520-8 Surging problem

[Ricker49 0]

I recently acquired a 1990 520-8. Great shape. 458 hours. Changed fluids, cleaned, etc. and runs great.

EXCEPT when it's been running a while and under load from the mower deck.

Surges badly. Have had it to a mechanic twice. Second time he cleaned the carburetor and pronounced it fixed.

Same thing. Any suggestions?  

[gwest_ca-(File Mod) 11,041]

Long shot but worth a look

Garry

[Ricker49 0]

Thanks for the help. Will give it a shot.

[Jerry77 1,218]

I bought a 516 and it was doing the same thing - after you ran it for several minutes and put it under a load it would surge badly - decided the fuel pump was weak ( but working ) and couldn't keep up with the demand so I put an electric pump on it and the surging stopped...could just be a coincidence  - or not -- I don't know, just happy that it stopped.  For what it is worth - hope you find the problem..

[Kurt-NEPA 755]

My 1888 520H was surging under load also.  I cleaned the carb three times and that didn't help.  Replaced the fuel filter, air filter, and added an electric fuel pump and that made no difference.  So I tried adjusting the governor linkage.  I moved the rod one way and the surging got worse, so I moved it the other and the surging was gone.  I still don't know what made it change, but that P220 is running like new now.

[lynnmor 7,305]

There is a welch plug near the idle mixture screw, be sure that it didn't fall out.

[608KEB 795]

Try cleaning the idle jets. It's a common problem  with onans.  I use a small wire to clean the holes in the jet. 

[tbarnhart 240]

You might also want to check the intake manifold. Those onans have two piece manifold that is put together with sealant. They are known to leak between the halves causing a vacuum leak and leaning out the mixture. I'd start with the carb, but you've been there. The manifold is just something else to check.

[BESTDOGEVER 218]

You can check the manifold by spraying carb cleaner or starting fluid along the edges of it if it speeds up you need to pull it apart and reseal it

[Bigfish 146]

I read the service bullitin and its for 300, 400, 500 and 700 series tractors. What is a 700 series? I have never heard of such a thing. 

[gwest_ca-(File Mod) 11,041]

700 are the zero-turn models

The first was the Dixie chopper and they later used 600 for the series.

 

Garry