Carb experts wanted!

[dan filipi]

Siphon can certainly happen as well as pressure buildup in the tank. There is only so much pressure the floats can stop.

 

[joedrum]

man the stock carb float and all are small ...things have be rather just right to work good ...not much of a margin

 

[ekvh]

The wearing surface of the brass which contacts the float needle can get a groove or a hole worn in it and cause the float to misalign with an aftermarket float or new oem float. I had this on one set. Couldn't see it with my glasses, but was obvious without my glasses. I dressed the wear point with a small file and it took care of it. Lots of things to look at with good eyes to ensure success with any carburetor.

 

[Ansimp]

ekvh » Fri Dec 19, 2014 3:26 am[/url]":fzpzu5b4]
Couldn't see it with my glasses, but was obvious without my glasses. I dressed the wear point with a small file and it took care of it. Lots of things to look at with good eyes to ensure success with any carburetor.

+1 :yes: :doh:

 

[RBG]

I am a little late to this but..next time bench test the carbs like in this pic..caps off so you can see the jet tops, carbs leveled on the bench, fuel source at least 6' high to simulate 2-3 lb.s pressure, leak up through the jets = floats or needle issues, between carb and plenum D ring issues, plenum seam = plenum gasket..easy to tell on a bench test which it is..

note my fuel source not high enough..shoudl be 6' min.

 

[joedrum]

good post .. that is something rather known here ...hard to get all things in a thread that applies to this subject ...thats interesting ...seems 6' is way to much ...but i am sure the small volume there makes that right in the pic ...large volume in test tank would reduce that ... seems in gravity feed oldwing set ups the tank is jut above carbs ....just to make things clear here

 

[RBG]

no at least that's what I was told my someone I trust a bigger source doesn't change anything it's the lenght of tubing

no sure what you mean here??
seems in gravity feed oldwing set ups the tank is jut above carbs ....just to make things clear here

 

[joedrum]

when people build custom oldwings the gravity feed tanks are just above the carbs and run fine ...more like 6" than 6' is all ....i am sure the weight of gas supply cant be taken off the table at all ...

 

[RBG]

Oh I get it..yep that's true but to simulate the pressure from a pump(OEM set up) you need the 6' feet as more pressure taxes the carbs ability to seal at all the points they can leak.

running with a gravity fed system the suck of the cylinder at higher RPM's helps the system to keep up with the gas requirements..to compensate for the lack of the 2-3 lbs. pressure the pump provides in a stock set up.

 

[dan filipi]

To know for sure, a pressure gauge on the test tank needs to be used.
Mechanical pump is 2-3 lbs. For bench testing purposes I would want to test at higher pressure, maybe 5 lbs to check float seats not leaking by then again at 3 lbs to measure the actual fuel level in the bowls after adjustment.

 

[zman]

dan filipi » Sat Dec 20, 2014 9:42 am[/url]":2wygci8l]
To know for sure, a pressure gauge on the test tank needs to be used.
Mechanical pump is 2-3 lbs. For bench testing purposes I would want to test at higher pressure, maybe 5 lbs to check float seats not leaking by then again at 3 lbs to measure the actual fuel level in the bowls after adjustment.

I agree, I used 5 elevated straight up and even filled the funnel to the top. Wish I would have been able to measure exact pressure.I would have tries 5 pounds even greater just to be sure of a solid seal.
5 feet and full to the top worked for me, next time I will try and figure a more accurate measurement of pressure, A pump and gauge of some kind.
Let it sit for a good 6-8 hours too.

 

[mcgovern61]

I use a gas tank from a lawn mower filled with a 1/2 gallon of gas for my simulations about 3' above the carbs on a table and that seems to be sufficient enough to produce leaks for me.

 

[dan filipi]

Well more fluid weight as in quantity above is going to cause a higher pressure below.
Only accurate way to know that I can see is to put a gauge on it.

 

[joedrum]

i give the best answer award to gerry 3ft above 1/2 gallion at most lawnmover tank is perfect test reguardless what the pressure really is ..worked for me ...yrs and yrs

 

[dan filipi]

The best answer will be from the first person that puts a pressure gauge on it lol.

 

[mcgovern61]

dan filipi » Sat Dec 20, 2014 1:55 pm[/url]":2wejbvic]
The best answer will be from the first person that puts a pressure gauge on it lol.

:smilie_happy: (I wish I had a gauge...)

 

[mcgovern61]

He we go again!!! :head bang: SAME THING!!

Carbs have been rebuilt, worked like a champ, but for some reason or another, with the petcock closed, gas is siphoning from the carbs while the bike is sitting in the garage un-started for more than 2 weeks. :cheeky:

Cleared the plugs and started the bike to finish pulling the gas down and they were only half full. (Only ran for 2 minutes before running out of gas, normally takes at least 5-6 minutes at 3K to run gas out.)

A bit perplexed here! Here is what I do know, they are fairly new seals, floats were properly set, but of course the needle tips might be dirty. These conditions happened the same way as in the beginning of this thread; warm garage, dramatic temp change outside which cools the garage, gas siphons.

As it so happens, I just happen to have an '81 1100 also sitting in the garage. The '81 has an empty tank and it is very clean, but there is some gas remaining in the carbs. Both bikes sitting in the same conditions.

I opened the petcock on the '81 and, lo and behold, I can HEAR SIPHONING IN THE TANK! I closed the petcock right away, pulled the gas cap and opened it again and for at least 3 seconds I could still hear air sucking in the bottom of the tank! :shock:

 

[mcgovern61]

So, the temperature changes and air pressure changes must really act on these carbs if they have gas in them. I talked to Pistol Pete and he agrees that at least the air pressure changes at a minimum will put pressure on a tank in a closed system. I am sure I will find the float needle tips are dirty again.

Thoughts? :read:

 

[dan filipi]

Well sure sounds like siphoning...but I can't see right off how a float valve leaking would cause a siphoning on the gas in the bowl if the petcock is closed and in fact the petcock is not leaking by.

 

[slabghost]

Running the gas out of the carbs leaves the circuit wide open with the only stop being the petcock. Which are not known for being 100% seals. Pingle manual petcocks do a nice job. No idea if any fit our tanks though.