B-pipe Carb jetting

[flyHigh]

I have a RN Sj which has the basic mods done like steering, impeller, intake... I bought a B-pipe mod a couple month ago and installed it. I was about to rejet my carbs(38's) when a Jetski mechanic told me its not necessary I will just lose riding time and he likes 130 mains better since the engine runs more "crisp". I should only check if it runs lean if so richen it up....Since I read a lot on this topic before I installed the pipe I was pretty set on putting 135 Mains...and its like the only topic the forum agrees on
So in the end after having my carbs already opened I closed them with stock jetting to give it a "careful" try. And with out touching anything the Motor kept its linear Powerband so no sign of running lean also I ran 5 tanks and at least 1h WTO(thought the engine would be blown after this if carbs are not set correctly)....So now to the question. Should I change to 135 if so why?. Also should I try to richen things up try to see what happens? Havent done any Tach testing either but the power is definitely there. And I know Factory's recommendation just thinking maybe someone can speak from experience.

 

[CRJ]

I have a RN Sj which has the basic mods done like steering, impeller, intake... I bought a B-pipe mod a couple month ago and installed it. I was about to rejet my carbs(38's) when a Jetski mechanic told me its not necessary I will just lose riding time and he likes 130 mains better since the engine runs more "crisp". I should only check if it runs lean if so richen it up....Since I read a lot on this topic before I installed the pipe I was pretty set on putting 135 Mains...and its like the only topic the forum agrees on
So in the end after having my carbs already opened I closed them with stock jetting to give it a "careful" try. And with out touching anything the Motor kept its linear Powerband so no sign of running lean also I ran 5 tanks and at least 1h WTO(thought the engine would be blown after this if carbs are not set correctly)....So now to the question. Should I change to 135 if so why?. Also should I try to richen things up try to see what happens? Havent done any Tach testing either but the power is definitely there. And I know Factory's recommendation just thinking maybe someone can speak from experience.

Loose riding time on a 130 to 135. Ha! This guy should retire. Jet it for piston wash and throttle response. if 130 feels good, plugs are golden and piston wash is the size of your thumb on the intake ports, your fine.

 

[flyHigh]

Yeah he meant until I have everything dialed in (only had 3 days of riding). The jet feels good, I did a impeller change at the same time from stock to a solas 13/17. Yea it runs great, I mean it accelerates without any hesitation or bog, and the power increase surprised me did not expect this much. Plugs looked good but I will pay closer attention to them next time I ride(which will be a while). Does it make sense to check for the piston wash if I have no clew how they looked before I installed the pipe? I have never had the cylinder head of and I expect to have around 150h on the engine(pistons) if that makes any difference.

 

[Vumad]

I'm running 140/75@42 at sea level with limited chamber, 170psi, 93 octane, stock carbs w/ 1 screen removed from airbox, lightened flywheel, 12/17 concord. This is a limited spec race boat, can load up a tad in the surf if you dilly dally too much but for the most part it runs perfectly crisp in the surf.

FPP recommends 135/70@55 on a stock boat at 730 feet.

I am not 100% on this, but I think a common jetting is 135/75@42.

Elevation and temp can change things, so maybe where you are in Germany it makes sense. I stuck a piston at 135/75@55 in Florida.

 

[flyHigh]

I still run 150psi I could not be bothered to check compression since the engine always ran real smoth. When I used my new setup(pipe and prop) it was a mild temperature around 17 degrees(Celsius) and with 93 octane at sea level. Just for my understanding, I believe I am not rich or lean(not enough mix), if anything the pipes reflection wave will push exhaust gas back into the cylinder but the air fuel ratio, supplied by the carbs, stays the same so it should run hot? Please correct me, as you see my knowledge is pretty limited in that field.

I will take of the head and check the piston wash to make sure I dont run lean dont want to stick a piston when it gets warm.
Next time I ride I will start slowly richening while monitoring rpms and throttle response. If I fell its to rich then I will back off again to far out next jet size...
Dont feel a rebuild anytime soon especially during my short riding season

Just saying it cant be to far of I blew through a tank in under 40min while riding buoys so basically WOT all the time and the engine did not blew. I felt the cylinders temp after the first 3 min riding WOT felt a little hotter..

Thanks for your input guys!

 

[Vumad]

I still run 150psi I could not be bothered to check compression since the engine always ran real smoth. When I used my new setup(pipe and prop) it was a mild temperature around 17 degrees(Celsius) and with 93 octane at sea level. Just for my understanding, I believe I am not rich or lean(not enough mix), if anything the pipes reflection wave will push exhaust gas back into the cylinder but the air fuel ratio, supplied by the carbs, stays the same so it should run hot? Please correct me, as you see my knowledge is pretty limited in that field.

