Onan runs good for a bit, then starts to stutter

[buell99 1]

Have a D160 with a Onan.....Was testing the tiller yesterday, and after a few minutes of running, the tractor started losing rpm and power.  I raised the tiller and shut pto off and kinda cleared the engine out.  But it doesnt want to run smoothly after.  Carb looks clean, gas tank is clean, new fuel filter and fuel.  Never messed with an onan carburetor, any simple suggestions?  Thanks

[lynnmor 7,585]

How long since the valves were adjusted?

 

When you say "carb looks clean" the outside means nothing, the inside needs to be clean.

 

Check for leaks in the intake manifold.

[buell99 1]

No idea on the valves....I took top of carb off, float seems to be ok, no debris inside...cleaned out orifices where adjustment screws are, sprayed around intake, couldnt detect any leaks

Edited May 2, 2016 by buell99

[boomers_influence 106]

buell

does the carb have a BRASS float?

thank you boomer

[buell99 1]

I believe the float is brass

[953 nut 58,079]

           Have you been using Seafoam; if not, why not?  Lots of folks here have had good results using it.

[Phatboy 565]

Before you go crazy taking this and that apart ,, start at the source,,, is your fuel pump providing enough fuel to the fuel filter ? Then next is the fuel filter clogged or vapor locking ? You can check this by simply removing the filter and putting a piece of tubbing in between to ends of hose and try running like that,,, if it runs good like that try replacing with a new filter,, if the problem comes back then the fuel pump is not providing enough fuel pressure for the filter,,, so you then need to check the vacum line that goes into the back of the fuel pump and check that you have proper vacum.. If not follow the hose back to manifold and check hose for cracks or leaks,,, also check fuel pump to make sure none of the plugs came off the pump ,,, vacum is a big thing with onan engines, also there is a rubber diaphragm in the fuel pump and if it gets a pin hole in it it will cause a lean mixture and act like that because of lack of fuel (rail) pressure , it is not your valve adjustment,,, it is either a problem with fuel pressure to carb ,, some dirt got in carb,,,or the next thing if fuel checks out would be if the electronics behind the. Flywheel are working properly and firing cylinders correctly ,, sometimes that module can go bad and misfire when it gets hot.. But i would start with fuel first and work your way from there,, if you have any questions  or if i can help in anyway just send me a pm ... Good luck..

Edited May 3, 2016 by Phatboy

[Dhodge 528]

I agree with phatboy.  Here is my .02 cents worth.  I have never had to put a carb kit on an Onan carbuator and have owned many.  I have, however had to clean them.  They will act up with the least amount of gunk in them.  The other common problem is as someone stated above---intake gasket at the intake manifold could be sucking air. 

Start the engine and have a squirt bottle of water with you as well as a can of starting fluid.  Once the engine is running spray the area of the intake manifold where it meets the engine.  Just one quick squirt then hit the other side.  Sometimes this will tell you if you have a manifold leak because the engine will smooth out or race a bit.  If so there lies your problem.  If not take your squirt bottle of water and lightly spray the back cylinder head while its running  (do both cylinders one at a time)  If you get steam than you know your firing on that cylinder.  I say this because these Onan's will run pretty damn good on one cylinder.  If you don't have steam from one of the cylinders then pray it is a ignition coil, which can easily be replaced.  These two test can help you quickly find an easy problem, but either one may not tell you much at all either, but it could keep you from doing a lot of unnecessary labor in the wrong area. 

Good Luck!! 

[gasman9504 2]

I have a 520h that will run good for a few minutes then start laboring so hard it acts like its going to stall. If I unhook the B+ wire from the rec/reg it seems to smooth out and run good again. Anyone had any experience with this before?

[Duramax7man7 506]

Beull99,

Questions:
-Did you try looking in the tank at that prefilter? Check for heavy debris around it.
-Have you loosened the gas cap and let it run to see if it was getting vapor locked? 
-Do you see smoke when the engine starts to bog down or nothing? (black or white)
-Any Abnormal smells? (Sweet smell?)

-Did you blow out the carb with carb cleaner spray and air after removing the one vertically placed jet, when you cleaned it?

-Checked the spark plugs for color? (black, brown or chalky?)
-Battery Voltage okay?
-If poor battery voltage did you test the RR for 14vDc output on the middle terminal? 
-If poor battery voltage did you test the outer terminals of the RR to see if the stator is putting out correct AC voltage?


Gasman9504,
 Did you test the middle terminal of the RR with a multimeter while the engine was running? If not you should and see what you get. This could tell you what is going on. Also, you can test the two outer terminals on the RR as those are the Stator contacts. That will 

[gasman9504 2]

been completely through the fuel system cleaned and or replaced everything

no smoke at all

no strange smells

carb has been through the acid bath and blown out with cleaner and air and torch tip cleaners

old plugs light brown brand new plugs still white

battery at 12 volts at rest 14 volts running

14 volts dc from middle terminal 28 volts ac from outer terminals

problem started with no spark one morning checked voltage and module in and out put at coil everything was to spec so changed the coil and wires with onan replacements still no spark now have 2 12 automotive coils wired up and is running on them for some weird reason but still wants to die as soon as volt meter hits 14 volts tried a borrowed RR just for giggles still does the same thing

bypassed the 9 pin connector and replaced fuse block

can try to post a short video if needed

 

Edited August 24, 2017 by gasman9504

[Duramax7man7 506]

That's odd. And it's the same amount of time that it dies each time? 

