Hey everyone! Back again!
I'm here again with another tuning issue. I come here because y'all never steer me in the wrong direction and tend to get me right back on track. I try and do everything I can to my knowledge or extent before I come here through researching forums and trying to figure things out on my own.. but I'm lost on this one.
Alright, so heres the deal:
Slight misfire below 2500 RPM. At first I thought it was too low of an octane rating or possible the chance of getting bad gas (due to high ethanol content and getting 93 from a station that doesn't sell it too often causing the gas to absorb water).. so I tried mixing 110 with the 93 and that seemed to cure the problem until recently it started it's weird little misfire again. This could be due to weather changes such as humidity or temperature. So I've kind of ruled that whole octane thing out. So I checked my plugs the other day and didn't see any signs of detonation (at least that I could see with my untrained eyes) and the plugs were showing decent color from probably running too rich of a jet (75/80).. but I did notice the electrode tips on some plugs were beginning to slightly melt! Which leads me to believe I'm running way lean at low rpm/throttle causing cylinder temperatures to sky rocket?? I'm only running 185* max temp and usually closer to 180*. So my main question is: What is causing this carb to go so lean at low rpm like this? Is there something I can do in terms of carburetor tuning to eliminate this low rpm miss and quit melting electrodes? To my knowledge primaries don't even kick in until about 2500 RPM which is what leads me to believe this is due to something in some circuit that I am completely clueless on tuning such as the power valve or idle air bleeds or PCVRs or some junk. As I've said this carb has no issues up above 2500 RPM or when I seem to get above about 15% throttle other than a flat spot in hard acceleration from lower RPM from what I assume is the incorrect secondary diaphragm spring. I do feel a surge in the throttle when I'm in first gear and cruising through a parking lot at around 2000 to 2500 rpm (like it's lean surging). I took the carburetor off and checked both primary and secondary transfer slots and they were both at the recommended .040" square and both idle air mixture screws are 1.5 turns out. What do I do to fix this? Powervalve? PCVRs? Mixture screws? Air bleeds???
The carb is a Holley 670 street avenger with the 6.5 PV, 75/80 jets, .035" squirter and blue cam on 2.. and fuel pressure is set to just shy of 7 psi with an electric pump.
Timing is 14 initial and 34 total all in by 2800 no vacuum advance.
355 Chevy 10.2:1
Flat top pistons
Edelbrock Performer RPM heads and intake (air gap)
236/236 @ .050" solid flat cam with .521/.521" lift
.040" squish (.025" deck .015" head gasket)
I'm hoping this is a carb tuning issue and I can go back to running straight 93 and maybe even hook my vacuum advance back up to try and save SOME gas.
I'm here again with another tuning issue. I come here because y'all never steer me in the wrong direction and tend to get me right back on track. I try and do everything I can to my knowledge or extent before I come here through researching forums and trying to figure things out on my own.. but I'm lost on this one.
Alright, so heres the deal:
Slight misfire below 2500 RPM. At first I thought it was too low of an octane rating or possible the chance of getting bad gas (due to high ethanol content and getting 93 from a station that doesn't sell it too often causing the gas to absorb water).. so I tried mixing 110 with the 93 and that seemed to cure the problem until recently it started it's weird little misfire again. This could be due to weather changes such as humidity or temperature. So I've kind of ruled that whole octane thing out. So I checked my plugs the other day and didn't see any signs of detonation (at least that I could see with my untrained eyes) and the plugs were showing decent color from probably running too rich of a jet (75/80).. but I did notice the electrode tips on some plugs were beginning to slightly melt! Which leads me to believe I'm running way lean at low rpm/throttle causing cylinder temperatures to sky rocket?? I'm only running 185* max temp and usually closer to 180*. So my main question is: What is causing this carb to go so lean at low rpm like this? Is there something I can do in terms of carburetor tuning to eliminate this low rpm miss and quit melting electrodes? To my knowledge primaries don't even kick in until about 2500 RPM which is what leads me to believe this is due to something in some circuit that I am completely clueless on tuning such as the power valve or idle air bleeds or PCVRs or some junk. As I've said this carb has no issues up above 2500 RPM or when I seem to get above about 15% throttle other than a flat spot in hard acceleration from lower RPM from what I assume is the incorrect secondary diaphragm spring. I do feel a surge in the throttle when I'm in first gear and cruising through a parking lot at around 2000 to 2500 rpm (like it's lean surging). I took the carburetor off and checked both primary and secondary transfer slots and they were both at the recommended .040" square and both idle air mixture screws are 1.5 turns out. What do I do to fix this? Powervalve? PCVRs? Mixture screws? Air bleeds???
The carb is a Holley 670 street avenger with the 6.5 PV, 75/80 jets, .035" squirter and blue cam on 2.. and fuel pressure is set to just shy of 7 psi with an electric pump.
Timing is 14 initial and 34 total all in by 2800 no vacuum advance.
355 Chevy 10.2:1
Flat top pistons
Edelbrock Performer RPM heads and intake (air gap)
236/236 @ .050" solid flat cam with .521/.521" lift
.040" squish (.025" deck .015" head gasket)
I'm hoping this is a carb tuning issue and I can go back to running straight 93 and maybe even hook my vacuum advance back up to try and save SOME gas.