Carburetor float needle

[marts99ss]

1989 Yamaha Pro-v 150 Three Nikki Carburetors. Hi everyone, sometime ago I posted a question about popping on the start crank, and fuel ball not getting hard very hard. Yesterday I took off the carburetors again and found out that sometime the float needles didn’t close. I found out that the floats opened up too much and they would get stuck on the bowl housing. I fix it by adjusting the tap just a little bit on the back of the floater. Now I would like to test my float needle to see if they have a good tight seal. I don’t think they do. What is the testing procedure? I also have a hand held pressure pump to gauge the pressure of the needle. What should the pressure PSI be at the fuel inlet line? I also did this test. I connected a 3/8” clear hose on to the in line of the carb and poured fuel in the bowl. I marked the line on the hose where the fuel showed. I waited two hours and saw that the fuel in the hoes decreased, about 1/2 “an hour. Is this normal? Is the fuel leaking from the float needles? If it is how do fix it? The float needles look good and they are 1 year old. Any help would be appreciated. Thank you.

 

[racerone]

Is the fuel in that hose evaporating into thin air ???

 

[rickryder]

Get rebuild kits and replace the needles and gaskets and seals....the kit will give you the proper spec and procedure to set your float heights...

 

[marts99ss]

Thanks for the reply. The kit is one year old and very low hours. It did this after I rebuilt the carbs. I thinking if I don?t find the problem it will do it again with a new kit. The needle seats are part of the carburetor. How do I clean them other then carb cleaner and over night in the carb cleaner? What about ultrasound cleaner? Is it safe? I like to test it after I clean everything and before I put it back on the boat. How do I test the needles for normal fitting? The float height is set by the book. I don't have any problems when it's running. I put a bolt on top of the hose for the evaporation. Is any amount of fuel drop normal?

 

[rickryder]

So your saying you are gravity feeding the carbs and the fuel level is dropping at a rate of 1/2" per hour through the carb?

 

[Silvertip]

After a rebuild, you verify the needle and seat are sealing by tipping the carb upside down. Blow into the fuel inlet. If air passes, you did something wrong and the needle is not sealing. If you can't blow into the carb, sealing is proper but you still need to make sure the float height and drop are set correctly,.

 

[marts99ss]

Thanks for the reply. Rick: That?s exactly what I?m doing. Is this a good way to test the seal? Is the rate of leak normal?
Silvertip: No air will pass through when bowing in to the inlet line. I just have this popping problem during the crank when I turn off the engine for an hour on the lake. Like fuel explosion. I thought that the seals have a very slow leak. I like to know if this rate of leak normal? How about testing it with a hand held pressure gauge?

 

[gm280]

Rick is correct in his assessment. However, I had a similar issue with a riding lawn mower . And I did rebuild it a few times as well. If would seal like Rick stated about turning it upside down and blowing into the inlet, but it still leaked anyway even passing that test. The issue was a factory issue. Seems the manufacture never offered the needle AND seat with their rebuild kits and only the needles were supplied in their carb rebuild kits. But their seat was the problem in so many that they decided to sell the seats as a supplementary to their own carb kits now. Once I changed out the actual seat, its worked perfectly since... So I go with the rebuild carb group as well, if you are changing both needle and seat. JMHO!

 

[rickryder]

There should be no leak down.... I bet if you look inside the carb while hooked to the fuel source you will see gas dripping in the carb....thats why you get the pop on restart....your cylds are filling with raw fuel IMO. I'm not sure if the seats are part of the carb body or removable seats are available since I don't know what particular Mikuni carbs are on your motor....

 

[marts99ss]

No Title

Rick: I have uploaded some photos. I?m sorry the carbs are Nikki. I think the seats are part of the carb. What do you think? One time on the lake I saw this mechanic that said that the popping is normal for these motors. I refused to believe that. The original carb kit didn?t come with and seats. What is IMO? Do you think that there could be an aftermarket seat for this carb?
GM: That?s what I think is wrong with this system. The seats are not designed to have a lot contact with the rubber part of the needle. At the seat; only that edge of the hole makes contact with the rubber part of the needle, and I think that?s not enough to seal for long time. Thank you guys for your time and help.

 

[rickryder]

IMO= in my opinion.. I'm not familiar with those carbs but it's a float and bowl carb...needle should stop fuel flow when the bowl is to spec with fuel...if the height of the float is off it could starve out at WOT or overflow with fuel at idle,drip fuel from overflow tubes if equipped....fill the carb till fuel runs out the main jet into motor.

 

[marts99ss]

I fond this page about float needle seat. http://outdoorpowerinfo.com/repairs/kohler_command_v-twin_nikki_carb.asp . I've copied what I think is happening with my carbs. This also explains why the engine drinks fuel like a V12. I can use 10 gallons in 2-3 hours of constant driving. Can I clean the carbs with ultrasound? Will this help? Can I clean the seats with q-tip and polish and a drill?

• #11. Float needle seat
• The rubber tip of the inlet needle must make a good seal with the inlet seat (#11, blue) or the engine will run rich, flood or the crankcase may fill with fuel over time.

 

[rickryder]

I really do think this is your problem that your needle is not seating...I wouldn't be playing with the seat ...just inspect it for flaws..I would start with that and recheck the float height settings as perv spec....if that fails maybe take them to a carb shop and have seats replaced...is it all carbs or one? You can isolate each card by feeding fuel to each carb one at a time with the gravity feed you were doing...

 

[marts99ss]

Hi Rick thanks for your help. Can you help me out with some questions? I?ll will check all the carbs for the leak down. So you are saying that there should be no loss of fuel from the gravity fuel line in any given time frame? Last time I check to see were the fuel is leaking from I didn?t see any wet area around the carb. Maybe I didn?t know where to check I?ll check again with all the carbs. The needles look very good they don?t have any marks on them. If the seats are the problem, do you think a carb shop can replace those seats? I also would like to do a PSI test when my pressure gauge arrives tomorrow. I was hoping I will do a PSI test just like the youtube video link I have attached for you. Do you have any idea what PSI I should look for?

 

[rickryder]

You need to look into the throat of the carb to see if fuel is leaking in up the emulsion tube....it's where your metering rod drops into... that is a great tutorial video that you posted...pretty much covers what you need to do... as far as psi they were doing 15 psi tests.

 

[marts99ss]

I got my pressure gauge. I tested all the carbs. The two top carbs hold up to 15 psi but the lower one only 5 or less on the port side. I changed the needles same result. Is there repair solution for the float needle seat? It?s pressed in the body. I don?t know if it can be taken out or changed or polished. I tried polishing it. It didn?t work.

 

[marts99ss]

I got my pressure gauge. I tested all the carbs. The two top carbs hold up to 15 psi but the lower one only 5 or less on the port side. I changed the needles same result. Is there repair solution for the float needle seat? It?s pressed in the body. I don?t know if it can be taken out or changed or polished. I tried polishing it. It didn?t work.

 

[rickryder]

I would check if you can find a local carb shop or a motorcycle shop and ask if they can change the press in seat.

 

[marts99ss]

The needles are sealing now. I have a problem of floats dropping too much and scraping with the bowl cover and getting stock. I found this out when I shook the carbs and found out that the needles would stay open sometimes and when I removed the bowl cover the floats would moved back and seal. Behind each float there is a tab to adjust how low they can drop. I like to know what is the process of the float drop adjustment? The Yamaha manual doesn?t say anything about this. Holding the carbs correct side up, should I let the floats drop to the point of where the bottom of the floats are even with the top of the main nozzle?