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Misfiring

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Goingtobeapilot

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Ok so I had the top end rebuilt on my 96 rotax 787 motor and I put it all back together yesterday. Well today I started it up for the first time and it sounds great..... Except for the occasional misfire :banghead: So now I need to diagnose this. I'm wondering if maybe it could be fouled plugs because it doesn't always want to rev up right away when you tap the gas... Sometimes it bogs down just a hair. But I also know that the previous owner said that he would mix some oil in the gas, as well as in the oil reservoir. So I'm also thinking that maybe the mixture might be just a little to far off considering that there is quite a great deal of smoke when I start it up. Anybody have any ideas???? Thanks! -Dave-
 
Goingtobeapilot said:
Ok so I had the top end rebuilt on my 96 rotax 787 motor and I put it all back together yesterday. Well today I started it up for the first time and it sounds great..... Except for the occasional misfire :banghead: So now I need to diagnose this. I'm wondering if maybe it could be fouled plugs because it doesn't always want to rev up right away when you tap the gas... Sometimes it bogs down just a hair. But I also know that the previous owner said that he would mix some oil in the gas, as well as in the oil reservoir. So I'm also thinking that maybe the mixture might be just a little to far off considering that there is quite a great deal of smoke when I start it up. Anybody have any ideas???? Thanks! -Dave-
Click to expand...

Is it on pre mix or injection?
Change plugs if they are fouled and see if it runs better.
Remember new top ends require extra oil 50:1

Did you or PO mess with rotary timing valve.
Its the half moon metal piece between ports on the case and intake?
 
So how would the rotary valve timing be checked/ adjusted? And ok I'll try some new plugs and maybe a little richer gas mixture... We'll see if maybe I can't just get this darn thing fixed
 
Yes it did run before I had the top end redone.. and in fact I really don't remember it misfiring in the few times I had it started before I disassembled the top end. Does that hint to anything? Would the rotary valve timing get messed up on its own without me touching it?
 
Goingtobeapilot said:
Yes it did run before I had the top end redone.. and in fact I really don't remember it misfiring in the few times I had it started before I disassembled the top end. Does that hint to anything? Would the rotary valve timing get messed up on its own without me touching it?
Click to expand...

It helps to determine whether it was moved to be out of timing.
You would need to take off intake and set MAG piston to TDC.
Put degree wheel and see if it's at the 65 degrees.
 
That really stinks that I have to take everything off of the side of the engine to get to it again. But basically what I'm getting out of what you are saying is that if it wasn't adjusted by a person then it won't just get messed up on its own? I'll go check the plugs and fuel really quick right now before I jump back into another big weekend project.
 
Goingtobeapilot said:
That really stinks that I have to take everything off of the side of the engine to get to it again. But basically what I'm getting out of what you are saying is that if it wasn't adjusted by a person then it won't just get messed up on its own? I'll go check the plugs and fuel really quick right now before I jump back into another big weekend project.
Click to expand...

yup :thumbsup:

Unless something more catastrophic happened like RV gear inside engine(brass gear went bad) or wooddruff key on crank is missing to cause backfires....
 
Well I just ran down to the garage and siphoned out 2 gallons of gas which was grey like iced tea. PLUS is has an oil reservoir that injects oil. So I'm thinking that my mixture is off pretty bad... Also, the plugs don't look to amazing so I'm going to go pick up some new ones and see if maybe either of these things are my problem. Wish me luck! -Dave- btw thanks for all of the help with this!!
 
twist the spark plug boots off and trim the plug wires back 1/4" while you are changing the spark plugs
 
:thumbsup::DI would start with the basics, if you spent all that money on a new top end. Drain all that old gas out of the tank, clean the filters, and at least buy a new set of spark plugs. Good spark and clean fuel make a real difference.
 
New spark plugs and some clean fuel did the trick. She runs like a charm! One last question though... Does the 1996 GSX have any way of pumping water out of the haul? I'm a little nervous about taking it out in the open water for the first time :blush: I ran it with the hose and there was a little water leaking from the exhaust where it connects to itself at the highest point in the compartment. I tightened the bolts up and now it doesn't leak, however there are a couple of tiny bubbles that still sneak out every few mins... I know its probably fine but it still makes me nervous. I'm starting to get excited for the first ride! -Dave-
 
there should be 2 bailers in the bottom of the hull held down by clips. they have a bunch of little holes in the bottom, you might want to make sure they aren't plugged. Also make sure the lines connected to the bailers are ziptied to the top of the hull otherwise water will backflow into the hull. The bailers work off of suction created by the venturi.
 
Last edited by a moderator:
correct. alot of guys on here will tell you to add an electric pump because the bailers can only handle limited volume. You can install a water activated pump as well.
 
bigJake said:
there should be 2 bailers in the bottom of the hull held down by clips. they have a bunch of little holes in the bottom, you might want to make sure they aren't plugged. Also make sure the lines connected to the bailers are ziptied to the top of the hull otherwise water will backflow into the hull. The bailers work off of suction created by the venturi.
Click to expand...

You will need to look from the rear of ski into the nozzel for two "tooth" looking tubes at 11 & 1 o'clock. These need to be in the thrust
water for the siphon system to be fully effective.
Seadoo 140MM jet-pump venturi bailer tubes - dual taper


Newer style tube '96-up white/clear Pt #271000464 lenghth 3 1/8" 80MM

Old School style '88-'95 black Pt # 293700017 lenghth 1 7/8" 48MM

I get these from RIVA.

Bills86e
 
Hi David,

Glad to hear you've got everything going on your ski. You were asking about bilge pumps, here's what I did. It's a Rule 500 PWC pump, auto sensing, I added a manual switch and also I use a battery maintainer when I leave the ski in the water. I put the discharge at the rear of the ski, you don't need to do this, it can discharge under the water line as long as the hose is looped above. Kinda like the bailers.

Lou
 

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