I will take of the head and check the piston wash to make sure I dont run lean dont want to stick a piston when it gets warm.
Next time I ride I will start slowly richening while monitoring rpms and throttle response. If I fell its to rich then I will back off again to far out next jet size...
Dont feel a rebuild anytime soon especially during my short riding season

Just saying it cant be to far of I blew through a tank in under 40min while riding buoys so basically WOT all the time and the engine did not blew. I felt the cylinders temp after the first 3 min riding WOT felt a little hotter..

Thanks for your input guys!

Compression doesn't significant'y affect carb jetting.

The pipe changes the mix. The stock pipe is restrictive. Like a larger carb, the pipe allows the motor to move more air. It also allows it to turn an extra 1000RPM give or take. Generally anything carbureted requires jetting changes after putting a performance exhaust on it.

 

[dirtydrew]

How many turns out are you running on your mixture screws?

 

[Vumad]

How many turns out are you running on your mixture screws?

Different for every boat. On stock setups the pipes are restrictive so it doesn't matter that much so there is a factory setting that is close enough. On a pipe, a half a turn can make a significant difference.

There's no port matching or anything on stock cylinders. They are graded for a fair range of spec. Screws are finely tuned so they can change based on the extra load of the rear cylinder, porting differences, etc.

Follow the tuning manual.

I had to run larger domes to get my compression right and larger jets to get my carbs right. I don't know why and it doesn't matter actually. That's what my motor wants and it runs good.

 

[flyHigh]

@ Vumad I guess your right. The exhaust gas will clear out of the cylinder faster due to the effect of the expansion chamber, hence higher refs. To do so you have to have a stronger vacuum in the exhaust(compared to stock) which will pull more fuel/air mix at a time...Will tune it the next time before I ride it.

@dirtydew no I did not dare to touch my carbs until now. Next time I am at the Jet I will check.

You guys think its worth going the ada route from 150 to 170psi? Dont want to go much higher than 170 cuz I love extensive wot runs from time to time, also I dont want to run race gas. 93 Octan is what I get at the gas station....
And if you run a head with dual cooling is it necessary to drill the b-pipe manifold for dual cooling?

 

[Vumad]

@ Vumad I guess your right. The exhaust gas will clear out of the cylinder faster due to the effect of the expansion chamber, hence higher refs. To do so you have to have a stronger vacuum in the exhaust(compared to stock) which will pull more fuel/air mix at a time...Will tune it the next time before I ride it.

@dirtydew no I did not dare to touch my carbs until now. Next time I am at the Jet I will check.

You guys think its worth going the ada route from 150 to 170psi? Dont want to go much higher than 170 cuz I love extensive wot runs from time to time, also I dont want to run race gas. 93 Octan is what I get at the gas station....
And if you run a head with dual cooling is it necessary to drill the b-pipe manifold for dual cooling?

180 should be fine for racing on 93. I am only running 170 because the 35cc domes put me at 210 and the 37cc domes put me at 170. Not sure why, maybe because I'm bored 1 over, but I wasn't having custom domes made for 10psi. I have an ADA girdled kit and am pleased, but I can't place a value on money / performance for you. Generally people do pipe, prop, head.

Have you checked to see if you can even access your needles? Most years of superjets came with a cap on the screws because of emissions. The caps can be a real pain to get out. I didn't use a slide hammer but I think it could have worked well. I replaced my stock screws with extended thumb screws from jetmaniac and also I switched the phillips heads on the diaphragm and fuel pump with allen heads also from JM.

 

[flyHigh]

180 should be fine for racing on 93. I am only running 170 because the 35cc domes put me at 210 and the 37cc domes put me at 170. Not sure why, maybe because I'm bored 1 over, but I wasn't having custom domes made for 10psi. I have an ADA girdled kit and am pleased, but I can't place a value on money / performance for you. Generally people do pipe, prop, head.

Have you checked to see if you can even access your needles? Most years of superjets came with a cap on the screws because of emissions. The caps can be a real pain to get out. I didn't use a slide hammer but I think it could have worked well. I replaced my stock screws with extended thumb screws from jetmaniac and also I switched the phillips heads on the diaphragm and fuel pump with allen heads also from JM.

Pipe and prop are already installed so a head would be the next logical thing to do

Yea I had my carbs apart, needle and jets where already out. Also I had new needles and springs but I listened to that guy and put the old stuff back in again... What stock thumb screws do you mean the Hi and Low speed adjuster? And the phillips heads on the diaphragm cover or actual in the carbs?

