Idles but will not take throttle

[Willie_Boi]

Over the weekend I bought a 1996 Seadoo XP with the 787. I picked it up and it will idle, but it will not take throttle. As soon as you start to give it about 1/4 throttle it starts bogging and backfiring through the carburetors. The previous owner said he just had them rebuilt and had the wear ring replaced. I immediately started testing and going through forums looking for answers but i am being stumped on what to do next. Compression is 150 both cylinders, plugs regapped, rectifier is at 13 volts from what I could tell and it did not act differently after unplugging the red wire. Whoever did the work on it replaced all the hoses, spark plugs and rebuilt carbs added an inline fuel filter right before the entry on the bottom connection for the carbs. When I first turn it on the inline filter is full of fuel but quickly gets sucked in after started and then while running there’s only about an 1/8 worth of fuel flowing through it. Once you turn it back off it fills back up. Any tips or advice would be greatly appreciated. Thanks for your time -Willie

 

[JeremyD615]

First get rid of that inline filter. They do more harm than good, as they are an additional spot for a potential air leak, and your stock fuel system already has three filters in it. There’s one on the bottom of the baffle, the water separator, and the internal filters in each carb. It sounds like you’ve got air coming in somewhere, so replace the o-ring on the water separator, and try bypassing the fuel selector. I’d also recommend at least opening the carbs up to see if they are Mikuni parts. If the diaphragm nipple is not red, you need to go back through and rebuild the carbs with the correct parts.

 

[Willie_Boi]

First get rid of that inline filter. They do more harm than good, as they are an additional spot for a potential air leak, and your stock fuel system already has three filters in it. There’s one on the bottom of the baffle, the water separator, and the internal filters in each carb. It sounds like you’ve got air coming in somewhere, so replace the o-ring on the water separator, and try bypassing the fuel selector. I’d also recommend at least opening the carbs up to see if they are Mikuni parts. If the diaphragm nipple is not red, you need to go back through and rebuild the carbs with the correct parts.

Much appreciated, I’ll be doing that after I get off of work today. When I spoke with the previous owner I was told it was rebuilt with SBT parts. But I would not mind opening up the carbs just to see for myself.

 

[RockwallRick]

I had a similar problem on my 97 GSX. I would recommend replacing the fuel selector if that has not already been done.

 

[JeremyD615]

Much appreciated, I’ll be doing that after I get off of work today. When I spoke with the previous owner I was told it was rebuilt with SBT parts. But I would not mind opening up the carbs just to see for myself.

In that case, you are definitely going to need to rebuild the carbs again. Unfortunately SBT carb kits are just like the other aftermarket ones. The check valves are thicker, the gaskets are not the same dimensions, and most importantly, the rubber compound that the diaphragms are made out of is much stiffer than the OEM Mikuni parts. You’ll be chasing tuning issues with this thing forever until you go back to OEM...

 

[Willie_Boi]

In that case, you are definitely going to need to rebuild the carbs again. Unfortunately SBT carb kits are just like the other aftermarket ones. The check valves are thicker, the gaskets are not the same dimensions, and most importantly, the rubber compound that the diaphragms are made out of is much stiffer than the OEM Mikuni parts. You’ll be chasing tuning issues with this thing forever until you go back to OEM...

Sounds about like my luck. Where would you recommend getting the correct rebuild parts?

 

[JeremyD615]

I’d get the “Back to OEM” kit from OSD. In your case, you’re going to want to change the springs, since you don’t know for certain that they were correct to begin with. Make sure you add the needles and seats as well. It’s no fun having to bite the bullet for the expensive OEM stuff, but it makes things so much easier to do it once and have it done right... I think every one of us here that preaches to fully rebuild the carbs with OEM stuff has been through the ringer of chasing down carb problems from aftermarket kits. There’s nothing more frustrating than pulling carbs for the third or fourth time only to wind up spending the money on the good stuff anyway.

 

[Willie_Boi]

I’d get the “Back to OEM” kit from OSD. In your case, you’re going to want to change the springs, since you don’t know for certain that they were correct to begin with. Make sure you add the needles and seats as well. It’s no fun having to bite the bullet for the expensive OEM stuff, but it makes things so much easier to do it once and have it done right... I think every one of us here that preaches to fully rebuild the carbs with OEM stuff has been through the ringer of chasing down carb problems from aftermarket kits. There’s nothing more frustrating than pulling carbs for the third or fourth time only to wind up spending the money on the good stuff anyway.

