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v4 looper running very rich?

9

90 140 VRO

Member
Hi, I have been restoring a 1990 140 looper. It has been running extremely rich and I assumed it was an ignition problem. More recently I was running it with the air box off. Never did that before. Well, I may have found the problem. Left bank carbs were trickling quite a bit of fuel prior to butterfly plates. The stream seemed to be coming from black bowl vent pipe? Not sure what to call it. I attached photos of plugs and carbs. Only one cylinder does not seem to be carboning up as bad. Also, temp gun reads 10-20 degree cooler on left bank cylinder head. Any how, before I F'up the motor I wanted to check in with the experts. The carbs were rebuilt with a sierra kit last year. I likely have the float to high on three of the four carbs.
 
Running rich is never an ignition problem. The floats need to be set to level with the gasket base. If you are flooding that bad you can make the cylinders run cooler than they should.
 
If the floats are to high? Would you see fuel trickling from carb throat towards throttle plate? Like I mentioned the left bank has visible fuel trickling and right bank does not.
 
Can you put a picture up and yes the floats to high will cause excessive fuel in the carb. But if it is just idling can be normal for fuel to puddle up in the carbs.
 
Hello, I saw your pic on the other website that is not a vent tube that is the main jet tube. It looks like your floats are to high reset them.
 
There was a steady stream of fuel and the plugs are nasty with grizzle on the left bank.. The right bank has no visible streams or puddles of fuel. Thanks for the assurance..
 
I think I mistakenly installed the seal under the float seat. I'm fairly certain that plastic OMC float bowls do not require the seal. The sierra mix and match rebuild kit includes the seal and I remember using it. WTF..... I would think this would raise the fuel level in the bowl enough to be a problem..
 
That would lower the fuel level because you bring the seat closer to the float. When you readjust your float flip the carb upside down and set it to level.
 
OK, hold it. Too much BS flying....

Study the relationship of the bowl to the float. You will see that the fuel level barely makes it to maybe 3/4 of the way up the sides of the bowl.
So, how can fuel flow out the main nozzle?

Even with the plastic washer on the seat (it should NOT be there), that is NOT enough to make a serious difference in fuel height in the bowl.

Two things....needle and seat leaking, causing fuel to flow out nozzle.
Or, you have mis-diagnosed it completely. Maybe the fuel is NOT really coming from the main nozzle.

I misdiagnosed one in just the same fashion. I diagnosed a fuel leak coming from that brass fitting in the front of the venturi, the one just in front of the plastic nozzle.

Freaked out that the fuel level could be so high. Of course it cannot. It turned out to be the formed fuel input line to the carb ABOVE, leaking around the outside of the carb body, and into the carb below.

Double check your diagnosis.

Subject of leaking needle and seat.....OK, first thing....does the primer bulb pump up firm and stay that way until you start the engine? If not, you got a fuel leak somewhere, or the bulb is bad.

Use your mouth. With carb off engine, in normal running position, blow into the fuel inlet. Air should flow freely.
Turn carb over and listen for float to change position...rattle. Blow again. No air should flow.
 
Before people say BS they should remember how carbs work so I will take you to carb school. The main jet is on the bottom which means when the bowl fills up you add extra weight in the bowl. This combined with fuel being pulled through acts as a siphon effect compound that with the pump pushing against it. I have seen it dozens of times and usually it's not much of an adjustment to fix it. The floats being high absolutely will cause this especially when it's 3 out of 4 doing it after a rebuild. Even with everything set the fuel in the carb is never level it is always moving because the motor does not idle or run absolutely smooth. I remember yamaha had a problem with one of their snowmobiles in the early 90s. When it was running the fuel actually walked up the side of the bowl and flooded them out.
 
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This database of comments and fixes for outboards needs to be kept as clean as possible.

In other words, NO BS. The response about "the weight of the gas in the bowls" is so wrong it deserves to be removed by the mods.
Most people do not like it when I openly criticize posts. Sorry. So sad. flying's schooling on carb operation is just plain wrong.

Now, to show you, I will take you to physics school....:rolleyes:

Consider the bowl and nozzle extending down into it. Basically a bowl with a tube coming in from the top.

If I fill that with water, the level of the water in the tube will be the same as the level in the bowl.
You say weight of new water will push more water (or gas) up the tube. OK put more water in. Level at both points goes up.
Remove water. Level at both points goes down.

Ok, if I fill the system with ANY liquid...alcohol, gasoline, massage oil....the level in the bowl and tube will be the same.

Now consider a 5 gallon bucket. Fill it half way with water, gasoline, I don't care. Insert a clear, 1/2 inch id vinyl tube. The level of the liquid in the bucket and tube will be the same.

Using the same setup, insert an additional clear vinyl tube. This time make it a 2" id tube. Much bigger, much more fluid inside it.
The level in the bucket AND both tubes will be the same.

