318 sputters under load

[drbbqking]

I have 2 chrysler 318's the port has started to sputter under a load. popping and hesitation at 6 knots it runs well but as I add throtle it starts to pop and sputter stall and backfire at the carb any ideas as to a fix I am using m.s.d. so I am getting a hot spark

[Commissionpoint]

whats your total advance, and how is the condition of your fuel/water seperators?

[prowlersfish]

Look the Cap and check your wires . what type of "m.s.d" unit are you using ? That also could be a proplem . You could also have a fuel issue . check your filters like CP said . but you could have trash in the carb. As you see there is not just one thing that can cause a proplem .

[jddens]

I agree, the MSD unit could be your problem. I had an MSD unit on my hot rod and it failed, the symptoms were like yours only intermittent......

[Paul]

I've had that problem due to a partially blocked anti siphon valve at the top of the fuel tank.

[drbbqking]

what are the initial setting for the carb ??? I have 3 screws 2 are the idle but what is the big one between them and what is the setting????

[larryeddington]

I assume you have Cart AFBs on both engines. Mine only have two screws which are the idle adjustment screws, high speed jets are fixed. If one engine is fine I would start swapping some parts from one to the other. when it cures you will have the culprit assuming the other engine is running well.

[ready123]

Can you switch the fuel supply? If you have a fuel manifold put the bad engine on the good engines tank and see if the problem goes away. That will answer the fuel supply concern..... Then you are down to carb and ignition problems and can work through those.
I had a partially blocked siphon valve at top of tank that prevented enough fuel flow at anything above low speed travel which showed same symptoms.... Mechanic had run to distributor problems first and it was not there.

[P-Dogg]

Two transposed spark plug wires would cause this problem. You didn't say, but let me guess: It spools-up fine in neutral, but not in gear?

Here's the deal: At low power output, the other cylinders are able to compensate for the loss of power from the "missing" cylinders. When you accelerate under load, the vacuum advance causes the spark timing to now occur when the intake valve on one of the screwed-up cylinders is still open, causing the backfire through the carb. As alluded to earlier, check to make sure that the plug wires are firmly on the plugs, and that they are in the correct order at both ends. And be sure to let us know what the solution was.

[todd brinkerhoff]

When was the last time you changed the plugs. If its been awhile, pull one out to see what it looks like.

[Martino]

Any updated info or results to the problem? Has it been resolved? Im also experiencing the same issue with my 1980 F32 with new 360's. Carbs are rebuilt. Anti syphons are good. Checked timing. Went through the suspected port carburator three times and even swapped the starboard carb to the port engine and it ran good.