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Onan 6.5 NH Running Badly


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  #1  
Old 05-06-2015, 05:27:11 PM
Viking66 Viking66 is offline
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Default Onan 6.5 NH Running Badly

Hi all I am having some trouble with my 6.5 NH at my Camp.

It is a Onan 6.5 NH-3CR 16004P Serial # L833729368

It wants to hunt real badly and then run ok for a few seconds, then hunt. I put up a video here which will show what I mean; http://youtu.be/qF2_IagRr5s

It does this on both Gasoline, and Propane. It started to do this one night and has continued since.

Here is what I have done so far. I cleaned and blew out the Carb, changed Intake Gaskets, New Governor Spring.

Can a leaking Intake cause this to happen? Clean behind the Heads and Valves?

Thanks all

Last edited by Viking66; 05-06-2015 at 10:01:05 PM.
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Old 05-06-2015, 05:57:00 PM
Max Thompson Max Thompson is online now
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Default Re: Onan 6.5 NH Running Badly

Sounds more like loss of ignition spark than fuel mixture (intake leak).

I would eliminate the low oil switch (after making sure the oil level is good), put a spark tester in the leads.

A test light on the + side of the coil will also let you know if the problem is in the low ignition voltage or possibly on the high side of the coil.

Someplace to start anyway.
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Old 05-06-2015, 05:59:27 PM
Sir Thomas Sir Thomas is offline
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Default Re: Onan 6.5 NH Running Badly

Before starting turn the main screw on the carburetor clockwise until closed but not too tight then counter clockwise 1 1/4 turn. Then turn the idle adjustment screw in clockwise till closed and the back out counter clockwise 1 full turn.
Check the length of the governor link. With the engine stopped and tension on the governor spring, the stop on the throttle shaft assembly almost touches the stop on the side of the carburetor. (One more turn of the governor ball joint would allow the throttle shaft stop to touch the
carburetor.) Tighten lock nut.
Check the choke setting.
Start the engine and see if the problem is corrected.
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Old 05-06-2015, 06:02:53 PM
yellowlister yellowlister is offline
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Default Re: Onan 6.5 NH Running Badly

if it runs fine for awhile is not the adjustments.. like max said ignition issue or vacuum leak.. check the points plunger it could be worn unevenly..

the spark tester will show whats going on..
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Old 05-06-2015, 06:11:13 PM
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lokay5 lokay5 is offline
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Default Re: Onan 6.5 NH Running Badly

I've found that hunting is often caused by a lean mixture, and being that it hunts on both gasoline and LP I would suspect an intake air leak, possibly between the two-piece intake manifold halves. A spray bottle of water is a good test tool.
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Old 05-06-2015, 06:29:47 PM
Viking66 Viking66 is offline
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Default Re: Onan 6.5 NH Running Badly

I did check and re-gap the points, but didn't check spark.

I have another Coil to swap out, and I will check the plunger. It just up and started doing it after a good 300 hours of running perfect.

As always, this place is awesome!!!!
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Old 05-06-2015, 06:33:12 PM
Max Thompson Max Thompson is online now
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Default Re: Onan 6.5 NH Running Badly

Quote:
Originally Posted by lokay5 View Post
I've found that hunting is often caused by a lean mixture,
Listening to the video, it is not "hunting", it is trying to die.
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Old 05-06-2015, 06:35:32 PM
MBB MBB is offline
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Default Re: Onan 6.5 NH Running Badly

You can check with carb cleaner around the intake near the gaskets and where the carb sits. If the engine speeds up when spraying those areas you have a leak.
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Old 05-06-2015, 06:49:30 PM
Viking66 Viking66 is offline
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Default Re: Onan 6.5 NH Running Badly

Now that you mention it, it is more like dieing than hunting. Thanks for the better terminology.

I did spray some WD-40 that I had out there, didn't notice a difference. Maybe Carb Cleaner would show it better. I will get some and try that too.

Last edited by Viking66; 05-06-2015 at 06:52:49 PM. Reason: Added info
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Old 05-06-2015, 07:21:24 PM
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Default Re: Onan 6.5 NH Running Badly

Or an unlit propane torch, when you get near the leak the Rpms will pick up. Cheers Dan
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Old 05-06-2015, 08:24:23 PM
David C David C is offline
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Default Re: Onan 6.5 NH Running Badly

It sounds like an ignition problem more than a fuel problem. I would take a spare condenser to the camp with you. I recently had a CCK that had been running for about 8 hours when it started acting up. It was running on N/G and adjusting the mixture did not help. I cleaned the points, which did not help, so I left the point box cover off while it was running and noticed that the points would randomly arc excessively when it acted up. Put in a NOS condenser in and the points arced less all of the time, plus it quit the random arcing. It saw another 8 hours of service with no more problems.

