416-8/P16 Onan Surgeing

[RJ Hamner 1,000]

I took the 416-8 out for her "shake down cruise" today. After getting the mower deck set went ahead and cut the front yard.

It was just humming along without any problems until I disengaged the PTO and the engine started to surge?

Engaged the PTO again and it runs real smooth.  Did this several times with the same results.

This is my first Onan so I'm kinda stumped

[Ed Kennell 35,892]

Dirty carb usually is the cause of the ONAN surge.    Only surging off load may be the low speed jet.

I would pull the jets and clean the orifices with spray carb cleaner.

[RJ Hamner 1,000]

Thanks Ed

I got out the manual for the trouble shooting guide and the only problem that was kinda close was “Governor Hunting”.  Went thru that list and it’s got good non corn sqeezins gas, new filter, and if it was a lean mixture I would wave thought that it would have a problem under load. But like I said this Onan is new to me.  
Guess I get to learn something new. Course that assumes I had a handle on the old stuff?

[oldlineman 1,450]

I just went through this with a 16 hp Onan surging at low speed would not idle pulled top off carb and cleaned tiny low speed holes and bingo good as new. Go with what Ed said ,would be a good and easy place to start. I also use non corn gas.

Edited September 20, 2020 by oldlineman

[lynnmor 6,802]

Agree with the suggestions above, the place to start is cleaning the carb, not making adjustments to the governor till all other possible faults are corrected.  Be sure to check or replace the screen in the fuel tank, all fuel lines and the fuel filter. 

[RJ Hamner 1,000]

Yep everything from the carb is new

[Bill D 1,611]

Carefully remove the top from the carb and clean the bowl and jets along with the needle and seat.  You can't remove the carb from the intake manifold with out removing the manifold from the engine.  Bill

[Bill D 1,611]

BTW, I love that little animated dog.

[RJ Hamner 1,000]

DOG??  That’s me before all my hair fell out!!!

[Bill D 1,611]

Sorry, I didn't realize!

[RJ Hamner 1,000]

A funny (not really) thing happened while taking Ed's advise. Couldn't get to the plug that covers the jet (this is a non adjustable G model).

So I thought that I'd just remove the carb and rebuild it.

Roadblock 1: can't remove the carb without removing the intake manifold (carb mounts from the bottom)

Roadblock 2:  cant remove the intake manifold without removing the exhaust manifold and muffler.

At this point the two tin covers, the hoist points and the oil filler tube bracket seemed like the easy part.

Whoever designed the Onan engine was a sadist.

While I have been waiting on parts I might have gotten carried away again but after soaking the card for two days in the mini dunk tank it is spotless.

And I have an extremely shiny intake manifold and a newly blasted exhaust manifold and heat shield with two coats of 2,000 degree paint

 

[lynnmor 6,802]

While you have the thing apart go a bit farther and adjust the valves.

 

Also, inspect the intake for leakage between the two halves and see if the tins cut into it.

Edited September 25, 2020 by lynnmor

[RJ Hamner 1,000]

To quote a line from an old movie "We got trouble, right here in River City"

Finally got all the parts and some time to do some work.

Got it all put back together

Tried to get it started and it was acting like it wasn't getting any gas.

Checked tank shutoff, on.  Checked fuel pump, shot a nice stream.  Checked filter, not clogged.

Pulled to of carb off. Bingo on fuel in the sump.  Pulled float and needle.  Float OK Needle looked OK then reinstalled (carefully)

Two revolutions fired right up EXCEPT it runs at full throttle reguardless of lever position?????

I didn't touch anything other than the rod going to the main butterfly

Read, reread and went over everything again in the service manual.

To put it mildly......I am stumped Like I said before Onan's are new to me.

[lynnmor 6,802]

3 hours ago, RJ Hamner said:

 

Two revolutions fired right up EXCEPT it runs at full throttle reguardless of lever position?????

I didn't touch anything other than the rod going to the main butterfly

 

If that rod has the double bend at the carb, maybe you have in the hole too far.

[Ed Kennell 35,892]

Does the throttle plate open and close properly when the engine is not running?

[RJ Hamner 1,000]

4 hours ago, lynnmor said:

If that rod has the double bend at the carb, maybe you have in the hole too far.

At present it is in the second bend in the rod?

 

4 hours ago, Ed Kennell said:

Does the throttle plate open and close properly when the engine is not running?

When the engine is off I can manually move the rod that controls the throttle plate 

[lynnmor 6,802]

Put it in the first bend, see the fuzzy photo.

 

[onanparts.com 178]

I put some corrective lenses on Lynnmors pic.....:) Note that the spring here is in the same hole as rod. Should be in the front hole by itself.

 

 

Edited October 3, 2020 by onanparts.com

[RJ Hamner 1,000]

When I was putting everything back together I had thought that it went in the first bend as shown in the pictures. But there is a brown spot on the rod (even shows up in the picture above) and it looked kinda like a wear spot and I thought that maybe I was wrong. Guess I shouldn’t second guess myself. Thanks to you and @lynnmor

[RJ Hamner 1,000]

Everything is back together. Fired her up and let her purrrr for a bit. Idles nice and the throttle now works as it is supposed to.

Went out and cruised the neighborhood through all the gears.

 I think my work here is done

 

Did blast and repaint the exhaust while waiting for parts.  Kinda stinky right now but that will pass.

 

Thanks @Ed Kennell, @lynnmor and @onan parts.com

[Bill D 1,611]

Glad you got it running again.  You may want to contact a member on here named @ALCO.  On September 24 he started a post about making replacement flyball spacer for Onans.  He had some titanium ones he made for sale.  You may want to put one on the shelf in case you need it.  The plastic ones are failure prone.  Bill

Edited October 4, 2020 by Bill D

[RJ Hamner 1,000]

7 hours ago, Bill D said:

Glad you got it running again.  You may want to contact a member on here named @ALCO.  On September 24 he started a post about making replacement flyball spacer for Onans.  He had some titanium ones he made for sale.  You may want to put one on the shelf in case you need it.  The plastic ones are failure prone.  Bill

Titanium?  Sounds pricey. I’ll check. Thanks

[Bill D 1,611]

He's asking $130 each.  Metal ones are getting hard to find.  If you're going to keep that tractor, you'll want to have one around.  Bill

[RJ Hamner 1,000]

Just when you think you have solved a problem......

Tried mowing yesterday.  Filled the tank with gas (fresh, corn free) and everything was running fine. 

After about 5 minutes the engine quit.

Restarted and it ran for another couple of minutes then stopped again. Was able to get it thru fits and starts back on the lift.

This morning went thru the troubleshooting guide going down the list and got to fuel pump.

Started the tractor and watched the fuel filter to see if in fact the pump was the problem.

Engine warmed up and the engine quit (still getting fuel so thats not it) BUT...

A movement caught my eye. Got the engine started again and it ran for a few seconds and the movement was the governor arm moved and pulled the rod to the carb shut.

So I am guessing that there is a problem with the governor when the engine warms up????????

[lynnmor 6,802]

Are you sure it was shut, the governor will fully open the carb on shutdown.