1998 Seadoo Challenger 1800 Won’t rev above 5k rpms

[GilDevil]

My HS screw cannot be taken out for it is unmovable, as if soldered to the carb body !

I have seen that you have 80 grams springs, according to Mikuni oldies book (downloadable from its site) you need 1.5 needles. If the previous owner did not tell you which needles he put then you are uncertain. According to the book a 2-needle would not go along with a 80 g spring, popoff would be too low.

From the first pictures you provided in June thread it seems to me that your carbs have been greatly modified wr to factory. Unless I find a fuel line like yours in a 1998 official manual, I would ask the previous owner what he did exactly, and why. By the way, when did he sell the jet to you ?

 

[racerxxx]

So when everyone rebuilds their carbs here for their skis they rebuild the fuel pumps. Since your fuel pumps are divorced from the carbs they have not been rebuilt in 20 years, you can not get a rebuild kit for them either. You just replace the entire pump. That part# is 270500388, they're still available yet guys say they aren't. I just bought 2 for my Speedster, no symptoms, just preventive maintenance. I confirmed they had them, guy told me over 60 on hand. I went direct to the dealers website (Just google leaders marine), guy shipped them that day. Not saying that is your problem, but they've never been rebuilt if they are still the original ones. If you some how happen to have fuel pumps on your carbs, then someone switched them over. Also, have you replaced the inline fuel filters? Is the vent line clear from the fuel tank? I'm just trying to throw some ideas out there.

Sea-Doo Boat New OEM Pump-Fuel 270500388 Challenger 1800, Speedster 1998-2002 | eBay



Here's what the fuel pump looks like, mounted to the front of the engine sorta under the exhaust over the mag cover.

 

[CadeZ]

Yes it has 1.5 needles and seat in it. I have checked MY rebuild work 3 times now (headbang). The previous owner did a rebuild on it but it was with an eBay kit, so I rebuilt them all my self.
Second, yes my fuel line might be routed in a different way, but they both go right back to the fuel tank with no hold back whatsoever. I have already narrowed my symptoms down. And both engines are getting fuel (actually probably more fuel than needed) so that is not my problem.

He sold the boat to me at the beginning of this summer still as a project.

Also, I have not replaced the inline fuel filters yet. I have a set of 2 waiting to be put on, but I can’t imagine that could be the problem since it is always getting fuel.

It seems like there’s a million people on this forum with the exact same problem and not a fix yet. Everyday almost I see a new thread come up with a boat not being able to get on plane or go above 5k rpms.

Anyways, Thanks again!

 

[GilDevil]

End june 2018, so the hindsight on good performing is very short, difficult to extrapolate that "it has been planning for long".

Mikuni writes that the fuel pump must be over the carb fuel inlet, otherwise the carb does not function as it should, and in your case your pics seem to show that the fuel goes into the carbs from above after an upward circle. I understand that it's like for aquariums where the air pump must be above the diffuser and even above the conveying hose to perform long and at best.

Another point is the length of your custom circuit to the carb fuel inlet: my factory one is the shortest, nearly a straight line. What's yours ?

A last point is the fuel pump itself, maybe too tired for the extra effort required by your non standard circuit.

You say your engines receive fuel but maybe without enough pressure.

 

[CadeZ]

Okay, I really doubt this is the problem but if you could send post pics of yours that would be helpful. The line could easily be cut shorter and routed different. But it’s not causing it to not have enough fuel.

Thanks

 

[racerxxx]

Post pics of your engine by cadez. Would be nice to see....just in case there is something obvious. I've walked into many service situations with my last job and was like "Oh, here's your problem" and the guys looked over the obvious. Post pics of the carbs the way the fuel line is hooked up on the other engine etc.....

 

[CadeZ]

 

[GilDevil]

Below is almost exactly what I have, 27 28 feeds in the carbs from below, 13 15 returns extra fuel to tank and in my case the route is rightwards direct to the tank and not turning around the carbs by the left. Main point is 27 28. Do your yellow silicons feed with fuel or return it to tank ?

PS Incidently, your silicons lie against the hot cooling pipes, one gets brown, silicon is said not to stand well heath, with fuel in it that could become dangerous.