 

Did you test the vacuum?

 

 Yeah post a video please. If started with no spark then maybe it's Spark Module. I have a 416 that I got and it needed a spark module. It would run for a few minutes and then die. 

[gasman9504 2]

It won't quit running but it gets so close that I might as well shut it off

it seems to be within a minute as to the time it will run good and start acting up its not long at all after the volt meter hits 14 volts that it starts in

vacuum gauge and power meter in dash both indicate same thing all is well till it acts up then vacuum plummets and meter pegs at 100%

I thought about the module but it passes all the test and trigger functions so didn't want to put out that much money until I am sure

to me it sounds like the stator is building a magnetic field somehow and fighting the flywheel but not sure if that's possible

been playing with engines for more years than I care to remember but never seen anything like this

will work on a video this weekend got to find the camera

Thanks

Edited August 25, 2017 by gasman9504

[Duramax7man7 506]

What Meter? The Volt meter pegs at 16 volts when the engine starts to bog down?

So did you test the middle terminal with the battery connected or disconnected? 

Generators do experience something called BEMF. Back Electromagnetic Fields... When the stator coils on a generator are exposed to a magnetic field of a spinning rotor with either fixed magnets on it or an energized set of coils to produce a magnetic field, voltage is produced, but no amperage. Amperage is the movement of voltage. So until something is attached to the stator coils and starts drawing amperage from those coils, no amperage (movement of voltage aka: current for those that are trying to understand this stuff) is made. When amperage starts being drawn from the stator via an attached electronic unit, the movement of electricity (Amperage) through the stator causes it's own EMF (electromagnetic field) and pushes [Back] against the rotors electromagnetic field. In the same way that two magnets push away from one another when the same poles are forced together. Being that there are alternating polarities on the rotor.

 

Generators are designed to have enough horsepower to overcome the full load capabilities of the stator so that the frequency of the electricity and voltage being created will not change any more than a coupe volts from no load to full load. I have a June build 1970 Onan CCKB 6.0; 50amp 120v Genny. The P series Onan engine on it is 19.5hp @ 1800rpms... It's a monster to say the least. 

 I'm not sure if I can bring myself to deduce that the tiny stator on the P220G could come close to producing enough BEMF to make the engine bog down that much at all. The stator windings are made of pretty small copper wire an so are the lead wires that run to the Rec/Reg. IF there were something connected to the stator large enough to draw the full 20amps that it's capable of creating, Anything more would fry the leads and burn out the windings on the stator itself. 

 So unless the tractor has very little compression in both cylinders to only yield a fraction of the potential HP, I don't see something like to much BEMF being created by the stator being the issue.

 It could be that the fuel pump or flow is limited and this is why the engine runs only for a minute before bogging down. The initial fuel reservoir is more full upon starting but doesn't have the fuel flow capability supplying it to keep the reservoir full of fuel once the engine starts and goes through the initial level of fuel. So when the fuel flow can't keep up with the fuel consumption, the engine bogs down. The Charging of the battery will only put so much (and very little in comparison) stress on the engine along with a minute amount of extra fuel consumption. 

 

QUESTION: Have you checked the Capacitor? Try switching that out with another and use the standard coil meant for the engine...? Not sure if that will help. Have you tried switching out Reg/Rec?

 

 

Edited August 25, 2017 by Mastiffman

[gasman9504 2]

compression is in the 130 range both cylinders checked the capacitor with a meter it reads within specs the only thing I haven't checked yet is the intake for leaks will get that done this weekend

volt meter hits 14 volts and engine starts to labor

tractor has an engine load gauge in the dash which is nothing more than a vacuum gauge

tested the RR middle terminal both ways 13.6 to 14 volt either way at close to wide open throttle

checked fuel pump flow seems fine also new pump

tried a loaner RR same results

my son just told me that he was trying to run the tractor and if he feathered the choke it will run better but its a fine line between running and flooding which leads me toward a vacuum leak

[Duramax7man7 506]

Keep us posted if you don't mind. Maybe a video too.

 

[gasman9504 2]

sorry for the delay but I've been through everything and resealed or rebuilt it. the only thing left is to pull the  flywheel and check the key and components under it but with a torn rotator cuff I will have to wait for my son to help cause I can't get enough umph on the puller to move the darn thing. can't figure out where I put the camera and the wife won't let go of her phone to get a video.

[Duramax7man7 506]

How about a pipe on the end of a breaker bar. That would get it. It will typically yield a good "POP" when it gives. 

[gasman9504 2]

the kid got rite away key is fine trigger ring is fine going to order a new ring and module soon and see if that clears it up it's the only thing left that hasn't been changed or rebuilt got to get it going I miss my little bucket tractor

[gasman9504 2]

no idea what I did different than the last 15 tries but went out today put it together enough to test turned the key and it fired rite up now need to get the tins on and let it warm up and see how it runs after warming up