Jump to content
cafoose

520-HC surging at idle

Recommended Posts

I just got done mowing and when I parked my 1988 520-HC with the 20hp Onan I noticed the engine was surging at idle between 1500 to 1700 rpm and the vacuum gauge fluctuated between 4 to 13hg. At full throttle it seemed to straighten out and run smoothly. Does anyone have any ideas what I should check? It ran fine while mowing at full throttle.

Share this post


Link to post
Share on other sites

I ahd a similar issue with my 520H.  the cure:  Take the top off the carb and clean it out....careful not to loose the needle seat valve under the float tab.   The is an instruction link in the forum somewhere on how to to this.

Edited by daveoman1966
  • Like 1

Share this post


Link to post
Share on other sites

I agree with Dave.  My 88 520H was doing the same thing.  I pulled to top off the carb and cleaned everything with carb cleaner and the problem went away.  You can pull one of the jets out from the top and clean that too.  Watch out for that needle valve and the link that connects to the choke, both go missing easily.

 

Kurt

  • Like 2

Share this post


Link to post
Share on other sites

OK I will clean the carb later and let everyone know what happens thanks for all the quick responses I really appreciate this forum and I'm glad to be a part of it. :thanks:

  • Like 2

Share this post


Link to post
Share on other sites

I took the top off the carb yesterday and blew out all the passages and cleaned the fins too while I was at it. I also removed the muffler to get the mixture screw out and blew through that passage as well. I used this post which helped a lot:

 

 

When I put everything back together it ran great with no surging and steady vacuum. :greetings-clappingyellow:  I would like to thank everyone for your help :thanks:

  • Like 3

Share this post


Link to post
Share on other sites

A steady low vacuum would indicate a vacuum leak.

 

A surging vacuum that moves in relation to the engine surging is just responding to the throttle plates opening and closing. That is just the governor trying to maintain engine speed.

 

A steady high vacuum under no-load conditions is a good thing.

 

Back in the days when cars had carbs, you would adjust the mixture screws to get the highest vacuum.

 

  • Like 1

Share this post


Link to post
Share on other sites
On ‎5‎/‎13‎/‎2016 at 1:18 PM, cafoose said:

I took the top off the carb yesterday and blew out all the passages and cleaned the fins too while I was at it. I also removed the muffler to get the mixture screw out and blew through that passage as well. I used this post which helped a lot:

 

 

When I put everything back together it ran great with no surging and steady vacuum. :greetings-clappingyellow:  I would like to thank everyone for your help :thanks:

It is always nice to hear "The rest of the story"!   I think it helps me when someone posts what they did and what worked when they had a problem!

  • Like 2

Share this post


Link to post
Share on other sites

Don't forget to ensure that your engine governor linkages are nice and tight. 

 You can do this by popping of the clips at each end of the governor linkage and lightly pinching them with some pliers to tighten them up. Sometimes the heat and rattling can loosen them up and cause surging as well... 

  • Like 1

Share this post


Link to post
Share on other sites

Whats the easy way to unhook choke link to just pull top of carb ?

Share this post


Link to post
Share on other sites

you can either unscrew the choke cable lock screw or unscrew the entire link from the carb. But it does wiggle free without those.

Edited by Mastiffman
  • Like 1

Share this post


Link to post
Share on other sites

You can just carefully lift carb top up and while being careful not to bend brass tube coming down from top into a hole in the main body, carefully tilt top and the small link will unhook.

 

Carefully remove this link and just reverse for reassembly. Do not drop or lose this link.

 

Once you have done this once or twice it gets easy.

  • Like 2

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Recently Browsing   0 members

    No registered users viewing this page.

  • Similar Content

    • By cafoose
      Does anyone have any pictures of how the lift assist springs attach to the Ber-Vac snowthrower on the 520-HC? I know it's past the snow season but I would like to get it done while it's on the tractor so I can remove it to put the deck on and be ready to attach it next year without any delay. 
       

       
    • By cafoose
      I just got finished making up a crank rod to turn the snow thrower chute on my 520-HC with a Ber-Vac snow thrower. Here are some pics of how I did it. I am very pleased with the results. I used a 3/8 drive universal and a 3/8 drive extension. My neighbor welded the extension into a piece of 1/2 inch conduit and the universal into a piece of 3/4 inch conduit. Then he welded the original crank handle in the other end of the 1/2 inch conduit. The universal snaps into the extension giving me the flexible joint I need for the angle and also it's easy to remove when I remove the snow thrower with no tools. I can let the universal attached to the snow thrower. The 3/4 conduit has a 3/8 hole drilled in it for a bolt to fasten it to the chute gear on the snow thrower. The 1/2 inch conduit fits perfectly in the hole on the support bracket attached to the tractor. All I need to do now is make an attachment for the lift assist springs on the front quick hitch bracket.
       

    • By cafoose
      I am still trying to attach the Ber-Vac W0246D snow thrower to my 520-HC. I was busy the last few days and just got around to working on it again. Here are some pics of the parts I have for it. I think I may be missing some parts. I got a lot of useful info from everybody here the last few days and I want to thank you all for your help so far. For more pics of what I have please see the topic "New Toy" I posted last Thursday March 3.
       

    • By cafoose
      I just got a 1988 520-HC with a Ber-Vac W046D snow thrower. I downloaded the manuals from here and they just basically show the parts. I would like to know how to attach it to the tractor. If anyone has any pictures of a similar snow blower on a similar tractor or could at least point me to a topic or thread that could help me attach it I would really appreciate it.
       

×