 

[GilDevil]

Concerning my own case, I would like to get a feedback from those who resorted to a Mikuni carb for 800 engines (OSD Sea Doo 787 800 MAG Side Carb [OSD_787MAG] - $209.99) instead of buying an OEM carb for the 787 engine of the Challenger 1800 1998 and some other Seadoo boats. Its price is way lighter than the OEM, but it was officially intended for jetskis not for jetboats ... and I need to pair it with the second carb, OEM this one. If the two carbs behave differently I will waste my life tuning the impossible team. I have bought it and it looks externally like an OEM for boat. Anybody has experimented this cheap carb on the Seadoo 787 engine ?

 

[racerxxx]

So I had all this typed hours ago and we lost power due to some storms. I digress......

Your boat is a 97 not a 98...I suspect. 98/99 had different carbs and a totally integrated MPEM, not the remote grey box like yours has on the starboard side. 98 had the coil boxes over the rear driveshafts, 99 had them to the sides of the engines, yours are in the gray box. I knew something was up........What are the last 2 numbers of your HIN?

Ok, here's my list of what I don't like.
Air boxes---They HAVE to be on there, your carbs will never run right with out them. They're jetted to run with them. You should be able to set the carbs to spec on the bench, put them on and go, with the air boxes. I have NEVER needed to "tweak" carbs on a stock ski or boat. Only the idle and even that is rare. The dome goes up on the flame arrestors too, you have them upside down.

Blue spark plug wires. If they're automotive spiral wound, that could be an issue. These things are as basic as it gets. All they need it regular solid core plug wires, literally multiple strands of solid wires and good ole' NGK BR8ES plugs, not 7's, not 9's, not irriduim. If those wires have any "leakage" it could screw with the electronics. I think the manual calls out the resistance of just the spark plug boot alone--removed from the wire---check that. Then check the resistance for that blue spark plug wire, again, I think it's in the manual or that might be the coil test, still check the coil

Here's 9'-10" of the correct spark plug wire

SEA-DOO GTI 278001268 SPARK PLUG WIRE NOS 9' 10" OEM WATERCRAFT FREE SHIPPING | eBay



So, lets check a few things first.

Do you have fuel shut off valves?

Are your fuel pumps on the carbs or are they separate form the carbs like I posted pics of?

If I can see them correctly they're on the MAG carb in one of your pics---again leading me to believe your boat is a 97. If that is the case all your fuel lines supply and return etc... are all 1/4" no 5/16 fuel line at all.

Back to what I see:

Fuel return line---my god it's HUGE looking but it could be stock, the fuel supply line looks the same. It could just be the "burn jacket" to make it "safe". The fuel supply "probably" was 5/16" (inside diameter) originally from the baffle to the fuel filter , from the filter to the pump and from the pump to the carb. The rest is all 1/4", even the return. Throw all that clear/yellow fuel line out and get straight black ethanol safe fuel line. I know, I know, how do I know if there are air bubbles in my fuel lines??? Don't know, all the manufactures used gray or black fuel line---If they don't care neither do I. Just stay basic. Guys always try and one up the manufacturers. Use hose clamps on all the connections, you can get full stainless mini clamps at Home Depot. NO CABLE TIES. But like I said, if your boat is a 97 it should be all 1/4" as per the microfiche.



This should be your fuel system, yes?

 

[CadeZ]

The yellow hoses are feeding the fuel into the carbs.
I always have the air boxes on, they were off for the pictures. You can see them on in the last picture.
Yes, you are right about to being a 97, I was questioning that myself but never really bothered to go super in depth to find out because they are the same for the most part that I see.
I do have fuel shut off valves.
Yes, my fuel pumps are on the carbs, one on each set.
Yes, the inner diameter is not the same as the outer on the fuel line, much smaller.
Okay will change out the yellow fuel lines.
Yes I believe that is my fuel system.

I was really looking at just getting the dang boat actually running right before I started doing the improvements to the boat. No need in spending extra money when it doesn’t even run correct.

Thanks for all the information.

This troubleshoot information in my manual seems like my symptoms. But changing the rave settings and cleaning them haven’t seemed to help.

Once again. Thanks!

 

[racerxxx]

I was really looking at just getting the dang boat actually running right before I started doing the improvements to the boat. No need in spending extra money when it doesn’t even run correct.

Ok, most if not almost all of us just make sure the engines even run and have good compression before we do anything. You're past that point, it runs. Now is the time where you go over all the past owners hack work in the last 21 years of it's life and make it right. We get them back to OEM specs and make them run properly so when you venture out into the water you know you're going to make it back to the dock----under your own power.

