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Horsing tuff

Onan Carburetor cleaning

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Can anyone direct me to a good step by step  Carburetor cleaning how to? For a mid 90’s 416. My horse is surging and I think it needs cleaning.

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You can try a non-invasive approach first -- add Sea Foam to a fresh tank of gas and run it; might take a few tanks to clean it all out. That was all it took to get rid of a mild surge with my 520H when I first got it. (It had sat too much the year before I bought it, so stale fuel had left some deposits.)

 

The traditional quick cleaning method with Sea Foam is to mix some with the fuel, and also start up the engine, open up the air filter housing and slowly pour Sea Foam into the carb -- slowly at first so it keeps running for 15-30 seconds, then let it flood with the Sea Foam. Let it sit for at least 15 minutes, then start it. It will be really smoky for a few seconds as the gunk blows out -- do it outside or have the garage door open. For "normal" dirty carb problems, this usually gets rid of the crud fairly well -- it will break down deposits and flush them out to be burned in the engine. Better than spray cleaner which tends to just drive gunk deeper into the carb.

 

For a carb that's been left to sit for a long time with some seriously stale fuel, you'll want to have the engine manual on hand to follow for disassembly and then give it a proper dip in carb cleaner. Ethanol-blended fuels can leave some nasty deposits if they're left to sit too long -- especially in an engine and fuel system that was never run much after the fuel chemistry switch. The ethanol partially dissolves all the old gunk and varnish in the fuel system -- but if you don't keep running fuel through it -- multiple tanks worth -- you don't get all the old gunk burned out. Then when it's parked, the ethanol evaporates and all the nasty stuff drops back out of suspension and makes a worse mess. And sometimes it eats into old rubber fuel lines and the like and makes more sludge.

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Thank you Eric. I got some “mechanic in a bottle”, to put in  the gas. Guys at my local mower shop said they have luck with it. My 416 has never acted like this before. They governor arm is pushing the throttle arm back and forth, making it surge a lot. Is that possible because the carb is dirty? I have ran the treated gas in it a little.  I have also made  the mistake of running a non-Onan oil filter. I will be changing that imediatly. Would that make the governor function improperly?

Any help would be great!

Mike

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6 hours ago, Horsing tuff said:

Thank you Eric. I got some “mechanic in a bottle”, to put in  the gas. Guys at my local mower shop said they have luck with it. My 416 has never acted like this before. They governor arm is pushing the throttle arm back and forth, making it surge a lot. Is that possible because the carb is dirty? I have ran the treated gas in it a little.  I have also made  the mistake of running a non-Onan oil filter. I will be changing that imediatly. Would that make the governor function improperly?

Any help would be great!

Mike

I don't think a non-Onan oil filter would cause a surging issue, but if the original fuel lines are still on there I wouldn't be surprised if that isn't most of your issue as I myself figured if they looked decent on the outside they were fine on the inside wrong my Anniversary 520H bought new started the dreaded surging even after trying the "easy" fixes like Seafoam/Berryman's B-12 ect new fuel filters pulling the top off the carb several times I still had black specs in the bowl from the rubber slowly deteriorating from ethanol fuel(kilked a fuel pump too) after a complete carb tear down/rebuild, new rubber lines and ethanol free fuel seems to be doing fine even sleeping for months between start ups (dedicated winter rig at moment) just a thought out my own experiences, Jeff.

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Update on my issue. I changed the fuel filter and running the treated gas in it. She now runs as smooth as a baby’s be-hind. Thanks for the help everyone👍

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Agree, the oil filter isn't going to affect the fuel system, and lots of us use alternates to the OEM Toro/Onan oil filters depending on local availability/preferences.

 

Ethanol in the fuel can definitely eat away at fuel lines from the inside out - which sends more particles and sludge into the carb. Older fuel systems built prior to the introduction of ethanol in fuel -- which started in the late 80s and early 90s -- are the ones affected the worst. Manufacturers had to change to ethanol-safe rubber compounds, so the 90s-era tractors aren't as likely to have this problem unless a previous owner replaced a damaged fuel line with some old tubing sitting around in the shop.

 

One thing I might recommend checking is the fuel shutoff/screen assembly at the tank. The screen should be present in the tank, standing up (not bent or crushed) and not covered in gunk. Sometimes the screens get damaged or clogged. If it's missing entirely, crud is free to get into the fuel lines which will definitely cause problems down the road again.

 

Any fuel filter will work, but the clear ones like Onan used (Doesn't have to be OEM, the generics are just fine) will let you check to see if gunk or particles are getting in. That way, if you suspect crud in the tank or fuel lines breaking down, you might spot the trouble early.

 

My experience with "ethanol-safe" rubber fuel lines is that they're usually fine unless some kind of harsh additive was used in high concentrations for a while. Once the rubber compound has been attacked, the ethanol in the fuel will continue to break down the inside surface of the rubber hose, releasing tiny particles -- bad on their own, and worse if they form a sludge-like mess. Meanwhile, the outside of the hose will seem perfectly fine.

 

Old, pre-ethanol rubber lines will tend to get hard and eventually crack and leak where they bend or where they're clamped. I had this happen on a motorhome built in the early 80s -- the hoses cracked at the fuel sender coming out of the tank. Which was 30 feet back from the engine, on top of an 80-gallon fuel tank that was not going to be dropped safely without cutting the rusty bolts on the straps that held it -- which was close to the area where the leak/fumes were coming from... So the solution instead was to measure carefully and cut an access hole in the floor above the sender so the old lines could be replaced (Did I mention this was a recirculating system, with a feed, return, plus breather/vent line, all cracked and leaking? :angry-banghead: ) The cut-out section of floor was mounted to an oversize metal plate so it went back in like a plug, and the flooring was put back over to hide the repair like nothing ever happened. What a mess!

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