Super Jet Dual or Single 44 Carb 718??? Help!

[Vumad]

Everyone running motors ..... are running for power. To say duals work better is pretty much untrue in alot of situations. And ive never had one cylinder run lean on a single carb setup. Never even heard that before. And i agree with eastcoastjumper , on these stock cylinder setups id put a stock carb setup by me up against anyone elses dual setup with the exact same mods.

So when you tune your motor, and your high speed screws are a half turn or full turn different, is that because of carburator inconsistencies not the cylinder? That turn doesnt matter any more when you have a single carb? What about motors that run staggered jetting on the rear cylinder? A single carb would resolve that tuning problem?

 

[WB1994]

Whos to say your two carbs aren't exactly flowing the same? Fuel and/or air? You just going to blame the cylinder? Have you swapped carbs front to rear, rear to front to make sure its not a carb issue or do people just stagger jet because? Why are some 760's stagger jetted from the factory? You think theyd just stagger jet instead of fixing a cylinder problem?

 

[eastcoastjumper]

They stagger jetting on the 760's in couches due to the load on the crank. Rear cyl has more load on it. Ski and passengers have more weight which made it worse.

Fuel Screw setting can be staggered from small casting differences in carbs correct?

I have never encountered a half or full turn difference in my carbs. It's much smaller like 1/16-1/8 turn that I have the rear cyl carb different than my front




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[Quinc]

Everyone running motors ..... are running for power. To say duals work better is pretty much untrue in alot of situations. And ive never had one cylinder run lean on a single carb setup. Never even heard that before. And i agree with eastcoastjumper , on these stock cylinder setups id put a stock carb setup by me up against anyone elses dual setup with the exact same mods.

 

[WB1994]

Getting back on track for the op , do you have a popoff guage? You should bring the carbs up to preasure just before popoof and see if the hold preasure , if not squirt some soapy water or window cleaner on the pump side. If the pump side gaskets are leaking it will never run correctly. I understand you did a good job rebuilding them but its one of the first things i check when chasing a tuning issue.

 

[Parsonsjb88]

@WB1994, Ya I have a popoff gauge and I tested both prior to assembly at 32psi each. I believe one was about 1 psi lower but its as close as I could get them.

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[cookn]

I got this from the carb database on here and I used this setup on a fully ported 718 as an upgrade from 38's. I didn't have to touch a thing and the ski ran great. Great starting point for a small bore freestyle ski running dual 44. This reverse jetting seems to work well, I know your carbs are the oem style. I heard the major difference is in the thread pitch of the high and low screws. I think aftermarket sbn have a fine pitch for more accurate adjustment. I could be wrong there, thats just off the top of my head.


Tuning info from Jetmaniac ,the ski now rips.

Brand = MIKUNI
Model = A/M SBN new
Size =44
Quantity = 2
Main Jet = 110
Pilot Jet = 125
Needle/Seat = 2.3
Spring = 95gr, 19 psi popoff
Pilot screw = 3/4
Main Screw = 1
- - - - - -
Gas Octane = 98
Altitude = SEA LEVEL
Main type of riding = FREE RIDE SURF JUMPING
Would it pass the 10 second WOT test = YES ALWAYS
Powerband = ?????
Motor type/setup =84 mm BB NW SLEEVES,PROX PISTONS,HOTROD CRANK, 61X CYL, 62T CASE BOTH PORTED,ADA HEAD 38mm DOMES, FP LIMITED PIPE, LIGHTEND FLYWHEEL,MSD CDI AND COIL,BOYESSEN INTAKE WITH RAD VALVES,RIVA CONE F/A[/QUOTE]

 

[cookn]

When I set these carbs up I also did full rebuilds and all brand new jets. I also cleaned them in an ultrasonic cleaner before I put the rebuild kits in. You need to be clean and meticulous when it comes to carb set up.

 

[WB1994]

If your running a prok style arrestor then 32 psi popoff is too much.

 

[WB1994]

@WB1994, Ya I have a popoff gauge and I tested both prior to assembly at 32psi each. I believe one was about 1 psi lower but its as close as I could get them.

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Make sure they hold preasure too. If your setup at 32 popoff you should be able to pump it up to 30 and it should not leak at the needle or pump side gaskets at all.

 

[Parsonsjb88]

@cookn I soda-blasted my carbs clean, carb cleaner, ultrasonic cleaned, dried, taped everything off, primed, painted, then installed the new carb kits and jets and even new low and high speed screws. The only thing I can think of is either the jetting is wrong or somehow something came loose inside the carbs. I will be disassembling them this week to double check everything.