 

[Vumad]

Pipe and prop are already installed so a head would be the next logical thing to do

Yea I had my carbs apart, needle and jets where already out. Also I had new needles and springs but I listened to that guy and put the old stuff back in again... What stock thumb screws do you mean the Hi and Low speed adjuster? And the phillips heads on the diaphragm cover or actual in the carbs?

If your stock screws are under brass caps, after you remove the caps, the screws are hard to reach. They are flat head and can be accessed but they are challenging to reach. Replacing them with tee screws can making tuning much easier. It's not a necessary expense if you are on a budget, but it is a luxury I enjoy. If you can already access your screws well, ignore this.



The screws that hold the diaphragm cover on, which is what covers the jets (not the kidney shaped item inside), and the ones that hold on the fuel pump, opposite side of the jets, can be replaced with Allen head screws. Again, this is not a required change if you are on a budget. You can also order them from McMasterCarr or buy them local. I just found @JetManiac to be affordable and simple, especially when ordering other stuff anyway. I upgraded to these on JM suggestion because I could not tighten my fuel pump cover down tight enough with the Phillips to get my pop off leak tests to spec. Also, they remove the whole screws getting stuck and the heads stripping annoyances.

Again, these items are not absolutely required, but if you have an extra $50, they are nice to have. JM can also set you up with a ADA gilded head kit, jets, and some helpful advice most of the time. His advice has been a great starting point and troubleshooting for me, but just remember you still have to do the testing and tuning yourself.

JM has his after Daytona sales and his Demo heads are a pretty great deal on what is basically a brand new part. http://www.x-h2o.com/index.php?threads/jetmaniac-2017-daytona-freeride-after-sale.180429/

Here is the link to all of his carb / tuning parts. http://www.x-h2o.com/index.php?thre...rb-parts-primers-filters-intake-reeds.144171/

This is his master parts list if you need to look into other stuff. http://www.x-h2o.com/index.php?thre...rb-parts-primers-filters-intake-reeds.144171/

Other things to consider while setting this up is tapping your pump for dual cooling if you want dual cooling (this requires an electric bilge pump setup) and a flow control valve. These are not necessary items and will require minimal changes if you decide to add them later. Also, you can get AM air filter, but I prefer the stock airbox myself.

The above are just some suggestions on parts I have and am pleased with applicable to the tuning you are doing right now. Not one single item I listed above is required if you are on a budget or are not comfortable installing or tuning them.

 

[tomski]

Different for every boat. On stock setups the pipes are restrictive so it doesn't matter that much so there is a factory setting that is close enough. On a pipe, a half a turn can make a significant difference.

The stock exhaust will still need to be jetted correctly for the best performance.


Those are the old Jetworks screws do not use them.

 

[Vumad]

The stock exhaust will still need to be jetted correctly for the best performance.


Those are the old Jetworks screws do not use them.

View attachment 327642

That was just an image I grabbed off google to show what tee screws are. I learned my lesson. Not hing goes in Munich carbs that is Not made by mikuni.

Just out of curiosity. What thd history on jetworks screws.

 

[flyHigh]

If your stock screws are under brass caps, after you remove the caps, the screws are hard to reach. They are flat head and can be accessed but they are challenging to reach. Replacing them with tee screws can making tuning much easier. It's not a necessary expense if you are on a budget, but it is a luxury I enjoy. If you can already access your screws well, ignore this.



The screws that hold the diaphragm cover on, which is what covers the jets (not the kidney shaped item inside), and the ones that hold on the fuel pump, opposite side of the jets, can be replaced with Allen head screws. Again, this is not a required change if you are on a budget. You can also order them from McMasterCarr or buy them local. I just found @JetManiac to be affordable and simple, especially when ordering other stuff anyway. I upgraded to these on JM suggestion because I could not tighten my fuel pump cover down tight enough with the Phillips to get my pop off leak tests to spec. Also, they remove the whole screws getting stuck and the heads stripping annoyances.

Again, these items are not absolutely required, but if you have an extra $50, they are nice to have. JM can also set you up with a ADA gilded head kit, jets, and some helpful advice most of the time. His advice has been a great starting point and troubleshooting for me, but just remember you still have to do the testing and tuning yourself.

