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Discussion Starter #1
Hey all! New member here, need some help understanding jetting basics. Problem: 98 Superjet smokes real bad at low RPM, cleans up at high RPM
History: Grenaded the modified motor several years ago, and replaced with a Yamaha factory short block. Kept the aftermarket 44 carbs,manifold, pipe, waterbox, on it. Recently replaced the MSD, CDI and coil with new ones, and rebuilt the carbs. Runs strong now but has always been too rich up here in Colorado at 5280 elev.
Question: What jetting should I use as a starting point? Current jetting is 120 slow jet, 1/2 turn out on the needle. 130 high speed jet, 3/4 out on the needle.
Pop off springs are the black ones.
Also would like to know if anyone knows what brand of pipe is on it, can't find any info on it.
I know all about dirt bike motors but this ski is a different beast, so bear with me if I seem to ask some stupid questions. I'm sure I'll catch on pretty quick.

 

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Thats a superjet dry pipe. The smoking down low rpm is normal. Its because the same amount of oil is being burnt at low rpm as high rpm because of pre mix. the only way to fix it is to install a variable oil pump which injects more oil as you squeeze the throttle. But you should just leave it and maybe run about 40:1 oil ratio. Are you running 1.5 needle and seats??
 

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Discussion Starter #3
Thanks for the reply. It has 2.3 needle/seat. I'm using Amsoil 2000 series racing 2-stroke oil at 50:1. I was concerned that the slow speed jet was way too rich, at 120, since stock is 70. But I think stock carbs are way different than the Super BN carbs that are on this unit. These carbs are some kind of aftermarket racing carbs that have been cut open and modified. But wouldn't a smaller slow jet let less oil and fuel mix through at lower RPM's, thus leaning out the amount of smoke coming out of the pipe. Also the plug is really wet when i check it after shutting it down after slow speed.
I know it has a dry pipe, was wondering what brand? A jet ski mechanic told me it was some special limited run pipe that they only made like 500 of them, and it supposedly is a very good pipe. Was just wondering if there are some jetting specs that go along with it?
 

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Yeah it is a good pipe. It was designed for surf riding and has a lot of bottom end. If you lean off the low speed mixture screws or jets, its ok as long as it doesn't die upon acceleration meaning lean. Its something you have to tune. Is the oil your using a TC-W3. Make sure it is and not a synthetic or caster oil as these will make more smoke.
 

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Discussion Starter #5
So, here's the latest. Found out the pipe is a Factory Pipe, standard dry pipe. Made for better all around power, but has mostly top end gains. The carbs on it are Buckshot 44's, and pretty much over carbs. the stock motor. So I just got some new pump gas 36 domes from Pro Designs and put the Coolhead back on it. That woke it up pretty good. It still runs a little rich down low, so I might just lean out the slow jet 1 step and see if that cleans it up. It rips up top so I think it is pretty close there. The pistons looked great when I changed the head, so I think I'll continue using the full synthetic Amsoil.



 
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