I'm stumped. After about a dozen weekends of trying and endless searching on this forum/ reading Haynes manuals- I need to swallow my pride and ask for help.
I have a 1970 240 that hasn't run since the the late 90's. Since then it was sitting in a barn in rural Nebraska until it came to live with me about a year ago. I've been trying in vein to get this thing to fire up to no avail. I've looked at fuel, spark, timing, and compression with no joy. Here are the particulars:
Fuel Pump- It has a new mechanical fuel pump that pumps gas when cranked. With the gatorade bottle method, I'm getting what I believe to be pretty good flow and can fill half of the bottle rather quickly. I've also added a clear filter so I can visibly see that fuel is coming from the tank. I've also opened the float bowls on both SU's (more on those in a second) and can see that they are about half full. There are no visible leaks throughout the entire fuel system and the return line looks clear as well.
SU Carbs- The carbs have been "rebuilt" by me in an attempt to diagnose the no start problem. And by rebuilt, I mean that I disassembled, cleaned, and replaced needles, gaskets, and the little valve that allows in fuel within the float bowl. The distance between the float and the valve is also within "spec" according to the measuring device you get with a rebuild kit as well as some googling. The jets have been centered and the jet height adjustment is smooth as is the piston in its operation (falls freely and smoothly with a "clunk") The gas line from the float bowl to the jet is clear of debris and has been thoroughly cleaned. The choke cable was adjusted to coincide with the full range of motion for the jet. Even with all this, I feel like fuel is not getting into the combustion chamber. There doesn't seem to be any suction and when cranking, I can't see the piston move. Should it?
There are also some open and capped ports above the Carbs- I have NO IDEA what these are and can't find any definitive answers online. I've attached a photo of them below. Any one know what they are? Should I be seeing vacuum in the carbs that draws up the piston / pulls in fuel vapor?
Battery- The car has a new battery and with a charger, I'm maintaining over 13V when tested.
Coil- Things are a little iffy here. The coil is getting 12.8V when the ignition is set to ON. When measuring resistance, I'm only seeing 1.8 Ohms which I believe to be low according to online resources.
Spark Plugs- The plugs are new and have gaps ranging from .3 to .35 when using a gap tool. I understand this to be within spec. When cranking, I've removed each plug individually and visually inspected the spark against a nut on the strut tower. All 6 plugs had blue/purple arcing which seemed to be strong.
Distributor- I'm also a little iffy here. The distributor has new points, condenser, rotor, cap, and plug cables. I measure 12V when touching the points and the contacts between the rotor and cap are clean as they are new. The rotor spins counter clockwise in sequence with cranking, but I really have no idea what I'm looking at here.
Starter- The starter is new and has tested positively at Autozone after I bought it. With the over 13V coming from the battery, the cranking is strong and consistent.
For some reason, timing this car seems like a dark art. I made the mistake of not adequately supporting the timing chain when attempting to adjust the timing sprocket, so I became intimately familiar with how the chain should be set. At TDC according to the marks on the crank pulley, the "-" is almost in line with the "V". I've adjusted it to be a little behind, but when looking today the marks have aligned themselves again. The oil pump shaft that connects to the distributor is at ~11:30 when showing TDC on the pulley marks. I believe that this could be a contributing factor to the no-start situation, but it could also be a red herring as I've previously adjusted timing to be correct.
I just ran a compression test prior to writing this and followed instructions to the best of my ability. The only caveat is that the motor is cold (you know, because it won't run). I'm sure that's affecting the readings, but am unsure if that's 100% the case here.
These seem low and the diminishing psi in the 4-5-6 cylinders is concerning. I have not performed a leak down test yet but if anyone recommends it, I'll go ahead and do one next weekend.
All fluids filters, and gaskets (oil pan, water pump, thermostat, valve cover) have been changed. There's new oil (10W-40), coolant (and radiator), and real gas with zinc additive.
When using starting fluid, I can get the carbs to pop and backfire with smoke, but the car WILL NOT start. The most I can get is a big looney-tunes style backfire out of the exhaust that leaves a black mark on the wall behind the car.
This is my first carbureted car and the fundamentals of the SUs seem incredibly simple- I just can't figure out what the issue is here.
Thanks in advance for the help. Any direction, assistance, or advice would be GREATLY appreciated.