Carb issue with video...

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95Bounder32

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Aug 19, 2018
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12
I have an Onan Marquis 7000 generator that was working fine until I went to start it one day and nothing. After some major research and diagnostics, I determined that it was a faulty control board. The symptom was that when I pressed the start button, all I would get would be a clicking noise which I discovered was the sound of the fuel pump. The starter was dead and the engine wouldn't turn over. Nothing. Just the fuel pump clicking noise. After research, I was able to bypass the control board and starting relay by using a jumper wire between the battery side of the relay and the shunt coil terminal which allowed the starter to engage. This pointed toward the control board as the culprit, and it was. After I installed the new board, I pressed the start button and it fired right up and ran for about 15 seconds and then shut down. I tried pressing the start button again and all it would do is turn over and dump fuel out of the air box. I waited a couple of days and tried and it fired up and then died after about 15 seconds and dumped fuel. Same thing as before. Here is a video. Does anyone think the float is stuck open or something? And if so, is there an easy way to loosen it without removing the carb? (I don't own any stubby open/boxed end wrenches which are required to loosen the carb nuts.) TIA!

https://youtu.be/uA3MpYwGFIs
 
  You can take the float bowl off by removing the bottom nut, I would try lightly tapping the side of the carb with the handle of a screwdriver...dont beat on it just tap it.....Taking the bowl off and putting it back on can sometimes be a little more difficult that removing the carb.

  can you pinch off the fuel line with a pair of vise-grips to keep the fuel from running out, then crank it and run it out of fuel, take the grips off and let it fill back up. do that several times and it may free up. 

    Chances are you will have to remove the carb after doing all that just to find the float has a hole and is full of fuel...flooded
 
Harbor freight sells a metric/sae stubby wrench set for about $10. No Onan genset owner should be without stubby wrenches and a magnet. I just put the magnet on the wrench becauseI know I?m going to drop the nut.
 
My Onan Marquis 7kw was doing the same thing about 3 weeks ago.... Took off float bowl, as others talked about above, and low and behold the float was full of gas. Ordered a new carb ($255) installed it and the genset now runs perfect. While I was in there I did a full service to it as well.
 
chopshop said:
My Onan Marquis 7kw was doing the same thing about 3 weeks ago.... Took off float bowl, as others talked about above, and low and behold the float was full of gas. Ordered a new carb ($255) installed it and the genset now runs perfect. While I was in there I did a full service to it as well.

Couldn't you have ordered just a new float?
 
Rene T said:
Couldn't you have ordered just a new float?

Unfortunately, from my research and what others said here on this forum, no. They do not make replacement parts, or should I say sell replacement parts, for the Onan genny. If I could've found a new float, I would've ordered it for sure rather than spend the cash on a new carb.
 
For what it's worth, the original part number on my 2004 Onan Marquis 7kw was #146-0774. The NEW replacement part number for that same carb is #541-0765.
 
So yesterday I finally had time to work on it. I removed the carb and opened it up. The needle looked pristine, the float action was just fine, the bowl was very clean. I disassembled the float and cleaned all ports. I put it back together and reinstalled it. The generator started up no problem and purred like a kitten... For about 30 seconds and then died. Tried to restart it and voila... the SAME THING! :banghead: Any ideas folks? Is the pressure too high causing the needle to unseat?
 
95Bounder32 said:
So yesterday I finally had time to work on it. I removed the carb and opened it up. The needle looked pristine, the float action was just fine, the bowl was very clean. I disassembled the float and cleaned all ports. I put it back together and reinstalled it. The generator started up no problem and purred like a kitten... For about 30 seconds and then died. Tried to restart it and voila... the SAME THING! :banghead: Any ideas folks? Is the pressure too high causing the needle to unseat?

That is a possibility, is it still spilling fuel like the video ?  One way to check for a defective float, other than the obvious, is to submerge it in hot water. If it bubbles, its bad.
 
Yes, it is. I will give that a try if it fails a different test a person on another forum suggested: Turn it upside down and try to blow air through the intake port. If air passes, the needle valve is bad. If air doesn't, the valve itself should be fine and I'll try your test... Thanks!
 
Curious about what fuel pump you have on this. The carter vane pumps can over pressure when the relief piston sticks, usually from ethanol corroding the housing and piston. I have had them peg a 20# gauge and blow fuel out of the float chamber vents.

Just mentioning this because you asked if the fuel pressure could cause the needle to unseat....short answer is yes.
 
Thank you for the confirmation. I'll look into that as well. The generator ran fine for several trips before this problem arose, so the pump is "original". Maybe the piston is stuck. Of course, the pump is on the very back, ie a pain to get to lol When I have time I'm going to try the two carb tests first since they're easy to perform... Thanks again.
 
If you are lucky like mine, the generator is shoehorned into a compartment with about an inch above it. Im sure I will have to drop the genny to change the rear plug. They sure dont make these things easy to work on.
 
muskoka guy said:
If you are lucky like mine, the generator is shoehorned into a compartment with about an inch above it. Im sure I will have to drop the genny to change the rear plug. They sure dont make these things easy to work on.

NAILED IT!
 
UPDATE 10/06/18

I removed the carb and held it upside down and blew into the fuel inlet. No Air movement. Turned it right side up and had movement. Removed the float bowl and this time low and behold, I saw an air bubble inside the float. After much research, they DO make a kit for this carb!

I have placed an order for the following float kit:

http://www.partsfortechs.com/asapcart/onan-1460453-float-package-for-carb-p-558.html

I'll report back when I get this puppy installed.

Thanks All!
 

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