Onan Commercial 4500 BGD spec J running until hot and shutting down

[cleghorn]

My BGD shuts off after about 30 minutes of running with or without load. I recently (2 years ago) changed the ignition module and capacitor. Since then it ran fine until a couple weeks ago, when it just shut down and has done the same thing since, shutting down when hot. This week I put on a new coil because the old one had a small crack between the low voltage terminals, and I changed the plug wires because one was showing insufficient resistance. These made no difference in the problem. It still runs from cold up to operating temp and shuts off. I have a service manual, so I have checked everything else as far as settings and tolerances. I pulled out the unit and cleaned it up. I have checked the gas filters, emptied the bowl, and hooked the generator up to a small tank of premium gas thinking maybe it was fuel related. It makes 117 volts at 55 Hz right up until cutting off. I also cleaned up the plugs and changed the oil and filter since it's a lot less of a mess to do while out. The ONLY thing that stands out to me is that the oil level seems to keep rising on the dipstick even though I have adjusted the level a good 5 times since changing. I have never noticed that before, but I wanted some advice before I tear into the thing and head off in a totally wrong(and expensive) direction.

[cornbinder89]

Oil riseing is a concern. Most likely a fuel leak getting into the oil. If enough fuel is getting in to oil, it could trigger a low oil pressure shutdown. Solve this 1st.
As far as temp shut down, 1st and foremost get an accurate mechanical gauge in the waterjacket and conferm the temps and when it shuts down. Shutdown switches can and do fail, and sometimes do so out of range, but a good mechanical gauge will show if that is the case or not.

woops its air cooled isn't it? I have seen some that if they get hot enough the valve clearance dis-appers and looses compression.

[Power]

changed the plug wires because one was showing insufficient resistance?? How so?

The key is rising oil level. Sounds like fuel pump diaphragm has been destroyed by ethanol gas.
Want to test?
Install fresh oil and filter. Disconnect pump, elevate tank 1-2 feet above unit and connect it to carb. If oil does not rise, you know pump is shot.

If you run the unit with gas diluted oil, severe cam wear occurs.

[cleghorn]

Thanks for your help. Fuel causing the level to rise never entered my mind. I assumed something in the oiling system. I meant when I said "hot" that it was at operating temperature. Sorry. And, I will check compression on both cylinders.

---------- Post added at 01:14 PM ---------- Previous post was at 01:01 PM ----------

Originally Posted by Power

changed the plug wires because one was showing insufficient resistance?? How so?

The key is rising oil level. Sounds like fuel pump diaphragm has been destroyed by ethanol gas.
Want to test?
Install fresh oil and filter. Disconnect pump, elevate tank 1-2 feet above unit and connect it to carb. If oil does not rise, you know pump is shot.

If you run the unit with gas diluted oil, severe cam wear occurs.

Thank you for the advice. My service manual says plug wires should have 3,000 to 5,000 ohms resistance, and I couldn't get them in that range, but no shock there, one of the ends on the back wire was burned completely off. I also will check the pump. Didn't know I could check it any other way than replacing, but I think a bad pump makes perfect sense. Does that mean I should replace or try to adjust the float needle valve?

[Kevin K]

Like others have said, let's solve the rising oil level problem first.

The BGD is air cooled, so it can't be coolant leaking into the oil. That leaves gasoline as the only other possibility. The BGD uses an electric fuel pump. An older mechanical fuel pump could have a leaking diaphragm, allowing gasoline to enter the crankcase. Since that's not possible here, the only thing left is gasoline entering through the carburetor. The carburetor is mounted above the engine. If the needle and seat are leaky, excess gas would run through the carburetor into the engine, most likely when the generator is shut down. I can think of three possibilities:

1) Your gas tank is above the level of the carburetor, allowing gasoline to flow through a leaky needle and seat when the generator is stopped.

2) Your fuel tank venting is bad, allowing pressure to build up on a hot day. The over pressure will push the gasoline up past the fuel pump, past the needle and seat into the fuel bowl, and overflow into the engine.

3) Somehow the fuel pump is staying energized when the generator is shut down, pushing fuel past a leaky needle and seat into the carburetor.

