Super Jet 62t impossible to tune

[bllewis394]

so i purchased my wife a 98 superjet with limited b pipe, ada head 170psi, msd enhancer, hooker 9/15 and i cannot get this bastard tuned.

it had fp recs for carbs but the f/a had been swapped with some proks so i lowered the popoff to 22 psi. this helped a bit but it is still sluggish on the bottom end.

now i am at 75 pilot, 130 main, 2.0 n/s, stock spring for 22 psi. i don't have a tach but i can tell you that when i run the adjusters out to richen it based on plug readings it feels like a fat pig. just wallows around until about 1/2 throttle.

FP screws are bottom closed, mid closed, top 1.5 turns. i installed restrictions in the lines for the stinger and the bypass on the pipe cooling to raise the water pressure and this helped a bit as well.

is it possible the ski is over propped? what would that feel like? you can feather the throttle off idle to get a little better response but it really has no crispness until 3/8 or half throttle.

one other thing, it has a remote mikuni fuel pump. should i remove that and put the carb fuel pump back in? the outlets on the remote pump are tee'd together and that line runs to the front carb. would running a line for each carb make a difference?

sorry for all the questions but i'm about to lose my mind over this one!

thanks for any help

 

[OCD Solutions]

sounds like something wrong with the pilot metering circuit or maybe a mismatched or fouled pair of carbs. Can you try a set of known good carbs from another ski?

 

[tor*p*do]

not over propped. I have a 10/16 in my SN.
blew my freestyle 701 and went back to my old 650
and prop still OK

 

[bllewis394]

sounds like something wrong with the pilot metering circuit or maybe a mismatched or fouled pair of carbs. Can you try a set of known good carbs from another ski?

the only other duals i have are the stock ones on my 09. i guess i could switch those onto it but i'd rather not mess with that one until i put a pipe and head on it.

 

[bllewis394]

not over propped. I have a 10/16 in my SN.
blew my freestyle 701 and went back to my old 650
and prop still OK

ok, i've read a couple places that over propped skis can cause weird stuff but like i said i don't think i'd know what over propped felt like versus out of tune.

 

[bllewis394]

for the record, i have tried punching the ski and that only bruised my knuckles. at least the reinforcement is solid.

 

[OCD Solutions]

The 9/15 should be perfect. I only suggested the carb swap as a temporary troubleshooting idea to see how it runs. If it runs better with the new carbs then you know the old ones need to be rebuilt or replaced.

 

[bllewis394]

The 9/15 should be perfect. I only suggested the carb swap as a temporary troubleshooting idea to see how it runs. If it runs better with the new carbs then you know the old ones need to be rebuilt or replaced.

i understand. i did change the n/s, test popoff, and replace the jets. without the fuel pump sides, the only other things would be the little check flapper and the diaphragm right? i checked the internal filters and cleaned the channels in the carbs to no avail.

 

[OCD Solutions]

That jetting should be very close. I'm not sure what the specs are on your carbs or the proper fuel line routing but is there a fuel line restrictor in the return line? If the restrictors have been removed from the carbs then you may be dropping fuel pressure at the lower rpms making fuel metering very erratic and jetting near impossible.

Was it running good for the old owner or did he sell because he could never figure it out either?

 

[bllewis394]

That jetting should be very close. I'm not sure what the specs are on your carbs or the proper fuel line routing but is there a fuel line restrictor in the return line? If the restrictors have been removed from the carbs then you may be dropping fuel pressure at the lower rpms making fuel metering very erratic and jetting near impossible.

Was it running good for the old owner or did he sell because he could never figure it out either?

probably that but who knows. he said he had back surgery and i'm inclined to believe him. the pipe was definitely set up like a racing ski would have been when i got it.

as far as the fuel restriction in the return line, i have wondered about that from reading about the a/m carbs that need it. i don't know whether they are removed or not. how would i ascertain that? if those restrictors are located in the fuel pump body then they are gone by default.

p.s. thanks for the responses

 

[OCD Solutions]

probably that but who knows. he said he had back surgery and i'm inclined to believe him. the pipe was definitely set up like a racing ski would have been when i got it.

as far as the fuel restriction in the return line, i have wondered about that from reading about the a/m carbs that need it. i don't know whether they are removed or not. how would i ascertain that? if those restrictors are located in the fuel pump body then they are gone by default.

p.s. thanks for the responses

Thats why I mentioned it, I ran a set of Novi 48's before and they wouldn't run worth a crap until I added the restrictor. I ran dual pumps so i thought I had enough volume to make it work but i still struggled to get it to hit off the bottom.

