1999 Challenger 1800 - one engine dies at WOT

[Captian_17]

Hello,

I've dug through the threads and can't find anything quite like what my boat is doing. I have a 1999 Challenger 1800 with twin rotax 787's. The issue I am having is only with the left engine. The engine starts, idles, accelerates and runs perfect up to about 6500rpm. Once I push it to 7000rpm it will maintain for between 45 seconds to 2 mintues and then the engine cuts off like someone hit a switch. I can run it at 6500 all day long, but when I try to sustain 7000 at WOT the engine dies. It will start right back up no problem at all.

Trying to troubleshoot I have thrown some parts and time at the problem. First I changed the temperature sensor to see if maybe it was giving a false reading at high RPM...That didn't work. Then I completely rebuilt the carbs and that didn't work. After that I cleaned my rave valves and replaced the bellows, which didn't help either. I also changed the fuel filter, which had no impact at all. I am at a loss for what could be causing the engine to die. The right engine runs perfect, has no issues and maintains WOT without trouble. I have thought maybe it was a fuel delivery problem, but that does not appear to be the case either. What am I missing? It's really strange that it operates great at 6500rpm and dies at 7000rpm. the only good news is that I am able to consistently recreate the problem, so there has to be something broken somewhere in the mix.

Any help is much appreciated. I love the boat and everything is great except for this one little gremlin that keeps eluding me.

 

[m.colley]

sounds like it could be a rev limiter but I'm no expert. My boat is the Sportster 1800 so my experience with the 787's is limited to a few friends with skis. Hopefully someone else will come along soon and chime in..


Martin

 

[Dr Honda]

You could have a broken/chaffed wire somewhere.... but it sounds like fuel.


Have you tried to pull the choke a little? a small air leak in the fuel system, will do exactly what you are describing. OR... a plugged filter. Believe it or not... but going from 6500 to 7000 RPM requires about 30% more fuel. So... a tiny air leak, or a lightly plugged filter will show up in that last few RPM.

 

[Captian_17]

I have not tried the choke. I meant to try that while I was out today and completly forgot. I'll give that a try next time out. I have swapped the fuel filter, so I don't think that is it, but maybe it's a fuel line issue. All the old grey lines were replaced, but maybe one of them is collapsing under high load. I never would have guessed the fuel demand would increase that much, but it would make sense given the issue I'm having. I'll also check for any leaks in the fuel delivery system.

One other question....any chance it's something in the carbs? I really don't want to take them off again, but was thinking maybe it's the fuel pump not working correctly at high RPM. I'll try anything before pulling the carbs again. In addition to fuel delivery, could it be electrical maybe, such as a weak spark at high rpm. I am completely stumped and guessing at this point.

Thanks again.

 

[Dr Honda]

I have not tried the choke. I meant to try that while I was out today and completly forgot. I'll give that a try next time out. I have swapped the fuel filter, so I don't think that is it, but maybe it's a fuel line issue. All the old grey lines were replaced, but maybe one of them is collapsing under high load. I never would have guessed the fuel demand would increase that much, but it would make sense given the issue I'm having. I'll also check for any leaks in the fuel delivery system.

One other question....any chance it's something in the carbs? I really don't want to take them off again, but was thinking maybe it's the fuel pump not working correctly at high RPM. I'll try anything before pulling the carbs again. In addition to fuel delivery, could it be electrical maybe, such as a weak spark at high rpm. I am completely stumped and guessing at this point.

Thanks again.

It's highly unlikely, that a fuel line is collapsing.


It could be electrical. I don't think it's a weak spark.... but the CDI or coil could be turning off. (possible overheat situation in the electronics) But, since it runs well at 6500... I don't think that's the prob.

If it was my boat... I would take the carbs off again. I know it's not a fun job... but it's not that bad. When you transition from about 3/4 throttle to full... you are relying completely on the high jet. Also, the internal vacuum will drop. So... I would double check the pop-off in that carb. I would also make sure the high speed needle isn't leaking around the O-ring. (put a little grease around it) And finally... make sure there are no internal leaks. (bad gasket, or seals)

Last thoughts.... do you have the stock air box on still? When you did the cleaning, did you change the springs in the carbs, when you cleaned them?

 

[racerxxx]

Since it's a twin with separate fuel pumps, swap them and see if the problem switches engines.

Sent from my SGH-T889 using Tapatalk 2

 

[Captian_17]

I'm gonna take the carbs apart and check everything in there is working right. Thanks for the ideas.

I am still running the stock airbox. I completely rebuilt and replaced everything in the carbs, so it was more than just a cleaning. Everything was replaced with stock OEM parts, including the springs. Everything has worked great with no problems at all until this just started happening.

 

[jhjesse]

If I were a betting man, I would put my money on the fuel pumps. Chances are good the fuel pumps are starting to wear out and need replacing.

 

[Captian_17]

Ok, I pulled the carbs and cleaned them up, but they look as good as when I rebuilt them except for a little crud in the fuel filters. Verified the pop off pressure and the checked the high speed needle. Then I moved onto the fuel pump which is full of stuff, so I am guessing this is where my issue lies. I've looked around online and can't seem to find a rebuild kit of any kind. Are the fuel pumps rebuildable or is this simply a replacement issue? Any ideas wherre I can find one?

Feeling like I am making some progress...

 

[jhjesse]

Ok, I pulled the carbs and cleaned them up, but they look as good as when I rebuilt them except for a little crud in the fuel filters. Verified the pop off pressure and the checked the high speed needle. Then I moved onto the fuel pump which is full of stuff, so I am guessing this is where my issue lies. I've looked around online and can't seem to find a rebuild kit of any kind. Are the fuel pumps rebuildable or is this simply a replacement issue? Any ideas wherre I can find one?

Feeling like I am making some progress...

No kits available and the pumps are not made anymore. A couple of folks here on the forum have found dealers with new old stock.
You can go with new mikuni high volume fuel pumps, but you will have to do some re-plumbing.

Check out this thread:
http://www.seadooforum.com/showthread.php?63577-fuel-pumps

 

[Captian_17]

Looks like I am going to go ahead and replace both with the high flow pumps you linked to in the thread and see if that solves the problem. Thanks for the advice.

 

[kilgorekb]

Looks like I am going to go ahead and replace both with the high flow pumps you linked to in the thread and see if that solves the problem. Thanks for the advice.

Captain_17,

Any updates on this? My 99 Challenger 1800 did the same thing this weekend, and I remembered looking at this thread. Like you, my carbs are freshly rebuilt. I've just had the boat for 1 season, and this was the first time I held the throttle wide open for longer than a few seconds. And also like you, it was around the 1 -2 minute point when the engine flatlined. It cranked right back up, and I ran 6500 all day just fine.

 

[Captian_17]

Yup, replaced both fuel pumps and it immediately fixed the problem. And it was super easy to do. Thanks for all the help everyone.