Mitymite MV8500 carb test

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oologahan

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I bought one of these testors and hooked it to the fuel inlet on my Homelite S1050 carb and it wont build pressure, it will build vacuum, but not pressure. Is this because the check valve is bad?
 
If it won't hold 7-10 psi it is leaking somewhere. The best way to find the leak is to keep the pressure line connected and dunk the carb under water. Locate the area where the bubbles are coming from. If bubbles come from the gaskets,you can locate the leak easily. If the bubbles come out of the venturi, it's likely a leaking metering valve.
 
If it won't hold 7-10 psi it is leaking somewhere. The best way to find the leak is to keep the pressure line connected and dunk the carb under water. Locate the area where the bubbles are coming from. If bubbles come from the gaskets,you can locate the leak easily. If the bubbles come out of the venturi, it's likely a leaking metering valve.
T1
 
if you turned the lever from vacuum setting to pressure on the pump itself

1. if it builds and holds vacuum then the main needle seal is probably good

2. if it wont build and hold pressure
a. the diaphragm is holding the main needle open for some reason
old dried wrinkled collapsed
b. the main metering spring is too weak to hold the main needle down on the seat with enough pressure.
stretch the spring just a tiny bit at a time till you get 7 to 10 psi of holding pressure. the exact pressure is not critical...as long as you have 7 to 10 minimum.

as said above the bubbles will tell you where the leak is

i forgot to mention...small infrequent bubbles forming around the edges of fuel pump side are not really a big deal, but if its a huge leak it needs to be addressed

you may have to remove the diaphragm side of the carburetor to see if the main metering needle is leaking, cuz is the diaphragm and gaskets on that side of the carb are air tight the air from the leaking needle will not make it out and form a bubble.

but ive worked mainly with tillotsons HL series and walbro HDC series, im not sure what carb your workin with
 
I removed the top, the diaphragm was hard and crackly and the bottom plate closest to the fuel inlet was loose, it now holds pressure. I really need to know whether or not I should change the check valve or how to tell f the check valve is working r not. You guys are great, Thanks
 
which carburetor are we talking about..
can you put up a pic of the diaphragm side of the carn with diaphragm removed

youve already removed the diaphragm
1. find a piece of hose thats about the same diameter as the top of the check valve opening
2. just use your fingers and put enough pressure down on the hose end and check valve to get a good seal
3. blow into the hose.. it should blow through
4. suck back on the hose and the check valve should pop up and block flow.
5. sometimes the check valve if its a flap or fiber type like in the hdc series carbs the little disc/checkvalve will dry and deform and requires you put some gas in it to
let it absorb fuel and regain its shape.
6. if the above dont work as they should it could just have some debris in it.. if you use carb cleaner or brake cleaner try to find the non chlorinated kind . the chlorinated stuff tends to piss
off the material these little fiber parts are made of.. use the little pipe thingy that comes 3with the carb cleaner to blow from the inside of the check valve
or use some gasoline in a syringe..most pharmacies have them, to blow fuel from the inside of the check valve you can bend the needle of the syringe to get up in there.
7. those little checkvalves tend to last forever though. ihopefully its just blocked or something easy

if you dont want to replace the check valve, which can be a PITA on the hdc series in my experience and sometimes requires that special little puller tool from the walbro tool kit.
you can pull whats left of the old check valve disc out through the top of the check valve body..after you remove the circlip and screen of course

since your rebuilding which i would at this point... you will have the left over material from the pump section on the opposite of the carb..the square piece with two flappy looking fingers on it...
you can make another little round disc the same size as the original piece.. and gently push that little sucker down in there
ive done this before cuz i could not find a check valve at the time and its still working on my 015L #2 you just have to make sure that the disc you make is not too big or it will not move up and down freely and get stuck
keep us posted on the progress
 
I'm working on a Walbro SDC-74 that replaced the Tillotson HL-222A on the late model Homelite Super 1050. I think all is good. I can blow through the check valve, but no air can be sucked back. It appears the check valve is good and I cleaned all the screens, it was pretty clean. The diaphragms were just really hard and dry and the bolts on the top of the carb were not tight at all. I really appreciate the help.
 
Here is the video, I need to slow the rpms with the T handle, the SDC-74 doesn't have Hi-Low adjustment needles, just low speed adjustment
 
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