How can this be, when the "weight" of the fluid in the small tube is much less than the "weight" of the fluid in the big tube?
Add more liquid to the system. The level in all tubes and the bucket rises to the same point.
How can this be if "the weight" of the added fluid pushes the fluid up the tube?
According to you, it should take more "weight" to push fluid up the big tube vs. the small tube. But the levels remain the same???!!!! Whaaaattttt?

So, your contention that the weight of the extra gas in the bowl pushes gas up and out of the nozzle, with the opening of the nozzle being at least 1 inch above
the level of the gas in the bowl is ridiculous.

The reason the levels stay the same in both tubes and the bucket is that the atmospheric pressure on the open bucket fluid is the same as the atmospheric pressure on the open ends of the two tubes. The atmospheric pressure "pushes down" if you will, on all fluid surfaces, and the levels equal out to the same point.

AND THAT IS A FACT.

There is NO WAY the small extra "weight" of the added gas from a raised float can "push" the level of the gas in the nozzle tube up an additional inch to have it overflow.

So how does the gas come out the top of the nozzle tube? That is for another lesson. But you can school yourself!!
Google is your friend.

Google "venturi effect" and get the answer.
Just to help you wrap your mind around the venturi effect, consider the air to be the fluid, because it is.

Oh, and here is another twist on the issue....it is just about the same explanation as to why plane wings have lift, and can fly.
 
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I will make this very simple . Why when you overfill a built in boat tank why does the gas come out the vent sometimes. According to you it cannot happen because the vent is usually 2ft higher than the tank. But it happens a lot combination of pressure and weight in the tank causes it to come out. So what you are saying is a carb cannot be overfilled. Also your theory of atmospheric pressure on both ends is wrong. The carb works under vacuum all the time if the motor is running so there is no atmospheric pressure inside the carb. Since you have vacuum and an overfilled carb where does that gas go does it just stay in there or does it take the path of least resistance which is out the jet tube. By the way your bucket and tube theory try this suck on the end of the tube and lay it on the ground the gas will siphon out even though it has to climb up the bucket to drain. This happens beacause the weight of the gas. Another your airplane wing theory proves my point there is less pressure above the wing which causes the plane to take the path of least resistance. Just think of the floatbowl as a small gas tank that is looking for a way to empty itself the float is the valve that controls that. You just need to remember carbs only work when the motor is running trying to adjust one when it's not running is just chasing your tail. I learned this because it has happend to me I set the carbs on a merc 150 could have sworn they were perfect. When you pumped the ball everything got nice and hard started the motor up gas was pouring out of the carb. Simple adjustment of the floats and all was well.This is my last post on this subject as I am not getting into to this argument I gave some solid advice did not expect this. By the way my knowledge doesn't come off of google I have my 30 yrs of experience to fall back on.
 
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Several of the floats flanges were bent and would obviously allow to high of a level of fuel. The main jet pick has a set of holes much higher than the others. I'm assuming this may be a tell tale built in for techs? Any how, everything else in the carbs looks pretty good. One thing I do not like is the tab that holds the metering valve has a small burr on it. It must be a miss match in the tooling that cut the stainless steel flange. I smoothed that out and polished it to a mirror finish. The rods that hold the float are crap too. It looks like they used plain old SS rod stock. So, I made up some new ones of the same dia. but polished SS. I'm fairly certain that this will help. Also, I did firm up the primer and it did hold. I also, drained the bowls carefully into small mixing cups to measure the amount of fuel in bowls for comparison. One was modestly low and one was very high compared to others. Anyhow, will fire up the lil biaaaaach tonight.
flyingscott said:
Just got a pm from the op the float levels are off he is going to let me know the results when he gets them reset.
Click to expand...
 
That's why I usually buy the factory carb kits they usually have replacement pins and floats just for future thought. They cost a little more but are usually more complete. Good job on diagnosing and taking the carb apart.
 
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???----When a motor is running there is atmospheric pressure in the float bowl on top of the fuel.--------The tube sticking down into the bowl is in the venturi and gets a negative pressure from the air flow through a venturi.---This brings the fuel up into the airstream !-------Some study of --" bernouli's principle " helps in understanding how this works !!!
 
Yep....what he said. ^^^^^^

It aint the weight of the fuel, and it aint the fuel pump pressure. It is as racer states.

I don't think the float level has very much affect on the way an engine runs, either. Consider the tilt angles the engine is expected to run under.
Just what does that do to a perfectly set float level? Fuel in bowl is all over the place when the engine angle changes.

In other words....the fuel level change due to a missing OR added plastic washer under the seat is NADA with regards to how the engine runs.
It just is not that sensitive.
 
Agreed , as an example my 1967 Lawn Boy power mower runs just fine untill just before the carburetor goes empty.-----Runs just fine when mowing on slopes too.--------Carburetion / float levels are often mis-understood
 
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