88 js550 bogging

[Jaxson]

I’m having trouble getting my 1988 js550 to run properly. Low speed it is fine but every time you get on the throttle all the way it goes good for a couple seconds then bogs way down and you have to flutter the throttle to keep going. Everything is stock besides aftermarket Mikuni sbn 44 with ocean pro vortex flame arrestor. And pjs intake manifold. Compression on the cylinders are good and pop off pressure is good aswell. Also has primer instead of choke now. We spent awhile trying to tune it but came up empty any suggestions helps.

 

[WFO Speedracer]

First we need to know what jets, needle and seat and popoff spring are in it now, without that info no one here can really assist you.

 

[Jaxson]

Here are the size jets that are in it

 

[WFO Speedracer]

From my notes you are way too lean on the main jet , you should be around 120 -125, I would get both jets , start with the 125 and if it needs it jet leaner till it pulls correctly , at 105 you are going to melt that top end .

Spring should be correct but you STILL need to check the popoff pressure , you are looking for around 20 PSI.

 

[Ryan Declark]

first id like to be the first one to say it as it was so wisely said to me on my 550 project so here it is... "its not to late to give that ski back".

second i have thread thats kinda all over the place but sounds like a similar setup when it comes to tuning the carb on your ski
here is the thread if you want to do a read.

I need some help from the wizards please.

Sounds like weak spark.. losing spark under compression. Do an ohm test on your stator. Also check for continuity between the plug wires. Should be around 5k ohms. Open would mean bad. Should be able to find plenty 550 stators and cdis out your way. Make sure your grounds are good and that...

www.x-h2o.com

never ended up adjusting the final numbers as i took it out a few more times and replaced a jet size again after i rebuild the carb completely


my final jet settings were 110 pilot 85 gram spring which was about 20ish psi 125 high and both low and high where about an 1/8 turn out
sounds like your high jet is too low. id start at 125 and do a 1/8 turn out and adjust from there. buy a 130 and a 120 too just incase you cant adjust through it.

also iv heard its common but if i wipeout on the top end the ski hates to start.

 

[WFO Speedracer]

You are correct Ryan , Its not too late to give it back and end the misery

 

[Ryan Declark]

You are correct Ryan , Its not too late to give it back and end the misery

passing the scripture as it was written by the ones before us.

 

[Jaxson]

Pop off pressure is good and is right at 20psi. I ordered a jetting kit from watcon that said if you tell them about your ski and where you ride they will send all the right size jets, etc. I’m wondering if they just made a mistake or what.

 

[WFO Speedracer]

If they sent you a 105 main jet then yes they did , we are giving you jetting specs that have worked through the ages , one thing is for sure on a stock engine you won't melt the top end down with a 125 main jet and two turns out on the high speed screw , at 105 on the main it's a damn good possibility that you will. regardless of where the high speed screw is set at.

 

[Jaxson]

Ok thank you for the help I will try with your advice and go from there.

 

[Ryan Declark]

Pop off pressure is good and is right at 20psi. I ordered a jetting kit from watcon that said if you tell them about your ski and where you ride they will send all the right size jets, etc. I’m wondering if they just made a mistake or what.

ya, i mean a wrong jet is a wrong jet. either it runs right or it doesnt.

idk how much you know about tuning carbs but i highly suggest this thread.
https://www.pwctoday.com/forum/pwct...west-pwc-riders/badgerland-jet-pilots/306829-

i currently am using this and the mikuni paperback book to tune any mikuni carb. having this link and the mikuni book is priceless.

assuming everything else in your boat has been inspected and gone through. following these items to the T will lead you too success.

 

[Jaxson]

Will the other jets, needle and seat be alright to keep?

 

[Ryan Declark]

hard to tell without actually riding the boat. if you have a 100 or so bucks squirreled away for a rainy day id suggest buying a couple sized lower and higher of your current jet settings, along with every spring available and needle and seat available.

thats just what iv done. that way the options are always available to you.
i never want to go and tune a ski and say "poop i wish i had a higher/lower jet to test"

 

[Jaxson]

Thanks, will do.

 

[WFO Speedracer]

You should be good with the needle and seat , popoff spring and low speed jet for now , the general rule of thumb is if you have to turn either screw more than one turn out from fully seated to make it run correctly you need to go one size up on the jet , conversely if the ski won't run unless the adjustment needle is almost or fully closed go down one jet size , you want to leave yourself room for needle adjustment in case you have to retune because of changing air or water temps , adding an aftermarket flame arrestor whatever.

