How many bypass holes on a SBN38?

5

59Hillbilly

Location
Redding, CT
1) How many bypass holes on a SBN38?
I am rebuilding some very corroded carbs on a stock Yamaha '98 dual carb superjet (SBN38's). I only see 2 bypass holes (plus the outlet on the engine side of the butterfly) but the corrosion could be hiding some. I would like to confirm there are only 2 and I am not missing 1 or 2. I did a search here and google and no one says how many there are.

2) What is pop-off pressure for a dual carb '98 w/ SBN 38's?
I am measuring about 50 - 55 psi, seems high. I have seen the chart that says "superjet 38-42" but I know there are 1 and 2 carb versions of SJ's with different size carbs, so I would be surprised its one setting for all Superjets.

Thanks in advance.
 
5

59Hillbilly

Location
Redding, CT
Bump -
I'm sure someone on this forum knows how many bypass holes there are in a Mikuni SBN38 !
I found 2 They are hard to count in the attached photo....
 

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5

59Hillbilly

Location
Redding, CT
Ha, They were really nasty. I got 2 '98 SJ's from a buddy, if I get both running I get to keep 1, he gets the other. They were used in Saltwater then sat in my yard for 10 years (full of water), so the carbs were completely full of this white powdery corrosion. Both sets look like that picture when I started. (new short blocks in both from SBT)
Anyway I did rebuild all 4 carbs and they seem to be working OK now. The first ski is running well except for transition from idle to 1/4 throttle. I attribute that to not knowing the bypass holes were there so they likely have 1 or more plugged. On the second ski I could not get it to run right (on a engine stand in driveway). On the 3rd rebuild attempt I found 2 bypass holes, cleaned them out and now that ski also runs great (in the driveway). Hope to try it in the water this weekend. AND I HOPE THERE ARE ONLY 2 BYPASS HOLES ON A SBN38 because that's all I found, but the walls are so corroded it took me a long time to find them.

Someone, somewhere, knows how many bypass holes there are...
 
mbrick

mbrick

Location
Los Gatos, CA
Yikes. I'd run those in an ultrasonic cleaner for a LONG time before even considering using them.

I've seen at least 2-3 unanswered posts lately about how many bypass holes there are.
 
5

59Hillbilly

Location
Redding, CT
With a HUGE THANKS & shoutout to Jonolove I have some carbs that are a way better than what I had. I'll be rebuilding them shortly, which I expect to solve my current carb problem.

Also these are clean enough to answer my original question - There are 2 bypass holes on a SBN38 carb. I'm sure you were all wondering ;)
 
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