Is it possible to access jets without removing carbs from ski?

So I bought an old roundnose a while back and I got it running about two weeks ago. Been riding the crap out of it and I think Im ready to try and get it jetted perfectly. I've been racing 2 stroke MX bikes my whole life and I know that major horsepower is being left on the table until you are right on the money.

My problem is Im afraid to remove the carbs because I'll probably tear one of these old gaskets and then ski will be outta commission for a while. And I don't want to make two seperate orders for gaskets and brass.

Is there a way to get into these carbs without removing them from the ski? they are the stock 38 mm mikunis with the chokes removed.
 
Ok, Ill order soon. It's not like the ski runs bad at all either, just need a little too much juice from the low speed screw to get a clean pickup from idle.

One last question, can I check pop off pressure without pullling the carbs?
 

Big Kahuna

Administrator
Ok, Ill order soon. It's not like the ski runs bad at all either, just need a little too much juice from the low speed screw to get a clean pickup from idle.

One last question, can I check pop off pressure without pullling the carbs?
Not accurately.
 
I have another question. Riding the ski yesterday I noticed that in a straight line 1/4 throttle hits a lot like full throttle and very little difference between half and full. I figured it must be lean as poop and surging so I rode it around at 1/4 for a while, pop the hood off and the engine is luke warm not even hot. Plugs everything, could easily rest my hand on any component and not get burned. Old plugs but they dont indicate a lean condition.

Is it pretty normal to not feel a huge difference between 1/4 and full throttle if the hull is already planed out? I can tell a difference if I have the thing buried in a corner. I think this motor might just be set up to hit hard off the bottom and doesnt have a whole lot to give up top, it's a JM 781 with a b pipe and enhancer, light flywheel etc. I run turbo blue 110 half and half with ethanol free 92, super M at 40:1. Bone stock pump from 2001

It's really hard to know whats going on when the only standups Ive ever ridden were roached out 550s that barely ran, really have no idea what these are supposed to sound like or anything.
 

Roseand

Ready to RIP
Site Supporter
I have another question. Riding the ski yesterday I noticed that in a straight line 1/4 throttle hits a lot like full throttle and very little difference between half and full. I figured it must be lean as poop and surging so I rode it around at 1/4 for a while, pop the hood off and the engine is luke warm not even hot. Plugs everything, could easily rest my hand on any component and not get burned. Old plugs but they dont indicate a lean condition.

Is it pretty normal to not feel a huge difference between 1/4 and full throttle if the hull is already planed out? I can tell a difference if I have the thing buried in a corner. I think this motor might just be set up to hit hard off the bottom and doesnt have a whole lot to give up top, it's a JM 781 with a b pipe and enhancer, light flywheel etc. I run turbo blue 110 half and half with ethanol free 92, super M at 40:1. Bone stock pump from 2001

It's really hard to know whats going on when the only standups Ive ever ridden were roached out 550s that barely ran, really have no idea what these are supposed to sound like or anything.
Somethings wrong with your setup. My 781 on 38s has power everywhere. I run a PFP which might make it a little different than yours but I'm doubtful a b pipe is causing your issue.
Pull your carbs and let us know jets. Blue has specs pretty dialed in. You could be propped wrong too
 

Big Kahuna

Administrator
What motor, what exhaust, what prop? We dont have enough info........... Sounds like you have a prop that is pitched to low and it is giving you all the thrust it will.
 

SXIPro

JM781 Big Bore
Why in the world are you running 101 octane gas in it? 220+psi or something?
Yeah, that sounds way off. Most of the JM 781BB are pump gas safe. Mine is. I run plain old 92 and it rips thru the entire power band, Hooker 10/17 in the pump.
 
It would be really dope if I didnt have to run so much 110, its so expensive and this ski eats it. I just run my 125 on the same stuff and the guy I bought it from suggested I use 100 octane av gas. Have not done a compression test but Im guessing it has the highest compression insert? I have access to eth free 92, which I am at least mixing half and half with my 110.