JM has his after Daytona sales and his Demo heads are a pretty great deal on what is basically a brand new part. http://www.x-h2o.com/index.php?threads/jetmaniac-2017-daytona-freeride-after-sale.180429/

Here is the link to all of his carb / tuning parts. http://www.x-h2o.com/index.php?thre...rb-parts-primers-filters-intake-reeds.144171/

This is his master parts list if you need to look into other stuff. http://www.x-h2o.com/index.php?thre...rb-parts-primers-filters-intake-reeds.144171/

Other things to consider while setting this up is tapping your pump for dual cooling if you want dual cooling (this requires an electric bilge pump setup) and a flow control valve. These are not necessary items and will require minimal changes if you decide to add them later. Also, you can get AM air filter, but I prefer the stock airbox myself.

The above are just some suggestions on parts I have and am pleased with applicable to the tuning you are doing right now. Not one single item I listed above is required if you are on a budget or are not comfortable installing or tuning them.

Thanks for your advice and all the information I truly appreciate your effort! Getting the tee screws makes perfectly sense to me and is just a matter of time (still to cold to ride anyway) I was already wondering how you guys reach the screw and make precise adjustments while tuning since the space is so limited. I will definitely hit up JM just going to wait till I know all the parts I need/want for shipping reasons. Was also thinking on getting the tee screws for the b-pipe from JM.

With the diaphragm cover screws I did not have any issues but I guess they will be on the list just in case also getting parts in germany can be a pricey bitch....

Dual cooling was not on the list to do...I was under the impression its not necessary for a 701 with running in "normal" water temperentes please correct me if I am wrong. Dont really want to pull the pump and do everything if i can spend that time on the water
When I installed my pipe I could not get the manifold drilled/tapered due to metric vs imperial systems......I spend 3 days running from shop to shop trying to get the right drill bit and thread cutter got sold the wrong one twice(due to conversion error by the sale guy) and almost started drilling. After I could not find a single machine shop or sales shop that could help me out(sell or do the work)I had no choice but to slap the manifold on as it was. Also I thought it cant be to bad with only one line going in since the factory sells them like this for a long time and should have changed it if it was crucial for the 701?
Also after installing the manifold I am not sure if I can actually get the bitchy screw out without any major effort (the screw from manifold to cylinder) cuz the bold head is not in the best condition and it sits really really tight felt like screwing in/a virgin (and yes I modified my wrench to make it work). Advice for any guy installing a manifold on a used cylinder head take a thread cutter and clean the threads before installment. I guess the would be a must for dual cooling and soon or later I will have to mess with it probably anyways just trying to put off as long as possible

Also if I use the tee screw for the carbs will the be one to one the same turn wise as the mikuni screws?

 

[flyHigh]

The stock exhaust will still need to be jetted correctly for the best performance.


Those are the old Jetworks screws do not use them.

View attachment 327642

I guess that implies that I have to mess around with my jetting. Power is not even my main concern but damaging the engine. As soon as I have some time and get access to my jet I will take of the head and upload some pics of the pistons to see the piston-wash. Want to know if I was running "dangerous" hot (hot gas from the pipe getting pushed back into the cylinders instead of more fuel air mix).

 

[flyHigh]

It time for a small and long overdue update.

I bought a second ski last summer so my priority was more set on riding than on screwing around. I put 135 jets in then I tried to adjust the carbs for being "to rich" screwed them all the way out. But it was weird there was no bog and the plugs where not getting darker and or damp it felt like there was not much change happening. After trying different positions with the mixture screws until I maxed it out I was thinking about going to 140 just to see If I can get the "rich signs" to show up.
In the end I did not bother and went back to the 130´s. The weather was too nice and I hate pulling the carbs while being in the water. I have been riding the ski like this for about 20-30 tanks with no issue also I have ridden other superjet's last summer that had the same setup as mine. Those superjet's where almost brand new looked fresh and they where setup by a "professional" jetski shops. Still the throttle response and acceleration was quite a bit better on my ski and top speed was the same.
Also I did not pull the head last year since I thought I might as well put in 135's and be done with it...
I guess my subconscious is waiting for a reason to rebuild the top end and while add it add cylinder head and MSD ignition.

 

[flyHigh]

After pulling the head I took some pictures of the pistons unfortunately the quality is not very good. To me as a non knowledgeable person the combustion looks "even" with no hotspots. Since I am upgrading I have to change my carbs settings finally. I ran more than one season with the 130 high's. The location is 18 meter above seelevel and temperature range from 10-35 degree Celsius. I guess it just underlines how different the jettings can be from boat to boat even if they are completely identical part wise.

 

[flyHigh]

Here are the pics

 

[p2im0]

Here are the pics

I'm no expert either but that looks too lean to me - scorching your pistons.... I'll be watching the thread for others to weight in. Similar mods list coming for my ski.