Polaris ATV Forum banner

1 - 11 of 11 Posts

·
Registered
Joined
·
81 Posts
Discussion Starter #1
So new carb and old carb both slightly leak fuel out the overflow only when moving. How can it not leak fuel, I read cam shaft could do this but I'd expect it while idel or rev also. Is this normasl as it seems like a bit of gas
 

·
Premium Member
Joined
·
3,558 Posts
Camshaft would have nothing to do with the carb leaking fuel. There are only a few possibilities there. The good news is all of them are fixable.

Inlet needle leaking
Inlet needle seat o-ring leaking
Float set too high
crack in the float bowl
overflow tube has a hole/crack in it.

It might only leak when it's running because the fuel pump is not working when the engine is off. If it leaks when running, then the engine is probably running rich too. You are gonna want to check the engine oil for fuel and pull the spark plug to make sure.

Why did you replace the carb? Is the new one a cheap knock off or OEM piece. Does it seem to run all right?
 

·
Registered
Joined
·
4,876 Posts
Stave is right on - it's definitely a carb issue and if the new one leaks, probably a float issue - the float level usually specifies a + or - 1 mm. I always set the float to the minus side due to alcohol not having the buoyancy of gasoline (floats float lower in alcohol than gasoline just like boats float higher in salt water than fresh water)
 

·
Registered
Joined
·
81 Posts
Discussion Starter #4
Camshaft would have nothing to do with the carb leaking fuel. There are only a few possibilities there. The good news is all of them are fixable.

Inlet needle leaking
Inlet needle seat o-ring leaking
Float set too high
crack in the float bowl
overflow tube has a hole/crack in it.

It might only leak when it's running because the fuel pump is not working when the engine is off. If it leaks when running, then the engine is probably running rich too. You are gonna want to check the engine oil for fuel and pull the spark plug to make sure.

Why did you replace the carb? Is the new one a cheap knock off or OEM piece. Does it seem to run all right?

It doesn't leak when running, only when moving. I have rebuilt the original carb 3x including setting the float to starvation level as test, put on 3 different new carbs oem. Replaced fuel pump with 3 new ones.

Pretty sure it's not a carb issue. I read that a warn out camshaft could do something like this though if fuel pump wasn't bad.
 

·
Registered
Joined
·
4,876 Posts
Camshaft has nothing to do with it - it is all to do with the carb - try plugging the carb drain hose and see if the engine starts running rich.
 

·
Registered
Joined
·
81 Posts
Discussion Starter #6
The amount it leasks is not enough to tell if it runs rich, and it only happens while moving...... I've read if the exha just valves do not open fully or at the right time that it will back pressure to the carb.
 

·
Premium Member
Joined
·
3,558 Posts
(It doesn't leak when running, only when moving.) So if you are pushing it in the driveway with the engine off, does it leak ? If not, then it leaks when it's running. Try running in neutral and raise the RPM see if it leaks then. What does the spark plug tell you? Is it all black?

(Pretty sure it's not a carb issue. I read that a warn out camshaft could do something like this though if fuel pump wasn't bad.)

Don''t know where you read it, but it's way out there..... The carb and cam are not connected. I will ask again, how does the machine run? What is your compression like? If the cam was worn out, it wouldn't run worth a hoot and the compression would be low as at least one valve wouldn't be opening all the way. The top end would rattle like crazy too. Again at least one valve would be way out of adjustment.

I am guessing that you have the fuel shut off left on when the machine is parked. The fuel pumps are vacuum operated with a low pressure, like 5lb or so. Shouldn't be enough pressure to push the inlet needle open and you have tried other carbs so that shouldn't be a problem unless all of them are bad.

You might be right that it isn't carb, but it isn't cam either. So far the only common parts with everything you have done is your engine and chassis. Let me start at the beginning. Did this come on suddenly? After it was worked on? After someone else worked on it? Or did you buy it this way? And what machine are we working on? I am not trying to be a dick here, just trying to figure out what the problem is. I do not have the professional experience that Latebird does, but I do have 40+ years of mechanical experience.
 

·
Moderator
Joined
·
8,770 Posts
Do you have the carb mount strap #12 and the rubber mounts #8 in place?
The carb will dribble the whole time your going from the engine shaking and vibrating it unless the carb is mounted correctly on the strap and rubber mounts.

Edited to add pic:
 

Attachments

·
Premium Member
Joined
·
3,558 Posts
The amount it leasks is not enough to tell if it runs rich, and it only happens while moving...... I've read if the exha just valves do not open fully or at the right time that it will back pressure to the carb.
If that is true, then every time the exhaust valve is out of adjustment every machine should be dumping fuel out of the carb. That doesn't happen so I don't think that is the case. I have seen 2 strokes that spit fuel out of the throat of the carb but never a 4 stroke.

Polman makes a good point though. If it isn't mounted solidly it could bounce around enough to dribble fuel.
 

·
Moderator
Joined
·
8,770 Posts
The amount it leasks is not enough to tell if it runs rich, and it only happens while moving...... I've read if the exha just valves do not open fully or at the right time that it will back pressure to the carb.
If that is true, then every time the exhaust valve is out of adjustment every machine should be dumping fuel out of the carb. That doesn't happen so I don't think that is the case. I have seen 2 strokes that spit fuel out of the throat of the carb but never a 4 stroke.

Polman makes a good point though. If it isn't mounted solidly it could bounce around enough to dribble fuel.
Yeah, had a guy bring one in a few years ago because it kept dribbling fuel while riding. It wouldn't leak a drop just sitting... only when riding. As I was getting ready to take it off to go through it I found the screws that hold the carb to the strap missing. Put the two little screws in just to try it before taking it off and no more dribbles.
 

·
Registered
Joined
·
81 Posts
Discussion Starter #11
The amount it leasks is not enough to tell if it runs rich, and it only happens while moving...... I've read if the exha just valves do not open fully or at the right time that it will back pressure to the carb.
If that is true, then every time the exhaust valve is out of adjustment every machine should be dumping fuel out of the carb. That doesn't happen so I don't think that is the case. I have seen 2 strokes that spit fuel out of the throat of the carb but never a 4 stroke.

Polman makes a good point though. If it isn't mounted solidly it could bounce around enough to dribble fuel.
Yeah, had a guy bring one in a few years ago because it kept dribbling fuel while riding. It wouldn't leak a drop just sitting... only when riding. As I was getting ready to take it off to go through it I found the screws that hold the carb to the strap missing. Put the two little screws in just to try it before taking it off and no more dribbles.

Pretty sure it's caused by vibration... how I get the vibration to be less, all new rubber dealing with carb stuff
 
1 - 11 of 11 Posts
Top