 

[bllewis394]

Thats why I mentioned it, I ran a set of Novi 48's before and they wouldn't run worth a crap until I added the restrictor. I ran dual pumps so i thought I had enough volume to make it work but i still struggled to get it to hit off the bottom.

interesting, i guess that would present the same issues as having the popoff too high. what size restriction did you run in the return?

 

[OCD Solutions]

I ran a 130 on my 48's to get 2 psi at idle and 5psi @ 5000 rpm but the 46's i run on my SS865 require a #60 pilot in the return. Not sure what the fuel pressures are like on my 46's but that's what X-scream specs for their setup.

 

[bllewis394]

i was just looking at the diagram in the mikuni manual and it's hard to tell where the restriction is before the return outlet.

edit: it's clearly labeled, it just doesn't specify whether it is in the carb body or the fuel pump body.

 

[OCD Solutions]

Here's some good reading for consideration...
http://www.groupk.com/tec-carbs97.htm

Return line restrictors - The round pump 44 Mikuni carbs were manufactured with an unrestricted return fitting on the carb. This causes them to return so much fuel to the tank that the fuel circuits can get starved for fuel. If you are using a round pump 44 Mikuni, be sure you have a restrictor jet in the return line whose inside diameter is no more than .030" (.75mm) All of the new generation square pump carbs have adequate "built in" return line restrictors.

LATENT FUEL PRESSURIZATION - The powerful fuel pumps on the new generation Mikuni and Kiehin carbs has mandated a need for much higher pop off pressures than that of the earlier round pump carbs. Pop off pressures in the 25-35 psi range are very common. Without these high pop off pressures, the powerful fuel pumps would quickly flood the motor. All in all, this combination of a powerful pump working against a high pop off pressure is superior in all functional ways...except one.

When the engine is at rest, the pressure in the fuel system is virtually nil. As the engine is started, there is easily enough fuel delivery and fuel pressure to feed the meager needs of the low speed circuit for idling. However when the throttle of a "just started" engine is drawn slightly, a temporary lean condition of the transition circuit often causes the engine to hesitate badly or even stop altogether. This lean condition takes place because the fuel pump has not yet fully pressurized the float chamber of the carb. The 20% - 50% range transition circuit is solely dependent on full float chamber pressure in order to deliver it's fuel. Full float chamber pressure usually takes place after about 10 or 15 seconds of operation under a load. For a recreational rider who is slowly riding away from the beach , this momentary lack of low speed acceleration is no problem. However for the racer who must start an engine at the line, and operate it at little or no load before the start, this momentary lack of acceleration can be a big problem. If you are running dual carbs, this fuel pressurization problem can become even worse.

Unfortunately the only mechanical ways to reduce this hesitation problem is to reduce the fuel hose length, reduce the internal air volume of the fuel system, or slightly reduce the pop off pressure.

On most stock fuel systems the pump must draw the fuel through about three feet of hose from the gas tank to the fuel valve. After that, through another two feet of hose and a fuel filter. This long length of hose saps off a significant amount of fuel pressure and increases fuel pressurization times. To help resolve this on race boats, a direct line should be run from the reserve pickup on the gas tank to the carb. Along with this, it should be understood that the air space in the fuel system is the area that must be pressurized. If the air space is reduced by filling the gas tank, pressurization takes less time. Unfortunately many racers don't like the "nose heavy" handling that a full gas tank yields. For them a smaller gas tank is a wise solution.

The risk of inducing an over rich transition circuit mixture makes "pop off pressure reduction" an absolute last resort choice for solving the latent fuel pressurization that takes place in the starting area of a race.

 

[bllewis394]

well, it sounds like this is my problem. i wonder if i need another restriction because of the remote fuel pump. i guess it's easy enough to install one and see what happens. i wonder if a 1.5 seat will do the trick.

 

[bllewis394]

I ran a 130 on my 48's to get 2 psi at idle and 5psi @ 5000 rpm but the 46's i run on my SS865 require a #60 pilot in the return. Not sure what the fuel pressures are like on my 46's but that's what X-scream specs for their setup.

common return line or 1 restriction per carb?

 

[OCD Solutions]

I'll bet almost any restriction is better than nothing. I've been trying to look up some better specs but haven't come across it yet. I spent 2 years tuning an old ski and i read so much info i just need to find it again...

 

[bllewis394]

I'll bet almost any restriction is better than nothing. I've been trying to look up some better specs but haven't come across it yet. I spent 2 years tuning an old ski and i read so much info i just need to find it again...

jeez, i don't have the patience for that. :banghead:

 

[OCD Solutions]

LOL, once i started i couldn't walk away. Here; check out this drawing..

http://www.novi-tec.com/images/installationmanuals/seadoo/DS-XR-P9.pdf