IH Hydro 70 gas running issue

I havent got a chance to look at this one in person. It is a friend of mine. He thinks its a 74

He says it runs good and clean when cold but as it gets warmed up it starts spitting and shutters off low idle. It also starts spitting black smoke

Before he bought it they had overhauled the carb, replaced cap rotor and plugs. Maybe other stuff. I cant attest to the quality of repair or parts.

He replaced the ignition coil but it still does it. I had him pull the plug wires while it was running bad. All cylinders had spark and no noticeable change in it running. Seems like the issue affects all cylinders.

Im leaning to it not being fuel because it is spitting and sputtering. I would think if it was rich it would just get soft.

Do you think the condensor could cause this? Ignition advance? Valve lash? I dont suspect valve lash since it usually runs smooth and normal at idle (sometimes it will run rough at idle also)

have been having similar but not exactly the same problems with my 666G hydro 291 engine I believe.. don't know if it would affect it or not, but is the heat valve on the manifold working?. bad manifold gaskets? Carb properly overhauled? Mine had a plastic venturi that got gotten too hot and was distorted. Hope you get some good suggestions that can help us both.

The black smoke indicates too rich. Do a plug reading, if they are sooty black, it is too rich.

Possibly the float set too high, a partially sunk float, or trash in the needle/seat. If the fuel is left on will the carb start dripping gas?

If the gas tank is contaminated, flaking rust, it will get in the needle valve.
Try taking a fuel sample from the drain plug in the bottom of the carb. See what is in the sample. if rust, dirt, water, the same will be in the carb, no matter how well it was cleaned. If this is a gravity flow system, you can also check the flow, it should have a continuous flow with the tank valve open. Not slow to a drip or stop flowing.

Be sure the filter screen is in the sediment bowl. There is probably a screen inside the tank above the fuel valve. Be sure it is clean and not corroded away or gone.

What type air filter does it have? If it is oil bath, there is a wire mesh filter inside the canister. It is often overlooked and may be packed with dirt and need cleaning. Also check the inlet for rat packing or mud dobber nests.

As for the ignition system, Do check the spark quality, when it is acting up. Check the spark at the plug wire end, should easily jump a 1/4" blue hot spark to ground. Check each wire one at a time.

Yes a bad condenser can cause weak spark. If you have an old one, try it.

As for the coil, need to be sure it has the correct coil. With the points closed, ignition on, check the voltage at the coil + primary terminal. If it is near battery voltage, there is no resistor and it needs a true 12v coil. The coil will have about 3 ohms resistance across the primary terminals.

If the voltage is lower than battery voltage, down around 6-8v, it has a resistor. It will need a 6v coil. a 6v coil will have about 1 1/2 ohms resistance across the terminals.

Many times this is not understood by counter sales people, they see a coil as a coil, not knowing the importance of getting the correct one. Get it wrong, it will have weak spark, or too much current across the points, burn the points and overheat the coil.

Also check the distributor for side play in the shaft. It must be tight for the points to stay set. Check the centrifugal advance, the rotor should turn a few degrees and spring back when released.

Just a few things to check when you get there, let us know...

I would suggest to check the last item Steve mentioned first, to see if the mechanical advance is free! All the other items he mentioned to look at will be a pretty thorough check.

I have had the oddest things from the simplest thing,check the firing order and the direction. When you pull a
plug wire and nothing changes check the order. Anybody can mess up the order,I know I have!