on the workbench covered with a rag during that time. I have the correct pump seat/seal installed for mopars (blue? I forget which one but its good). Float height was set to factory settings a couple months ago, everything inside is clean and in good working order. Fuel in tank was seasoned with sta-bil before sitting for the month. Car has been in a garage the whole time. Clear fuel filter, I can see flow to engine.
Timing is set to 12deg BTDC with the vac advance unhooked and carb plugged. Car may want more advance but im not going to mess with that until I get the issue figured out. A couple degrees of fine tuning should not cause this bad of a throttle response.
When I apply throttle at lower settings, response is great and power is good. When i stomp on it, or get up to higher throttle settings slowly, it runs like crap and backfires.
So here's my troubleshooting theories:
1) somehow I did not install the chain perfectly lined up, mechanical timing is off. I put new chain on without turning anything in the motor, and the timing dots lined up exactly with a ruler. So this seems unlikely.
2) new intake manifold, ignition and chain were a radical enough difference to air/fuel demand that the carb needs jetting changes. Again, seems really unlikely.
3) carb has a plugged jet or passage or something? Has 2 fuel filters leading to it, and it sat in a clean garage covered up. Worked perfectly when removed. Seems unlikely.
4) Something is wrong with the ignition. High-speed miss or something. Arcing, grounding out? Again, my wiring job is solder connections, heat shrink, double and triple checked. And starting is super reliable. I ran it for over an hour today flushing the radiator too, engine was at operating temp for a long time (idling) with no issues whatsoever. So does not seem to be heat related.
I am going to run it tonight when it is pitch black and look for arcing, just to rule it out.
What do you guys think?
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