Dual 44 Mikuni observations

[Mark44]

p

been running stuffers for 3 years, no tuning issues.

Man they just didn't work for me I chased jetting for a couple months then pulled out the stuffers and pow it hit and ran great. Wax told me to loose them.

I meant Limited chamber sorry and it was ported by Magoo and hits real nice.

Mark44

 

[crammit442]

yeah no reed spacers/stuffers/crap

here are the specs i got from paul
115h/120L/2.0/95

oh yeah and pipe is mod b-pipe port matched of course

anyone else want to chime in?

If paul gave you those specs, why don't you just run it the way he said? Why bother getting his or anyone else's specs if you're just gonna come on a public forum and get advice from a bunch of strangers, most of which can't tune their own boats?

 

[teton]

crammit, i just hate running my motor and realizing that i need a different jet etc.....and having to wait a week for my order to come in, i would rather order a bunch now so i have them at my disposal.....

plus i got those specs from paul before i knew my carbs were oem, before i filled my crossover etc.. not to mention it seems like these carbs are more difficult to tune than most and even the best tuners specs are only a baseline.

I'm not doubting Paul and i know he is a very good engine builder (in fact his specs will be the first i try- he has been extremely helpful, this was over the phone, i have never actually met him in person)so he is just as much a stranger as a lot of the other people on this site........just want to minimize the non-riding time while i switch the cases/carbs on my motor. seems like wax, matt, and the like have gone though what i am about to. im just trying to speed the process along. without ordering jets a set at a time. isnt that what its all about....more riding.....less tuning/downtime.

and does anyone know what the deal is with the 4 low speed holes in the carbs ?

 

[XtSuperJet]

back to the top again

sorry guys to bring such an old thread back, but I thought I would ask for help in here since this has been a great thread.

I recently got myself Paul's lehr 61x big bore freestyle ported cylinders with R&D manifold that works with Vforce 2, protech griddle head with 35 dooms (~187 psi is the actual compression), hooker 10/16 impeller, and dual AM 44mm silver carbs with brass 90 degree fittings. the carbs were jetted by Paul as follows.

120 pilot - 1/2 turn out
130 mains - 1/4 turn out
2.0 L/S and 95 grams spring
62.5 main in the return line.

that went into my 04 superjet with Rad flywheel, B-pipe mod with dual cooling, MSD enhancer.

with the above jetting, I had off idle lean hesitation and OK snap. I will list what have I done in terms of jetting and my findings below.

- increased the pilot to 125, that made the hesitation much less obvious, but the throttle response was worse. final jetting was 125/130/2.0/95
- dropped the pop off by using 80 grams spring and kept everything else the same, that made the hesitation go away, but the throttle response was even worse. 125/130/2.0/80
- dropped the pilot to 115 just to see if the throttle response improves and upped the main, that made the throttle response better but the off idle hesitation was pretty bad. 115/135/2.0/80
- went back to 125 pilot and dropped the high to 130 but this time I thought I would try even higher pop off, so I went with 115, that made things 10 times better (or I thought so) so I was not getting any off idle hesitation and the hit was good but

while I was going at a steady ~1/3 thottle or so for 4 seconds, the ski suddenly lost power and the exhaust sound was muted, it almost felt like seizure. let go and tried again, same thing. so I thought I would richen the low screw and see if that helps, and it did, I turned the low screw to 2 full turns and that took care of that issue. I stoped there and decided to go home and do a compression test and the numbers were healthy (~187 in both)

next day, I thought I am not that way off, so I lowered the pop off via using 95 spring instead of the 115, and that did not help, the very same thing happened (seizure) put bigger pilot (127.5) still the same thing but this time if I turn the lower screw at 1.5 turns it will run ok (however by now the throttle response is no longer that great)

so I got kind of sick and put 130 pilot and 80 grams spring at the same time, and that sure took care of the seizure issue, keeping on mind that this only happens when steadily ride at ~1/3 throttle for several seconds or so not WOT at all.

