SX/SXi/SXi Pro Just finished build, not running right!

[Big Pin]

Hi Everyone,

I have a 2001 750sxi Big Pin that i just purchased off my buddy. Last year someone sank the ski and we rebuilt the ski ground up.
The ski has the following mods:
48mm Carbs
ADA Head
Factory Dry Pipe - Dual cooling
Dual exhaust
small bore around .10mm
Riva Reeds
Bildge pump
Ride Plate
intake grate
Prop
MSD
Fuel Pump Brand new


and a ton of other stuff.

We just finished the build from the ground up, new crank, pistons, gaskets etc. Before the ski seized up it ran perfect, the tune was perfect, it was reliable and everything. So with the small bore the tune should not need to be touched.
When i was go through the break in the ski was fine, did 1/4 throttle half tank gas, 1/2 throttle half tank gas, 3/4 throttle 1/4 tank gas and then some small WOT pulls. We had noticed during the break in the ski had poor mid range to high end. So i checked Pop off even though Pop off is for low end. My Pop Off was all over, so i put the old springs back in, and now Pop off is sitting at around 20-22psi even in both. Does any one have any idea where my Pop off should be for the mods i have??

I took it out again after changing the springs and the ski still didn't run right, low end felt a little rough, mid range was garbage, and top end was clean but still didn't feel like it was hitting the full powerband.
I checked compression last and i had an even 180psi in both cylinders and my plugs were perfect.

Could someone please shed some light as to what i should check? I'm not over heating boat is staying at a perfect hot coffee temp.
Please let me know what you think my Pop off should be?
We are also going to clean the carbs once again just to be sure but we just rebuilt them.

There may be a chance it could be tuning but i doubt it, there has been no changes to the ski since it was last perfectly tuned.

Thanks for your time,

Adam:Banane09:

P.S I'm trying to get the boat ready for Hurricane ISSAC!! New Pole should be in, in a few days also!

 

[Big Pin]

Bump, could really use some help on this one.

Anyone?

 

[sxipro02]

I would double check for air leaks around the head and base gaskets, also check the front and rear seals for leaks. If thats not it I would suspect carb tuning. Your engine might have been running great before but could have had lower compression due to cylinder/piston wear and is now corrected causing the tuning to be off. Your pop off sounds about right if your running A/M air filters, I set mine close to that and it runs fine. I tried running 28psi and it wouldnt come off idle so I had to drop back to low 20's.

 

[High Speed Industries]

Where do you have your adjusters set at and what needle and spring do you have? Do your plugs look the same? I'm guessing the carbs are sbn style. I'm runnin dual sbn 44s ok my setup. The carbs have a 2.3 needle and 95g spring in them which makes for about 20 psi. But my motor setup is a little different. I have the group k hammer 92 kit with a limited pipe, carbs, reeds ect. Do both carbs have fuel pumps? How many pulse lines are you running?

 

[Big Pin]

Yea, i think it may come down to tuning, compression was around 140 and now it is at 180. I would like that to be my last outcome to start messing with the tune. The plugs are a perfect brown color, both are the same. Does that not mean it isn't the tune?

However it was originally tuned for 180psi

 

[Big Pin]

Where do you have your adjusters set at and what needle and spring do you have? Do your plugs look the same? I'm guessing the carbs are sbn style. I'm runnin dual sbn 44s ok my setup. The carbs have a 2.3 needle and 95g spring in them which makes for about 20 psi. But my motor setup is a little different. I have the group k hammer 92 kit with a limited pipe, carbs, reeds ect. Do both carbs have fuel pumps? How many pulse lines are you running?

I have Makuni 48's on mine. I only have one fuel pump with two pulse lines. It's a brand new fuel pump as well because i didn't want to take the chance with the old one.

My bud just backed out one of the needles and noticed some rust, it was the one thing we did not change or clean so hopefully cleaning them up will solve the issue. Hopefully it was just a lack of fuel.

I will let you know how it turns out.

 

[Big Pin]

Thank you SXI pro and RdToy.

 

[Big Pin]

Back to the drawing boards-

Carbs were clean, and everything is to spec.

However, the gas looked weird, it should be a purplish color and the gas was a yellow color.
Since there are all new fuel lines we think there may be some corrosion going on in the gas tank. Will be emptying the tank tonight to see if this is the case. Kind of like a varnish in the gas.

If not does anyone else have any thoughts for me?

 

[Big Pin]

Update:

Carbs were cleaned, gas in the tank was fine. Took the ski out Sunday and was riding pretty good but still will not open up, down low felt really weak and up top feels like it has more to go but will not open up.
Any thoughts?

What would be one of the major reasons for losing down low power?

The ski stalled out on me half way to the island and would not start again, towed it back to the island and looked at the plugs, had almost no spark at all. I'm hoping it may be an electrical issue and i may just have to replace the computer or the ignition.

I'm going to probably do it all new ignition, wires, coil pack, computer etc. When looking at the plugs it looked as though the rear cylinder wasnt even firing, which would explain no power down low.

Any thoughts will help?

Ski will be down for about a week,, i have a new pole i putting on and i want to fix this electrical issue and i should be good to go. I will post pics of my ski in here when the pole is on and everything is complete.

Thank you

 

[sxipro02]

I would start with a coil. (it will come with new wires) If that dosent fix it then possibly look into the cdi. The MSD cdi's are very prone to fail fyi. Thats the only reason I never went to a AM setup, I will trade a little power for better reliability