PS: This is what JetManiac had me at originally:
115 Main Jet -start at 1 1/2
120 Pilot Jet - start at 1 1/2
2.0 Needle/Seat
95g Spring

Problem is when I first started it up and tuned for the day somehow I forgot to put in a low speed jet in the stator side carb. Needless to say I thought it was my jetting, took apart the carbs found I was missing the jet but because I was out at a jetski event I didn't have the right size jets and no body had the correct size that JM suggested. I ended up finding a set of 110 pilots and used those and when I informed JM that I was getting around 24 psi popoff with 95g springs he suggested I go to 115g springs which got me to the 32psi popoff i have now. So by no means am I saying that JM's tuning didn't work cause I have yet to actually test that exact setup.

Now moving on, I recently tore down the motor and found probably a half cup of of oil, fuel, and water in my stator side crank case. (Mostly fuel and oil, with probably a tablespoon of water droplets floating in it (I'll post a pic). My question is I'm wondering if this was my problem all along? Could I have literally filled my crankcase up with fuel and oil when I was missing that jet and it was flooding the motor? Then, once I threw in the new jets, that extra fuel and oil was being atomized by the spinning crank causing me to run super rich on that cylinder? Now that I think back it always seems like no matter how much I leaned it out it was always too rich once I got it running but if I leaned it out too much it wouldnt start. Am I crazy or is this plausible?

 

[Parsonsjb88]

Make sure they hold preasure too. If your setup at 32 popoff you should be able to pump it up to 30 and it should not leak at the needle or pump side gaskets at all.

Yup they held pressure, no leaking at all, soon as it hit 31-32psi, they pop and the pressure would drop to less than half and hold again.

 

[jetx]

I think jetmaniacs jetting suggestion is going to be a good starting point...and since you haven't actually tried it, id start there...one thing that jumps out to me is you said you thought you had water getting into the cylinders...this would wash any carbon buildup off the Pistons and cause you some bogging issues aswell

Sounds like you have multiple issues going on...id address the motor and get it sealed up and rejet to jetmaniacs suggestion and start from there

 

[Parsonsjb88]

I think jetmaniacs jetting suggestion is going to be a good starting point...and since you haven't actually tried it, id start there...one thing that jumps out to me is you said you thought you had water getting into the cylinders...this would wash any carbon buildup off the Pistons and cause you some bogging issues aswell

Sounds like you have multiple issues going on...id address the motor and get it sealed up and rejet to jetmaniacs suggestion and start from there

The water is definitely from riding. I know during a backflip attempt the engine took on a little water, but not enough to worry me at the time. Also I found a minor amount of rust around the o rings on the cylinder sealing surface to the head. The cylinder surface was flycut before install so it definitely occured during the few rides. Is it possible my head was leaking water into the chamber(s)? (Even though I used all new o rings) Maybe one of my domes is warped? I just spitballing ideas now so I know of things to look for. I just don't want to start throwing money at it again lol

 

[Parsonsjb88]

Just for reference I had 190psi in both cylinders first start, before dissassembly it was 185 in the stator side, and 190 drive side.

 

[Parsonsjb88]

So, I took apart one of my carbs, nothing stood out that would be an issue. Cleaned it all up again and reassembled, popoff @ 30psi. No leaks, holds all pressure up to around 29psi then pops around 30.

 

[Parsonsjb88]

If your running a prok style arrestor then 32 psi popoff is too much.

So I forgot I picked up a new set of 1.5" Tall Hot Products filters and rain coats to cover them. Not sure if that will make a big difference to required pop-off. What would you guys recommend I aim for-for pop off?

 

[jetx]

It is definitely possible you could have a water leak from the head...although if you did I would bet you would have found traces of the water and oil mix on your plugs, assuming you check them often

The 110 pilot u were running and 120 you were recommended are a good bit different in size...id start there, bet it runs much better...I think stock 760 is 115 so you were running leaner than stock with a modded motor.

 

[jetx]

I'd keep your pop off where it's at and change one thing at a time...if your going to richen up your jetting and lower pop off it might be too much and bog down, changing one at a time will help you know what it needs...the pop off might be just right with a richer pilot as it is

 

[WB1994]

So I forgot I picked up a new set of 1.5" Tall Hot Products filters and rain coats to cover them. Not sure if that will make a big difference to required pop-off. What would you guys recommend I aim for-for pop off?

Between 20 and 25 imo. I say closer to 20.

Fuel in the crank case should burn off after beating on it for a few. That will definitely make it run like crap till it clears out. But your saying its not clearing out or its refilling. Thats a problem.