Pop off test bleed off

[Jchildress0418]

96 gsx 787 all stock. 160 compression both cylinders. Was sitting in a field for a year before I got it. 2 of them exactly the same actually. Cleaned the carbs and got it running. Took it out not knowing what to expect as I have never ridden a pwc before ( rode and built race quads for the dunes). It ran really well. 6500 rpm at wot full speed. Then started shutting down at wot. Would still idle and get to about 3k before wanting to die. Brought home and pulled carbs. Green slime inside again. Changed the gray hoses to new ones and installed inline fuel filter. Carb rebuild kit with new n&s. Pop off pressure was previously 30. It was about 26 with same springs with rebuild. Switched springs and bent arm down and got 36 in both. High set at 0 and low at 1 turn out.Reassembled and took it out. Hard to start now where before it snapped right on and would idle all day long. On take off it dies alot. You have to feather it alot to get it past the flat spot. Dies a few times before this is achieved. Once you get it past that on up on the plane it takes off like a rocket! Excellent all day long on the top and mid while up on the plane. Can cruise down to about 3500rpms and hit it and takes off fine. Back off to idle and have to feather it again to get it past the flat spot. Easier to do once it has been running awhile. Thinking I should lower the pop off down to 30 even though it's still in speck now. And when testing pop off the pot carb when pumping went up and stayed at psi until pumped up to pop off. The mag carb would pump up and drop 2psi immediately with each stroke of the pump but then hold there. Is that a problem I need to try and solve also? Kinda weird cuz it would hold after initial 2psi drop as long as you left it. Thanks for any input. Jason

 

[mikidymac]

Did you buy Genuine Mikuni carb parts?

You can't bend the arm up or down more than about 1mm it should be flush with the carb body.

 

[Jchildress0418]

I got mikuni n&s and Ebay rebuild kit. The only thing I used out of the kit was on the pulse block the top gasket and plastic clear gasket. I tried the rest of the parts but it wouldn't even let me pump it up for pop off test so I took them all out and just kept the 2. I'll check the arm and see if I bent it down too much. Thanks

 

[mikidymac]

I you got genuine mikuni kits and couldn't hold pressure then you did something wrong.

 

[Jchildress0418]

It's not that it couldn't hold pressure it's that you couldn't pump it up like the circuit was blocked. Put all the original parts back in and it pumps up fine. Just on the 1 carb only every pump it goes up and falls 2psi then holds- goes up more then falls 2psi and holds. Pops off at 38psi just like the other carb.

 

[Jchildress0418]

So does a higher pop off # equal a leaner low speed circuit with the low speed needle set at stock 1 turn out?

 

[Sportster-2001-951C-Stock]

FWIW, in case of "Hard to start now where before it snapped right on and would idle all day long. "Key to the old 10 minute heat soak 1st-pull (starter bump) restart test is there's gotta be the correct amount of fuel trapped inside the crankcase. Too much or too little fuel makes for lots of cranking till the ratio reaches the ignition point.

So ask yourself if there's too much fuel in the crankcase for a nice hot restart, or too little.

Idle mixture adjustment: Too rich of idle mixture leaves excess fuel in crankcase at shutdown. To avoid this, idle should not be trending rich (thus mixture adjust screw is too far open).

I high(er) pop number means more vacuum is required to pull the metering needle off the inlet seat orifice, too high of pop then you might have difficulty getting fuel unless you use the choke to coax the metering diaphragm into bumping the metering needle open.

Changing the design of (or removing) the flame arrestor to flow more air will require lower pop due to there will be less negative pressure in the intake tract and incidentally, may also require larger jets, depending. Thusly, I recommend to run the factory flame arrestor unless you love tuning carbs and really gotta have/need that extra 25RPM for some reason.

 

[Sportster-2001-951C-Stock]

So does a higher pop off # equal a leaner low speed circuit with the low speed needle set at stock 1 turn out?

Short answer is yes.

 

[Jchildress0418]

Awesome thank you. That tells me alot. My idol was down to 1350 in the water where as it was 1500 last time out. I will raise it back to 1500 after I set the pop off to about 30 and take it out to retest . I have the stock flame arrestor and cover on. None of the 3 gsx I have had the big filter that seals to the seat bottom. Thanks for your help!