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  1. #1

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    Pressure tested XL1200 are these numbers good? Now what?

    Little background here to help understand what’s going on. Bought the jet ski last year right off the bad had a lean runaway. Took the engine out, talked to a local jet ski mechanic who told me 90% of the time it the carbs. Took the carbs to him he rebuilt the carbs and first time out came back to flush it out and the lean runaway was still there. So update to this year, I just took the engine out and found a few posts here on how to do a pressure test. So this is what I did, used shower pan liner to cover the carb base gasket and exhaust base gasket. Looking at the carburetor side of the engine I took the far left and middle pulse lines and joined them together, I took the far right pulse line (towards front of engine) and this is where I pumped the air into the engine. Also connected the exhaust header waterlines to each other. Hopefully all these terms are correct. Used my Harley Davidson suspension pump to add air to the pulse line via the Schrader valve. Did three tests. First test pumped to 8 lbs came back 15 mins later and found it dropped between the 6 and 8 lb marks so about a pound loss. Second test 10 lbs waited 15 mins dropped between the 8 and 10 lb mark again roughly a pound or so. Third test pumped in 10 lbs according to my HD suspension gauge also checked it with my monkey grip digital tire gauge which had the reading at 14lbs not sure why the difference. But after 15 mins when I checked it was between the 8 and 10 lb mark on the HD gauge and it was at 13.5 on the monkey grip gauge. Also during the last test I sprayed the gaskets with dish soap and water (twice) and did not see any bubbles from the gaskets around heads and jugs nor did I hear air escaping. So if everything was hooked up right and with a loss of a pound or so it appears the gaskets are good? