Running lean

[Wheelhorse84 87]

I just went through my 416 with an onan. Plugs fresh filters you name it. I just took a new plug out to check cause the old ones had white on them. The new ones already have white on them after a half hour of run time. What could cause this? It runs fine just a very slight surge.

[puddlejumper 67]

I am not a onan mech by no means, But white on them should be a sign that it is burning a little oil, Does it smoke any or have you added any additives to the fuel, Marvel mystery oil are anything of that nature, Since you just purchased this tractor maybe the PO did,Give it some time and run a tank or two of known clean fuel through it before getting to excited about onan valve guide issues and such.

[Callen 64]

It could be the additive package in your gas. In the summer, I've seen red and blue tinted plugs from our Honda clone race motors.

[TT-(Moderator) 1,131]

Does anyone else remember when light-colored plugs and exhaust meant an engine was running perfect?

 

In the case of the P series Onan, it might be an intake manifold leak - but you also might need to get in there and really clean the high speed circuit in the carb.

Since it might be wise to remove and soak the carb, replacement of all intake gaskets should be done then.

 

You can check for vacuum leaks, but I will not tell you what product to use due to the liability.

If you Google it, you will find various suggestions on what to spray in the area to find the leak(s).

[Wheelhorse84 87]

He did put sea foam in the tank but I drained all the gas And put in fresh new gas.

[Wheelhorse84 87]

Will it hurt the engine if I run a tank or two through it running lean?

[puddlejumper 67]

Yes, TT and somehow I read white and flakey not just a light residue. Guess to eager to find a problem.

[Wheelhorse84 87]

The crazy thing is other than a little surge here and there it runs great. Kinda strange

[TT-(Moderator) 1,131]

What does it do under load?

 

My 1990 416-H will surge a little at full throttle until it starts working.

I suspect a little slop in the governor and/or a weak spring, but it has never bothered me enough to address it.

[Wheelhorse84 87]

When I engage the pto no mower deck is on the machine it ran fine. The surge is very slight and intermittent.

Would it run fine if is running lean?

[TT-(Moderator) 1,131]

Will it smooth out if you close the choke a little? (mine does)

 

How about a nice, clear, close-up picture of the spark plugs?

[Wheelhorse84 87]

On its way

[Wheelhorse84 87]

Old oneNew one

It's hard to see on the new one

[JackC 617]

Any surging that I experienced with my 20hp Onan went away after the carburetor was soaked and cleaned and new gaskets installed.  

I could not believe the crap that was in the bowl and around the float valve seat when I disassembled the carburetor.

I also could not believe how quickly it started and how good it ran after the cleaning.

 

A carburetor cleaning and overhaul is probably one of the single best tune up procedures you can do.

[Wheelhorse84 87]

The surge is very slight I'm just concerned with the white plugs

[puddlejumper 67]

That doesnt look bad to me,are you letting the engine warm up and run awhile,I know its cold up there just curios what kind of run cycle the plug expierenced since installed. Is it setting at a idle or running full throttle for a while. Really and truely that looks pretty normal from here.

[sorekiwi 761]

I'm kinda with Mitch here, I dont think I'd be too worried about it.

 

It takes a while for the insulator to get that tan color that we get used to seeing.  And it looks as though its getting a brownish ring around the centre electrode.

 

I think I'd give it a few more hours work and then have another look, assuming that the engine is running OK.  As Terry mentioned above, a good quick check to see if its running a little lean is to wait for it to get to normal operating temp and then try just a little bit of choke - if the motor likes it you are lean.

[artfull dodger 394]

From my Onan service manual, if the engine is surging, then its running lean.  The surging comes from the govonor trying to compensate for the lean mixture.  The white plugs are the result of such.  Considering we have a known issue of intake valve seats popping out of the alum block.  Running lean = running hot and thats not a good situation for the valve seats. I would also do a valve adjustment to the book specs as that can also cause a lean running engine by not allowing the intake valves to open enough to get a proper charge of air/fuel mixture in the cylinders. Spec for the valves on a cold engine are .005 intake and .013 exhaust. You should hear the valves ticking at low rpms if its set correctly.  My buddies JD318 with a replacement Onan had valves way out of adjustment at 475 hours.  Intakes were over .13 and the exhaust I was unable to get the .05 feeler gauge inbetween the valve and the lifter. It was hard starting, and running lean enough that it was heat bubbling the new hood decals on each side from the muffler heat. The carb did have issues as well, it had the accelartor pump design(poor carb set up and known issue).  I installed a brand new carb from Onan, still a sealed design but no accelerator pump set up.  Tractor starts much better, and runs smooth with no surging under load or no load.   So, I would recommend a good carb cleaning and adjusting the valves.  Onan recommends this every 400 hours for engines run on gasoline.   Mike   P.S.  I use carb cleaner to spray along the joint of the 2 piece intake manifold to look for leaks.  If the engine stumbles, then it sucked in some of the carb cleaner. There are other things you can use, but IMHO the carb cleaner is much safer around a running spark ignition engine.  The 2 piece intake leaking is another known Onan issue on older engines. easily fixed with permatex gasket maker.  

[Wheelhorse84 87]

Thanks guys the machine has 369 hours on it so I guess ill check the valves. Are the accessible or does the engine need to be taken out?

[TT-(Moderator) 1,131]

Manual (pick one) : http://www.wheelhorseforum.com/files/category/14-onan-service-manuals/

[Wheelhorse84 87]

Thanks TT

[Hydro 131]

I'm curious to know if the engine idle speeds up when it's hot?  The plug tips where white like that on my 16 and I thought it was running hot.  It never surged though.  

[JackC 617]

Some recommend that the valves be checked and serviced every 200 hours.  Minimum should be 500 hours.

Good to learn how to do it or make sure you have a spare engine on the shelf.