onan 4.0 fuel problems

[bill emery]

 i have a onan 4.0 model # BFA-1R/16004C . i had a problem in the main gas tank of the RV. the fuel pick up rotted away inside the tank. It left alot of small black mesh stuff in the bottom of the tank. I had the carb replaced on the onan and installed a inline fuel filter and changed it every time we went out for the weekend.

 It ran great for a year now i don't have gas in the carb.i replaced the fuel pump, installed a new fuel filter. It just won't fill the carb bowl. it will run if i spray carb cleaner into the carb but i think it is only running on the carb cleaner not gas. what could keep the gas from going into the carb? is there a fuel shut off on the carb? thanks for any help you can give..bill

[Russell E Johnson]

Sorry, I am not at home so I cannot look at my Onan to tell you how to get it off.  I was just thinking from rereading all the posts again, is the linkage free or is it bound up?  If the linkage is bound up then the throttle is not going to operate and allow gas to go from the bowl to the carb.  The linkage will be the hardest part of removing the carb because you do not want to bend it.  The linkage is hooked to, for lack of remembering the proper name, a sensor.  This sensor is activated by the generator.  When an increased load is added the generator sends a signal to the engine which increases its speed to keep the generator putting out power.  

I am sorry I don't remember for sure how it functions but I think it is by vacuum.  If the diaphragm is bad the linkage will not move and the motor will not start and it would account for why it just quit running.  Try checking the linkage for movement  and see if what the linkage is hooked to will also move freely.  

As for taking the carb apart, the jets are preset so there is no adjusting them, the linkage and the float are where particular care is needed to keep from bending them.  You will need a gasket set and there should be no need to mess with the idle screw.  

If the linkage and what it is hooked to move freely personally I would take the carb to a mechanic and have them rebuild it, more expensive but in the long run it may be cheaper.  

If the linkage is hooked to a vacuum/diaphragm set up you can check it by using a syringe to see if it moves back and forth, if not then it is bad and may be the cause of all the problem since the bowl is already full of fuel and thus the float is in the closed position and not allowing more fuel to enter.  

Sorry this is so disjointed, but I hope you get the idea.

[bill emery]

 the linkage moves freely. i think it is working. i like the idea of blowing air into the fuel line to dislodging  the junk in the card.. have to wait till tomorrow to go to the yard where the RV is

[Matthew Tritt]

Does it have an electric fuel shutoff switch? If not, them the greatest likelihood is crud stuck in the float valve. As you already know, getting working access to many RV gensets is a major PITA, but Onan sets are usually pretty easy. Or not. Regardless, it sounds like you're going to have to get in there and see what's up.

[John "T" Nordhoff]

  Bill, Im late here Ive been to a tractor show all week so here goes. As I recall???? that's an older Onan and actually those carbs are simpler and easier to work on then later ones.

 If gas cant flow into and fill the carbs bowl she cant get gas and run. It enters the needle valve and if the float is low in the bowl the valve is open so the bowl fills. HOWEVER if the needle valve is stuck closed from gum or varnish or rust or crud gas just cant enter and fill the bowl. Those carbs aren't hard to get off and disassemble but you gotta get the needle valve and its seat clean and free so as the float rises and falls in the bowl the valve opens and closes when it should. id take the carb apart and clean the bowl and float and especially the needle valve and seat. If I recall (no warranty I may be thinking the wrong Onan) that carb has an adjustable power valve in the bottom center of the bowl which richens the mix if its turned out but leans it if screwed in, SEE IF THAT HAS A KNURLED TURN NUT AND SCREW IT IN AND OUT A FEW TIMES RETUIRIGN IT TO THE SAME APPROXIMATE POSITION which may be something like 2 or 3 turns out from screwed in???

 I think your needle valve is stuck closed not allowing gas to enter and fill the bowl but Im not there

 John T 

[bill emery]

 thanks John, i am going to try to remove the carb tomorrow after work. i will look for the screw at bottom of the bowl

[John "T" Nordhoff]

  Bill, BEFORE you remove it, one last thing to try, the needle valves is the first thing gas encounters when it enters the carb so you may try to remove the gas inlet line right on the carb and spray Gumout Carb Cleaner in as you tap the side of the carb which may let a stuck needle valve release and drop down. Again if its the older Onan??? (new ones no adjustment) it will have a power adjustment screw in the very bottom of the bowls center that adjusts the main flow but that has nothing to do with a stuck needle valve which may not be letting  gas enter the bowl in the first place. Still it needs to be open (maybe 2 or 3 turns) to run.

 John T 

[Matthew Tritt]

The "power valve" you're talking about is actually the main metering jet needle. If there is indeed varnish/gummy crud stuck in the float valve aperture, it will also be in the float chamber. Even though the heavy stuff falls to the bottom of the chamber it will, most reliably, find it's way into the jet(s) and idle supply tubes during operation. The only sure way to prevent this is to remove and thoroughly clean the carburetor.

Better to do this at home than in the campground.

Matt

[John "T" Nordhoff]

  I definitely agree, my first advice would be to remove and clean the carb as nasties can accumulate in the bottom of the bowl, I just mentioned he might try to spray gumout  into the inlet which might free up a gummed varnished stuck needle valve.

 Very fun chattin, hope we get him going

 John T

[Matthew Tritt]

Hope so! Hard doing this from afar, isn't it?

[james]

Hey guys...have a 1972 dodge sportsman rv with a 318 my guestion is do i need to incorporate a lead substitute in the fuel or were the vavles converted by then?
It runs good and i dont want to burn it up...also..what is the top highway speed its capable of..it hasnt left its nest yet

[Lakota Wolf]

On your dodge sportsman,,( I had a 79 with the 318),,, cruising speed is safe around 60 to 65,  because you dont need to be running nascar timming when camping. and as far as the valves,,,, yes, some gas stations have put in methanol etc,, and if your not getting spark knock,, That valve ping niose, ya should be ok.. BUT,, I had the 79,, 318 and I would put in a half bottle of LUCAS OIL in each fill up and never had a problem. I sold my 79 and they guy who now owns it has rolled 40 K plus miles and still runs Lucas Oil on every fill up and he said still runs like a champ and he cruises 65 on average.. You should be ok either way,, I just chose to use the additive on the old motor,,, plus kept the ole 2 barrel clean.

[bill emery]

  i would like to thank everyone for their response. it has been alot of help. the problem tured out to be little bits of black rubber in the carb. they were blocking the the flow of fuel into and thru the needle valve. i think i will replace the fuel line all the way to the fuel tank.sorry it took soo long to get back to everyone, finally had time to work on it..thanks everyone