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2002 GTX Mikuni SB 46I Problem

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wblocher

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I bought this jet ski after it caught on fire by the idiot owner. One of the spark plug ground points was broken. Engine was flooded, took plugs out to clear, left spark plug connected to wire and poof.
I replaced all the melted hoses and rave control valve and the broken ground posts.
I cranked over the engine and lots of fuel gushed out of the first cylinder. I bought two Mikuni rebuild kits and new needle and seats.
Put them back in and both cylinders now flood when trying to start. It is like fuel is being dumped without atomizing.

Any ideas? One of the carbs was missing internal gaskets, so it was obviously messed with.

Much appreciated!
 
I am new to skis but my first thought would be, what is your pop off pressure set at. If needle and seat do not seal you get too much fuel.
 
I have a pop off tool, but didn't use it. The rebuild kit came with a 95 gram spring, but I couldn't find a gram rating for the seadoo part number, so I left the old springs in. The inside of the carbs were very clean so I thought not to mess with the springs. I was thinking that maybe super high fuel pressure could force the pin open as well?
 
I would always check, you have no idea what someone before you might have done, I did that with my carbs, put everything back, still had problems, found 1 pop off @10psi, another @42 psi, same engine, 2 skis, similar setting on both carbs from other ski. According to Mikuni you should have, 162.5 hi speed jet, 77.5 low speed, 2.0 needle valve with 95g spring. 2.0 needle and seat, 95g spring = 25psi pop off in Mikuni SBN manual. There are others here that know a lot more than me that should get in here before too long and offer more advice.
 
I bought this jet ski after it caught on fire by the idiot owner. One of the spark plug ground points was broken. Engine was flooded, took plugs out to clear, left spark plug connected to wire and poof.
I replaced all the melted hoses and rave control valve and the broken ground posts.
I cranked over the engine and lots of fuel gushed out of the first cylinder. I bought two Mikuni rebuild kits and new needle and seats.
Put them back in and both cylinders now flood when trying to start. It is like fuel is being dumped without atomizing.

Any ideas? One of the carbs was missing internal gaskets, so it was obviously messed with.

Much appreciated!

If the internal metering needle isn't sealing in it's seat or if the o-ring around the seat is leaking, the fuel will easily flow through the carb and flood the cylinder.

You can do a kind of leak check the same way you'd check pop off, by closing off the fuel return and pressurizing the fuel inlet of each carb separately, you should not be able to blow fuel into the fuel chamber of the carb until the pop pressure is reached.

I'm betting the o-rings around the metering seat are missing or secondarily somehow you didn't assemble the metering spring/lever correctly.

The other possibility might be you installed the round metering diaphragm incorrectly or it's the wrong one and it's pushing on the metering lever and keeping it open.

The way these carbs work is fuel on demand, that demand is determined by vacuum in the intake manifold. The vacuum travels from the intake manifold via the pilot and main venturi orifices into the fuel chamber and pulls the round rubber metering diaphragm in towards the fuel chamber and causes the nub on the diaphragm to press against the metering lever. Once this happens, the metering needle is allowed off it's seat and fuel can flow into the fuel chamber by coming up through the metering needle seat.

It may be for some reason your metering needle is not sealing in it's seat, or there's too much vacuum (if the choke is completely closed there will be too much vacuum for controlling the fuel metering.

So check all that stuff! :)
 
And, it's always best to use the original springs if they have not been monkeyed with, I have 80 gram black springs in mine currently and they work fine but will install the original silver 95's next time but no rush b/c the hot starts are FANTASTIC using the current combination.

There are two silver springs, one is 65 gr and the other (correct) one is 95 gr, so I'd avoid getting that wrong. Although even with a 65 gr spring the carb wouldn't be flooding the cylinder like that, so I don't blame this on the springs. I wouldn't use the 65 gr spring b/c I think it might cause a rich spot in the low end of throttle.

BTW, the metering seat orifice should be 2.0, so I hope that's what you put in there.

Also check the metering needle to make sure the rubber tip isn't damaged, if the tip is damaged (such as missing or torn) you will experience this type of flooding issue.

That is, there's something wrong with the way the fuel metering diaphragm/needle/seat/spring are installed, causing this problem. I'd guess the previous owner was in there monkeying around and assembled sumthin incorrectly.
 
One more thing, I guess you must have already but google "Mikuni SBN46i manual" and you can get the mikuni factory manual that has all the part number info in there you could possibly need. Nor seadoo numbers in there though, and some of the advise can throw you off so if you deviate from original stuff pas it by us here first so we can save you some time.
 
I would check the pulse diaphram too for a rip or tear. If its ripped, it could be sucking raw fuel in right into the crankcase and flooding out, or siphoning into the engine. Bottom line, carbs have to come apart unfortunately.
 
I would check the pulse diaphram too for a rip or tear. If its ripped, it could be sucking raw fuel in right into the crankcase and flooding out, or siphoning into the engine. Bottom line, carbs have to come apart unfortunately.

Good point BIRKS, that fuel pump pulse line is attached to the PTO (rear) cylinder crankcase so the PTO cylinder might flood in this case! It can be checked by simply pressurizing the pulse line to the carb fuel pump (mounted on side of MAG carb (front, or bow, carb), disconnect from crankcase and pressurize it a few psi and make sure the plastic mylar diaphragm inside the fuel pump isn't leaking! It should hold pressure quite well and if not then there's a hole in the fuel pump diaphragm.
 
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