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Discussion Starter #1
hey guys,
I'm new to the site but have read many posts, so here is my story. I have 2 skis:
1998 xl 760
1998 xl 1200

I bought them 6 months ago from florida and have riden them 3 times which ran fine. they are both oil injected.

first for the 760:
ok, it shut off on the 4th ride 10 minutes out, so I found a broken hose to the air intake area under the Riva single carb, fixed that and still had no crank over. It started, then ran like crap. towed it home. pulled the head and cyl and found front piston broken around the edges, kinda of minor but melted the rings and light scoring. I found out that its a sbt motor. I called a shop called "Full Bore Online" and the guy stated I needed to resleeve them since the piston has 1.00 stamped on it. about $450 will get the sleeves, new platinum pistons, all gaskets etc. Any ideas on that option? As far as the crank, it doesnt appear to have any pieces in there, appears clean but what should i do to be sure. I would rather do it once. OH, also before it broke down, I found a crack in the exhaust hose in the rear tub. sealed that, not sure if it contributed, example, blockage? anyways.

Now for the 1200
When i bought it, it was hard to start cold. when it was warmed up, it ran fine. about 130 in all 3 cyl's. I'm not sure if the carbs were rebuilt or when. the waterflow out the side is weak, but its a stream (should i worry?) so i trailered it 3 miles to home and attempted to flush. rpms at 4000, so i shut down, restart then 5000, shut and start then a full throttle run away, got it to shut off within 20 seconds with pulling the throttle (BLOWN MOTOR FLASHING IN MY HEAD). I havent touched it since. I know this is a lot but any ideas would be a help. Im not sure about the age of the 1200 motor or bore sizes. Should I worry about run away IF i decide to ride the 1200? Insurance incase I have to bail off? thanks and safe riding!!
 

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No, is it premix? I would say its just leaned out on the 760. When you rebuild the engine, you should pull the crankcase apart, that will give you a good look at the crank and seals are only cheap if it is good. And you will have to resleeve the barrels because it is 1.00 O/S. You should always check the carbs when you rebuild it. Check all three of the little plastic valves in the carbs (make sure theres no holes and they are sealing). That exhaust hose wouldnt contribute to blowing the motor but I would replace it. I know the hose your talking about and they are a regular problem on those.

The 1200 is leaning out. You should pull off the carbs and check those plastic valves and give them a good clean. Also an extra 1/4 of a turn on the low speed mixture screws will help.
 

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Discussion Starter #3
ok, took the cyl and piston to a guy locally and they measured the piston and calculated it as standard size although the piston is stamped 64x and 1.00 on it. they said take to machine shop for inspection. otherwise i was going to send out to have resleeved and a new kit purchased to match the size. i will look over the crank but seems good. as for the 1200, im going to play with it tomorrow. is there a simple way to get better flow on the water that shoots out the side? i was told to check the diaphrams in the carbs. you mentioned 1/4 turn, is that in or out. i have a manual, should i reset to the book? both are oil injected and running 89 octane gas. thanks for the help! ALSO ANY RECOMMENDED SHOP FOR THE RESLEEVE?
 

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Im in Australia so i cant recommend any shops. 1/4 of a turn out which richens it up. The water stream out the side is usually not high pressure on the right hand side. Should spray out but not nearly as much as the left hand side. Pretty normal I say. As long as its not overheating. Yes, check the diaphrams, the most important part of the carbs is the check valves in the fuel pump. They can cause the engine to run lean eventhough you may feel the engine is performing normal. Also, they must be clean. I would say your local mech is wrong. 64X means it is a genuine yamaha piston, and if it has 1.00 on it then i would believe it.
 

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Discussion Starter #5
ok, working on the 760 now. pulled the bottom end and inspected, bottom looks ok, but front rod looks darker (overheated?) instead of brown like the other one. to the eye looks straight. both rods have slight play left to right. front cyl has almost no oil and rear has a bunch. so, i'm trying to determine why failure. it has a Riva single carb and I' m not sure of one hose. It connects to "pulse" on the carb and connects to the top of the block just in front of the reeds (top view), on the front cyl. the back cyl has rubber block off. i'm opting either a rebuilt motor for 745. or top end, just dont want to do it twice.
 

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Discussion Starter #6
looked in a manual and its the "pulse" line that split when motor failed. can anyone explain how that "pulse" line works? thanks!!!!
 

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pulse line pulses aas it suggests the carb fuel pump to pump the fueal into the carb. Uses the suction of the crankcase where to drive the fuel pump to draw fuel through the lines and through the carb. Can cause damage by making the cylinder run lean.
 

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Discussion Starter #8
sounds simple. thanks. since I have one riva carb set up, would there be a reason there is oil in the rear cyl and almost none in the front (which blew). also since the engine is out, i plan to check the rest of the hull. should i be able to turn the shaft by hand? If so, I cant. im going to work on the 1200 on monday, so if i run into trouble, i will post picks if possible and ask. again, thanks for the info.
 

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The shaft may be a bit tight if the impeller and liner are tight. Only a problem if it doesn't turn over while cranking the engine. And you can check the bearings in the pump vein unit and short shaft housing by pulling it apart. If it only has one line of oil feeding the oil to a single carb, the front would have leaned out due to a fuel issue masking the oil in there and making it look all grey.
 

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Discussion Starter #10
ok. im working on the 1200 and its killing me. checked the compression, its actually just over 100 for each one. installed new plugs. reminder, this is the one that had a runaway a few weeks ago. my problem is very low idle even boggs out. started today and had to feather throttle to keep running. so reset the low speed screw to 1-1/4. too low, shakes like crazy. so set to 3/4, still same. set to 1-1/2, and ran better but still bogged out. fuel filter looks ok. has good suction at each carb. any ideas besides rebuilding? the spark plugs have some oil and gas on them.
 

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you can keep fluffing around but it will be the carbs and fuel pump. Take them off and clean them both and the problem will be fixed. No additives or shortcuts will fix it.
 
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