Here's what I would do if I were in your shoes:

Last test before the parts replacement. Have you ran the boat in the water with the red wires disconnected from the rectifiers? If the rectifiers are bad they will throw AC back into the electrical system and really screw with electronics. RPM can come and go and really screw with you.

Replace every last piece of fuel line in the supply and return system. For now....I would bypass the selector switches(save enough fuel line to reconnect after I bought new ones) and just run a new filter inline with the carbs. Not a fancy one, just a regular plastic inline filter. You want to try and eliminate any outside hardware that "could" introduce any problems. Simplify for now.

Here is one I just put on my speedster so I know it works.
Advance Auto Parts - Down for Maintenance

Change those plug wires back to stock wire. Make sure that 9'10" of spark plug wire is enough if not there are more guys selling it on ebay, but that was the most for the least.

So far I could see this costing you around $100. Filters $10 for 2, $50 in fuel line (2 25' spools with left over). Maybe $40 in spark plug wire if the first isn't enough.

It could also be metal fragments in the MAG housing screwing with the pick up, that work is a little more in depth and labor intensive, I'd save that for last. There definitely appears to have been several hands in that boat. The one engine is not original to the boat. That would be the starboard engine. I think 97 was the first year for the big serial tags on the engine, so the port engine might be an original, who knows. The big tag engine should have a counter balance fill plug where the starboard engine has the small serial tag and no counterbalance fill plug. 97 was the first year for that fill plug.

Remember, these are just ideas, it's a gamble. Not to sound harsh, but if you can't afford to waste $100 to try and get it running better perhaps this isn't the best hobby. Without investing, you're not progressing forward. To put it in perspective, if your boat has 40 gallon tank which I think it does.......a full tank is gonna cost you $100 every fill up without your oil that you need to premix into it. If you use Seadoo oil, throw another $45 on top of that fuel. Every fill up is almost $150. I premix my Speedster (switching back to injection this winter) I burnt 30 gallons in 3 hours towing the kids on the tube every time we go out.

 

[CadeZ]

Yes. When I got the boat, it was running way better then it is now. So I know the dang thing will run. The reason I changed everything is because I was pointed towards doing a carb rebuild with Mikuni parts. Which I agree with. So I followed mikidymac’s carb rebuild thread. Replaced everything. Got it back on the water and the symptoms were all over the place. Realized the pop off pressure was way off, not even sure how it ran the way it did with the old carb parts. Anyways, changed the pop off pressure and ended up cleaning the rave valves as well. Got it back out and neither engine would go above 5k at all. So we replaced both rectifiers. Got it back on the water and it’s plowing/holding back at 5k until it gets on plane. Then they jump up.
Anyways, I’ll answer your questions.
No I never pulled the red wire, I ended up just replacing both of them. Thinking this would finally solve the problem. No, but it did change the symptom to what it’s at now. (Plowing until it gets on plane)
I already have the fuel filters. Just haven’t replaced them yet.
I will look into replacing the fuel lines and spark plug lines.
Yes, when we first got it we found out that one engine was from a previous year. We were going to do an oil change and realized there was no fill plug. Lol.

As you can see, it’s not about the money as much. I’ve already spent a decent amount on this boat. More about my time, I’ve spent a lot of time with trial and error and have gotten no where but backwards. The dang boat ran better with the eBay carbs!!

But okay, thanks for all the info. Will look into everything.

 

[racerxxx]

Gotcha. Not sure how swapping soft parts in the carbs would cause your issue.....unless something is not right. I know, you went back over them several times. Do you have pics of the internals of the carbs disassembled, underside of the valve body? I'd still check the rectifiers since you didn't physically check them just swapped them. Doubtful, but when you're troubleshooting you can assume anything.

I remove everything from the carbs and verify the passages are clear with carb cleaner then with red automatic trans fluid, then carb cleaner again. I pump it(trans fluid) thru the passages and I can see the red physically ooze from the orifices. I use a Plews oil gun like in the picture.

 

[GilDevil]

If you read http://www.mikuni.com/pdf/sbn_manual.pdf you'll see that many changes as simple as aftermarket flame arresters can disturb the balance in internal fuel pressure achieved with the factory set of needle, spring, jets and speed screws turns. Changing drastically the fuel circuit like done on your boat is a main change regarding pressure balance, I believe.

