Help- starting Jetting for 61x ported LPW

[orangefinger]

Set up

61x/61x Ported LPW
44mm Single SBN
Boyesen Reeds
ADA Girdled Head 180 PSI
Coffmans sizzle ma dizzle
Lightend Flywheel
MSD Enhancer


Jetting so far

N/S 2.3
MAIN 140
PILOT 120
Spring 65 G POP off # 16
High Screw 2
Low Screw 2


Not too happy with arm-pull factor, any help greatly appreciated !

Thank You !

 

[Mouthfulloflake]

where is it weak?

2.0 seat, and 95 gram spring

I was closer to 3/4 turn on pilot, and 1.25 on high ( with a 145 main though)

 

[orangefinger]

weak spot right at the beginning, I am having a slight hesitation when I hit the throttle...

BTW I have finally gottne arround to take the 760 out....

 

[Superjet3]

I would Contact LPV for a suggestion. Who is LPV?

 

[The Penguin]

Lamey Power Valve most likely.

 

[orangefinger]

Lpw...

 

[The Penguin]

well - looky there, I was wr..wr...wr...wr.... incorrect.

I don't know much about tuning, but I'd start with a 95gm spring in there and either a 1.5 or 2.0 n/s

 

[SuperJETT]

First off, is it an oem Yamaha carb or a regular Mikuni? They jet a little different on the low end.

 

[Matt_E]

Your popoff (N&S and spring) are a bit different than what Paul recommends, from I recall.
Try to get a 24 psi popoff with a 2.0 N&S.
Then adjust the low mixture screw while the boat is in the water, idling. You might turn the idle stop screw up a little so it doesn't die. Adjust the low mixture screw until you find the spot where highest idle is obtained. Then back the idle stop screw down to where you want the idle to be.
After that, if it hesitates upon take-off, increase your pilot jet. If it blubbers, putters, and takes a couple seconds to clear out, decrease your pilot jet.

 

[Mark44]

What Matt said but use a tachometer to read your RPMs anything else is just a guess.

Mark44

 

[Mouthfulloflake]

it sounds to be loading up.

if you can determine whether its the pipe loading up with water, or the carb loading up with fuel, it would be helpful.

But honestly, this is where I am stymied on tuning myself, ive pretty much decided mine is loaded up with water though.

I ran a restrictor in the Stinger of the sizzler, and that helped to keep the waterbox drier somewhat.

reduce the amount of water going thru the pipe, and see if that helps.

also, do the old idle for a minute, then hammer it. what does it do? ( this is what matt_E was addressing after tuning the lo speed screw)

 

[crammit442]

Why are you not talking to paul about this?:thinking:

 

[orangefinger]

Solution !!

Hi ,

Ok today was the day and I am willing to share....

Engine 701 Ported
Single SBN 44mm
ADA Girdled head 180 PSI
Coffmans sizzle ma dizzle ( I still love this pipe ).
Lightned Flywheel
MSD Enhancer
Wetwolf Cone
13/16 Solas
Aftermarket Flame arrestor

I had 3 carburators along with different jettings ( I like to switch carbs rather than small jetts & stuff at the lake ) also 4 different restrictors Stock opening arround 7.8mm then 5.4 mm 4.4mm 3.4 mm..

And this set up was friggen narli

MAIN 145
PILOT 120
N/S 2.0
80 g black Pop off # 17
High screw 2
Low screw 2

3 waterlines coming of headpipe, only restricted line from back of headpipe to stinger with no T restricted 4.4 mm....

Pipe gets hot/hot but no melting rubber couplers and no sizzle..

The ski never ran so good and also never hat such a great throaty sound....

Cheers !

Thank you everyone for help and advice !

 

[bassman215]

Your popoff (N&S and spring) are a bit different than what Paul recommends, from I recall.
Try to get a 24 psi popoff with a 2.0 N&S.
Then adjust the low mixture screw while the boat is in the water, idling. You might turn the idle stop screw up a little so it doesn't die. Adjust the low mixture screw until you find the spot where highest idle is obtained. Then back the idle stop screw down to where you want the idle to be.
After that, if it hesitates upon take-off, increase your pilot jet. If it blubbers, putters, and takes a couple seconds to clear out, decrease your pilot jet.

I tried setting my idle using this method above today. I have been trying to get my ski all tuned in for a while but just haven't had much time to mess with it. My setup is very similar to orangfinger's that's why I thought I would just post this here. Mine is a home ported 61x w/o any of the msd stuff.

My jetting right now is 140 main 120pilot w/ 2.0n/s and 95gr spring which was giving me 30psi pop off. I switched to the 80gr and that brought me to about 24psi pop off. Seemed to help. I had had my low speed screw set about 1.5 turns out before. After setting my idle like you said Matt E my low speed adjuster was only about .75 turns out. Now I've got some lean hesitation, I switched down to a 65gr spring to see if that would make much diff. It did not. So I guess I need to jet up now? How much? Maybe to a 125?

 

[Matt_E]

The idle mix screw is used ONLY for idle mix.
If you find a lean hesitation after adjusting the idle mix screw properly, you will need to either lower the popoff, or increase the pilot jet.
Then, you must re-do the idle mixture screw.

Does that make sense?

 

[bassman215]

Yeah that makes sense. That's why I was thinking jetting up was probably my next step.

Another question...

My ski will idle all day long with no problems. But if I blip or let off the throttle quickly from holding it at higher rpms then when the rpms come down the ski will not idle (it will but just for a few seconds), it just dies. If I rev it up, and then ease off the throttle it will idle great. Didn't know what might cause something like that?

 

[Superjet3]

From my experiences with riding other peoples boats with LPW ported motors is they are a little flat directly off idle and tend to come on strong in the mid range. I am not trying to be negative, just letting you know you might not get the instant off idle hit you are looking for. It could be in the port mapping. Also you ,ight want to get your hands on a mikuni manual they cover tuning the carb really well.

 

[INDebtSJ]

I have the same engine in my ski and it hits hard off the bottom.Of course I had the Paul assemble and tune it for me.
Hits good enough for me to wait to install the 785 big bore!

I,ll see what mine has cause I dont remember.

 

[bassman215]

With setting the idle like Matt E said I am at about .75 turns out. If I ride the ski for one minute at 1/4 throttle and punch it, I have bad hesitation. I turned out the low speed screw to 1.5 turns and this almost cleared the hesitation up. Since that helped that means I should jet up to maybe a 125 pilot from the 120 I am running right now, correct?

 

[Matt_E]

I'd go to a 122.5 first. :biggthumpup: