Rebuilding a Mikuni Diaphragm Carburetor (BN, SBN, SBN-I, etc)
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- Опубліковано 26 чер 2024
- This style carb is used on Seadoo, Yamaha, Kawasaki, Polaris, Tigershark, Mastercraft (yes they made some PWCs), and probably nearly all PWCs out there aside from the few that used Keihin carbs.
These carbs are a little different than most, and it is imperative to the enjoyment of your PWC to have them dialed in just right.
Here is my process of disassembling, cleaning and getting them ready for tuning on the water.
➡Carb Specs and information: trythistv.com/mikuni/
Everything you may need to do this:
SBT Kits: (These are what I use)
➡SBN & Square body BN (A lot of Seadoos 717 and smaller engines, Yamaha, Tigershark, Polaris): amzn.to/3xPS8J0
➡SBN-I Seadoos (951/947 97.5-03): amzn.to/3k365v1
➡SBN-I Yamahas (PV Motors 800 & 1200): amzn.to/3v7uaXS
Genuine Mikuni kits:
➡SBN & Square body BN (Pre 97 Seadoos, Kawasaki 750 98-02, Kawasaki SX-R 800 03-08, Likely others): amzn.to/3rK9GSS
➡SBN-I Seadoo (Seadoo 951/947 97.5-03): amzn.to/3k2tuga
➡SBN-I (PV Yamahas): amzn.to/3Kcr09O
Spare parts:
➡Internal screws that hold down the metering block (C5-0414-G): amzn.to/3MufWq3
Tools:
➡Manual Impact Screwdriver: amzn.to/3EJFFIs
➡Carb cleaning needles/brushes: amzn.to/3OueINc
➡Brake parts cleaner: amzn.to/38bKspH
➡WD40 or similar lubricant for popoff testing: amzn.to/3L9EhRF
➡Pop-off tester: amzn.to/3ENP4yE
➡Fuel pump checkvalve tool: amzn.to/3EJc3uz
Disclaimer: Links on this channel may be affiliate links, which earn me a commission at no additional cost to you, that helps me keep making more videos like this one! - Авто та транспорт
Carb Specs and information: trythistv.com/mikuni/
Everything you may need to do this:
SBT Kits: (These are what I use)
SBN & Square body BN (A lot of Seadoos 717 and smaller engines, Yamaha, Tigershark, Polaris): amzn.to/3xPS8J0
SBN-I Seadoos (951/947 97.5-03): amzn.to/3k365v1
SBN-I Yamahas (PV Motors 800 & 1200): amzn.to/3v7uaXS
Genuine Mikuni kits:
SBN & Square body BN (Pre 97 Seadoos, Kawasaki 750 98-02, Kawasaki SX-R 800 03-08, Likely others): amzn.to/3rK9GSS
SBN-I Seadoo (Seadoo 951/947 97.5-03): amzn.to/3k2tuga
SBN-I (PV Yamahas): amzn.to/3Kcr09O
Spare parts:
Internal screws that hold down the metering block (C5-0414-G): amzn.to/3MufWq3
Tools:
Manual Impact Screwdriver: amzn.to/3EJFFIs
Carb cleaning needles/brushes: amzn.to/3OueINc
Brake parts cleaner: amzn.to/38bKspH
WD40 or similar lubricant for popoff testing: amzn.to/3L9EhRF
Pop-off tester: amzn.to/3ENP4yE
Fuel pump checkvalve tool: amzn.to/3EJc3uz
Disclaimer: Links on this channel may be affiliate links, which earn me a commission at no additional cost to you, that helps me keep making more videos like this one!
Thanks
What kit should be used on a 1997 gp 1200?
@@markbrown309 Your 97 gp1200 is a 1200 Non-PV engine, so:
SBT: amzn.to/3xPS8J0
OEM: amzn.to/3rK9GSS
Great video! Thank you! If this cures my TigerShark jet ski issues Ill post again
howd you go?
doing my 95 barracuda now too
Thanks for the information!! I am doing 2carbs this week for the first time.
Have fun!
I want to give you a compliment because you answer almost all the questions, you don't see that very often. 👍
Thank you very much, I try my best to be of help to anyone I can!
GREAT VIDEO, THANKS LEGEND
Glad it helped!
Great video thank you
Glad it helped you out!
the reason the screws on mikunis strip out often is because people mistake them for a phillips head screw , they are actually JIS (Japanese industrial standard) screw signified by the little dot on the head , jis has a different depth and blade angle than phillips and will easily strip when a phillips head driver is used, use a true jis screwdriver when rebuilding and you'll most likely have 0 issues.
You're absolutely correct. I read that somewhere a while ago and still haven't picked up a set of JIS screwdrivers. I'm ordering some now, we'll see if it makes a difference! Thanks for the reminder!
Good video. I have a yamaha Gp 760 with the self-carburetter. Do they all have the same basic setting?
So long story short, I’ve got a buddy’s 1999 gp1200 and someone before me has torn into these carbs that didn’t know what they where doing and I need some guidance on this. What is the actual pop off pressure and what are the low and high screws supposed to be set at?
hello very good video, where I can get that manual for Yamaha it would be of great help 😀😀
Super and useful! thanks.. do you use another aftermarket carb rebuild kits like WSM, winderossa (made in thailad)? carb gasket kits from aliexpress is ugly and badly ??
Typically I use OEM or SBT kits, I do buy some things from WSM, and have had good success with all of them, but haven't tried their carb kits yet.
I have have very good success with OEM and SBT kits, some of the super cheap no-name kits do not last, some don't fit properly to begin with, I would say OEM, SBT and WSM are all sufficiently big enough that if something was that awful in their kits they wouldn't still be selling them.
thx for a great video . can you tell me where i can get info / jetting charts /specs on rejetting a carb for different altitudes. i m moving a 1986 js 550 from a colorado elevation of 5000’ to sea level altitude in florida. thx for any advice you have!
I'm not aware of any charts, I would love to find those myself, I would think that kind of elevation change may need a little change, you could try a size bigger and do some plug reads to see if it looks lean.
Wish I had more insight for you, I do a lot of my fine carb tuning by feel and plug reads to get the best performance from the stock recommendations.
Great video. Doing carbs on a 98 xl1200w npv i believe the carbs are a bn-44, correct me if i'm wrong, will the kit listed above work on these if not what kit would. Thanks
You are indeed correct, so the kits you're wanting is one of these choices: (You will need 3 kits since you have 3 carbs)
OEM Mikuni:
SBN & Square body BN (Pre 97 Seadoos, Kawasaki 750 98-02, Kawasaki SX-R 800 03-08, Likely others): amzn.to/3rK9GSS
Aftermarket SBT:
SBN & Square body BN (A lot of Seadoos 717 and smaller engines, Yamaha, Tigershark, Polaris): amzn.to/3xPS8J0
What carburetor are you working on a bn 38?
hi great vid thanx for that! do you know the rotation i need for the low and high speed needles? i have a yamaha waverunner 650
My info says it should be 1 1/8 turns from gently seated on the low and high screws on the 650 yamaha engines, popoff set between 25-35psi
great video. i took the 'accelerator assist' apart and noticed the little round rubber orange piece came of, how important is that? thanks
If I'm thinking of the same thing, its the check valve, and is essential for the accelerator pump to function. if it ripped, these should be the same thing: amzn.to/3E5oPE3 otherwise if if its still good, you should be able to pop it back in place.
This video helped a lot! When installing the check valves I’m really struggling with putting the black grommet into the seat. I keep poking holes in them and tearing them. Probably need new ones right?
Yeah, if those little rubber grommet things end up with holes in them the fuel pump wont work very well. Those things can be a real pain to get in. They make a special tool for it, but I've yet to try one.
@@trythistvended up getting new grommets because I screwed them up and ordered the tool with it. Little silicone spray on the grommet and pushed right in no issue!
Awesome video. Rebuilt many carbs but never a mikuni. 1 question how do you know what carb you have. Is it labeled?
There is a website called seadoosource that has specs for which machines have which carbs, I'm not aware of any markings that easily identify them, there are sometimes a part number on the base that can be cross referenced, but you can also identify them based on the size and shape of certain features.
@@trythistv thanks I'll go look now.
What are three small o rings for? I have them left over and came here to find where they go.
most likely there is one for the high speed needle, one for the low speed needle and one for the needle and seat. I avoid removing the needle and seat unless it is leaking, and the adjustment needles I change the o-rings when I clean out the needle passages if there is any suspicion of debris that could have clogged the passages.
Where do I find thee pop off specs for various carb applications? Ty!
I'm working on a page to consolidate all the specs I can get from the factory service manuals: trythistv.com/mikuni/ otherwise, googling service manuals or popoff specs for your year make and model can locate the specs. seadoosource has a bunch of seadoo specs
Thank you very much for the video! I have a 1997 Wet Jet Kraze with the Yamaha 701 engine in it. I believe this is the carburetor I have but now 100 % sure. The internet has so many different opinions. Would you happen to know?
I've actually got a 94 Yamaha waverunner 3 gp right now that also has the 701cc engine, and as long as your wetjet has the same carb, you do indeed have a mikuni sbn, which will take one of these kits:
Aftermarket kit:
SBN & Square body BN (A lot of Seadoos 717 and smaller engines, Yamaha, Tigershark, Polaris): amzn.to/3xPS8J0
Oem kit:
SBN & Square body BN (Pre 97 Seadoos, Kawasaki 750 98-02, Kawasaki SX-R 800 03-08, Likely others): amzn.to/3rK9GSS
@@trythistv awesome! thanks so much for the response! Thanks again for your instructional video! This gives me some confidence to dig into it and get her running smooth!
Which is the kit you use to fi. Carbuteror?
So this list is a little exhaustive, it is in the description for the video but it seems like thats getting harder and harder to find so I'll post it here too:
SBT Kits: (These are what I use)
SBN & Square body BN (A lot of Seadoos 717 and smaller engines, Yamaha non-pv, Tigershark, Polaris): amzn.to/3xPS8J0
SBN-I Seadoos (951/947 97.5-03): amzn.to/3k365v1
SBN-I Yamahas (PV Motors 800 & 1200): amzn.to/3v7uaXS
Genuine Mikuni kits:
SBN & Square body BN (Pre 97 Seadoos, Kawasaki 750 98-02, Kawasaki SX-R 800 03-08, Likely others): amzn.to/3rK9GSS
SBN-I Seadoo (Seadoo 951/947 97.5-03): amzn.to/3k2tuga
SBN-I (PV Yamahas): amzn.to/3Kcr09O
Spare parts:
Internal screws that hold down the metering block (C5-0414-G): amzn.to/3MufWq3
Tools:
Manual Impact Screwdriver: amzn.to/3EJFFIs
Carb cleaning needles/brushes: amzn.to/3OueINc
Brake parts cleaner: amzn.to/38bKspH
WD40 or similar lubricant for popoff testing: amzn.to/3L9EhRF
Pop-off tester: amzn.to/3ENP4yE
Fuel pump checkvalve tool: amzn.to/3EJc3uz
I watched you video as I was rebuilding mine all I done is change gasket and the small filter and the clear parts well before I took my mikuni bn 40-38 carburetor off the jet ski I took pictures of the hoses. Well I changed it all out I replaced the carburetor back and now I'm not getting fuel. I was getting fuel before I took it off but now I'm not. What could I do or try to help it out?
Are you sure you got the hoses on the same way around, turned the fuel selector on (I've done that little trick more than once lol), and sometimes it may take a while for the little diaphragm pump to pull the fuel all the way back from the tank.
On your site the chart has mag and PTO for carb screw settings. What does this mean? I have a 1994 yamaha VXR Pro with the 701
Whoops. That is for dual carb machines. Forgot about single carb specs!
On your machine Low should be within 1/4 turn of 1 7/8 turns, High should be within 1/4 turn of 1 5/8 turns out.
@@trythistv okay thank you so much!
