440 4bbl Not Start after around the Block

[RV&SAIL]

1977-8 Engine, 440-4bbl, is in a Motor Home, Sportsman- Coachmen. I cannot start it now. It has started several times over the last month (while working on tune-up and brakes)- on the first crank. I took it for its first drive around the block in 3 yrs, Now No Start: it cranks strong, spark comes out of plug wire, it appears to be timed OK, but no combust at all. The carb was runing rich and fast idle, but I have not done any adjustments(on purpose). I have been into the wiring & Tranny Safety Switch since the little trip. The new plugs are as black as the old ones with carbon. Tried to unflood the engine. Don't know what to do next.

[denisond3]

The carburetor is the likely culprit, especially if the plugs are dark - but to be helpful we would need to know if it is a Thermoquad, (which is what it probably came with) or some other carb that might have been installed in the last 30 years - like a spreadbore Holley or Edelbrock. Its is not likely the original carb would still be working properly after that length of time - without having been rebuilt (at least once, if not every decade). Other possibilities would be that you have a bad ignition resistor, a bad ignition module, a bad pickup coil inside the distributor, feeble interconnecting wires, of loose interconnectons - like the one right by the steering column) or even a bad 'ignition-2' circuit. When the engine is running, the ignition module gets its current via the 'ignition-1' circuit in the ignition switch. When you have the key in the 'start' position, it would be using the 'ignition-2' circuit. This bypasses the ignition resistor to give a hotter spark during engine cranking. If it quits working, due to a dirty ignition switch or a melted wire in the bundle that runs down beside the engine (just above the exhaust manifold on the drivers side), then the engine wont start - though it might run fine once it was started.
The ignition resistor is known for going out - so I even carry a spare one. Its of white ceramic, about twice the size of a pack of chewing gum, and normally located at the top rear of the motor, along with the ignition module. This could depend on the RV coach manufacturer though, as they sometimes relocated it to have the front floor an inch lower.
If you could stop fuel from getting to the carburetor (by disconnecting a fuel line and capping it off), you could try cranking it and spraying starting fluid down into the carburetor. That would at least indicate if it was carb or igntion.
You can of course test for ignition by having one spark plug wire with an old plug in it, lying atop the engine in sight (with the engine cover and air cleaner off). You should have a fire extinguisher handy when doing this, due to the possiblity of fuel being present. It could be there if the needle valve inthe float chamber was jammed open by a chunk of crud. I had that happen to me when the rubber diaphram in the fuel pump had begun to disintegrate. Now I change my fuel pump each ten years so it wont happen again.
I think there is a plug in the bottom of the plastic part of the Thermoquad carburetor that has been known to fall out. That lets fuel from the float bowl drain right into the carburetor primaries - and floods the engine out. It doesnt happen until the carburetor is many years old though.
Here is a link about Thermoquads: tocmp.com/manuals/Carbs/Carter/Thermoquad/1972/index.htm
so you can at least see if your carb IS a Thermoquad.
There are outfits that rebuild Thermoquads or sell aftermarket equivalents. I only know of one such site: www.carbsonly.com, but Im sure there are many. You might also poke around at www.allpar.com - which is a mopar site.
Be sure to pull off the distributor cap and rotor, and put a couple of drops of oil onto the wick at the inside-top of the distributor shaft. This is the only lubrication the centrifugal advance mechanism ever gets. You should be able to grab the rotor and twist it counter-clockwise about 7 or 8 degrees, and have it spring back fully to the 'clockwise' position. If it gets sticky it can give you fits of depression, tying to set the spark timing properly!
Im going to send you a p.m. about another internet site where the folks deal with balky Dodge based motorhomes - for fun.

[RV&SAIL]

It was the spark plugs.
The choke had the butterfly closed while I did idles on the jack stands.
Someone said I can clean the plugs.
I think I will go with new ones at todays prices.
And see what can be done for the choke.

[denisond3]

Our RV had a manual choke conversion when we got it in 1991. The Holley carb may have been aftermarket, as I think the 413-1's originally came with Carter 4 bbl carbs. They had square bore manifolds, unlike the 440-3's standard spreadbore intake manifold.
Anyway, since my wife almost never drives the vehicle without me being along, I can remind her to push the choke button all the way back in after we get up to 40 mph for the first time in the mornings.
I did have to oil the choke cable about about ten years; when I took the carb off to put new gaskets on it last time.