loss of power - Daytona 640

[JClark]

Hi Guys. I just got my 94 Daytona back on the water for the 1st time this season. I'm having an issue w/ power loss. She'll run perfectly for 20-30 secs at WOT, then begin depowering. If I time it right, I can cyclicly release the throttle for a few seconds and get back on it w/ no prob. If it depowers, I must either wait at idle for 15-20 secs, or kill and restart the engine to get back WOT power. I'm 100% convinced that the issue is ignition related, but not sure what to look for. I know automotive ignition, not big grey box ignition! It "feels" like a capacitor that isn't holding enough juice to sustain high rpm fire, and must be recharged frequently. [img]graemlins/cwm3.gif[/img] Any suggestions? Thanks.

[Bryan Glynn]

Uhhhh.....it sounds to me like a fuel flow problem...I would be checking your fuel supply, possibly carb pumps. You may be running slightly lean at WOT and coming down in throttle position is giving you fuel back - test with your choke or primer - hold it and when it starts dropping choke or prime it real quick - see if it kicks back up for a second.

[JClark]

From the symptoms, I can't see how fuel supply could be a problem. Could be, just acts more like an ignition issue. I can't test with the choke, as the choke plate has been removed (the choke plate shaft broke and I decided to simply remove it and plug the holes).
When the symptoms start, nothing related to throttle position helps (pumping included). If I kill and restart immediately, the symptoms go away, but for a shorter period than if I wait through it. Like I said, I can prevent it from happening all together if I back off of full throttle for a couple of moments every 15-20 secs. Is there a component of the ignition (perhaps something inside the brain box) that could fail in this manner? I'll be pulling the box soon to look for anyhting obvious. Thanks again, Justin.

[ May 07, 2002, 01:07 PM: Message edited by: JClark ]

[Bryan Glynn]

Try running with your fuel tank vent check valve off, or carefully with your fuel fill cap open. You could be developing a vacuum if the valve is broken.

[JClark]

Will do. Thanks. I hope it is something as simple as the atmospheric vent!
Any idea why killing and restarting the engine clears up the symptoms? I can kill it at full plane as soon as I feel it losing power, and restart it before I have fully lost the plane and it runs strong again.
I have to commend your site. It is definitley one of the most insiteful I have come across. I "almost" can't wait to need a new engine!

[Bryan Glynn]

Hmmm...well, that doesn't sound like a tank vent...it takes some time for the pressure to equalize. Unless the symtom returns almost immediately. If it's something that *resets*, and the duration is always the same, then we might look elsewhere.

[JClark]

If I use the kill/restart method to overcome, the engine operates normally for a shorter period than if I wait. 15-20 secs vs 20-30.
Can I safely test WOT at home for these durations (<1min) running water through the system? I only ask b/c my nearest ski friendly water is an hour away.

[Bryan Glynn]

No, that will not simulate any of the conditions neeed - no load on the engine, you will hit the rev limiter with just 5% throttle, and you will not draw enough fuel to create a vaccuum.

If it's the tank vent, you would see it happen sooner with a full tank than a near emtpy one - do you notice any difference?

[ May 07, 2002, 02:09 PM: Message edited by: Bryan Glynn ]

[JClark]

Good point about the fuel level. No, there was no difference. When I first launched it, I had @ 1/4 tank, ran till nearly empty, and refueled. I noticed no difference in the duration between any of those levels.
I still think it is something in the ignition system. Perhaps something has become very heat sensitive or something that should have capacitance is not functioning properly, or something that shouldn't have capacitance is acting like a capacitor. I'm pretty much in the dark without atleast opening the brain box to see what components are housed within. I may have to break down and get a service manual on this one (I can handle most situations w/o one). Thanks for your time and attention!

[Bryan Glynn]

Hmmm....well, I don't know about a T640, but some other skis have occasional problems with the stator coils getting heat-soaked...

[JClark]

I'll definitely post when I get it resolved. I'm leaning toward something getting heat soaked. I've been told that the ignition will go into "limp home" mode if the temp sensor reads too high, and is reset if you kill the ignition. This would explain why idling for a period - or killing and resarting - clear the symptoms, and for different lengths of time. What I don't know is why something would be getting too hot. The water system is functioning properly. I haven't had another opportunity to hit the water, but I should this weekend.

[russthemuss]

im interested to find out what it was!!
My moneys on the fuel problem not the electic's.CDI either works or dosn't from my expierience. Impulse diaphram? sounds like its starving.

[JClark]

Finally found the problem. A month ago, the bracket mounting the tuned pipe to the block sheared in two. I didn't notice it right away, and after two hours of riding the load imposed on the main pipe-to-manifold connection sheared three of the five bolts. I pulled the exhaust, had the sheared bolts removed, fabricated a steel replacement bracket and reassembled. In the process, I checked fluid flow through the main pipe. It was almost zero. Something was blocking the outlet port. Since this is where the exhaust temp sensor is located, it was reading high really quickly and putting the ski into "limp" mode. I blew out the obstruction before reassembly, and she ran beautifully all day long on the last trip out. Thanks for the input guys.

[dank]

I had the same problem this spring with my wifes ski. Sorry I missed you original post, could have saved you some time. Also woked on one where the wires leading to the sensor melted on the pipe and caused it to run in limp mode only. Keep an eye out for this also.