| Slant Six Forum https://slantsix.org/forum/ |
|
| Hot Carb Problems https://slantsix.org/forum/viewtopic.php?t=57296 |
Page 1 of 1 |
| Author: | SpaceFrank [ Mon Mar 16, 2015 11:21 am ] |
| Post subject: | Hot Carb Problems |
I am running a Holley 2300 with an adapter plate on an aluminum super six manifold and stock exhaust. The engine will start easily with a pump or two of the pedal when cold; it just takes a minute or so of goosing the throttle until it will stay running, because the carb has no choke plate. Once it's up to operating temperature, if you shut it off and restart it immediately, it will fire up again but with a little hesitation. Call it 3-4 seconds of cranking. The problem really shows up when the engine has been running nice and hot, then you shut it off and let it sit for a few minutes. It will then take a good 10-15 seconds of cranking before it fires up again. In this situation, the accelerator pump will still fire a shot, but I'm not sure how much it helps startup. I tend not to pump the throttle very much on a hot restart because I don't want to flood it. More data could be collected to see what effect different amounts of pumping have, but as I recall it doesn't seem to make much difference when the engine is hot and left to sit. Also, when coming to a stop after running hard for a while (either the track or the highway), the engine has a tendency to sputter and die. The car has a big damn aluminum radiator with a (relatively small) electric fan and a 180 degree thermostat. Coolant temps on track never get above 210. The fan seems to keep up with the car idling at rest when you first start it up, but it will get hotter than that after you come off the track. Another issue which may or may not be related. On the track, the engine has a tendency to sputter and/or die when going into or coming out of a corner. The Holley has a properly-calibrated center-hung float, so I'm pretty sure this isn't a G-related fueling problem. I think instead it's just another instance of the car wanting to die at low RPMs after running hard and hot. We've always used the same carb, aluminum super six, and cast iron exhaust. The carb was rebuilt a few years ago, and I have it jetted somewhat rich. The accelerator pump works and has a very strong shot. The fuel pump works fine, and I have performed the fuel line mod (didn't seem to make a difference at the time). I have no vacuum leaks that I can see, although there has always been an exhaust leak of some form or another (planning to fix this soon with new gaskets and proper high-temp RTV application as detailed in the tech article). The heat riser valve also works as designed. These are all issues which have existed in one way or another for as long as the car has been racing, it just seems to have gotten a bit worse since we rebuilt the engine. I don't know if this matters at all to the present situation, but I do have the base timing set less advanced than normal, maybe 3 degrees BTDC as opposed to the 7-10 we normally run. (I read somewhere that you shouldn't set the timing very advanced during engine break-in. Not sure if that was particularly good advice.) The engine bay temps are typically pretty high. Is this a heat soak issue? Should I add a heat shield or a phenolic carb spacer? Is the too-small radiator fan contributing to the problem? I've considered blocking off the heat riser pocket, but I know that's not recommended and will probably just make cold starts more difficult. |
|
| Author: | Danarchy [ Mon Mar 16, 2015 11:50 am ] |
| Post subject: | |
phenolic carb spacer seems like a quick and easy thing to try, but with the aluminum intake I would look at a heat shield along with the spacer next! |
|
| Author: | '67 Dart 270 [ Mon Mar 16, 2015 12:39 pm ] |
| Post subject: | engine bay |
I switched my '67 over to double electric fans, it kept the engine plenty cool, but the engine bay was always way too hot. I went back to mechanical fan and it cools the engine bay adequately. I use this flex fan and a shroud: http://www.summitracing.com/parts/flx-1080/overview/ This one might move even more air: http://www.summitracing.com/parts/flx-1818/overview/ brian |
|
| Page 1 of 1 | All times are UTC-08:00 |
| Powered by phpBB® Forum Software © phpBB Limited https://www.phpbb.com/ |
|