787 Backfire \ sputter - Video - Need help please

[night34606]

Ok I have a 96 GTX with a 787 ski I have been getting back up and going. I took the ski out on the water for a test run a week ago and went fine except 2 times I was flying along and it died - I had done a seafoam treatment so assumed something hit the carbs since it fired back up and went on. Went out this weekend and went OK for a few minutes then she stopped. I was able to get her limped back to dock idle (was not far out at all). It sounded like I was backfiring under me but when I got to the dock I was able to take a video. At the end its not me turning the ski off I actually thumb the gas and it dies. Trying to get an idea - plugs are new, I checked compression awhile ago but can recheck. I am thinking fuel delivery but would like input from some vets on here.

[video=youtube;vQkMS0ryW2o]https://www.youtube.com/watch?v=vQkMS0ryW2o[/video]

 

[AdamXP800]

That sounds wayyyy worse than any fuel delivery issue that ive ever heard.

 

[kicker]

:agree:
Dont run it until you do a compression check, that thing sound very loose to me, hopefully its just the recording. If there is something that is starting to let go, you dont want to cause more damage.

You can also take the plugs out and look into the holes with a flashlight and see if there is any obvious damage in there.

 

[Bnelson]

:agree:
Dont run it until you do a compression check, that thing sound very loose to me, hopefully its just the recording. If there is something that is starting to let go, you dont want to cause more damage.

You can also take the plugs out and look into the holes with a flashlight and see if there is any obvious damage in there.

+1 on that.... Something major is going on in there

 

[night34606]

I'm going to do a compression check tomorrow but can someone explain loose... I'm not heading any crank or for knocking if that's what ur referring to. The engine does sound different on the video but it sounds normal in life minus that choke every couple of seconds. Watch again and when I pan to the water u can see the sputter and the sound right when that happens


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[Bnelson]

To me it's that tap tap tap tap sound that I'm referring to... For me it's hard to explain loose, loose is just loose lol.... Sounds almost like valves rattling in a car or like a slight piston slap... It definitely has some sort of carb issue, (hence the backfire) but I think your issues are worse than just a carb problem...Here is a link to the same motor running in a different ski (XP).... If you will listen to the way that motor sounds, they are night and day http://m.youtube.com/watch?v=_30ey7k1CO4

 

[night34606]

Ok - I did a compression test and sure enough one cylinder is practically no compression at all. Now I took and dropped a teaspoon of 30 weight oil in and redid the test and compression did come up about 25 psi. If I recall my redneck mechanic basics that should mean its not a rod or something but more likely a ring correct?

 

[KayakNFly]

Time for a full rebuild. Top and bottom. Don't just do the top because the bottom won't last long with a new top. I would bet you still have gray fuel lines on there also. Your carb probably got clogged from the old lines and ran lean on one cylinder. So change all the lines and rebuild the carbs while the motor is being rebuilt.

 

[night34606]

So the answer is rebuild everything. That is easy to say vs actually execute. At that point I minus well part this one out on ebay and buy a different ski. Just in parts you talking about throwing over 1000 bucks into a ski that down where I am can be purchased for 800 - 1500 all day long.

 

[Bnelson]

And that may be what needs to happen.... But there are times I disagree with a full rebuild. If there is no damage to the bottom end you could possibly pull the jugs and have them bored and install new pistons and rings... I've seen many skis run a long time with just new top end jobs... All depends on the tightness of your connecting rods and condition of the bearings... A new top end can be redone for around $300 bucks depending. Again there are many variables to this.. Any clue how many hours are on the current crank?

 

[night34606]

I dont know how many hours were on it. When I got the ski it was a pair. One of the skis had low compression this one was good. I pulled that ski apart and parted but I still have the engine and carbs. This ski was the one that was not registered I believe because the gauges were not working and some other minor electrical - well it obviously sat for a long time since mice ate the wiring up. So I moved the gauges from the low compression ski over and repaired wiring. Cleaned out the fuel and changed the fuel lines. Ski ran good and showed good compression. I have maybe 10 hours on it max and then the this.

I dont have a lot of money into this considering I got both GTXs and a really nice trailer for 1200 bucks. I dont mind spending some money but no point sinking a lot of cash into it when I can sell both motors, working guages, and make a profit or at minim break even and still be ahead with the badass trailer then spend the cash on another ski.

 

[Bnelson]

It sounds like you already have the right plan together.... Sell all the parts and put towards another ski.

 

[eddie708]

seafoam is not going to fix fuel delivery problems. if a 2 stroke cuts out when riding, stop riding it. when they run lean there is no lubrication.

 

[kicker]

So the answer is rebuild everything. That is easy to say vs actually execute. At that point I minus well part this one out on ebay and buy a different ski. Just in parts you talking about throwing over 1000 bucks into a ski that down where I am can be purchased for 800 - 1500 all day long.

I hear what your saying and it makes sense for the most part. The only problem I see is that an $800-1500 ski can grenade the next day as well, only cause you dont know the history or how well the ski was taken care of. It always seems to be a roll of the dice with these older skis.

That being said, if you are parting it out, I would be interested in your core if it is a rebuild-able core.