96 xp 787 misfiring after warm

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doomann88

doomann88

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Ski runs pretty well for about 10-15 mins then slowly begins misfiring till it doesn't want to rev enough to plane out. When cold has a small hesitation at WOT going from 45-50 mph before things go downhill.

Carbs rebuilt with oem mikuni parts
New lines, installed correctly - most testing was done running directly off reserve pickup
Tank pulled and cleaned
Front cover removed verified pickup is looking good, no shavings, no cut wires
Connector pins clean and in place (stator cover and rear box)
No blown fuses
New coil and plug wires and plus
New rectifier, no ac current found at batt
Stator tests correctly
Charging is good at 13.5 volts
Engine has 150 hours 140 & 150 comp
RV set correctly no play in it
Cooling is good, pisser is peeing
No exhaust leaks
Rave valves cleaned and writing correctly
No weird shorts in writing harness
All grounds good
Tried known good cdi and mpem from another ski, same symptom

I have nothing else to give on this one right now, please help!
 
Tell me the worst case scenarios, nothing I can't handle just don't know where to go next? I haven't really dug into the tank vents but it doesn't clear up when I pull the gas cap off. Is it somehow going lean or something with heat or losing compression? Carb backfire/misfire seems to come evenly from both cylinders when I have the flame arrestor off. Also the ski is 100% oem
 
Check the pulse line going to the Mag Carb.

Also pressure test the fuel lines.

Just thinking you could be sucking air somewhere.
 
rvaughn704 said:
Check the pulse line going to the Mag Carb.

Also pressure test the fuel lines.

Just thinking you could be sucking air somewhere.
Click to expand...

X2 on pulse line. When I replaced the fuel lines my pulse line had a slight kink in it. Didn't see it at first. Drove me nuts until I found it. Shortened the line and drew the kink out of it. Runs like a champ.
Hopefully yours is something simple.

Also maybe check the O ring on the water seperator.
 
Yea the pulse line has always been a little loose on the block side connection. I don't have super high hopes but I will most certainly give it a try.
 
Where is this pulse line located. I'm at the lake now and it runs like a champ and will stall out and the kick back in and run again maybe this the problem
 
The pulse line is located on the Mag Carb. That is the frt Carb. It is a little black line that goes from the carb to the side of the engine. It is a short line.
 
It's kinda funny it will top out at 3000rpm and then it will cut loose and run great then when u kill it it does it all over again
 
I read your long list of repairs...but i didn't see a fresh set of plugs. I have seen plugs that limit to 3k rpm. then work fine, then do the same thing again. sometimes barely running. (normally its one plug acting up, but i always replace in pairs) just had this happen on my speedster. And i've had it happen to a couple outboards before too.

Replace the pulse line IMO. start fresh. And run a piece of fuel line with an inline paper filter straight to the fuel baffle. Bypass everything that isn't essential to the fuel system then try it.
 
Ok. My son in law cut the red wire and it ran fine all day. Do now it's the rectifier.. there goes another $100...lol
 
For the original poster- I agree with the others. The fuel system requires everything to be perfect and the pump working well. You say most of the testing has been done off the reserve pickup. I assume you are going directly to the fuel pump and not through the water separator? Perhaps the fuel pump has an issue. Leaking vacuum when it is warm? Is the battery dying and eventually starts a low voltage miss? Ground cables vibrating loose? Did you open the mag cover and look at the stator? Perhaps it is loose?

For sure let us know what it was when you find it. Good luck. It must be something simple now.
 
Only a couple of hours I think. The battery will slowly die. You are now running a "total loss" system.
 
I've had seat time in it 20 mins set a time lol... but the new pulse line did make a difference. Idle is much better and popping went away, however it still just loses its will to have any power once it's warm. Found a loaner set of carbs to borrow so ill go from there when I get a chance to try it out.
 
have you checked the vent line to the fuel tank ? if the tank is not venting it will slowly starve the motor of fuel. just a thought

skipped right over post #2 so scratch that idea
 
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-Where did you get the new rectifier from? Do you know of a friend or do you have an extra good known working ski to borrow one from?

-Disconnect the red wire at rectifier and take it out again on your next voyage. See what happens. Ive seen weirder things! It could be a bad new rectifier. Also I know you said you checked your grounds in original post, but what is the continuity reading from battery neg. wire connection to starter ground connection?

-Rob
 
im getting a very low resistance from the starter ground to the batt, and even have an additional ground going from the top of the head to the neg batt terminal.

i bought two new rectifiers (china ones) and same result with either one. red wire test has no effect on any of the three different rectifiers ive used.
 
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