I bit the bullet and ordered an OSD 787 dual carb kit, with all of the extras they offer. like you recommended. Will I need anything else? One thing I noticed is that the description on the kit says that there is no pop off required. Do you know how true this is? Also on a Mikuni carb rebuild write up I was reading on the sight said I will need a special Japanese screwdriver set. I was curious if it was just recommended or required. Also any tips or tricks to pulling/rebuilding the carbs would be greatly appreciated. I apologize for all the questions, but I am truly thankful for your help. I am mechanically inclined, I work on all of my own vehicles, lots of atvs, dirt bikes and even a hand full of newer 4 stroke jet skis. But the 2 stroke Seadoo world is completely new to me and I’m hoping to enjoy it.

 

[Ckrawiec]

I bit the bullet and ordered an OSD 787 dual carb kit, with all of the extras they offer. like you recommended. Will I need anything else? One thing I noticed is that the description on the kit says that there is no pop off required. Do you know how true this is? Also on a Mikuni carb rebuild write up I was reading on the sight said I will need a special Japanese screwdriver set. I was curious if it was just recommended or required. Also any tips or tricks to pulling/rebuilding the carbs would be greatly appreciated. I apologize for all the questions, but I am truly thankful for your help. I am mechanically inclined, I work on all of my own vehicles, lots of atvs, dirt bikes and even a hand full of newer 4 stroke jet skis. But the 2 stroke Seadoo world is completely new to me and I’m hoping to enjoy it.

There is a Sticky POST at the top of the 2 stroke forum about how to rebuild the carbs. Follow it like the BIBLE, no shortcuts. YES, you should always check the pop-off pressure and leak test the carbs AFTER re-assembly (I learned this the hard way).....it is very easy to build a pop off tester out of a bicycle pump and some misc pieces and parts, or just buy one, not that expensive. The Mikuni kits don't come with the right springs either.....a '96 XP dual carb setup uses the 80 gram springs. I'm not 100% sure IF the OSD kits include 80 gram springs (but they can be purchased individually).

The Japanese screwdriver is recommended, but not mandatory. Use good judgement and prudence with a Phillips head or Straight blade or a manual impact tool to loosen anything really tight. If the carbs have already been mucked with...chances may be good that the screws are not "moose" tight....hopefully not anyway.

Working on a 2 stroke is not rocket science....sounds like you have the skill set to dive right in, just be aware...older seadoo jetskis will keep you humble......just when you think you got it licked....bam, something else pops up....THEY ARE labors of love....but once they are dialed in right....much fun.....my '96 GTX is my personal favorite of my bunch of stuff.

 

[JeremyD615]

The OSD kits SHOULD come with the correct spring in them. You should definitely check the pop off pressures when they are reassembled, but they should be within spec and not need adjustment using those kits, as long as everything is assembled correctly.

The JIS screwdriver is recommended for sure. I use a manual impact driver myself, as mine fits those screws perfectly, but I wouldn’t use a standard Philips. Those screws are really soft and easy to strip out.

 

[Willie_Boi]

So I talked with a guy this morning while trying to buy some oil at a shop and he told me that I jumped timing and that my motor is toast. I find that hard to believe but is it possible? If so is there a way that I could check to see if I have jumped timing?

 

[JeremyD615]

Oh I hate the people in powersports shops these days. There is just so much bad advice that gets put out there and people run with it because it came from “the shop.”

It’s possible that you have a timing issue, but the carbs are far more likely to be the issue. Even if you did have a timing problem, that doesn’t necessarily mean the engine is toast. First, take care of the carbs, and then if there’s still a problem we can walk you through pulling the rotary valve cover to check the timing. We’re just not at the freak out point yet on this thing...

 

[Willie_Boi]

Oh I hate the people in powersports shops these days. There is just so much bad advice that gets put out there and people run with it because it came from “the shop.”

It’s possible that you have a timing issue, but the carbs are far more likely to be the issue. Even if you did have a timing problem, that doesn’t necessarily mean the engine is toast. First, take care of the carbs, and then if there’s still a problem we can walk you through pulling the rotary valve cover to check the timing. We’re just not at the freak out point yet on this thing...

Sounds good, I ordered the OSD stuff last week but they are on backorder, and I’m waiting on confirmation. Guess I’m not the only one trying to rebuild carburetors.

 

[JeremyD615]

Yeah, there’s been a shortage of OEM parts from Mikuni since this whole pandemic thing started. You might contact Nick and see what the ETA looks like. He might be able to help you out.

 

[Willie_Boi]

Yeah, there’s been a shortage of OEM parts from Mikuni since this whole pandemic thing started. You might contact Nick and see what the ETA looks like. He might be able to help you out.

