Super Jet Carb tuning - from the hose to the lake, how to compensate?

[Midlake Crisis]

My ski has been running good so far this season but has an annoying little hesitation off idle that I have been trying to tune out at the lake.
This afternoon I was running it on the hose in the driveway and seemed to be able to eliminate the hesitation completely by fattening up the low end screw quite a bit, maybe 1/3 to 1/2 turn out from where it was.
I have read the tuning threads but don't have a tachometer to test with and expect it will need adjustment when it is under a load at the lake.
Is there a general rule of thumb to help me anticipate what adjustments I will have to make at the lake to get it close to the result I got in the driveway, or is just like starting from scratch?

 

[Waternut]

Do you notice the hesitation when you're riding normally or is it only when you let it idle for a bit and then try to nail it? Can you tell if it's a lean hesitation or a rich hesitation?

 

[Midlake Crisis]

Do you notice the hesitation when you're riding normally or is it only when you let it idle for a bit and then try to nail it? Can you tell if it's a lean hesitation or a rich hesitation?

I can't tell if it was lean or rich hesitation - in the driveway it did the same thing until I fattened it up quite a bit.
It has been doing it pretty much all the time.

 

[D-Roc]

by richening the low screw you are "adding" fuel to the system. if adding fuel to the system helps, then it is safe to say that you have a lean hesitation. you can lower pop off so the carbuses the main jet fuel a bit earlier, if that is indeed the problem. you can also go up in the pilot jet. these two overlap and is what is used to get the smooth transistion from the different circuits with the different throttle positions. read the mikuni manual and learn about the different areas of the carb and its tuning.

 

[D-Roc]

a lean hesitation feels like you hit the stop for a sec and then it pulls hard. a rich hesitation will increase rpms abit but also takes a bit to clelan up and pull hard. i usually try pop off first because jetting specs can usually be close and the pop off needed from one motor running a certain intake/flame arrestors may vary. remember the pop off and the pilot jet somewhat overlap.

 

[Mark44]

Adjust for the highest RPM. Take a tach to the water with you.

Mark44

 

[smoofers]

Hesitation off idle is directly related to pop off and low jet.

Tuning with a tach will not solve your off idle situation, but it will get you a perfect combo for full top end (remember, 1/2 to full throttle is a combo of low and high speed jet). This will just confuse you even more though. Wait to tach it until you have the off idle situation solved.

If your ski ran fine before and just now started doing this, I would lean to pop off. Have you recently rebuilt the carbs? If so, did you verify pop off before/after the rebuild? If the arm or spring in the carb was messed with, pop off could have been changed.

Check your pop off, write it down (check it 3 times, take the avg). If you have a lean hesitation, lower your pop off a few psi (~3-5psi) and retest. If it is a rich bog, add a few psi to the pop off and retest.

All of this is assuming you have a clean carb with good diaphragms etc. If not, check your pop off, write it down. Count the # of turns in the high and lows screws take. Write it down. Take notes of jetting sizes and then rebuild the carb.

Let us know your results.

 

[kevbo]

You can set the low screw at idle on the trailer, everything else must be checked on the water.

 

[D-Roc]

the only thing turning the low screw does on the water is to possible help you figure if your hesitation is lean or rich. it says right in the mikuni manual to use the low screw to make a nice smooth idle. to check if your idle is smooth and perfect, let it idle, shut it off, push the green button and if it starts without throttle, you should be good. lol. that is the easiest part of tuning the carb. haha.

 

[Midlake Crisis]

Thanks for all the input -

I rebuilt the carb within the last few months but can't find my notes at the moment, if I find them I will post up the details.
This afternoon the ski ran better than ever, fattening up the low speed adjuster significantly smoothed out the power band on the bottom end, so apparently I was dealing with a lean bog situation. The improvement was so good that I didn't even mess with it today, just enjoyed riding.
I think I may need to fatten up the high speed adjustment as well - sometimes it starts to cut out on high speed runs, and immediately following a trick that causes a high rpm spike with a fast drop to idle sometimes it takes a few seconds to get back to normal. Both of these conditions are worse when fuel in the tank is getting low.