Dual 44 Mikuni observations

[ROTATION]

There are two parts to your problem you must change first:
The manifold, you need to block the crossover passage for signal clarity
The stock airbox is upsetting airflow, if you set the carbs up with it removed you will find the ski runs rich when it is bolted on, change to 2/ 61X airboxes

Also check that none of the progression holes are blocked.

 

[waxhead]

i am concenred you are running that bigger a low as well as high
i think you should be abotu 100 on the high

 

[QJS]

Geek,
The low speed adjusters were set at 1 turn out. Good advice from Rotation about blocking the crossover passage if you havent already.
Wax, you should know everything is upside down here...or is it over there?lol
Chris.

 

[freestylegeek]

There are two parts to your problem you must change first:
The manifold, you need to block the crossover passage for signal clarity
The stock airbox is upsetting airflow, if you set the carbs up with it removed you will find the ski runs rich when it is bolted on, change to 2/ 61X airboxes

Also check that none of the progression holes are blocked.

Something I haven't thought of yet.
I find it hard to believe that the airbox has ANY effect at idle.
However, the crossover passage certainly would...

And yet, there are plenty of other fellas running stock intake manifolds with OEM 44's that are at 1 turn (SuperJETT, PancakePete, etc...)

I can tell you that all the progression holes are clean.

 

[freestylegeek]

i am concenred you are running that bigger a low as well as high
i think you should be abotu 100 on the high

I could very well end up there Wax.
I need to get my low-speed stuff working first before I even think about my high-speed circuit.

 

[freestylegeek]

Geek,
The low speed adjusters were set at 1 turn out. Good advice from Rotation about blocking the crossover passage if you havent already.
Wax, you should know everything is upside down here...or is it over there?lol
Chris.

Is your cross-over passage blocked?

 

[Matt_E]

the pop-off circuit feeds through the low jet.
The needle and seat are used as a fuel regulator (when the suction is created by the vacuum the engine makes against the throttle plate).
The low jet is an orifice used as a fuel-flow limiter (when the suction is created by the velocity of the air moving through the carb.

If tuned correctly, the needle should be off the seat from 1/4 throttle on up.
Thats when the jets restrict the flow into the carb, and the remaining fuel heads down the return line.

Thanks for clearing that up...but you get the point. Changing the combination of popoff and low speed jet doesn't necessarily change the amount of fuel, but rather the curve, for lack of a better word. I had jetting with 32psi and 17 psi that worked identically.

 

[freestylegeek]

...Changing the combination of popoff and low speed jet doesn't necessarily change the amount of fuel, but rather the curve, for lack of a better word...

bingo. :cool2:

 

[ROTATION]

The best way to jet is to use a tach and set the LS screw at one turn and then get the jetting so that max sustainable rpm is at 1 turn on the HS screw.
You then have the total jetting number for the ski, if the ski has a lean hesitation increase the LS jet size and decrease the HS jet size by the same amount, do this until you get the ski to run best. If there is still a hesitation, then decrease popoff one step at a time until it goes away.

 

[freestylegeek]

Well, as of 3:52 pm today, I have officially given up on jetting for this summer.

I now have a boat that runs EXACTLY the same with 120/110/2.0/95 and 120/135/2.5/80 - as well as every combination in between. It runs the SAME all the time!!! The low screw must be at 2 turns to start and idle.

I am leaving the 120/135/2.5/80 in and am at 2 turns on the low screw, and 2 turns on the high. I let it idle for 3 minutes, then opened it to full throttle and had no loading or hesitating - good enough for me. Then I held it at 1/4 throttle (almost on plane) for 1 minute, and opened it to full throttle, and there was a hesitation. HOWEVER, that is the ONLY time I can make it hesitate. It WILL NOT hesitate while I'm riding around, so I'm just going to leave it. I am runnig a stock 61x ignition, so if I was rich by any indication, I would certainly know it. I think I will run this way for the rest of the summer, and look for some 46's this winter.
For now, I'm done fiddling, and now I am going to ride.:irked:

 

[freestylegeek]

I wonder if dual 38's with an external fuel pump would work?....onder: :nono: :1zhelp: :disappointed:

 

[SuperJETT]

tuning wuss....

 

[x-jetter]

Well, as of 3:52 pm today, I have officially given up on jetting for this summer.

I now have a boat that runs EXACTLY the same with 120/110/2.0/95 and 120/135/2.5/80 - as well as every combination in between. It runs the SAME all the time!!! The low screw must be at 2 turns to start and idle.

I am leaving the 120/135/2.5/80 in and am at 2 turns on the low screw, and 2 turns on the high. I let it idle for 3 minutes, then opened it to full throttle and had no loading or hesitating - good enough for me. Then I held it at 1/4 throttle (almost on plane) for 1 minute, and opened it to full throttle, and there was a hesitation. HOWEVER, that is the ONLY time I can make it hesitate. It WILL NOT hesitate while I'm riding around, so I'm just going to leave it. I am runnig a stock 61x ignition, so if I was rich by any indication, I would certainly know it. I think I will run this way for the rest of the summer, and look for some 46's this winter.
For now, I'm done fiddling, and now I am going to ride.:irked:

damn man i'd just leave that alone. if my ski ever ran half as good as what you're describing i would be jumping with joy.

 

[freestylegeek]

damn man i'd just leave that alone...

that's kinda where I'm at.
Maybe after a month of good riding (and successful double troubles) I'll try tuning again.

 

[freestylegeek]

tuning wuss....

well, my ski has more epoxy resin and metalflake in it, so there. :tongue:

 

[Big Kahuna]

hey Matt, see if you can round of some plain old aftermarket Mikuni 44's........ like you would buy from Riva or Protec, no modifications..........send them to chucky (Contact Pat Bogart for this setup), I bought a set that Pat had Chucky set up for Derek (FLSuperjet)..... they work perfect...... Chucky does some light circuitry work, but that is it, I can get you my jetting numbers, but I dont think they would work with your OEM 44s.........

 

[Island750]

I 2nd that Abe(sj13) had a set done by him and put them on the ski that you built Geek, and all he did was bolt on and off he went. They were off by about an eighth of a turn!!!

 

[freestylegeek]

happened to me a few years ago
the spacer shoved my carbs up against my exhaust and i would full up with petrol as well
happened when i went from an riva to an r&d layback spacer
the fix was simple i drilled extra holes in the diapram plate

I have NEVER checked that!!!
I will look tonight.

Wow, that would be sweeeeeeet if that was the issue.

 

[freestylegeek]

I have NEVER checked that!!!
I will look tonight.

Wow, that would be sweeeeeeet if that was the issue.

Crap, just remembered the diafragm plates are facing the engine on a stock manifold...definitly not the problem.

I filled in the crossover tube, and will get in the water tomorow.

 

[Freestyleriverrat]

I rode squids 24/7 boat with Full Specs and I have to say that those carbs are awesome! We have pretty much the same set up but his just hits better and cleaner. If you have the means definatly look for a used set of full specs! Nice!