What side on the check valves. SBT says darker blue up but mine look the same either way
I've never seen any directions on the check valves, they are just strips of plastic ultimately, as long as you put them on the correct side in the pump where the seat is, I can't see how it would make any difference what direction the plastic faces.
The reason they tell you to put the blue stripe up is because in the factory they cut it of a roll of plastic.
And because it is a piece of a roll it can be curved a little bit.
To make sure the convex part is upward from the seating they marked it with a blue stripe.
Did you replace the check valve after cleaning the jets?
The one I mentioned at 11:30? I typically always replace them on customer skis, but it isn't always needed, the rubber parts fail long before the plastic checkvalves in the fuel pump or the metering block do.
What spring gives u what pop off pressure
The very rough draft of all the charts I'm slowly working on is located here (trythistv.com/mikuni/), I've got the popoff specs for spring vs needle/seat sizes, and Yamaha skis either done or mostly done. Other makes will eventually make their way on after I've confirmed specs and made it look nice on the page.
What’s the pop off pressure specs for a 1995 Yamaha WaveRunner 3 with the 650 engine/ Mikuni carburetor?
I bought your recommended pop-off tester gauge/kit and followed your rebuild steps but the problem I’m having is when I start to pump up to pressure when I reach almost 20psi I start losing pressure and the needle slowly plummets… even with my finger over the recommended spot it’s not popping off nor allowing me over 20 before the needle gauge just drops . Any recommendations would be greatly appreciated for this DIY’er lol 😂😁🤙
I was sure I responded to you the other night. I must have forgotten to actually click the send button.
You should be in the realm of 30psi popoff. Are you getting bubbles or anything around the needle?
@@trythistv after re-watching your video and messing around with it I realized it was the wrong spring , my new rebuild kit came with two new springs so I swapped out one for the other and that fixed the problem!
SLT 780 jetski triple carb leaks gas. I checked all the fuel lines looks good. i got a rebuilt carb , wondering what would be the reason for gas drip when i rev high.
Higher RPM could slightly raise the fuel pressure because the pump would be pumping faster, maybe you've got a little pinhole in a gasket or something that only drips as the pressure goes up?
why not carb cleaner instead of brake clean? and why not JIS screwdrivers instead of Philips? Is the junk from cleaning the jets not going into the carb if you clean them without taking them out? can WD-40 swell the gaskets if your using wd-40 when checking the pop off pressure?
Excellent questions! I have found little to no difference between brake cleaner and carb cleaner, if anything, brake cleaner seems mildly more aggressive so it cleans better but either would work fine.
The screws are jis screws so it would make more sense to use a jis screwdriver, but they are not super common and a Phillips works fine, the internal screws typically strip out regardless of what screwdriver you use, so I replace them with the stainless Phillips screws listed in the description to avoid problems in the future. The debris from cleaning the jets typically gets flushed out with the brake/carb cleaner, and if not, breaking it up and loosening it will make it flush through with gasoline once the engine is running. Haven't had any issue using WD-40 for the popoff in the past, typically I just use premix fuel in a small container, but WD-40 has not given me issues with swelling gaskets. Now brake clean or carb clean will swell any rubber nearly immediately and often it will not return to it's original size no matter what you do, so don't get any of that stuff on the new gaskets. Hopefully that answers your questions, I'm certainly not an expert, but have been rebuilding these carbs for years on customers skis, just sharing what has worked well for me!
Great video! Wondering how to identify exactly what carb my 1994 seadoo SPX has on it. I want to purchase the proper rebuild kit in advance of pulling the carb. From what I’m seeing sounds like the carb in my PWC is a BN-38. Just wanted to confirm. Thank you!
Indeed you are correct, you should have a BN-38 (which is considered a Super BN in some documents and carb kits) on a 657cc engine.
The green looking hard gasket that was left over on the pump side isn't necessary?
It depends on the carb. These did not use that specific gasket anywhere, but the kits come with styles of gaskets to work on multiple carbs. Best thing to do is match them up as you disassemble yours, there will likely be one or two that are not applicable
@@trythistv i did put that hard green gasket over the diaphragm, at around 8:55 on the video is where i placed the gasket, the base on my carb is a little different but still a mikuni sbn38, taking it off would be the best choice?
