At the end of the season the car started to run poorly it will start and idle fine and run great until it you open the accelerator about half way. After half throttle it starts to miss and pop. Sometimes it simply will not rev. If you back out of the throttle it clears up and pulls clean. I figured it was time for a set of points since I could not remember the last time they were changed. I did points, cap, rotor, and plugs. Problem was still the same. So at this point I bought a rebuild kit for the carb as its probably a 20 year old Holly 4160 600. That up till last year ran perfectly. Yesterday I pulled the cap off to check and make sure the advance weight were free and moving properly. All was good there. They only thing I noticed yesterday was it seems as though the mechanical pump is putting out a ton of volume. I started to pull the carb to rebuild yesterday and when in removed the fuel line is seemed to have a ton of pressure backed up. A couple of years ago I replaced the fuel pump with one that had two ports as opposed to my original one port. I was told the second could be caped off. I was dead on the side of the road and it was the only one in stock. I have checked float level and it will just dribble out by leaning on the fender. Could caping the second port cause to high of pressure. The car ran fine for over a year this way. Anything else to check. Its a 300 that is basicly stock with headers and the previously mentioned holley carb. Thanks for the input guys.
Did you check for carb dripping from Venturi? The carb retains pressure, so yes there can be up to 7-8 psi. You will need to investigate more. As what you described in normal so far. What oil are you running? With zinc? What is timing set to? Did you test vacuum advance? Is it connected to manifold vacuum or ported vacuum? Original distributor? Where spark plugs black or wet? Did you try when problems happen to pull over and open gas cap then reinstall and accelerate? You may want a vacuum gauge on there. Especially when accelerating
I have not checked the venturi for a drip I will do that. Oil is 10-30 with a zinc additive I have 25 psi of oil pressure hot idle which starts to rise with any throttle and goes to about 50 at wot. It stays around 40 at 2200. Its the original points distributer. Plugs looked good no signs of pinging on the electrode and porcelin was a light tan. Early last season I took it on a 200 mile trip and got 20.7 mpg calculated with GPS milage and gallons to fill back up (2004r with 3.23 gear). I am suspect of the advance canister so I have to get my vacume gun from my dads. I have a vacume gauge in the car. At idle it pulls 18 hot. Check gas cap with no change in symptoms. I checked for vacume leaks at every hose connection, base of carb and along intake. Vacume advance is to manifold vacume not ported. I want to check timing as well as I have not in some time. Thanks for the ideas I was just thinking there was something I may have been missing. I am gonna rebuild the carb and investigate the advance cannister .
I had a friend bring a 67 Chevelle to me with that problem. Ended up being the condenser, I didn't see that mentioned. The vacuum advance is easy to check, pull vacuum on it, pinch the hose, remove the vacuum source and see it it holds. or Rotate the point plate, pinch the hose and see if it holds. Hope you find it!
Thanks for the info guys this problem gas gotten progressively worse so it has to be something like this thanks for all you help as always
I put an electric fuel pump at the tank with an on / off switch on the dash. I did this simply to prime the carb after the car was sitting so long and to help with vapor lock. My 300 runs fine but at times with a steady increase in speed like on a highway it will stall and sputter like you are experiencing, almost like it is running out of gas. I turn on the fuel pump switch for a couple of seconds and it straightens out the stalling and then runs fine. Last weekend I did about a 150 cruise with my car club, it did this stumbling once on the highway. Not sure what it is but it's like a vapor lock issue, I have replaced the mechanical fuel pump, the carb has been rebuilt but that was around 8 to 10 years ago now I guess. So, I use the electric fuel pump for a few seconds to start the car after it sits a few weeks and then on rare occasion when it stumbles upon acceleration. I have the Electric Limited points conversion, been running that for about 4 years now, plugs are fine, compression good and even across all cylinders. Fuel tank maybe needing replaced? Another carb rebuild?
Electric pusher pumps are great, but they are a restriction to fuel flow that the mechanical pump must pull through. If the mechanical pump gets a little weak, I can see where it might create a problem even under low demand. In the past, I used a Holley Red in conjunction with the Stage1 pump. I used a relay and switch to turn it on. Once when I was on the highway, going 75-80 MPH, the engine started to stutter, turning the pump on rectified the problem. At one point, I used the gas pedal kick down switch to turn on the pump under high demand, but there were still some conditions where it needed more fuel sooner.
OK guys it been a while but I made some progress this weekend. I have tinkered with it before but nothing seemed to make a diffrence. This weekend I rebuilt the very old Holly that was on it. The main body was warped pretty good so some time with a file and all was square again. Cleaned everything and put it back together. My original problem has be fixed. It pulls clean all the way to 5000 were the 2004r shifts. But, know it has a off idle stumble that was not there before. And at very lite throttle it surges. Give it any gas and it clears up and pulls nice and clean. I set my mixture screws with my vacume gauges to get highest reading.it has the same reading it has had for the 29 years I have owned it. I thought it was accerlator pump but it pulls clean at everything but right off idle. Accelerator pump arm was adjusted per my Holly book and shots fuel as soon as you move the throttle. On the highway it cruises just fine. Floats are set correctly even with bottom of threads. Points are new condenser is new and checked. It got dark so I will do some more this week. Any ideas for my new problem.
Change the small cam on the on the pump shot. First go to the #2 slot on carb and if you are there already try the next up cam then go back to the #1 slot for that then try #2 slot if not quite enough. After that you would have to go up on the primary shooter. you did change pump diaphragms correct? Make sure points set first then timing. Also the point set that is put together with the condenser on the same plate is not as good as the set that is separate.
Cool deal the carb was pretty messed up the metering plate was lose. Then the acclerater pump arm was way out of adjustment. I had to file the body a lot to get it flat. I will check all those things this weekend thanks for the help guys.
Sean, Will look forward into getting that book! I have a 300 2bbl engine but sitting on the shelf in the garage is a 300 4bbl manifold, headers and a complete original stock 4-speed conversion (all needed and correct parts) from the steering column to the driveshaft. Just waiting for me to pull the trigger and get it done. I'll add your book to my collection.
