Blowback through both carbs

[BoJaXz]

In the case of the oil injection, make sure the spring-loaded ball check valve in both oil injectors isn't stuck open or gummed up. I don't recall how much pressure is necessary to dislodge the check ball off it's seat (mouth pressure?) but if you're down there messing around with that feel free to refresh my memory. A stuck open injector check valve will allow oil to drip into the crankcase and flood the crankcase with oil while sitting over a period of time. Be careful if you try to remove the injector it will probably snap/break off so it's better to blow them out with solvent (carb cleaner) and compressed air to get them cleaned out.

Part throttle hesitation makes me think the pilot holes (mikuni term) aren't fully clear but also the mylar reed type check valve covering the hole on the metering plate may be responsible if it's an aftermarket mylar reed may be too stiff (too thick) and doesn't allow the high speed circuit to flow early enough.

Hopefully that makes sense.

Banjo fittings are good, tried two new ones and the check valve works on both, and a new oil line, no change in it, just strange. I can try to change the plastic check valve on the metering plate. It's in good shape, but I have plenty of extras to exchange it with.

 

[Sportster-2001-951C-Stock]

High RPM and Full Throttle the plugs are black and wet. I can't open the HS adjuster at all without losing RPM. Low end is slightly rich.

Plugs should not be black or wet or sooty, your eyes shouldn't be tearing with raw fuel irritation but your hair might stink a little (take a shower, man! ).

The factory spec tune works, so stick to that and look for problems (like someone modified something or something's clogged/broken/misadjusted).

HS adjusters are normally closed all the way, so this means the factory HS jet is slightly too large to make peak potential power, still meets EPA requirements and keeps the novice tuner/tweeker from running too lean and roasting a piston. If you go with smaller HS jet than factory # then it'll be necessary to open the HS mixture adjuster. First though before deviating from factory jet #s, make sure the fuel metering orifice is the correct size and in my experience stick with factory spec orifices unless you really are bent on that extra 25 RPM WOT then go for it.

In the case of being too rich mid and upper range, make sure the fuel metering seat orifice isn't too large, someone may have changed it to a larger one? If so, don't forget to retest pop pressure b/c it's dependent on orifice diameter. FYI, Stretching or otherwise massaging the metering lever spring to change it's shape is a mistake, best get the right one.

WOT (HS) rich - In the case of high speed being too rich besides just the metering orifice being oversized, confirm the high speed jet isn't too large b/c someone may have changed it (or drilled it out?).

Midrange rich - It's also possible your low speed jet is too large (check the spec book #) causing mid to be too rich but I kinda like to hear hints of 4-stroking under about 3k RPM in the water anyway, just not so fuel rich black smoke and a plume of unburned fuel rolls out the exhaust and wafts around your head burning your eyes, that's way too rich, lol.

Hopefully that helps iron thing out.

 

[Sportster-2001-951C-Stock]

Banjo fittings are good, tried two new ones and the check valve works on both, and a new oil line, no change in it, just strange. I can try to change the plastic check valve on the metering plate. It's in good shape, but I have plenty of extras to exchange it with.

The mikuni OEM mylar check valve is the one that works properly, if it's mikuni then it's unlikely the problem. Too thick of mylar results in HS circuit is delayed and lean hesitation occurs at transition.

 

[Sportster-2001-951C-Stock]

The mikuni OEM mylar check valve is the one that works properly, if it's mikuni then it's unlikely the problem. Too thick of mylar results in HS circuit is delayed and lean hesitation occurs at transition.

I doubt tweeking/lowering pop-off will alleviate a lean HS transition but you might find it floods at low speed.

 

[etemplet]

I doubt tweeking/lowering pop-off will alleviate a lean HS transition but you might find it floods at low speed.

Been doing that all along (rich at slow speed) with the pop off at 23psi. The skis like it at 30psi. I checked all the other stuff you mention. I've been in the carbs for a couple months. Jets are the correct size etc...

What I am going to do today is, install Mikuni 1.5 needle and seat, see where the pop off ends up with the black spring. I have 140mm jets I am considering installing but may not. I am undecided. The Low speed circuit on this ski working pretty good but not as well as the ski with the pop off at 32psi. This ski has a good response but is a tad rich..

I'll be checking the impeller sizes too.

Thanks so much for taking the time to post that great information. It is helpful to everyone !!