 

[john zigler]

Pop off pressure is good and is right at 20psi. I ordered a jetting kit from watcon that said if you tell them about your ski and where you ride they will send all the right size jets, etc. I’m wondering if they just made a mistake or what.

Every ski / build / location elevation, etc is different, and can require different set ups. We in no way say our specs are the end all in tuning. It is just a good starting point.

That being said, we have built MANY stock 550's here over the years, and this is what works for us here. You are in a very similar climate, and even higher elevation than me. We use these jetting specs over, and over on a good solid stock 550. Terry (WFO) is down south, and a different climate, and elevation. His specs may work for you, but I think you would be very rich at a 120/125 pilot jet.

I will say all too often we find people want to just throw parts at a poor running ski, without really knowing why it is running bad in the 1st place. Why did you replace the carb?

I have a few other questions for you.

What carb are you running? I know "SBN 44" BUT is it a genuine "Mikuni" carb? (Or Amazon China knock off?) Is it new, or used? Is it a stock carb from another application? (IE Yamaha , Tiger shark, etc?) If it is used, did you rebuild it? Genuine Mikuni Kit? Are you certain you have the correct gaskets/diaphragms on the fuel pump side?

Have you done a leak down test on your engine? An air leak from crank seals, intake/carb gaskets, cly base gasket etc can and will cause a lean condition.

What is the condition of the rest of your fuel system? Fuel lines, fuel pick up, fuel select, etc.

What is your high speed screw set at? Have you tried turning it out more? Does the ski run better as you do turn it out?

Again, I am not saying you that you may or may not need to jet up, BUT I just don't want you band-aiding another issue with richer jetting. These skis are old, and many times just worn out needing more attention than just a new carb.

John

 

[WFO Speedracer]

John I won't get into a pissing match here with you ( or maybe I will, the day is still young ) but I personally have found over the years that it is always best to jet from rich to lean , way less chance of motor damage that way especially if you are a novice , if you are on here asking questions about jetting then it's a pretty good bet you are a novice and to me (It's always better to foul a plug than buy a jug ) as us oldtimers say.

My jetting advice leaves room for a margin of error , yours does not , I will say this barring complications like leaking crankshaft seals , some other air leak or a cooling system issue if he melts a top end using my specs I will buy him a new top end , I hereby challenge you on open forum to match my offer and remember one important thing here I haven't sold this guy anything nor am I trying to.

 

[Jaxson]

It was running good before we got the upgraded carb. We just decided to switch carbs because we heard the Sbn was a good upgrade to have. And yes it was a genuine Mikuni carb bought brand new.

 

[Ryan Declark]

Again I'd stick with WFO's advice.

Buy a jet size up and below of his recommended settings (maybe 10 bucks worth of jets.)

2.0 needle seat 20psi pop off

Start half turn out both top and bottom screw.

Also what Watcon is saying is true to an extent. You should go through your system if you have not done so already. If you don't know when the last time you've done your c/s seals it's probably time to do them. If the carburetor hasn't been rebuild If it's a used carb, rebuild the carb.

With that said If all you've changed is the intake manifold gasket due to the spacer needed to install the carb and the ski was running correctly before then it would kind of point to improper jet settings.

The cool thing about skis is they are unique depending on what has changed from the factory, where you ride, prop settings, etc...

Bad thing is if 1 thing changes aside from cosmetics, it's likely going to need an adjustment somewhere.

You can lead a horse to water but you can't make it drink. Again, iv left a link above that is a good way to start learning how to tune a carb, what it sounds and feels like when something is off.

HIGHLY RECOMMEND.

 

[WFO Speedracer]

The link Ryan posted is the same one I post to people , it doesn't matter if you like the guy or not , personally I do , we are friends , the advice he gives is spot on and you won't go wrong following it to the letter, John is correct in that your jetting may be different in your area but there are 3 jet sizes between a 105 and a 125 and that's not counting half sizes on jets , 3 jets sizes is a lot, if you were skiing in the skies out in Colorado at 1312 ft then maybe you would have to change that many jet sizes but most people won't and most will fall into a range pretty close to what I recommended.

As an example where you are at if you are riding on the rivers is 360ft above sea level , where I ride on Lake Marting is 491 ft , Montgomery is at 240 ft and Lake Gantt where I also ride is 197 ft. , the jetting does not change when I ride on Lake Martin and the next weekend ride on Lake Gantt , the ski runs the same , so much for those elevation changes and in case you haven't figured it out yet we are in the same elevation range.

If you can't dazzle them with your brilliance then baffle them with BS I always say.