Onan engine problem?

[hummod 0]

I have an Onan 16 horse engine that I installed into a 520 temporarly until

I can get the valve seat fixed on the 20 horse. Everything went well and the

engine ran great. The problem is that a few minutes after engaging the mower

deck the engine rpm will start to creep up. I have to set the throttle 1/2 way

to get the same rpm as when I started. Once I disengage the mower deck and

wait a few minutes for the engine to cool things go back to normal. The governor

is working fine and I took the top off the carb and it was clean. It does seem to be

a heat issue but how hot is too hot? I do expect temperatures to rise under the load of a mower deck. I get no temperature alarms on the 520 assuming they work. I did use the intake from the 20 horse on the 16 horse. Could I be dealing

with a faulty carb. I plan to change the carb and intake back to the 16 horse tonight to see what happens. I cant think of any reason that the carb would change a given rpm at a set throttle position. Maybe a temporary lean condition? Any thoughts? The tractor runs and mows fine both ways but I know this is not

right and don't want to hurt the engine.

Thanks

Larry (hummod)

[htopjimmy26 3]

I wish I knew more about Onans but, it kinda does sound like a governor issue to me, you could check and see if you have a intake leak sucking air or maybe try the old 16hp carb. Good luck :scratchead:

[hummod 0]

Thanks for the reply htopjimmy26. I did get out and put the other carb on the

engine. What a difference! Problem gone. What I noticed right away was the

gas filter was at the normal half full. Before the swap the gas filter was full of

gas without any air at all. The engine seems to run cooler and no more backfire

out the muffler at throttle-down. There must be a problem with the carb from the 20 horse engine. That could have been what caused the 20 horse to drop

it's valve seat. Now to figure out what the problem is with the carb.

Larry (hummod)

[canam1991 2]

if you think its running hot take the sheet metal panels of the motor and power wash the cooling fins on the jugs and head

[davovinch 0]

Hello Hummod,

I just joined up b/c I got a '89 416-8 with the onan motor. I put a bunch of time into this tractor and took it out to mow the other day and lo and behold it started to creep up in speed after I was mowing for about 15 to 20 minutes. AARRGH! what a bummer, I felt like a fool because I thought the only repair would involve tearing down the governor. Carb? issue? did you ever figure it out? I started another post not knowing you had run into this.

Best Regards,

Dave

Meadville, PA