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Onan p216G bad after 10..15 minutes

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Hello Guys,


After having had a little fun with my "new" 316-8 onan P216G version.

The engine sounds like it is short on fuel...I don't hear any backfiring.

But i think i do hear "strokes" without a "firing" (ill record it later sorry...hope u know what im trying to indicate)


Now, i want to have it "perfect" as far as i can do...im not knowledgable but the forum is of great help !


So far:

I changed fuel lines, I did a decarbon (heads came of) I cleaned the carburetor all new gaskets, new sparks ...

-BPR5EFS (seems to be the same)

-I measured the coil ...ohms are within specs.

-new air filter, fuel filter etc.

-While cleaning the heads i didn't notice anything wrong with the valve seats but that could be of course...

-And set the valve distance to specs (0.13...0.33mm..(speaking from my mind))


Put it all back and it did ran a whole lot better...no smoke..I can engage the PTO without shutting the engine down which seemed to be the case previously as it was really struggling.....but still.... it isnt running that well (after say 10min just like previous).


The engine is back on my desk, as for me it was rather dirty the first case and i didnt do "all" my mistake, bit to excited about my first horse !

...and you just can reach everything better...i want to be "sure" (also remeasured the valve clearance) etc.


I dismounted the flywheel, and yes, there was loads of rubbish the magnets all clean now.

(Made sure the flywheel came of nice and easy...btw...got that warning :-))


Im now thinking in lines of : (planning to do:)

1- not enough fuel... (but why would that "happen" after 10...15 minutes ? maybe the fuel pump ? I can check that if it runs bad..and i "put a litlle in the carburetor"

2- due to heat "something" changes and bad air gets sucked in...I can check that if i have it mounted back on by bringing some WD40 while it is running and see if the sound changes

3-The carburetor has vacuum issues ? ...or perhaps the "float" isn't good. I will check that..

4-I didnt do anything yet with those breather intake tubes and filters...maybe its there... need to read up on that.



Im now at the stage where i'm trying to "search" reading a manual i read :

IMPORTANT: Do not hold flywheel from turning with a pry bar in the fins. Doing so may damage the fins.

That line i do not understand ... its from another forum but should be about the onan engine. 

Could some one give me a hint ?


Other "hints" that i could do to "verify" now...while it is on my working desk would be highly welcomed !!!


Ill go back to "cleaning" ... Thank you for your time in advance !

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check the gas cap, it has a vent that may be blocked and will cause a vacuum on the gas tank. When engine starts to shut down try opening the cap and see if that helps.

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my guess is a bad coil.

You checked the resistance when it was cold. However, after 10-15 minutes you would pick up enough heat on a weak coil to change your good number.


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Did you make sure to re-install the heat shields over the exhaust ports located under the air cleaner assembly. 

I've seen where that can cause vapor lock to occur. 

Good luck and keep us updated.



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Hello All !


Thank you all for responding !...really need it to get this sorted.



I cleaned all... i checked valve distance still 0.13mm and 0.33mm

The heat sinks are "on".


I changed the float of the carburetor so it was "flat" when it was upside down.

It was a bit to low


First test... It started at once and sounds oke... but then..after a while it goes again.

I removed the gascap and I put some pressure on the tank, maybe it was wishful thinking...but perhaps it did run a bit better.


1- Measured the ignition coil after 5 minutes and resistance went up to about 20 Ohms (thats just beyond specification..so ill probably get a new one...just in case)

2- Measured compression .... the cylinder close to the the steering wheel gave 75 psi the one up front 55 psi. (oeps)

   (measured with no spark plug inserted, engine was cold, no air filter, choke and throttle both wide open, and rotated the flywheel by hand...(hope this is correct?)

3- I notice the oil pressure light blinks when i "switch" the test button (the others just light up)

    I notice the oil pressure light blinks when i start but turns off as it runs

4-When it runs...and i push throttle i actually do see "smoke"..

5-When it runs and i put my hand in front of the exhaust...some strokes (just every now and then) seems "with more power"

   With that said, i think i also hear a "no explosion" stroke ...or it did not fire....not sure how i should call that...

6- The governor doesn't seem to be 100% ...at full throttle it slowly goes down in RPM.

7- The longer it runs the worse it gets..


Actually had a saturday night spare "google" hour and looked at some small diesel engines to replace the Onan, but...

IIm not "done" yet hihi... 



Think i need to test compression valve leak before i take the head off.

I will verify all the "torques" (head / manifolds)

Perhaps next time ill run it with a tank on top to "by pass" the fuel pump...just in case..


On the positive side :-) ....im starting to be really good in dismantling the engine hihi




EDIT: .... I put about a spoon full of straight SAE 30 in the front cylinder and did the same test...though its no easy to verify but i gained roughly 10 psi on that cylinder.. so that tells me the piston rings or piston needs to have a second look.

But then still...it is "low".. and doesnt sum up for the rest of the issues..

Edited by henryhpsd

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oke... I have two "Torq wrenches" ...

One  2 to 20 N/m and the other from 19 till 100 newton meter.


If used the big one now.. and set it at 22 N/m

The headbolts all needed and extra halve turn compared to my "other" (both brand new)

...and front cylinder compression now is @ 75 newton/meter just like the back one is... thats positive !!!

Think ill stop right now hihi..did have so many positive feelings last couple of days 


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Putting it back together I noticed another "thing"..

The sparkplug head (?) from the ignition..one i could press firm and would hear the connection...

With the other i couldnt hear it, so i took a screwdriver and tried to push the connection a bit tighter (also cleaned it)


Just went for a quick test run...


I drove for 5 minutes being the happiest man on earth...good day today !


It ran as smooth as it ever did.

But still, when i move the throttle it "holds back" and needs a second to level out (?) ..its not action-reaction..

but more like:


"hmm not sure but ill change rpm" .

owh there is where he wants me to be...

and smooth.


(during that "thinking" time" it sounds like the choke is open or so)


I'm almost certain it isn't producing the RPM's it could and RPM's go down ..while driving (full throttle) then i adjust the throttle back up...and oke again


I'm thinking those issues are governor related ?


Possibly my the "biggest" problems were solved by updating torque on head bolts (maybe my 1 new torque wrench isn't that good?) and possible the bad spark plug connection ? Almost scared of giving it another go ....hihi


Feeling im almost there :-) 

Edited by henryhpsd

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Did some "governor / carburetor adjustments


What do you guys think ?



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