It's a bone stock pump/prop 2001 round nose.

Ski does not seem to run that bad at all, no bogging or loading up. 1 turn out on low speed and 1.5 on high speed screws. If i go in to 3/4 turn on low it will bog off idle, and I think it picks up a touch nicer at 1 1/8 turn out. Havent messed with the high speed screw yet but doesnt scare me when its held wide. Gonna try to get a plug chop tmmrw
 

Roseand

Ready to RIP
Site Supporter
It would be really dope if I didnt have to run so much 110, its so expensive and this ski eats it. I just run my 125 on the same stuff and the guy I bought it from suggested I use 100 octane av gas. Have not done a compression test but Im guessing it has the highest compression insert? I have access to eth free 92, which I am at least mixing half and half with my 110.

It's a bone stock pump/prop 2001 round nose.

Ski does not seem to run that bad at all, no bogging or loading up. 1 turn out on low speed and 1.5 on high speed screws. If i go in to 3/4 turn on low it will bog off idle, and I think it picks up a touch nicer at 1 1/8 turn out. Havent messed with the high speed screw yet but doesnt scare me when its held wide. Gonna try to get a plug chop tmmrw
If that's a stock prop that's your issue. Get a 10/16 hooker!
 

JetManiac

Thinking about shredding
Site Supporter
Vendor Account
If you still have the stock prop, then you seriously need an upgrade to a modern prop pitched for bb motor. Stock 01 prop is terrible, even on the stock ski, add a bpipe and head and it is cavitating and crying already.
 
If that's a stock prop that's your issue. Get a 10/16 hooker!

If you still have the stock prop, then you seriously need an upgrade to a modern prop pitched for bb motor. Stock 01 prop is terrible, even on the stock ski, add a bpipe and head and it is cavitating and crying already.


I was going to mention this, it is pretty much common knowledge that stock props are no bueno. I want to add that I had a long history in powersports and tuning before riding jet skis and while they are incredibly simple, there are some special differences that you might not immediately pick up on. 1 being that pop off pressure is very important to how your ski runs and "hits" 2 the fuel system needs to be sealed completely, any leaks on a line or fuel cap can add to minor jetting issues. 3 air leaks do develop over time and to insure your getting the best performance and least amount of unnecessary wear, you should ideally confirm you have no air leaks by pressure testing your engine out of the hull. I don't trust anything haha not that you need to rip the ski apart but I just wanted to mention those few vital details that can contribute to what seems like a minor jetting issue! ;)
 
Get your impeller right then focus on carb tuning. You get it dialed with the impeller you have, you'll probably have to do it again after you get the impeller right since your current one isnt loading the engine enough.
 

bored&stroked

Urban redneck
It would be really dope if I didnt have to run so much 110, its so expensive and this ski eats it. I just run my 125 on the same stuff and the guy I bought it from suggested I use 100 octane av gas. Have not done a compression test but Im guessing it has the highest compression insert? I have access to eth free 92, which I am at least mixing half and half with my 110.
I would mix 1 gallon 110 to 3 gallon 92 and see what happens, or even better pull the head and see what domes it has exactly. I run 195psi and mix 50/50 100 avgas and 91 octane pump.
 

Vumad

Super Hero, with a cape!
So I bought an old roundnose a while back and I got it running about two weeks ago. Been riding the crap out of it and I think Im ready to try and get it jetted perfectly. I've been racing 2 stroke MX bikes my whole life and I know that major horsepower is being left on the table until you are right on the money.

My problem is Im afraid to remove the carbs because I'll probably tear one of these old gaskets and then ski will be outta commission for a while. And I don't want to make two seperate orders for gaskets and brass.

Is there a way to get into these carbs without removing them from the ski? they are the stock 38 mm mikunis with the chokes removed.

Make sure you use exactly the right size flat head for the jet.


 
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