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Walhonding520

520h "surging?"

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Now that it starts and everything else seems fine, it is "surging."  From idle all the way to full throttle, the engine seems to rev up and down without touching the throttle.  Seems to be less obvious the longer it runs but it still continues? I'm not very good with carbs but I ran a lot of cleaner through it and that helped fit a few minutes but problem persists. Thankd

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WildHorses    121
Posted (edited)

Sounds most like a dirty carb, probably need to clean the jets and the bowl. I would also make sure the fuel filter is new/clean and check the fuel line and make sure the fuel tank is clean. 

Edited by WildHorses
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WildHorses    121

You don't want to run carb cleaner through a carburetor without taking it apart btw. Carb cleaner will swell up rubber pieces and make them no longer work properly.

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Nothing through the carb directly. Just sea foam in the fuel. Lines and filter are all new. I guess next step is to just take the carb off and clean it.

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WildHorses    121

I think you can do most of it without taking the carb off as I recall.  Take off the air filter housing and the top end of the carb will give you access to the jets. Make sure to close the throttle and the choke in case you drop the screws. 

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daveoman1966    1,128

You can take the top off of the carb,...but BE CAREFUL not to drop tiny parts into the throat.   FIRST.... clean off al the dirt and crud from the outside surfaces.  Take a pic or two of how the linkage goes toegether.

Here is the NEEDLE VALVE....it is kinda hidden,so take extra care.  Once the top is off, use your carb cleaner and a tiny brush to clean out the float chamber, both sides.    

520 ONAN (10).JPG

520 ONAN (7).JPG

520 ONAN (4).JPG

520 ONAN (1).JPG

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lynnmor    354

Look at the last photo above.  Down near the bottom of the carb you will see a welch plug, make sure it is still there.  I have had one fall out and it gave the same symptoms you described.

 

As always, check the compression first thing.

 

It may be a good idea to just pull the exhaust, intake, carb, and valve covers and do it right.  The exhaust can then be painted, the valves adjusted, the intake checked for sealing and the carb cleaned thoroughly.  Intake gaskets, especially cheap ones, can get sucked in causing similar problems, so use real Onan gaskets there.

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So I pulled carb all off and cleaned exhaust as well. It was a real mess. It runs much better now but the governor still surges up and down for the first few minutes it runs. If I throttle it down then it seems to be fine at idle and all the way up again. Is it normal for the governor to do this for a few minutes?

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lynnmor    354

Did you adjust the idle mixture screw to get the best idle?  The later model carbs are a bit cold blooded.

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lynnmor    354

If it has an idle mixture screw, it should have been removed and cleaner sprayed in the hole.  After reassembly, it would need to be adjusted for best idle.  The governor cannot work right when the engine does not respond well.

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I did a search for idle mixture screw or adjusting it but nothing popped up. I'm not sure which screw it is or how to adjust it. Ran it a little bit tonight and the tractor runs but surging continues at different times depending on where the throttle is.

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Thank you. I am going to get into it this weekend. 

Is it possible that the spring is to "soft" and won't hold the governor out enough? My neighbor is an old car guy and just suggested it.

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lynnmor    354
10 hours ago, Walhonding520 said:

 

Is it possible that the spring is to "soft" and won't hold the governor out enough? My neighbor is an old car guy and just suggested it.

I doubt it.

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Ok so I've adjusted what I believe to be the idle screw (spring loaded screw with the head facing the muffler).  I don't think the carb could be cleaned anymore. Sometimes the surging or hunting almost goes away but then it comes back. Today while mowing I looked at the fuel filter when it started to act up again and it looked like there was very little fuel in it.  Going up air down hills caused it to surge as well. Is it possible that sometimes it's just not getting enough fuel? I'm just looking for something else to try and getting it running smooth. Thanks

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A slightly different approach but must have been a problem to generate a service bulletin

May be the same but has a different service bulletin number

 

Another

 

Garry

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cleat    1,778

I had one of my 520's act up a year or two ago and it turned out to be the fuel line was touching the oil filter and getting hot.

 

A quick relocate of the fuel line and all was well once again.

 

I have also had one hard to start and that was a fuel pump with a short pine tree needle caught up in a check valve (I don't know how it got in there).

 

Cleat

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Thanks again everyone for the fast replies with a variety of options. I'm going to pull each fuel line and valve under fuel tank just to make sore it's all clean. I will post updates.

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lynnmor    354
10 hours ago, Walhonding520 said:

Ok so I've adjusted what I believe to be the idle screw (spring loaded screw with the head facing the muffler).  I don't think the carb could be cleaned anymore. Sometimes the surging or hunting almost goes away but then it comes back. Today while mowing I looked at the fuel filter when it started to act up again and it looked like there was very little fuel in it.  Going up air down hills caused it to surge as well. Is it possible that sometimes it's just not getting enough fuel? I'm just looking for something else to try and getting it running smooth. Thanks

 

The air in the fuel filter is normal.

 

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Ok. Just used tractor for 5 minutes and surging was terrible. However I just noticed that the tank is almost empty and it was getting worse the less fuel there was in the tank as I finished mowing yesterday.  So it seems that when fuel gets low, the surging comes back and increases. Any thoughts?

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ericj    763

have you cleaned the tank and replace the fuel shut off and fuel line. did you check for leaks around the carb and intake ? with the engine running spray carb cleaner at base of carb and along the seam of the intake. did you check to see how strong the fuel pump is, if the surging is worse on an almost empty tank could be a sign of weak pump.

 

 

 

 

 

eric j

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How do I get the dang valve out of the bottom of the fuel tank. I want to clean it and the screen. Does it just pop out or do I have to unscrew it. I've been careful so far as to not damage it. 

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WVHillbilly520H    2,170
13 minutes ago, Walhonding520 said:

How do I get the dang valve out of the bottom of the fuel tank. I want to clean it and the screen. Does it just pop out or do I have to unscrew it. I've been careful so far as to not damage it. 

Pry it out with needle nose pliers ,the rubber is the seal to the tank the barb on the valve holds it tight, it might not come out without ruining though, Jeff.

Screenshot_20170812-215658.png

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