superjet will not run right

[jetski9010]

This superjet has not ran right all summer and I am out of ideas to fix it. It is a 62t cases with 62t cylinders and a 64u head. The cylinders were mild port cleanup and had a small u shape cut in the bottom intake side of the sleeve. Its running the stock 38 carbs. Right now it has a protec pipe on it that might be for a 650 but was taken off a running 701 so I dont think its the pipe holding it back but I just bought a factory type 4 pipe coming any day now.
All the ski does is bog down low and will not increase rpm's inless you start hopping out of the water then all of the sudden it will hit some point and the motor will just scream and take off. first we were running a 70 low jet and a 135 high with a 1.5 n/s and 65 gram spring. We had tried 80 low's, 65 low's, 18 psi pop off and every change we did it still ran the same. The hull is a custom modified hull and the exhaust comes out the water box and goes up and over to the left front of the ski where it comes out. We pulled the water box out and found the line that came out the of the water box to the outlet was kinked so we replaced that and still same thing. We have tried two other total electric systems on the ski and still ran the same way. We had tried a total different set of carbs and still nothing. I had cut all water off the stinger to see if that changed anything and it didnt. The ski runs great out of the water but will bog as soon as its in the water. The plugs look normal maybe a little on the rich side. I am not sure what is going on here if the pipe is sending the signal back to soon and keeping exhaust gas in the chamber or not. The only thing is this pipe ran on a 701 before and my brother has the same pipe on his 701 set up and it runs fine. I am about to burn the ski to the ground and start over. Anyone got any input?

 

[MADMAT]

Whats the compression? And post pics of plugs maybe.

 

[jetski9010]

His compression was 140 psi but we thought maybe it was a base gasket leak so we put the thicker stock gasket back in and it lowered the compression to about 130-135psi. I will try to get some pics of the plugs up.

 

[jetski9010]

Here are some pics of the plugs from yesterday. I know these look really rich but this is when we tried the 65 lows in it just to make sure. The plugs are BR8HS thats all we could get on the way to the lake. We were running B7HS before.

 

[MADMAT]

Plugs look nice but that compression is crazy low, right? If thats not in I don't know. time for the pros to chime in!

 

[CoreyLKN]

Putting the thicker base gasket in lowered compression right?
Well in that case you'd need a thinner one to raise compression.

 

[jetski9010]

Yes putting the thicker base gasket on lowered the compression. I am not the one that built this motor so I am just trying to figure it out now. I was told that this head was shaved down and should have around 180 psi of compression. The squish was also setup before the thicker gasket had to be put on. I am about to tear the whole motor down and check all the stuff for myself but lets say it did have low compression from worn rings, pistons, cylinders or whatever would the motor run like this? Has anyone seen a motor run like this. Also is the 64U head the one off the blaster 701 or is this off a 760 motor. If it is off a 760 motor the domes would be the wrong size and that is why it could have the low compression.

 

[jetski9010]

Here are some pics of the plugs from yesterday. I know these look really rich but this is when we tried the 65 lows in it just to make sure. The plugs are BR8HS thats all we could get on the way to the lake. We were running B7HS before.

I ment to say look really lean

 

[MADMAT]

Yea a lil lean IMO too I guess.....should be chocolate milky.

 

[jetski9010]

I just checked the compression for myself for the first time and I got a little over 150 psi in both cylinders right now so I would think the compression is alright. Does anyone think it could be the jetting and we are just that far off? The highest low jet I had in it was a 80 I really dont think it would need more than that.

 

[tipafew]

65 gram springs? I thought I ran a lot higher pop off than that with my 38's.

 

[rollin5150]

Sounds like you are running lean on the low end. Plugs look lean as well. You did move the pop off down but how about running a larger N/S. Say go up to 2.0??

 

[jetski9010]

I first set it up to stock pop off at 55 psi I was told and then droped to a 65 gram spring then tried a cut spring that gave me 18 psi. I was going to try 2.0 n/s too but I would think with the pop off set at 18 psi would be really close to it being a 2.0. It does still have the stock spark arrestor on it too.
When it is bogging at low end the exhaust still has a good amount of smoke. I am wondering if I should just put a 100 low or 120 low in it just to see what it would do.

 

[SUPERTUNE]

Use 2 new 1.5 needle valves with a pair of 95 gram spring and put in the stock SJ main jet (130) with a 75 low, set high speed screw to 1 turn, set low to 2 turns and start there.
Don't use any aftermarket carb parts, use only Mikuni OEM parts.

 

[jetski9010]

Use 2 new 1.5 needle valves with a pair of 95 gram spring and put in the stock SJ main jet (130) with a 75 low, set high speed screw to 1 turn, set low to 2 turns and start there.
Don't use any aftermarket carb parts, use only Mikuni OEM parts.

This is what we started with in the begining. The n/s are brand new and were check with a pop off gauge to make sure they didnt leak.

 

[SUPERTUNE]

Does it idle good on the trailer and backed into the water to load the pump?

 

[jetski9010]

Does it idle good on the trailer and backed into the water to load the pump?

Yes runs great on the trailer. It idles fine in the water. It has throttle response from idle till 1/4 throttle but if you go to open it up full throttle it will just run at 1/4 throttle then bog acting like it is being held back by something. if you bunnie hop the ski out of the water a few times and get the pump unloaded then it will take off full throttle. If you let off and like it idle back down it will do the same bogging thing.

 

[SUPERTUNE]

Well I guess that means the reeds are good...
Take a couple of pic's of the engine setup and let me look...How do you have the cooling lines run? Is this a stock SN waterbox or a RN aluminum box?
What impeller do you have?
Is this setup with a MSD Enhancer?
I have to think that the Pop off is too low...back to 1.5 and the stock 115 gram spring and a 80 low and the stock 130 high.

 

[Crab]

my T cylinder ran great with B pipe and jetting 70/135 and 55 psi, stock reeds, it runs best with 175-185 psi head. Its sensitive to pump load a bit off the bottom, hooker might not be the best choice unless you shim it out a bit, 12/15 solas X or concord might be better suited. With type 4 use 75/140.
(my .02)

 

[tbaer]

my old 650sx used to do this. it was because the pipe was getting so full of water it would run under load. so it would run great on the stand and idle all day in the water but as soon as i would full throttle it would bog down and run like crap but if i pumped the throttle and bunny hopped it would take off . So check your water lines!!