so my final jetting so far is 130/130/2.0/80 the good thing about that is I no longer have off idle hesitation nor 1/3 throttle seizure. the bad is I have what feels like rich spot at almost 1/4 throttle (if I advance a tiny bit after that the skit would jump right off the water) off idle response is kindda lazy/muddy and loading during tail stands.

so what do you guys think I should do next, I mean having 130 is kindda big, but any lower than that and hesitations and seizures happen. should I leave the pilot at 130 and drop the main to see if that helps?? I don't have a tach to tune my high end though, I have been trying to find one in here but could not so far

any help would be greatly appreciated, please note that Paul has been trying to help me and I have had an excellent experience going with him for my build, but I guess he has been either busy or away in the last couple of days and that's why I thought I would ask you guys for help until he gets back to me with his thoughts.

thanks

Ahmed

 

[waxhead]

try 125 low
110 high
19psi pop off

 

[Matt_E]

In an almost identical setup, I ran 112.5 pilots, 122.5 mains.

 

[XtSuperJet]

Matt, do you remember what was your pop off pressure as well as needle screws settings for both low and high.

thanks

Ahmed

 

[tofa]

A few of use over here in nz run
137.5 main
120 pilot
1.5 n/s
95gram spring
1/4 turn high
1 1/2 turn low

havent tried to many other set ups as this seems to hit pretty hard and you can wot all day long if you want.
id be interested to hear if any of you try it and see what you think.

 

[XtSuperJet]

Tofa,

could you please list your mods, so I know we are comparing apples to apples here.

thanks

Ahmed

 

[tofa]

760 62t 85mm pistons
ported cylinder and cases
v forse2 reeds
ada head 175psi
light weight charging fly wheel
44 sbn carbs with standard filters
riva manifold and spacer
msd enhancer
factory b pipe with mod chamber
standard water box..

 

[Matt_E]

Matt, do you remember what was your pop off pressure as well as needle screws settings for both low and high.

thanks

Ahmed

2.0 N&S for 23-24 psi popoff. I think that was a 95g spring.

 

[XtSuperJet]

Waxhead,

I tried what you suggested and it did not work very well, it was way too rich everywhere, and it was nearly impossible to start once it sat in the sun for half an hour or so (weather here in UAE is pretty damn hot ~105) I think the low pop off pressure and with the sun heating the fuel tank and creating pressure, it leaked and made it almost impossible to start.

I did find one problem that I did not notice before, and I was hoping to god that that was it, but unfortunately no I found my water box and the beginning of the exhaust chamber where it attaches to the water box was overheating as hell, I mean when i sprayed water on it it sizzled for sometime before it stopped. obviously my jetworks control valve was not letting water out to the water box. anyways, I cleaned the jetworks a bit and got it to work properly again.

this however got me thinking, maybe what I think is seizure at 1/4 throttle (remember I feels like power loss and change in the exhaust note) is just my jetwoks letting water out at this specific RPM and filling the water box. could that be it?? the thing that puzzels me though, is why if I richen the lowend it kindda cures that, well maybe because I was running it way to rich to where I was not making enough power to loose any once the jetworks opens up lool.


anyways, I found that running 125 pilots, 135 mains, 2.0LS and 115 grams spring is where it ribs so good (with the exception of the 1/4 seizure that now I hope is only my waterbox being filled with water at this specific throttle position/rpm/water pressure.) I guess I will go out tomorrow and bypass the jetworks and see if that power loss/ exhaust tone change goes away, if it does, then I will go ahead and use 4mm restrictor instead of the jetworks vavle. what you guys think??

thanks

Ahmed

 

[SUPERTUNE]

Waxhead,

I tried what you suggested and it did not work very well, it was way too rich everywhere, and it was nearly impossible to start once it sat in the sun for half an hour or so (weather here in UAE is pretty damn hot ~105) I think the low pop off pressure and with the sun heating the fuel tank and creating pressure, it leaked and made it almost impossible to start.

