650 x2 The last piece of the puzzle (CARB issues)

[callmefinch]

i picked up an 86 x2 that motor wise was trashed, i purchased another 650 motor to drop in that has 155 compression in each cylinder. after a few weeks of work i have the motor and everything put in new fuel lines, carb rebuild kit and a new fuel pump. also new gaskets

unfortunately the float arm and or needle are not allowing fuel through without me helping it. i am getting roughly 5 lbs of pressure coming from the fuel pump, and roughly 3 coming from the pulse out of the motor.
i am completely baffled on what to do, ive taken the carb on and off atleast a dozen times by now. i was really hoping to get this ski finished by saturday but thats not lookin too good.

am i not getting enough pressure to pop up the needle? im getting loads of fuel coming out of the return.

the carb is properly but together
all my fuel lines are correct
wiring is all correct

only issue is why the float arm will not rise on its own.
ive been using the shop manual everything appears correct on my end.

 

[derekshep]

Have you done a pop off test on the carb?


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[callmefinch]

How do u do that?

 

[derekshep]

You need a gauge with pump and pull the carb side off to see the needle and seat. Plug the return line and hook the pump to the in line. Start pumping till the needle pops

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[callmefinch]

I watched a youtube video on how to perform the test. I put a pressure guage on the vacuum line coming out of the carb intake and im getting roughly 4 lbs. Im supposed to be getting around 30.

 

[derekshep]

That's a pressure test on the pump. Not s pop off test on the needle and seat


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[callmefinch]

Okay i get its a test on the carb but arent i supposed to be getting the same pressure coming from the pulse line? Or does the fuel pump amplify the pressure going to the carb. After i find the pop of pressure what do i do next.

 

[Vumad]

Okay i get its a test on the carb but arent i supposed to be getting the same pressure coming from the pulse line? Or does the fuel pump amplify the pressure going to the carb. After i find the pop of pressure what do i do next.

I'm not sure what test you are attempting to perform but I've never heard of it. There are generally only 2 tests performed on the carbs.
1) Check the fuel pump for leaks.
- popoff tester on inlet
- blocked outlet
- pulse open
- Pump popoff tester to 10 psi
- it should hold this for 10 minutes. Any leaking, spray wd40 around the seals and find the leak. I have fixed leaking fuel pumps by just opening and cleaning, but you may need a rebuild kit.

2) check popoff pressure
- popoff tester on inlet
- blocked outlet
- pulse open
- there should not be fuel in the carb (hold needle open and pump to push out excess fuel)
- spray wd40 on the needle (it only works right when wet)
- Pump popoff tester until needle pops. gauge should not drop while pumping, if so, find a leak.
- It should be a nice firm pop, no sputtering or bubbles. See video.

Mikuni popoff test. Pump is on the intake, outlet is capped, pulse is open.

Only other test is a leak down test on your motor. If you don't have a case leak, then your fuel pump should be working (assuming the above and carb is in good condition).

I only use Mikunis, so things could be a little different for you.

 

[callmefinch]

i did the carb pop off test and it popped at 36 psi, isnt that high

 

[Vumad]

yes and no...

On a superjet, stockpopoff is 52, jetmaniac suggestes 40 i think, mine is 18...

Its relative to your setup. Stock machones run it pretty high