While you are solving that problem, pick up a few tools if you don't have them:

A compression gauge. Taking a reading after the engine has shut down will tell you if compression is a problem. An overheated engine (say, from a mouse nest in the cooling fins) can cause the valve clearance to be reduced to a point that you lose compression.

A gap type spark tester that mounts between the spark plug and the spark plug wire. This will allow you to test for the presence of spark when the engine shuts down.

A spray can of carburetor cleaner. A shot of this in the carburetor throat will tell you if it is lack of fuel that is shutting down the engine.

You might also check to see if the choke plate is fully open when the engine shuts down.

[cleghorn]

Thank you Kevin K. I do know the part number of the pump- 149-2331-02. I am pricing them now(ouch)..., and as the oil drains from the oil pan. A needle valve will be much cheaper, so I will order it when I get that part number to start with instead. The gas tank has always been the same level(an OLD Winnebago), the only change was when I put a locking Stant gas cap on when gas went to $4/gal. I do, however, have it hooked to a Snapper mower tank to work on since the camper doesn't move and is 15 miles from home.
I do have a compression gauge, but I will pick up that type of tester you mentioned, and I always have carb cleaner. The choke is electric, but when I go test it in a few I will be sure and watch down the carb throat to see that it stays open. Thanks again for all the ideas.

[Kevin K]

You can test the fuel pump with a pressure gauge to make sure the output pressure is in the range of 2 to 5 Psi.

If you need a replacement, I have had good luck with a Facet 40105 I ordered from Aircraft Spruce.

http://www.aircraftspruce.com/menus/...telectric.html

Don't forget to buy the 479735 fuel filter $4.45

The threads on the inlet and outlet are 1/8" NPT. The pump output pressure is 3 to 4.5 PSI. The specs on the pump are available from the Facet web page:

http://www.facet-purolator.com/cube-fuel-pumps.php

---------- Post added at 02:44 PM ---------- Previous post was at 02:38 PM ----------

Originally Posted by cleghorn

...the only change was when I put a locking Stant gas cap on when gas went to $4/gal.

Was that about the time the problem started? Or did the problem start when the weather got hot? The new cap may not be venting properly. You might want to leave the cap loose for a few days to check for an over pressure problem. Any pressure build up in the fuel tank over 6Psi or so will push the gas right past even a good needle valve and flood the carburetor.

[cleghorn]

Originally Posted by Kevin K

You can test the fuel pump with a pressure gauge to make sure the output pressure is in the range of 2 to 5 Psi.

If you need a replacement, I have had good luck with a Facet 40105 I ordered from Aircraft Spruce.

http://www.aircraftspruce.com/menus/...telectric.html

Don't forget to buy the 479735 fuel filter $4.45

The threads on the inlet and outlet are 1/8" NPT. The pump output pressure is 3 to 4.5 PSI. The specs on the pump are available from the Facet web page:

http://www.facet-purolator.com/cube-fuel-pumps.php

---------- Post added at 02:44 PM ---------- Previous post was at 02:38 PM ----------



Was that about the time the problem started? Or did the problem start when the weather got hot? The new cap may not be venting properly. You might want to leave the cap loose for a few days to check for an over pressure problem. Any pressure build up in the fuel tank over 6Psi or so will push the gas right past even a good needle valve and flood the carburetor.

Much better price than the $109 Cummins part. Still looking for that float needle part number for my Onan 146-0630 carb if you know of anything. I haven't replaced it in the 8 or so years of owning the generator.

---------- Post added at 02:54 PM ---------- Previous post was at 02:49 PM ----------

Originally Posted by Kevin K

You can test the fuel pump with a pressure gauge to make sure the output pressure is in the range of 2 to 5 Psi.

If you need a replacement, I have had good luck with a Facet 40105 I ordered from Aircraft Spruce.

http://www.aircraftspruce.com/menus/...telectric.html

Don't forget to buy the 479735 fuel filter $4.45

The threads on the inlet and outlet are 1/8" NPT. The pump output pressure is 3 to 4.5 PSI. The specs on the pump are available from the Facet web page:

http://www.facet-purolator.com/cube-fuel-pumps.php

---------- Post added at 02:44 PM ---------- Previous post was at 02:38 PM ----------



Was that about the time the problem started? Or did the problem start when the weather got hot? The new cap may not be venting properly. You might want to leave the cap loose for a few days to check for an over pressure problem. Any pressure build up in the fuel tank over 6Psi or so will push the gas right past even a good needle valve and flood the carburetor.