As others mention, I would hook a test light to the positive side of the coil to see if you losing power to the coil.

David C.
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Old 05-06-2015, 08:35:36 PM
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Default Re: Onan 6.5 NH Running Badly

Sounds like bad points.
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Old 05-06-2015, 10:09:23 PM
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Default Re: Onan 6.5 NH Running Badly

Since it does this on both gas and propane it pretty much can't be a fuel issue. Others have said crappy points, maybe plug wires arcing maybe a loose/poor connection in the ignition circuit somewhere, maybe a relay contact is iffy, maybe a wire is broken inside the insulation, wiggle them all to see if you can force it to happen. Tighten all screws on terminal blocks. My buddy replaced about 10 thermocouples on his boiler before calling me, I replaced it again but then noticed a loose crimp on a spade terminal Cheers Dan
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Old 05-07-2015, 10:22:17 AM
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Default Re: Onan 6.5 NH Running Badly

Viking 66 last year about this time my 6.5 NH started acting up like this I had it tuned up and running like a new one it had new plugs points and condenser for 5 days it had me pulling my hair out . Jack DD said it sounds like a bad condenser ? so I put the old condenser back in that goes to the points hit that start switch and it ran like a new one. never gave the new condenser any thought it had less than ten hours on it. OD
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Old 05-07-2015, 10:42:56 AM
RSCurtis RSCurtis is offline
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Default Re: Onan 6.5 NH Running Badly

I'm with Max, it has an ignition problem.
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Old 05-07-2015, 11:12:41 AM
Sir Thomas Sir Thomas is offline
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Default Re: Onan 6.5 NH Running Badly

To measure resistance in the primary circuit,
connect one ohmmeter lead to the positive (+)
terminal and the other to the negative (-) terminal
on the coil. The resistance should be between
3.87 and 4.73 ohms. A high resistance value indicates
an open circuit or poor connection inside
the coil, and the coil should be replaced.
To measure resistance in the secondary circuit,
connect the ohmmeter leads to the two high tension
terminals (see Figure 6-8). The resistance
measured should be between 12,600 and 15,400
ohms. A lower resistance value indicates a
shorted secondary winding. A high resistance
value indicates the coil has excessive internal
resistance or an open circuit. Replace coil if not
within specifications.
-
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Old 05-07-2015, 12:36:51 PM
len k len k is offline
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Default Re: Onan 6.5 NH Running Badly

I agree on trying to die. Since it's doing same on gasoline and vapor fuel it's likely not a fuel issue, I say ignition problem.

Check for intermittent low voltage connections first, put a small 12V test light between coil + and engine frame, check to see it stays on steady while engine is trying to die. Then put it across coil and see if it changes brightness as engine tries to die.

Back in the day on cars first thing you do for a problem like this is replace points and condenser, they go bad. Were cheap to replace. With no points in modern cars easy to forget you have to do this periodically with old engines.

Last edited by len k; 05-07-2015 at 12:52:18 PM.
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Old 05-07-2015, 04:49:26 PM
Viking66 Viking66 is offline
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Default Re: Onan 6.5 NH Running Badly

Thanks all.

The points I have are fairly new, but I think I have a new set and a Condenser here in my Garage. I now think, since it was pointed out...lol that it is ignition since it is doing it on both fuels.

I will not be able to go to my Camp this weekend, so I will not have a report back until a week from tomorrow. I will let you all know what it was.

Thanks as always!
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Old 05-15-2015, 03:10:16 PM
Viking66 Viking66 is offline
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Default Re: Onan 6.5 NH Running Badly

The Winner is..........Condenser. :

That was the first thing I decided to change and got lucky. She purred just like she had been doing before

I truly appreciate all of the suggestions and advice.

As always, this place is Awesome!!!!
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Old 05-15-2015, 06:06:01 PM
Max Thompson Max Thompson is online now
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Default Re: Onan 6.5 NH Running Badly

Thanks for letting us know what the outcome was.
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