I did find one problem that I did not notice before, and I was hoping to god that that was it, but unfortunately no I found my water box and the beginning of the exhaust chamber where it attaches to the water box was overheating as hell, I mean when i sprayed water on it it sizzled for sometime before it stopped. obviously my jetworks control valve was not letting water out to the water box. anyways, I cleaned the jetworks a bit and got it to work properly again.

this however got me thinking, maybe what I think is seizure at 1/4 throttle (remember I feels like power loss and change in the exhaust note) is just my jetwoks letting water out at this specific RPM and filling the water box. could that be it?? the thing that puzzels me though, is why if I richen the lowend it kindda cures that, well maybe because I was running it way to rich to where I was not making enough power to loose any once the jetworks opens up lool.


anyways, I found that running 125 pilots, 135 mains, 2.0LS and 115 grams spring is where it ribs so good (with the exception of the 1/4 seizure that now I hope is only my waterbox being filled with water at this specific throttle position/rpm/water pressure.) I guess I will go out tomorrow and bypass the jetworks and see if that power loss/ exhaust tone change goes away, if it does, then I will go ahead and use 4mm restrictor instead of the jetworks vavle. what you guys think??

thanks

Ahmed

A 4mm restrictor is too big, use a old 2.5 needle valve if your running dual cooling lines.

 

[waxhead]

if that was to rich then i think your carbs need looking at

bypassing the fuel sounds like leaking n/s to me also check out the anti siphon valve
the tank breather should release the pressure long before it blows open your n/s

even if the ns is new it can still leak and dribble
you need to make sure you have a good clean pop off

Getting your pop off correct is the key if you dont have a gauge to check it your only ever going to get your ski close at best

 

[RoscoeJ]

Must revise this great Thread ! Tuning Yamaha 760 with dual 44mm carbs

if that was to rich then i think your carbs need looking at

bypassing the fuel sounds like leaking n/s to me also check out the anti siphon valve
the tank breather should release the pressure long before it blows open your n/s

even if the ns is new it can still leak and dribble
you need to make sure you have a good clean pop off

Getting your pop off correct is the key if you dont have a gauge to check it your only ever going to get your ski close at best

I have a stock 760 Yamaha 62T with stock dual 44mm carbs. I have run this motor alot in my Waveblaster2 .I just installed it in my Waveblaster 1, B1 and moded my Factory B Pipe manifold,and installed motor carbs and electrical box from my B2.all Stock.
Ski would not start without squirt of fuel into carbs. i opened low speed to 21/2 turns out on both low speed screws,much better,but still starving for fuel. Should I keep working on low speed screw,or am I in wrong area? I only added the Factory B pipe.
I now have extra 3/8 cooling line ,which is unrestricted out the side of my ski. Let me kow what your thinking, Its hard to start,Starving. and even when I start it I have to feather the throttle to get going,once going ski is fine. Thanks in Advance

 

[Matt_E]

I only added the Factory B pipe.

You need to increase your main and pilot jets and lower your popoff via a smaller spring. Adding a b-pipe requires rejetting and cannot be done with just the adjuster screws.
Look at Factory Pipe's website for instructions and jetting suggestions.

 

[RoscoeJ]

What spring would you suggest ? what is stock spring set at? do you have and recommended turns out on the high and low to start with after replacing the spring? I will check out Factory pipe site for jetting ,and post results.Thanks

 

[waxhead]

2.3 needle and seat and a 95 gram spring will work very well with that setup. the 760 carbs work very well, don't listen to the rumors.

 

[Legdragger]

I am tuning the exact same setup. a B2 760 in a B1 with a factory Mod pipe. Right now I am running 120 low/ 120 /high and I have tried 20, 25 and 30 psi pop off using different springs with the 1.5 needle valves.

So far I got it to run ok at best off the bottem but still can't get it to hit midrange with any authority. The motor ran so much better in the old hull with the stock pipe. Kind of annoying it is lazy in the B1 hull.

 

[waxhead]

your lows are to small and your highs are to big
your pop is to high causing the fuel to start flowing later. lower your pop off to about 20 psi put a 125 low in it and 115 high

Dont just put a bigger low in it and say it didnt work
you need to reverse jet it correctly and these things hit hard