loss of power/rpm

[Scubadave16]

1996 Sea Doo Challenger 787. So after replacing my wear ring (OK, the shop did it). my boat ran OK for a while, but this week after sitting a couple weeks I took it out and it started and idled just fine all through the marina. When I opened up full throttle out in the lake it revved up for about 3-4 seconds, then hiccuped, backfired and wouldn't go above about 3500rpm. so idled back. engine "pops" once in a while all the way back. So I checked the fuel filter- clean. sprayed some sea foam in the carbs- nothing. no matter what I do it doesnt rev up and it backfires quite a bit when I open the throttle. I even sprayed sea foam directly into the fuel filter- nothing except backfiring. with the throttle wide open it runs maybe 3500rpm. every once in a while it almost sounds like it will rev up to full RPM, but then backfires and goes into a fairly smooth low rpm. nice water stream. plugs a bit dirty, but nothing really scary. Like i said, the shop had it in June and it was running fine for them, so this is something new. What should I check next?

 

[Dr Honda]

First... spraying anything into the carbs, and filter wont do anything. In fact... it could damage the rubber parts of the carbs. Not to mention, it's a solvent, and displaces oil. since this is a 2-stroke... and needs a very thin layer of oil to survive... using a spray product can literally KILL the engine. SO... if the carbs or any other part is suspect... then they need removed, and peoperly serviced.


Second... with your description (random backfire) then my finger is pointed directly at the pickup coil for the ignition. Pull the MAG cover, and I'm sure you will find it sitting on a broken mount.

 

[Scubadave16]

Is pulling the mag cover something an untrained person can do while the Boat is in the water? Seems pretty buried down in front of the engine.

 

[Scubadave16]

Yeah I watched a couple you tube videos and they all show the flywheel and magneto assembly being removed with the engine out of the boat. I don’t see how that could be done as it is now. Even if I could get a puller in there (assuming I had one which I don’t) how would you keep the engine from turning when you remove the flywheel? One guy filled the cylinder with trimmer line but that seems petty odd to me. Seriously is this something I should even try? Taking the boat in to the shop means losing the rest of the summer so not a good option. I suppose option c is just to walk away. This boat has been horrible for the 4 years I have owned it. It has spent far more time in the shop than on the water.

 

[Dr Honda]

You don't need a puller. The 800 engine has an inverted flywheel. SO... removing the cover will let you see all the parts.

I don't recommend working on any boat in the water... but it's not impossible. Not to mention... the boat you have isn't rated to be left in the water. The driveshaft seals leak by design, and you may find it sunk.

Lastly... if you can't work on it yourself... then you have no reason to own a +20 year old boat. (you wouldn't expect a 20 year old car to run perfect, would you?) Shops are dumb, and will cost you more than the boat is worth... and they will generally just guess at problems, and in turn, cost you more $$$. Sell it... but a new boat with a warranty.

 

[Scubadave16]

OK. interesting. kinda the whole point of having the small boat is to keep it in the marina so I can take it out in short notice. There are probably 15 of those small boats in the marina now. but anyway i don't disagree with your statement about working on it yourself. I have spent far more in the shop than I paid for the boat originally. However, buying a new one is completely out of the question (and budget).

So back to the original problem... if the pick up coil is the issue, would that result in the low RPM? I can see the intermittent backfiring, but not the rpm/loss of power. of course I am no expert, but I thought that it was a fuel flow and/or carb issue. a buddy and I took the carbs out last year and went through them and they were spotless. doesnt mean some crud didn't break loose and plug something in the mean time, though, which was my thought using the sea foam.

Oh, I did swap out spark plugs, too. no difference.

guess I will try to pull the cover and hopefully not drop any parts down below the engine.

as always, I appreciate honest information even if I don't like it! Thanks!

 

[Dr Honda]

Not a prob... I like to help when I can... and after reading my last post... it was kind of negative. (didn't mean it that way)

Anyway... yes, the RPM could be low if it's not firing all the time. Generally the only thing that makes these engines backfire, is spark at the wrong time since they have a rotary valve. If that valve stopped spinning... it wouldn't run at all... and if it was just out of time... it would be harder than heck to get it started.

It's kind of an known issue with the 800 engine. The pickup mounts break, and move around. In turn, causing all kinds of issues.