Hello, great video. I rebuilt bn44 carb on 92 Yamaha wrb650. I followed your video. Cleaned all jets. Replaced pop off spring. Now pop off is at 24 psi. Pressure stays steady after pop off occurs. I've Replaced fuel filter, check valve by tank. I've pump out tank and inspected tank. New gas. Starts really easy. Runs OK till I start accelerating. I'm getting bad sputtering. Idling around 1300 rpm. I have high speed screw at 1 5/8 turns. I've adjusted high speed and does help. Any suggestions?
A good way to tell whats going on is to get it where its sputtering, and pull the choke, if it dies or gets worse, your carb is too rich. if it takes off and runs ok, then its too lean.
Alternatively, get it to where its sputtering, and turn the fuel selector off, if it dies, its too lean, but if it takes off and runs ok for a few seconds, its too rich. It will cut out after a few seconds because its run out of fuel in the carbs, but I have nursed a machine that was flooding really bad (leaky needle and seat, or fuel pump diaphragm was torn, I don't recall 100%) over to the trailer by modulating the fuel valve on and off to keep it running.
@@trythistv thanks!
Hello again, I did as you suggested. Accelerated till sputtering and pulled out on choke. It starts to die. I must have something wrong cause I turn in high speed screw so only out half a turn and same thing....I have a manual, so definitely turning in high speed
Hello, very interesting video. I have 2 Mikuni 38 carbs on my Kawa jet ski. I changed nozzles and gaskets, cleaned everything.... I put transparent hoses to see the fuel. Problem after filling the hoses with a syringe, the engine runs but the gasoline does not arrive (see the little that remains tends to go back to the tank (no suction to the carbs)? I connected the fuel correctly carburetor according to the plan (intake, return, low engine pump)? I tested the pressure for opening nozzle 19 psi
THANKS A LOT
Has to be related to the little fuel pump integrated into the carb. If you pull the lines off and stick them in a bottle of fuel does it pull fuel then?
I've seen them get hooked up to the wrong tubes on the fuel tank, or a plugged selector valve that doesn't let fuel pass in ON, but does in Reserve or things like that, putting the lines from the carb directly in a little bottle of fuel (gatorade bottles work great) would prove if it is the carb/fuel pump malfunctioning, or something else in the fuel tank/valve
Thank you for that answer. I'm going to try
thank you for your interesting answer.
I will try to put all the hoses in a bottle.
I'll let you know.
Eric
Leave the pulse line attached (goes to the fitting on the engine) but yeah the fuel and return lines on the carbs in a fuel bottle will show you if its pumping.
@@trythistv Thank a lot
I try it ......
Hey does it matter about the blue line on the check valves some people saying that blue line gotta be facing up its that truth??¿
I have heard the same, so I try to do the same now, I'm certain I have ignored that many times before, and have never noticed any ill effects, but if they say the blue line goes up, I try my best to follow that.
The reason they tell you to put the blue stripe up is because in the factory they cut it of a roll of plastic.
And because it is a piece of a roll it can be curved a little bit.
To make sure the convex part is upward from the seating they marked it with a blue stripe.
You can use a pin punch to drive those stripped screws back into shape...and then they will come out with the impact driver almost every time. It is not always necessary, but when all else fails.
That is an excellent tip, I'm gonna lock that one away for later.
I run into so many of these that have been "fixed" previously and the screws are either totally round or have been dremeled into a flathead. I replace them with new ones so the next guy doesn't have to fight with them.
Where are you getting new screws these days. The only place that I found them was out of stock when I was looking.@@trythistv
These are the ones I've been using: amzn.to/3MufWq3
They are not official Mikuni screws or anything, but are stainless steel and seem to hold up well so far!
Hello watch ur video what can I do if carb not pulling the ⛽
If it isn't pulling fuel, first thing I would check if it will pull fuel if you put a piece of fuel line from the carb directly into a small container with gas, like a water bottle full of gas right near the carb with a little piece of hose, because sometimes the old lines will leak air, fuel filters will crack or develop leaks, and you get air in the lines instead of fuel.
