1998 Yamaha 1200 XL Fuel Issue/Lean Runaway - PWC Forum: The best hang-out for Personal WaterCraft enthusiasts
 
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post #1 of 7 (permalink) Old 06-05-2017, 12:00 AM Thread Starter
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1998 Yamaha 1200 XL Fuel Issue/Lean Runaway

Need help. I have a 1998 Yamaha XL 1200. I got it from somebody who just gave it away(said it was taking up space) it sat for a few years. He did carb rebuilds and broke the throttle cable. I replaced the throttle cable. Buttoned everything back up, and attempted to start the ski. It Just cranked wouldn't turn over. I took out the plugs and tested for spark all good. Dropped some pre mix gas into the cylinders. Then started it. It Ran for a few seconds then cut out. I reset all the carburetors to their factory settings. I primed the fuel lines with low psi into the return on the tank until it was flowing bubble free on the carb end. I Buttoned it all back up again and started it and it ran for about 10 seconds then I shut it off to take it outside and put water on. Once I got it outside I noticed the number 2 carb pump was leaking fuel, as well as the fuel petcock valve was leaking. I removed both and dissembled them cleaned them and put it back together. I re primed the lines and then started it. The ski started, and then I cut it off to get the water ready again. Once I started it again I got a lean runaway condition, the ski wouldn't shut off until the fuel line was pulled off the carb. Posting to see if anybody has ideas/similarities? I'm assuming it's a carb issue? Crank seal is another possibility, hopefully not the issue. I've gone through all the fuel lines theres no tears or rips. I also double checked the throttle position to make sure it wasn't sticking. There's a little more than 1.5mm clearance at resting position between the valve and the wall in the carbs. I have not done a leak test yet. Hoping it won't be a difficult fix. Open to suggestions/ideas.
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post #2 of 7 (permalink) Old 06-05-2017, 06:36 AM
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Should be some slack in the throttle cable. Did you try and adjust the idle lower ? Make sure the manifold bolts are tight at the reeds.
What did you set the high and low speed screws to ? Did you check the pop off and make sure the needles and seats were clean ?
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post #3 of 7 (permalink) Old 06-05-2017, 01:08 PM Thread Starter
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The throttle cable does have some slack yes. And for adjusting the idle I had been playing with it up and down initially it was to low and wouldn't stay running unless the throttle was slighty open and then it ended with the lean runaway. I have not looked at the other carbs yet, I'm going to disassemble them this week and clean them all out and do a pop off pressure test. The settings I used were the ones in the repair manual: #1 & 3 High 3/4 +/- 1/4 #2 1 +/-1/4 turns out, and for the low 1 +/- 1/4 turns out.
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post #4 of 7 (permalink) Old 06-06-2017, 06:32 AM
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I would check and make sure the carbs are still synced, and make sure the fuel pump diaphragm and pulse diaphragm are in good shape and are not the woven material. A faulty fuel pump, or high pop off will make a lean low speed condition.
It is possible that the crank seals are bad and pulling air. Only way to find that out is to do a pressure check on the engine.

Last edited by rodsatheart; 06-06-2017 at 06:38 AM.
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post #5 of 7 (permalink) Old 06-10-2017, 11:39 PM Thread Starter
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Finally got the ole ski in the water today. After disassembling the carbs fully cleaning them, re-adjusting the H&L screws, synchronizing the throttle valves, and resetting the idle screw. The things that I found that contributed to the runaway lean idle: unsynchronized throttle valves, idle screw a tad too far open, and a faulty fuel pump on the number 2 carburetor.
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post #6 of 7 (permalink) Old 06-11-2017, 08:06 AM
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Cool deal. I assume it ran good ? I would say the biggest contributor was the fuel pump. They are weird sometimes. I have had them not supply enough up to 1/4 throttle, but be good in mid and high rpm. That from a inferior diaphragm material. Took a long time to diagnose, and finally just decided to stick a old diaphragm back in to see. Glad you went the extra step to sync the carbs. Most don't, and can affect idle and performance.
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post #7 of 7 (permalink) Old 06-11-2017, 08:42 AM
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did you do the fuel return mod to the carbs while they were off? a very good mod that makes a big difference if one pump becomes weak or quits. found it in the how to's on another forum will post should be put in how to's here as well Carburetor Drilled Return Pressure Balancing Modification GPR, XLT, GP, SUV, etc.

Rod can you sticky this or put in how to's

I did this to my gp800R as I was rebuilding mainly because the return port was corroded shut and I couldn't get it clear. but after reading it I determined it's for the better.
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