Map63Vette
Well-Known Member
So I did a 5.7 Hemi swap into my Dart a few months back and decided to carb it for now (Carter AFB 625 cfm) so I could get it back on the road and then think about fuel injection later when I had the money to do it right. However, I have had nothing but trouble trying to get the carb dialed in.
Right now the car suffers from a stumble on a full throttle hit. My best guess is that it is getting way too much gas on a hit since it feels more like a bog than a cut, but it responds a little different every time I take it out. On some hits the car will just take off and haul, and other times it will just sit and shake until it works itself out (more often than not this is the case). The latest driveway tuning I did consisted of stabbing the throttle at idle with the car out of gear and the engine up to temp. It seemed like it was really bogging down, and as I kept taking out pump shot it would recover from the bog faster. Since I was at the end of the pump lever, I stepped down the primary jets from 0.98s to 0.95s and on the smallest pump shot it was as close as I was going to get it to having no stumble with the parts I had to tune with.
However, since I still have the O2 sensors from the Hemi and I have bungs in my headers I put them in and checked them and the car is running lean at cruise and still has some hesitation on a hit. I'm not really sure what to do at this point. The engine seems to respond to hard throttle hits better the leaner I go, but I'm worried I'll start torching parts if I lean it out any further. The other problem is that the smaller jets are really hurting the top end right now. I was looking into getting new rods to richen up the power side, but I don't want to keep dumping money into carb parts if I'm chasing the wrong problem. Any ideas what other tests I can do to try to narrow down the problem? I've checked all the intake bolts and any potential vacuum leak sources and everything seems to check out, running out of ideas on what to try next.
Right now the car suffers from a stumble on a full throttle hit. My best guess is that it is getting way too much gas on a hit since it feels more like a bog than a cut, but it responds a little different every time I take it out. On some hits the car will just take off and haul, and other times it will just sit and shake until it works itself out (more often than not this is the case). The latest driveway tuning I did consisted of stabbing the throttle at idle with the car out of gear and the engine up to temp. It seemed like it was really bogging down, and as I kept taking out pump shot it would recover from the bog faster. Since I was at the end of the pump lever, I stepped down the primary jets from 0.98s to 0.95s and on the smallest pump shot it was as close as I was going to get it to having no stumble with the parts I had to tune with.
However, since I still have the O2 sensors from the Hemi and I have bungs in my headers I put them in and checked them and the car is running lean at cruise and still has some hesitation on a hit. I'm not really sure what to do at this point. The engine seems to respond to hard throttle hits better the leaner I go, but I'm worried I'll start torching parts if I lean it out any further. The other problem is that the smaller jets are really hurting the top end right now. I was looking into getting new rods to richen up the power side, but I don't want to keep dumping money into carb parts if I'm chasing the wrong problem. Any ideas what other tests I can do to try to narrow down the problem? I've checked all the intake bolts and any potential vacuum leak sources and everything seems to check out, running out of ideas on what to try next.
