Other Carb/Pipe/Pump Tunning - Talking Out Loud

[2lick]

When working on a problem, I've always found its helpful to talk out loud and correct myself or see what advice others may share. Sometimes I even forget what I've learned or miss the obvious in front of me. Chime in if you have anything to add

I have owned this package for four years, running it for the first three in a carbon brawler with a 144 pump. She was setup well and ripped! This year I moved the package into a Glass XFR with a 155 pump. Other than a new pump and prop, I gave the ski zero tuning attention and rode it in the surf and have been flipping off vwakes this summer so far. Now its time to dial it in and see what power I can tap into.


Brap Package:
Jetworks Superbore (88.5mm - stoke stroke) 836cc
Ported Cases (From LPW, not Jetworks)
Pump Gas Domes (compression is even but my gauge sucks, need to test on an accurate one)

Full Spec 48s
Boyesen manifold and rad valves with 3 stage carbon reeds
TA 2inch Pod Flame Arrestors

RRP Laydown pipe
Manifold port matched to cylinder
I always mess with Pipe jets and tend to run 97.5 more than any other (85-110 range I play in)
RRP waterbox & carbon fiber waterbox (just swapped in CF one)
Flow Control Valve keeping water box dry at low RPMs

MSD Enhancer
OCD Coil (4 years old)
#zero super lightweight FW
Stator advanced 2 degrees

8-vien couch 155 pump (no adjustable cones for this pump)
7/16 Skat Trak -5mm
Thrust Trim Stock Bore 86mm

 

[2lick]

Task One – Carbs

Riding lately, the ski feels rich and weird. Crappy on second brap to hit a setup wake, great in a fast-straight line, usually good to hit a v-wake. It’s been a year while since I had the carbs apart so I decided to check if my popoff moved and where the rest was at.

Garage tear down showed:
Front Carb

• 23 PSI
• 137.5m
• 125p
• LS – 1 turn
• HS – 1 turn

Rear Carb

• 22 PSI
• 137.5m
• 125p
• LS – 7/8 turn
• HS – 1 turn

I chose to adjust popoff and even them up at 23 dead nuts on both. Needle tips were replaced last year and still look good. Both pop clean every time. Thinking I was rich all the way around, I dropped both jets by one.

I went to the water with even in each carb.

• 23 PSI
• 135m
• 122.5p
• LS – 1 turn
• HS – 1 turn

 

[2lick]

My carb tuning knowledge comes from the Mikuni manual and experience working on many skis. I still confuse my self tho. Heck I've even laminated manual pages and they stay in my kit

After a quick rip, I tied my ski up to the dock. I put the tach on and began searching for a smooth idle at around 1600rpm. Up and down with the idle set screw first, then twisting each carbs L screw in or out to watch RPMs gain and drop in reaction to the fuel I gave it or took away. My goal is to find the top of the rich condition where adding fuel causes RPMs to drop, then I backed off a tad to where RPMs where at the peak again. I got the ski to idle fairly smooth at 1600rpm tied to dock.

I went and rode the ski. On and off throttle multiple times, then let it come to idle. It was in a rich condition after the brap, but waiting about 30 seconds letting it idle and work thru the excess fuel (during this time it was at 1400rpm) it would clean it self up and reach 1500rpm purring like a kitten with me on her. Not a vibration on the ski. It could idle for hours. Shut it off, wait two minutes and with the tap of the button it fired right back up. Perfectly happy with this idle!

Next....
First test, ¼ off test.
Hold ¼ throttle for 1 minute, let off, pin it.
Gave me a severe lean hesitation.

Second test ¼ on test.
Hold ¼ throttle for 1 minute, don’t let off, straight pin it.
Gave me a mild lean hesitation.

I assumed this is low jet.
After this I went into shore and bumped my low jet back up to 125 from the 122.5 it has in it.

 

[Jr.]

Hey Nick!

My 2 cents..........

Carbs, Typical FS uses 1.8 n/s with 80 grm spring? Is this what you have??
Try a 1.8 / 95 gram spring with a 127.5 pilots? Should clean up the bottom

Pump, That setup normally likes an 88mm nozzle bore......

Ski ya, Paul

 

[2lick]

In theory, as I understand, changing the low jet should not effect the idle. Especially this small of a change. Well it did. It wouldn’t idle at all. Had to hold throttle to keep it running. Ignoring the bad idle for the time being and tried my two tests.

First test, ¼ off test.
Hold ¼ throttle for 1 minute, let off, pin it.
Good response, maybe a very very small lean hesitation.

Second test ¼ on test.
Hold ¼ throttle for 1 minute, don’t let off, straight pin it.
OK response, defiantly not lean, maybe rich took .5 second to really kick it. Could be pipe relates tho.

I came back to shore and started working on my idle again. I found I had to turn in my idle set screw more to give the ski more throttle, so it would idle how I wanted. I played with the L mix screw in the same way. I though Id would need more fuel here since I added air, but after re reading the manual I see I am wrong. Turning in the idle set screw and adding air actually richens you idle mixture.

I got the ski to idle at only about 1500 RPM on the dock, and 1400 in the water. No where near as nice as last time.
Sunset and loaded up. More testing to come.

 

[2lick]

After going home and reading, I think I need to change my popoff NOT my low speed jet to fix the severe lean I had off idle and on ¼ throttle rips.