If it doesn't pull fuel with that setup, likely the internal fuel pump diaphragm is damaged, or the fuel filter in the carb could be plugged. If you have a Seadoo, the grey "tempo" fuel lines are notorious for degrading internally and clogging filters, as well as restricting or completely blocking fuel flow.
Good video but you didn't show how to adjust the pop off if it was not in spec.
Good point. Adjusting the popoff is a combination of the right spring with the right needle/seat oriface size. Generally speaking if it's wrong, try a different spring, I either have a chart on the website, or I need to put the chart on the website of how each spring and needle/seat set corresponds to popoff pressures, I think I already put it on there though
Yes chart please
JIS screws
So, you completely skipped over the installation of the high speed check.........
Have to disagree with you on the choice of rebuild kit. Just buy Mikuni OEM… it’s five dollars more and will last many more seasons. Those aftermarket needles leak.
Its a great debate. I haven't had a single carb fail with good quality aftermarket kits, some customers carbs have been going strong for 8 years now.
BUT, With that said, a genuine kit is a better bet than taking a gamble on some random no-name kit, those are almost always going to fail.
Have to say I am with you on this one, I cheaped out and went aftermarket and later when I had the cash an OEM kit for "when the first one fails"... and it's been 5 years now and haven't had to swap it. Seems like at 40% the cost, it's pulling it's weight. Thanks for the video and knowledge sharing!
The Sbt kits are oemthats y he don’t have no issues cheap eBay bs is the problem
@@devshewitt4809 SBT is NOT oem. Mikuni made products and sourced materials will always be better than any aftermarket kit. Please don’t spread that misinformation.
Because my jet ski is not running properly. I have the low speed screw at 1.5 revolutions and the high speed at 2.5 revolutions
Yamaha 760cc should be around 1 5/8 turns out on the low and 3/8 turn out on the high adjuster, there is a table of specs on my website here: trythistv.com/mikuni/
You forgot to put the fuel filter back in
8:25 ?
WOW. You shouldn’t be using wire wheel at all on soft aluminum, or even sand paper unless you are resurfacing. Why don’t people understand a painter’s razor held perpendicular to the gasket surface with light pressure is all you need to clean without causing any damage to sealing surfaces.
I'll send the next petrified gasket I get your way, I've caused way more damage with a razor than with a wire wheel, but I do agree, a wire wheel used too aggressively will damage the sealing surface. But so will a razor, and you won't get the gasket material off a 30 year old carb with a razor. Nowadays I tend to use a soft scotchbrite pad on a rotary tool.
@@trythistv funny, I apprenticed under a master automotive mechanic for 10 years and that’s the only way we were allowed to do it when working with soft metals. Excellent results.
The heat, ethanol, oil and whatever else happens in these carbs petrifies the paper gaskets so bad, I've never had issues scraping gaskets from an automotive style carb or anything else with a razor, but these gaskets harden up like it's a part of the metal. I've broken razors trying to scrape these things off, so I opted to very carefully use a wire wheel, and then later began with the scotchbrite wheels, which has worked excellent for the past 10 years I've been doing this, but I am extremely careful to just get the gasket off. Haven't had any issues with leaking fuel or vacuum yet, but I am well aware it's a dangerous game
So long story short, I’ve got a buddy’s 1999 gp1200 and someone before me has torn into these carbs that didn’t know what they where doing and I need some guidance on this. What is the actual pop off pressure and what are the low and high screws supposed to be set at?
trythistv.com/mikuni/ has everything you need.
You should have a 1200 non-pv on a 99 gp, so the specs should be 38-42psi, low screw should 1 1/8 turns out from lightly seated, and the high screw should be 1/2 turn out on the mag and center carbs, 7/8 turn on the pto carb, and those are of course starting points, your machine may need more or less fuel depending on other mods done, your elevation, fuel type, health of engine, etc.
@trythistv what is mag and pto??
It refers to which cylinder, PTO being power takeoff, so closest to jet pump, rear cylinder.
Mag is cylinder closest to magneto, which is the front of the engine, stator and flywheel housing cylinder.