04 SJ tune up!. help - houston area

hey there im looking for someone that knows how to tune these superjet carbs anyone have any suggestions or know anyone in or around houston
 
So my sj is 100% stock. What I had to do was this I bought the ski and it did not have carbs installed it came with them but 1 of them was kinda screwed up in bad shape with that being said . I ordered another mikuni sbn 38 that had same pulse fitting deal as the one I needed to replace. Rebuilt both using genuine mikuni rebuild kit along with took out (jets and pop off spring along with needle out the bad oem carb and put it in the sbn I picked up that way both carbs have the same setup jet and pop off wise. The only 2 things that could not be swapped from that oem carb to the replacement sbn carb I bought where the H/L adjustment screws bc the oem sj carbs are course thread and the carb I bought which is a sbn 38 but it has fine threads ..and I saw one 1 post that the fine thread carb tuning on those is different. ( oem calls for 1 1/4 turns on the L .. I read on a post that the fine thread carbs need like 2 1/2 turns on L). So I used that and 1 oem sj carb well when I started it acted like it was reving to the moon but was not a run away as I was able to shut the engine off using the kill switch button . and note this engine is crazy low hours barn find thing was maybe ridden 20.timez total lol.replaced all carb gaskets and carb mounting gaskets. only thing removed didnt touch intake manifold or anything was carbs so everything else should be as is . .

If I cannot figure out the tuning I may have to switch over and mod the oem.carbs for primer BUT i like having the chokes incase a run away situation on the water that's why I got a new carb its choke plate was 100%
 
So the OEM Carb has a Choke and the A/M Carb does not? Air Flow will be DIFFERENT...

Since you got the SJ with the Carb Set removed, must wonder what problems the SJ was having...Not sure why a SJ Engine used "20 times" would have a bad Carb?

Post some Pics of the Engine and Carbs.

1st thing would be to do an Air Leak-Down Test to ensure that Engine has NO AIR LEAKS. If it does, Tuning will be a waste of time.

2nd Do Pop-Off Tests on each Carbs to make sure the Needle Valves are popping nicely and have the SAME Pop-Off Pressure.

2nd, the Dual OEM Carbs have a Master/Slave Arrangement. Master has the Pump and feeds the "Leftover Fuel" to the Slave Carb via its Return Line. And both Carbs have a #60 or 0.6 mm Restriction Orifice in the Return Outlet. What size is the Return Orifice in the A/M Carb? If it's too big, most of the Fuel will go to the Tank and not feed or bypass the Carb giving a Lean response or runaway.

3rd, are both Throttle Butterflies SYNCHRONIZED , meaning do the have identical positions at all Throttle openings?

4th, install T-Handle Carb Adjustment Screws for ease of Tuning. Otherwise, it will be very difficult to turn the Adjustment Screws once installed in the Hull.

You have some work to do before you can start tuning...
 

Big Kahuna

Administrator
Location
Tuscaloosa, AL
Sounds like you now have mix matched carbs. The one you ordered is going to be an Aftermarket SBN vs the OEM specific. These are carbs that are built just for the dual carb setups as they come from Yamaha. "Fine thread carbs need like 2 1/2 turns " That is bad info. at over 2 turns out your not changing anything. typical tuning range is 0-2 turns. If jetted correctly, being around 3/4-1 turn is ideal. this gives you room to adjust.
 
Both carbs have the choke . The only thing different was the H/L screws threads .
my buddy told me the reason they took the carbs off was the jetski would bog when riding it ( they also replaced some of the fuel lines .) which i blew air through and all seem right. but thats it i assume dirty jets since its a 04 and had never been had the carbs cleaned that and coming from 2 stoke motorcross bikes/atvs since the plugs are brand new ( but would still run start and idle ). he tried to even take the ski to our local yamaha dealer but they dont work on stuff earlier that 2008 .. so they took the carbs off to clean them but did not have the mechanical know how to get that done. so i put both carbs in my ultrasonic cleaner completely torn apart then rebuilt both of them . also like i mentioned ordered all new gaskets and rebuild kits .
im thinking likely im going to try and break down the oem carb what happen was a common issue i know ( choke plate stuck). so i may try and get that out today and see if i cant swap it off the ebay carb which moves as should and or just go ahead and swap to a primer that way i know both carbs having the same settings and see if that helps .

So the OEM Carb has a Choke and the A/M Carb does not? Air Flow will be DIFFERENT...
-they both have chokes.

Since you got the SJ with the Carb Set removed, must wonder what problems the SJ was having...Not sure why a SJ Engine used "20 times" would have a bad Carb?
- i personally know the guy i bought it from 1 owner some rich kid.. that hardly used the thing sat in a barn at his lake house only fresh water as well.
Post some Pics of the Engine and Carbs.
-ill do that later today after work .

1st thing would be to do an Air Leak-Down Test to ensure that Engine has NO AIR LEAKS. If it does, Tuning will be a waste of time.

2nd Do Pop-Off Tests on each Carbs to make sure the Needle Valves are popping nicely and have the SAME Pop-Off Pressure.
- did this and pulled all the parts out the oem carb so the pop off springs and all that are the same in both . will do a test today

2nd, the Dual OEM Carbs have a Master/Slave Arrangement. Master has the Pump and feeds the "Leftover Fuel" to the Slave Carb via its Return Line. And both Carbs have a #60 or 0.6 mm Restriction Orifice in the Return Outlet. What size is the Return Orifice in the A/M Carb? If it's too big, most of the Fuel will go to the Tank and not feed or bypass the Carb giving a Lean response or runaway.
-ill check this today ,this maybe the issue . i plan on trying to get the oem in useable shape and steal the parts off the a/m carb .
3rd, are both Throttle Butterflies SYNCHRONIZED , meaning do the have identical positions at all Throttle openings?
-yes on this
4th, install T-Handle Carb Adjustment Screws for ease of Tuning. Otherwise, it will be very difficult to turn the Adjustment Screws once installed in the Hull.

You have some work to do before you can start tuning...
 

Big Kahuna

Administrator
Location
Tuscaloosa, AL
You still have a totally different carb installed with your OEM carb. The circuits are going to be different....... Your best bet is to buy a matching carb to the one you just bought and go that route.
 
update!. i was able to get the bs out the oem carb so it is usable now depending on if i can get the choke to operate smoothly i may do that or just go ahead now and throw on a primer kit on both oem carbs like big kahuna said that way there matching and i know on the same settings. I would rather not buy another carb if I can use the oem stuff that way setting and tuning the carbs I can go off the manual and all that jazz not chasing down tuning issues. Had I known that there are different sbn series of carbs I wouldn't of did what I did to begin with.!
 
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