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Onan 4.0 BF 3CR


I have a Onan 4.0 BF 3CR genset with low hours that I use for emergency power, It has not been used...

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Old 03-27-2006, 07:55 AM
Jim Lane Jim Lane is offline
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Default Onan 4.0 BF 3CR

I have a Onan 4.0 BF 3CR genset with low hours that I use for emergency power, It has not been used for some time since we don't get too many outages in Southern California so I went to start it and it cranked over, started normally but then died. I tried again but now I smell gas so I removed the inlet elbow from the carb and gas is flooding out over the top so I figured the float was stuck from the old gasoline.
I removed the top from the carburetor and cleaned out the internal parts with spray cleaner and compressed air then reassembled it, after I dried out the plugs
It started up and ran but now the engine hunts without a load and varies between 120/130 volts when it is cold but when I load it with about 500 watts it smoothes out at about 120 volts.
After the great flood, I checked the oil and it smelled like gas so I drained and refilled with fresh oil. {what is the best oil to use?}
The set still hunts without a load.
When I removed the parts from the carb I counted all the turns and replaced the adjusting screws back where I thought they should be.
What adjustments do I have to make so it runs smooth gain? What is the procedure?
Also what is the best procedure for storage?
Running the engine until it dies from no fuel?
That is what I do and this is the first time it got stuck.
Thanks for the help.
Jim
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Old 03-28-2006, 07:51 PM
Gunny Gunny is offline
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Default Re: Onan 4.0 BF 3CR

Jim:

Sorry it is giving you some trouble. Those are some very well made and reliable machines.

The hunting is you because of an incorrect air fuel mixture.


Straight 30 weight, 20 50, a good synthetic, what does the manual recommend for your expected temperatures? If it was mine, I'd run 20W50 synthetic because of the encountered in these air cooled engines.

Good idea to run the carb dry if you plan to not use it for a while.

My Onan manual sez that on your BF, Idle out 1 1/4 turn, main out 1 1/4 turn, float should be 5/16 with a tolerance of + or - 1/32".

To set the float level: Invert the fuel bowl cover so that the float assembly is resting on the inlet needle valve. Place the bowl cover gasket on the bowl cover. Measure the distance between the bowl cover gasket and the end of the float (side opposite the needle valve). If the setting is incorrect, remove the float assembly to adjust. Bend the float near the shaft to obtain the correct level.

Mixture screw adjudtment should be checked with every engine tuneup and when ever a carb problem is suspected. Before adjusting, be sure the ignition system is working properly. If the carb is totally out of adjustment, use the settings above as a starting point.

Start the engine and allow it to warm up until the choke is fully open.

Remove all load and connect a voltmetter and frequency meter to the generator output.

Pull the governor linkage towards the front of the set so that the throttle lever on the carb is resting aginst the throttle stop screw. Adjust the throttle stop screw to obtain 90 to 100 volts on the voltmeter.

Continue to hold the linkage. Determine the best idle mixture by first turning the idle adjustment screw inward until the voltage drops(indicating a lean mixture) and then outwards until voltage drops again (rich mixture). Over the narrow range between these settings the generator voltage (or frequency) will remain at its highest, Set the idle screw slightly rich from the midpoint. Still holding the linkage, readjust the throttle stop screw to obtain 90 to 100 volts.

Release the throttle and apply full load. Set the main adjustment screw using the same proceedure as above in regards to the voltage drops. Again run it slightly rich. Remove th eload and set the governor to at no less than 108VAC and 57 HZ with full load and no more than 132VAC and 63 Hz no load. 57Hz is 1770 rpm and 63Hz is 1890 rpm.

Add and remove the load several times to make sure the generator does not hunt of bog down.

Carb problems nor resolved by mixture adjustments are usually the result of worn parts or gummed up internal passages. Carb rebuild kits are available. A thorough cleaning may be the solution to your problem.
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Old 03-29-2006, 07:40 AM
Jim Lane Jim Lane is offline
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Default Re: Onan 4.0 BF 3CR

Thanks for the information; I will have to see if I can adjust the carburetor just as soon as it stops raining here in sunny Southern California. It is now officially annoying.
I also have a 4.0 CCK-3CR {I think it is a 3CR, can't remember} a bit heavier than the BF-3CR I got from a guy who couldn't get it to work, A new set of brush springs and it works like new.
In the control box there are 2 wirewound resistors and several relays seems real simple, anyhow one of the resistors and the wire looked a bit toasted and the wire had a bad connection. I resoldered the wire and all seems fine
The manual {Parts Manual CCK Genset #927-0220} I have for it shows all of the parts but it does not have a schematic or wiring diagram covering the controls.
What part of the circuit are these for? Battery charging, regulator?

Also are the relays on these units proprietary or they an industry standard unit?
I guess while they are working I should disconnect them and log the coil resistance and characteristics so I am not thinking I shoulda done that after they burn out.

{Quote}
Release the throttle and apply full load. Set the main adjustment screw using the same proceedure as above in regards to the voltage drops. Again run it slightly rich. Remove th eload and set the governor to at no less than 108VAC and 57 HZ with full load and no more than 132VAC and 63 Hz no load. 57Hz is 1770 rpm and 63Hz is 1890 rpm.

How much of a load do you mean? 1000 watts or the full 4000?


BTW is there a SERVICE manual and OWNERS manual in addition to the PARTS manual made for both of these units?

Thanks for the help.
Jim
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