Did you change the fuel lines yourself or did you get them as they are now ? If you inherited them, the previous owner may have found a balance using a non factory set of needle, spring, jets and screw turns, using his own recipe. The Mikuni manual opens the door to such personal adjustments.

Now if you have brought back your carbs to the factory settings then you lose the balance reached by the previous owner. Have you talked with him recently about all this ?

 

[CadeZ]

No I don’t have anymore pictures of the carbs. Yes, next time we take it out I will pull the red wire on the rectifiers. All of the passages were clear but next time we take the carbs out I will check again.

No, I did not change the fuel lines my self. I got them the way they were. The previous owner was very busy and had the boat “broken down” for a year or two before selling it to me. He replaced the carbs with eBay parts and then never got it to run the way he wanted. So he sold it to me.
All of the “settings” except the pop off pressure were still in oem specs. The only thing that was different is that the parts were eBay.

 

[GilDevil]

A long and winding road that leads to the fun ...
You are now like a police detective or a code debugger

No one wants to make a summer series of it, so here is my last sincere advice:

Suppose these are only the carbs that make trouble and the ebays work well, then what you need is read carefully the Mikuni manual first and then you'll agree you must come back to the factory fuel circuit for carb internal fuel pressure reason. Pay also attention to fuel gaskets regarding the pressure. Try to find an actual challenger 1800 to watch inside if you have hard time reading BRP diagrams. And youtube provides also some nice tutos that you can download in mp4 on your HDD forever.

From manual you'll learn that popoff has nothing to see with your 5000 pm barrier to planning, neither the spring and needle, but that the high speed screw has a lot to do.

You'll learn also you need to have factory specs parts, for example the flame arresters and the rebuilds (needle, seat, speed screw, spring and of course the classical soft parts), because Mikuni explains they have spent years to achieve a stable balance with their own material.

They write that once you follow their procedure you don't need to tune on the water, it's one shot, at least for non racers like us. I've been told by a parts seller that Seadoo boats assembled the pre tuned Mikunis and did not check the behaviour on water, because they knew it worked.

Last, my own jet does not go planning instantaneously, there is a threshold due to water friction, I need to wait a little, I don't push the levers to full power to avoid flooding the engines. But it's also true I have an ailing carb. As I said before, putting it down on the table I've found a high speed screw way too loose but non tuneable because stuck in (fun !), I am changing the carb right now. The wrong carb drinks too much fuel and caps at 5000pm, like yours. The correct engine has been helping the ailing and both were able to make the jet plane over long runs (15km one way). I did not make the carb change before because there is a trial about it. If the expert asks to see again the boat on water I'll put the ailing carb again for the expertise day.

Bonne chance !

 

[GilDevil]

Summer jetboating is over for me and I'm back to headtown. Some feedback anyway.

I had concern about using a Mikuni MAG carb for 800 engines (OSD Sea Doo 787 800 MAG Side Carb [OSD_787MAG] - $209.99) instead of buying an OEM carb for the 787 engine of the Challenger 1800 1998. Well I had some hassle putting the new carb in but finally made it.

I followed very narrowly the advices and specs of Mikuni and BRP about tuning the carb and by the same token the other carb to be kept, the PTO.

Out of the sea it was impossible to rev the engine as recommended by BRP.

On the sea the two carbs, the new OSD 800 and the OEM 787, pushed the engine to 6500 rpm and possibly above but I didn't try. The second engine followed suit. The jet reached easily 70 km/h with each engine at 6500 rpm. I had a slack of 500 rpm, BRP saying I can up to 7000.

The 70km/h run was steady over say 5 km, on a rather flat sea on the way to harbour. It was a wonder.

Before changing the MAG carb the ailing engine couldn't go over 5000 so I had to push the other at 6500 to reach 50 km/h. Now when both are at 5100 rpm I ship at 50km/h over 15 km one shot no stop with small waves on sea. Gas consumption has gone down. So cool !

As a conclusion OSD 800 replacement MAG carb works (but needs adjustment) and following precisely the Mikuni and BRP specs works also. I also rebuilt the PTO carb but did not change the carb, but I tend to believe the main problem arose from a high speed screw that was too far open and stuck to the MAG carb body, so impossible to be turned tighter.

Hope this helps and gives heart to those who try to have their jets plane.