18HP Twin Vanguard, Horizontal shaft motor. Uneven surging issue

You might use something like SeaFoam in your fuel per instructions on container before getting into tearing things down, some people have had very good luck with it. Never used it myself, never needed to.

Walt Conner
 
Before tearing into the carb I would be checking the ignition system. I know everyone is focusing on a fuel problem, but a chaffed spark plug wire or kill wire would have the same symptoms. I’d be hooking my inline spark testers to both plugs and make sure that I wasn’t losing spark to one or both cylinders.
 
I would start with a clean fuel system. From the gas cap to the carb. Mower this old and OP found trash in the line. No doubt got passed onto the pilot and main jets ect.... Time for a "Bert-boil" carb cleaning.

On the ignition, I would remove the coils. Sand slash polish the mounting areas to refresh the coil mounting ground. Give the coils a proper shot at either working or not.

Have you ever removed the engine cover and cleaned the cooling fins and ALL around the block? Yearly maintenance item and super critical to these air cooled engines. Fins need to be like a new engine clean.
 
Well, I just replaced the entire fuel system. I verified the Gas tank is clean inside, that it is flowing fuel out fine. I replaced the lines all the way to the carb. New Fuel Pump, and new fuel filter. It is still doing the same thing. I went ahead and threw the in-line spark tester. The left side spark is constant, even when the power cuts out briefly. The right side is not as constant, and when the power cuts out, the in-line spark goes away briefly, then cuts in again and the motor comes back up.

I did not tear into the carb today, but I am not sure that is an issue here. I will probably attempt to get at the solenoid and do a carb clean tomorrow. I have a multi-meter, is there a way to check that the ignition coil is actually bad? I'd rather test it first then spend 50$ on a guess/misdiagnosed part.

EDIT - For some reason the comments after my last post did not refresh until I just posted this. Didn't mean for it to sound like I was ignoring anyone, I appreciate all the advice and help so far :)
 
slomo said:
I would start with a clean fuel system. From the gas cap to the carb. Mower this old and OP found trash in the line. No doubt got passed onto the pilot and main jets ect.... Time for a "Bert-boil" carb cleaning.

On the ignition, I would remove the coils. Sand slash polish the mounting areas to refresh the coil mounting ground. Give the coils a proper shot at either working or not.

Have you ever removed the engine cover and cleaned the cooling fins and ALL around the block? Yearly maintenance item and super critical to these air cooled engines. Fins need to be like a new engine clean.
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I just got this at an auction 2 weekends ago, I am slowing bringing this back to 100%. I do need to pull the engine shrouds and such off. The mechanic who I had originally dropped it off at to get working said I might need to lift the engine out of the frame to get at the coils. I also need gaskets for the valve covers, i see them seeping a little.
 
Testing with the inline tester indicates to me you have an ignition not fuel problem. Looks to me like your going to have to pull the engine on that unit to access the coils. Sometimes you might get lucky and just have to remove the hood. No way to test todays electronic coils without special equipment, but I’m guessing you will find bad wires as I posted before. If so you’ll just have to repair the wiring.
 
Rivets said:
Testing with the inline tester indicates to me you have an ignition not fuel problem. Looks to me like your going to have to pull the engine on that unit to access the coils. Sometimes you might get lucky and just have to remove the hood. No way to test todays electronic coils without special equipment, but I’m guessing you will find bad wires as I posted before. If so you’ll just have to repair the wiring.
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Winner Winner chicken dinner! Found half of a dried husk of a field mouse, and a bunch of chew marks on the coil bodies, and the wires going to and from the ignition coils. The worst one might have been making contact with the engine shroud:

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Also, the bad coil side was where I found the field mouse body, and has a valve cover leak which packed the fins in good. I have to run to the store and get some more cleaning agents, but I already cleaned a lot of packed in greasy dirt on the back side of the cylinder:

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So to be safe I am ordering 2 valve gaskets and 2 ignition coils to be done with it.
 
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Does the surface on the flywheel/stator contacts need to be rust free? All the plates that look like they are for the stator/generator on this thing have surface rust. Wasn't sure if that mattered.

EDIT - Might be the spots for the ignition coils actually; they line up with the body of the coils as it rotates.
 
I see no reason to worry about a little rust on the flywheel or stator. If you have a pressure washer and air compressor or leaf blower, I would be using the to clean and dirt that unit. To bad you threw all that money into the fuel system.
 
Rivets said:
I see no reason to worry about a little rust on the flywheel or stator. If you have a pressure washer and air compressor or leaf blower, I would be using the to clean and dirt that unit. To bad you threw all that money into the fuel system.
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I don't mind. The hoses were starting to disintegrate on the inside. Just from moving them around, the fuel that came out had lots of black sediment. Plus, I don't have to worry about it for a long time now, as the lines I got are formulated specifically to resist ethanol and additive breakdown. If not now, I'd have had to deal with it in the near future probably :)

The hardest part now is waiting for the parts to come in and then remembering where all the shroud bolts go haha
 
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