I reached out to them through their contact system. But unfortunately they are closed from the 9th to the 13th, so hopefully I’ll hear back from them today or tomorrow. Hopefully the back order isn’t ridiculously long.

 

[Jbuckets]

There is a Sticky POST at the top of the 2 stroke forum about how to rebuild the carbs. Follow it like the BIBLE, no shortcuts. YES, you should always check the pop-off pressure and leak test the carbs AFTER re-assembly (I learned this the hard way).....it is very easy to build a pop off tester out of a bicycle pump and some misc pieces and parts, or just buy one, not that expensive. The Mikuni kits don't come with the right springs either.....a '96 XP dual carb setup uses the 80 gram springs. I'm not 100% sure IF the OSD kits include 80 gram springs (but they can be purchased individually).

The Japanese screwdriver is recommended, but not mandatory. Use good judgement and prudence with a Phillips head or Straight blade or a manual impact tool to loosen anything really tight. If the carbs have already been mucked with...chances may be good that the screws are not "moose" tight....hopefully not anyway.

Working on a 2 stroke is not rocket science....sounds like you have the skill set to dive right in, just be aware...older seadoo jetskis will keep you humble......just when you think you got it licked....bam, something else pops up....THEY ARE labors of love....but once they are dialed in right....much fun.....my '96 GTX is my personal favorite of my bunch of stuff.

have you ever had to replace mpem on your 96’ GTX? Wrong thread but have some questions

 

[Willie_Boi]

I got the carburetors rebuilt, 110% by the sticky. Who ever went through them before I did had done a bad job on cleaning. Also it was apparent they didn’t change all the components. I managed to get them back on this afternoon and unfortunately I’m still dealing with the same issue. It idles really strong and as soon as I give it gas it bogs down and then starts the back firing through the carburetors. Any ideas on where I should look next?

 

[Willie_Boi]

Yeah, there’s been a shortage of OEM parts from Mikuni since this whole pandemic thing started. You might contact Nick and see what the ETA looks like. He might be able to help you out.

Also wanted to mention I replaced the spark plugs, since I personally didn’t know how old the previous ones were. I also noticed while the carburetors were out that the bolts holding the rv cover had paint missing on the inside. So I’m assuming at some point in time someone had that piece off as well.

 

[JeremyD615]

Well now it’s time to pull that RV cover and check your timing. You’ll need a new o-ring and a degree wheel, or you can print one out if you don’t want to buy the plastic one.

 

[Flysooner9]

I’m having similar issues but it’s not back firing just bogging. I think I may have fixed it, needle rocker arm was bent to high so I think the needle was being held open.

However the previous owner did a top end and has a ridiculously rich mixture of fuel right now (runs pre mix) so I think I’ll try getting it back closer to 40:1. Right now it just smokes so horribly and it’s just fouling the plugs. Smokes to the point that when I pulled the plugs couple minutes after running smoke was coming out of the plug holes.

 

[Willie_Boi]

Well now it’s time to pull that RV cover and check your timing. You’ll need a new o-ring and a degree wheel, or you can print one out if you don’t want to buy the plastic one.

As of right now I’m waiting on the timing wheel and my new oring as we speak. The pop off on my carburetors was about 38psi and I was curious if there was supposed to be another rubber gasket other than the oring on the pto carb. I pulled one off but there wasn’t one in my kit to replace it. According to someone else on another page I read there isn’t supposed to be anything other than the oring.

 

[JeremyD615]

Which o-ring are you taking about on the carb? The formed o-ring? Some of the carb kits include them and some don’t, but it needs to be there...

 

[Willie_Boi]

Seems I answered my own question. I went back and looked at the rebuild thread and found it. When I opened the PTO carb where the fuel pump is on the MAG side, there was a thin rubber gasket over the fitted o-ring.

 

[Willie_Boi]

Which o-ring are you taking about on the carb? The formed o-ring? Some of the carb kits include them and some don’t, but it needs to be there...

Retimed the rotary valve on the XP today. Fired it up and still having the same issue with backfiring. I’m open to more suggestions. If I hold the choke semi shut it only bogs down. I’m not sure if that helps but it’s something else I noticed. I’m open to suggestions. Just a recap on what I’ve done. I have changed spark plugs, with correct gap and NGK number. I have done the red wire test on the regulator and also put a meter on it. The meter test showed it was low 13s. I couldn’t rev it very high at all, obviously because it will bog and backfire through the carburetors. I rebuilt both carburetors with the genuine parts and both carburetors were at 37-38 psi pop off. Rebuilt straight from the sticky. And now I have done the rotary valve timing. Any suggestions? I am truly open to any other tests or possible fixes.