While you can do both, I think I need to lower my popoff from 23 to 21psi. and keep the same 125 jet first to try, then maybe go back down to the 122.5 if the 21psi helps and now its rich.

More to come, but I welcome others thoughts!

 

[2lick]

Hey Nick!

My 2 cents..........

Carbs, Typical FS uses 1.8 n/s with 80 grm spring? Is this what you have??
Try a 1.8 / 95 gram spring with a 127.5 pilots? Should clean up the bottom

Pump, That setup normally likes an 88mm nozzle bore......

Ski ya, Paul

Hi Paul, thanks for the tips!
Yes, I am getting my 23psi with a 1.8NS and 80g spring.

Q1 -What PSI am I aiming for with 1.8ns and a 95g spring. That should take my popoff up correct. I have many springs and arms to try with.
Q2- Then if I move popup up reducing fuel into fuel chamber, I'm guessing this is why your saying also move up one jet to 127.5.

 

[Quinc]

Have you tried reverse jetting?

Something like 135 Pilot and 125 Main. I haven't used FS carbs but my BJ 48's liked the pop off around 18psi

 

[2lick]

Have you tried reverse jetting?
Something like 135 Pilot and 125 Main. I haven't used FS carbs but my BJ 48's liked the pop off around 18psi

I have not yet, but would be willing to later on. For now I wanna chase this route then when its perfect depending on time of year I may see where I can get with reverse jets.

 

[Jr.]

Hi Paul, thanks for the tips!
Yes, I am getting my 23psi with a 1.8NS and 80g spring.

Q1 -What PSI am I aiming for with 1.8ns and a 95g spring. That should take my popoff up correct. I have many springs and arms to try with.
Q2- Then if I move popup up reducing fuel into fuel chamber, I'm guessing this is why your saying also move up one jet to 127.5.

Q1, Will be right around 32# pop Also verify return jet is a 70

Q2 Correct

P

 

[2lick]

Q1, Will be right around 32# pop Also verify return jet is a 70
Q2 Correct
P

@Jr. Thank you! I will add your idea to what I try. I currently have a #60 in return line.

 

[Big Kahuna]

My simple response, which sounds like Paul answered, when your landing your first flip, ski its water, impact may cause the needle to "open" and cause more gas to dump, on the start of second flip, excess gas is causing to go rich "Fuel" for just a few seconds..................... Stronger spring will help prevent this........ Now Paul can tell me to get off the computer.......... oh wait, he is in a plane.............

 

[Jr.]

My simple response, which sounds like Paul answered, when your landing your first flip, ski its water, impact may cause the needle to "open" and cause more gas to dump, on the start of second flip, excess gas is causing to go rich "Fuel" for just a few seconds..................... Stronger spring will help prevent this........ Now Paul can tell me to get off the computer.......... oh wait, he is in a plane.............

Maybe you should stick to flooring???

 

[2lick]

Ah ha! I knew something fishy was going on!!!

One
I found the bottom reed on each valve was stuck open nearly 1/4inch each. I had actually ordered a new set form Boyesen last week since I had suspected this. I was getting what I thought may be fuel blow back in the FA and Carb bells.

Two
I also "may" have had a leaky o-ring in the head. I pulled the head to inspect and found rear cylinder all wet and milky. Domes outside edges are getting eaten by corrosion from sleeves and o-rings looked bad. Also could be water coming back thru waterbox and RRP pipe. Either way I decided to put in my new race gas domes I had in a box.

Old domes (40cc) read 150ish. Though my reader sucked but bought a new better one and it reads the same.
New domes are 37cc. In garage after bolt on with lots of oil wiped on bore it read 190 and 195. After some water testing dropped to 180-185.

Bore has some rust and looks ruff. Used a pen cam and I even see spots of rust on crank rods. Time for a rebuild.
I hope to limp it along until I get parts in and want the down time.

If I rebuild pistons are special order from Jetworks/Wiesco and I'll be on last bore.
Debating on going 4 or 5 mil crank instead of stock as well.

 

[Quinc]

Some light surface rust wont hurt anything. But still worth checking the bearings and replacing the wrist pin bearings. Also after every ride:

 

[2lick]

I recall seeing you fog yours on the beach after the ride. Got to thinking, its smart. Especially with a wet pipe, letting all that evaporation back in while it sits.

 

[Quinc]

Little insurance in a can! Plus I spend most of my time with the ski upside down and swimming.. lol

 

[2lick]

Little insurance in a can! Plus I spend most of my time with the ski upside and swimming.. lol

Same!!!

 

[kevbo]

Is your tank vented? If not then warm gas will effectively lower your popoff due to increased vapor pressure. This does show up with low popoff pressure. I would shorten the duration of 1/4 throttle holds for tuning. The ideal pilot will tend to be very rich after a few seconds.

 

[2lick]

Is your tank vented? If not then warm gas will effectively lower your popoff due to increased vapor pressure. This does show up with low popoff pressure.

Yes, the tank has a standard vent. I checked and it operates normal allowing me to blow air into the tank, but not allowing me to suck air out. I do however often have excess oily residue on my cases under where the vent ends....

I would shorten the duration of 1/4 throttle holds for tuning. The ideal pilot will tend to be very rich after a few seconds.

Thanks for that tip, I'll consider it!