Woops. Missed the last part. When I am up there where the generator is usually mounted I leave the fuel cap loose(Should have posted that). It's too much trouble to fumble through the 40 keys to refuel. Thanks for that idea though.

[Kevin K]

An email address that can accept large attachments (1.7Mb) will get you the 965-0228 parts manual for your BGD.

[cleghorn]

Awesome! That email is bigyellowjeepman@yahoo.com. I have wanted a parts manual forever! Thanks!

[Kevin K]

You've got mail!

Other manuals available:
Service 965-0500
Install 965-0632
Operator 965-0135

[cleghorn]

Got it! Thanks again!!

[cleghorn]

There was trash holding the float needle from the seat, and I cleaned it out with compressed air. I then changed the oil and filter again, BUT the problem STILL exsists! Shouldn't the voltage coming to the fuel pump when unplugged have a 0 volt reading? I just checked and there is .18-.20 volts when the generator is silent. Would that be enough voltage to spin the pump, and if so, is this caused by a bad board?

[Power]

Originally Posted by cleghorn

filter again, BUT the problem STILL exsists! Shouldn't the voltage coming to the fuel pump when unplugged have a 0 volt reading? I just checked and there is .18-.20 volts when the generator is silent. Would that be enough voltage to spin the pump, and if so, is this caused by a bad board?

2 tenths of a volt! Less than a flashlight battery = Possible, but unlikely. Still, I would want to know why and fix it.
Per post 3, I would "Disconnect pump, elevate tank 1-2 feet above unit and connect it to carb". If oil does not rise, you know pump is an issue. If it still does, suspect carb.

[Kevin K]

The BGD is a compact generator, which makes it difficult tell if the gasoline is leaking past the needle and seat. There is no need to keep flooding the crankcase with gas. Remove the carburetor, fuel pump, and metal gas line from the generator. Using wooden blocks, or whatever you have handy, mount the carburetor, fuel pump, and gas line in their normal positions. Run a hose from the fuel pump intake to a gas can. Now apply 12 volts to the fuel pump, and let it sit there and run for a while. If you see gas dripping from the carburetor, the needle and seat are still leaking, and you have work to do. If you can get it to run for ten minutes or so with no leaks, it's probably OK. At that point, I would mount a gas tank a few feet above the carburetor, and let it gravity feed (fuel pump not energized) all night as a final check.

I would not put the carburetor back on the generator until I was sure it no longer leaks gas.

[cleghorn]

Will try that today. After reading the service manual last night, I am also first going to take off the carb(again), flip it upside down, and check the measurements for the float level. I have had the fuel bowl off so many times in the past I may have bent the float getting the bowl off since it's a pretty tight fit. I didn't notice that measurement in the manual when I blew the trash out of the seat. I guess I was in a hurry. I will then mount the carb and gas tank(up above like you suggested) in a couple vises in my shop to see if the needle will seal, and to keep from changing yet another gallon of oil. Yesterday, I tried momentarily connecting, and then disconnecting the lead to the fuel pump to see if I could keep the generator running, and there was no change in the oil level and the unit ran fine. I am trying to avoid buying both the carb AND fuel pump. I also didn't know if it was normal to have a couple tenths running to the pump. When all this started I had checked with Flight Systems just out of curiosity to see if my board could be rebuilt after reading some posts on here, and they said no. Thanks again for all the help.

Sorry. Did not see your 7:46 AM post when I finally responded. Sounds like a plan.

[cleghorn]

I did just as Kevin K suggested and tested the pump/carb. I loosened the carb away from the intake and inserted a piece of cardboard between them to keep any raw gas from getting back into cylinders, and ran the pump for about 10 minutes. Did not leak. Then took carb off and set float setting of .63 inches to bottom of float from casing. When I reinstalled and tested the generator ran perfect for about an hour, and shut off. No fuel from pump. Ordered the Facet 40105 with the 479735 filter from Kevin K's above link, and have them coming at less than $50 including shipping! Waiting on UPS.