Superjet has no lowend power

[BlueBreadTruck]

OK guys, Ive been through everything on this ski, and CANNOT eliminate the low end having NO power on this ski! It kind of makes a "blubbering" sound down low-mid range, but rips up top!


Specs; Rebuilt 701 w/ head. NEW SBN 44, Factory B-pipe. Installed a new stator, coil, and new MSD CDI, so im certain its not the electronics...it was doing this before.


I guess im back to the carb! Im using Factory pipe's specs for the limited chamber B pipe..... Can anyone help?

 

[Matt_E]

What is the carb jetting?

 

[SUPERTUNE]

If using a new SBN carb unless you bought a stock REPLACEMENT carb you probably have the retail aftermarket one. You need to use the stock spec's then add a little more jet size depending on how much the engine is modified.
Start with 1.5 needle valve, 95 gram spring, 120 low, 130 high for a standup ski with the usual mods like pipe, head, aftermarket F/A, aftermarket waterbox, Jetworks valve, and MSD Enhancer.
Set high screw @ 1 turn out, set low screw @ 1 3/8 turn out to start out with.
Chuck

 

[BlueBreadTruck]

Thank you, Here is my jetting, exactly as per factory pipe... ONE exception though, i bought a NEW sbn44, not a factory one!!!!!


Main Jet : 145
Pilot Jet : 120
High speed screw : 12 turns out from closed (i assumed it ment 1.5 turns, 2.5 turns?)
Low speed screw : 2 2 turns out from closed
Needle & Seat : Stock
Spring : 95 gram

 

[SUPERTUNE]

Did you take out the needle and seat and look at the size?

 

[BlueBreadTruck]

yes, i have a 1.5 n/s and 95 gram spring now

 

[SUPERTUNE]

Did you adjust the needle adjuster and change jets to how I said? How does it run now?
If you did, maybe need to try the 115 gram spring and see if anything changes...

 

[BlueBreadTruck]

not yet, I will this weekend. Thank you very much for helping me here. I had no idea that the carbs were different!

 

[SUPERTUNE]

Yes, OEM carbs are different than the retail aftermarket.
This has been covered a LOT here on the board, but I think your new here...
The stock Yamaha carb uses very fine threads on the low speed adjuster and must run them about 2 1/2 turns out, on the aftermarket carb the adjuster uses course threads so the run about 1 1/8 out to 1 5/8 out at the most.
If you had a 61x 701 single carb they only use a 3 hole low speed circuit, the 6m6 and the aftermarket Mikuni uses a 4 hole circuit so it will run richer off the low end! (this is good for high performance though).

 

[BlueBreadTruck]

First of all, thank you supertune! my superjet runs MUCH better!

However it still has a BIT of low/middle range blubbering. my brother's RN has MUCH more mid power, pulls alot harder and is smoother. What color spring should I try?

 

[BlueBreadTruck]

I just found a gold spring in another sbn I had, I installed that and will try it tommorow. Should I leave the needles as you said for now?

 

[SUPERTUNE]

Open the high speed needle to 1 1/2 turns out with the 115 gram spring.
How far closed is the low adjuster now?

 

[BlueBreadTruck]

I am now running

1.5 needle valve, Gold spring, 120 low, 130 high

high screw @ 1 turn out

low screw @ 1 3/8 turn out

I will do as you say and turn the high to 1 1/2 turns out

Thank you VERY much, again! That you are taking your valuable time to help me is very appreciated

 

[SUPERTUNE]

See how that goes, if you start to pick up a hiccup right off the bottom, go out to 1 1/2 on the low adjuster, if your idles get real bad, adjust the curb idle a tick more, if still bad then you need to go up to a 122.5 or 125 low jet and back in to 1 3/8 for the low adjuster.
Have fun and keep us posted!

 

[DC SUPERJET]

You are the man supertune. I love seeing threads like this where people actually help people.

Oh, and good luck with the ski BBT.

Dave

 

[FyrHazard]

Subscribing because knowledge is POWA!

 

[BlueBreadTruck]

Ok, it is still doing it, i mean it really is better now, but still dosent have close to the smoothness or lowend power than my brother's rn

here is a video I took, you can kinda hear it

 

[SUPERTUNE]

Now that your at this stage let's go further...
Keep in mind this is a 61X/61X engine and NOT a RN 701 62T/61X engine with dual carbs, these won't compare with performance until you really do more modifications to your 61X/61X.
Now tell us a few things about your ski...
How are your pipe adjusters set on your headpipe?
Do you have a Jetworks Flow Control Valve?
What impeller are you running?
Have you measured the exit nozzle to see what size you have?
Where does your stator timing marks line up? At stock?
Are you running a stock/lightened flywheel or an aftermarket aluminum one?
Did you use a stock ignition coil or a rebuilt one?
Do Not use a MSD replacement red coil as they're junk sorry to say!
The MSD Enhancer is a great CDI for what it is.
In retrospect, I would suggest getting a better designed head like a ADA head that has way better combustion chamber squish clearances and squish ratio's.
Chuck

 

[BlueBreadTruck]

Thank you again supertune.

At this point, I might have given up and accepted that the dual carb engine just has more power, and this is a good as I can get, however the fact that it still dosen't run clean in the low-mid rpm makes me think there is an issue. You cant really hear well in that video, but it still makes a almost blubbering sound in that area. The round nose runs smooth, and dosent make the same sound, and has much more power down low/mid. and his is worn out with a stock head!

One thing I was thinking, Im still running the stock reeds...That may be something i need to check now?
Now, for your questions:

Im not sure of the pipe adjustors.....i bought the pipe used, and they are siezed....However i want to lean twords the wet side, because the pipe runs real cool.

I dont have a flow control valve, but I did restrict the water into the stinger with a mikuni needle valve seat in the hose

Im running a brand new hooker prop (cant remember the pitch, but its set up for a stock/mild engine)

I have not measured the nozzle, but it has an ocean pro steering nozzle

I timed it at stock

It has a stock flywheel

I thought this miss was electrical related, so i bought a new stator, and a Brand new coil, and a brand new MSD cd.....and it ran the same....damn


Thanks soo much for the help again

 

[SUPERTUNE]

OK,
Need to know what pitch the impeller is, I would definitely bore the exit nozzle to at least 83-84mm's to start.
Doesn't the OP steer nozzle have the divider in it?
Mandatory you fix or buy a new headpipe so you can KNOW how the adjusters are set! Too wet will also kill power! And you need to know which ones are open or closed!
Jetting down the stinger is just ok, (oldschool) but the Jetworks Valve is really the way to go and helps make jetting easier.
Also did you measure your headpipe outlet size when you put it on?
You need to make sure you have the 2nd generation manifold and headpipe or make sure you bore and port it to at least 47mm I.D.
Having your flywheel lightened will help a little too for the $$. TBM offers the best aluminum charging flywheels but require the 62T- '96 up stator.
Chuck