How much fuel should be in the fuel filter?
I recently disassembled and cleaned the Nikki carburetor on a17.5 HP engine. I replaced the needle as well as the gaskets.
And noticed that there's barely any gasoline in the clear fuel filter. I have a photo that maybe hard to see but it was half full before I did the cleaning.
Now hardly any fuel is in the filter. I am wondering if this is normal or symptom of something I did wrong. I did mow for 20 minutes and did not seem to run out of fuel. But what caused the difference?
To be sure it wasn't a blockage, I removed the fuel line from in front of the filter and the tank drained with full force. I then refilled the tank and remove the line at the carburetor and it also drained fine after a couple seconds. The filter is a couple weeks new.
Good to to know.
Can someone explain why before the carburetor rebuild it would be always at half but after so little? Did I have a micro leak that was allowing air in?
Since I bought this mower I had drained the tank . One was to change the filter and one was to remove the shut off on the bowl to drain. Each time that filter was half full and after carburetor clean, the amount is very little.
I am glad it is normal but I am curious why that changed.
It is normal for the filter to fill when sitting, but appear to empty out when the engine is running, or after you shut off the engine. It has to do with the filter being on the intake side of the fuel pump and the pump reduces the pressure in the fuel lines when running and the filter acts like a restricter as well as an expansion tank, therefore causes the fuel to vaporize in the filter. Different filters will fill at different rates due to variations in filter media.
I will see if I notice it but over a two day period it did not fill up any more. Before cleaning it was always half full. As long the new level works, I fine with it .I was just curious about why it changed states.
The fuel inlet is flush with the end of the filter body but the outlet is a tube that goes all the way to the end of the paper cone,
Thus you get air trapped in the end of the filter.
Usually with bouncing around the ait will find its way into the outlet and the filter will fully fill.
Some times I put them on backwards for cutomers who do not understand fluid dynamics and think it should always be full.
Different bands of filter will have a different outlet tube length.
The long tube is to support the weight of the wet paper element.
From a filtering point of view it makes no difference which way they are fitted other than the junk will be inside the paper so you can not see it.
Thanks. This is all well and good. However, the answers are about why it is normal to have little fuel in the filter.
What I am asking, and Maybe no one knows, is why the same filter would be half full, all the time, and after the carb service is at very little. It is the same filter. Was it a sign something was not as tight in the carb an was leaking air so more gas could leak in?
#9
BlazNT
OK so if you want it full then put the filter on the gas tank side first and wait till it fills up then put the carb side fuel line on. Its level has to do with the way you put it on. Trying not to spill fuel.
OK so if you want it full then put the filter on the gas tank side first and wait till it fills up then put the carb side fuel line on. Its level has to do with the way you put it on. Trying not to spill fuel.
It is OK if you dont know the reason. The filter was not removed or changed. Same direction in each case and installed as the arrow on the filter shows.
I am not saying I want to have it full. At first I wanted to be sure this was not a sign of something negative from working on the carburetor . Please understand this. I understand it is working fine as it is the lower level.. That was not the question I have been raising since then. . The question was out of curiosity of why there was the level change that was immediately noticed as different.
#11
cpurvis
Go to the nearest university that has a school of engineering, seek out a Fluid Dynamics professor and ask him.
He will immediately begin spewing out Greek-letter named variables that explain the balance of pressures in painful detail. Painful, incomprehensible detail, but detail, nonetheless.
disclaimer: I do not know why. I can only fathom an "IF, AND, THEN" type guess.
IF the filter is on the suction side of the fuel pump, AND something is causing a restriction of flow between the fuel tank and the filter, THEN the filter is a space in which fuel can vaporize, causing a bubble.
Gasoline vaporizes readily. That's what we like about it. (Unless it vaporizes before it gets to the jets.) It doesn't take much of a pressure decrease to vaporize gasoline.
It is OK if you dont know the reason. The filter was not removed or changed. Same direction in each case and installed as the arrow on the filter shows.
I am not saying I want to have it full. At first I wanted to be sure this was not a sign of something negative from working on the carburetor . Please understand this. I understand it is working fine as it is the lower level.. That was not the question I have been raising since then. . The question was out of curiosity of why there was the level change that was immediately noticed as different.
Ok. so you remove the gas line when you worked on the carb? Did you raise the fuel line above the gas tank so gas would not leak out? Did you drain the tank so it would not leak? Did fuel have time to evaporate out of the fuel filter? I would think you would have had to do one or more of the things I asked about which would change the fuel level in the filter. This is only guessing.
So when I changed the fuel filter the gas was drained from tank and lines as I bought it used and wanted a fresh start.
The filter filled up to the level seen in the first photo. There wasn't any delay. When I fully tested the mower I wondered about a surge on start up and it was suggested it could be Dirty carb. So I put Seafoam into see what it would do before taking off the carb. I thought maybe there could be a mess in the bowl so took off the fuel line from the carb and drained all through the filter if I recall. I did not have a shut off nor did I want to crimp The line so I just thought it was easy enough to drain since I didn't have a lot in the tank.
No matter where the line was disconnected, the filter Always returned to half full in short order.
I reset the valve spacing and when that did not solve my issues, I went the route of removing the Nikki carburetor to clean. It was very clean inside. I ran a wire and cleaner through all the Jets and such to be sure.
I replaced the needle and paper gasket and bowl gasket.
Yes, the tank was fully drained by taking the line off at the carburetor and drained it through the filter into a jug.
It was only after I put it all back that the amount in the filter changed. I ran it for 20 minutes and it was fine, sat a few days, no level change, and I had it running to adjust the cable and fuel mix screw. Level still as photo 2.
What some are getting hung up on is trying to tell me why the level is so low and it is normal.
As I said, great I will take it!
However, why it was different than before was not explained. I was only curious.
So my educated guess is that air was leaking at the carb enough to allow more fuel to enter the filter.
#14
Boudreaux In Eunice La.
I can buy 10 filters from the same shop and each one will have a different level in them. Barometric pressure has a lot to do with what you are talking about.
You are getting into the brass tacks of things when you ask a question about why did it do that. Simple.........
Look at your coffee cup when you pour coffee in it. If the bubbles go to the outside of the cup then it's high pressure. If the bubbles stay in the middle then it's low pressure..... Thats your barometer right there.........
You can fill it up by tilting the outlet side of the filter up (the side with yellow clamp) when the engine is running. The carb will start sucking the air out of the filter chamber. If the carb is working properly, the engine should run normally but the filter will be filled. Activating the choke will speed up the process.
Thanks but I am not asking for how to fill it. I am not trying to get it back as it seems to be running with the lower level.
I while I had concern when I first posted, now merely pondering the reason for the difference.
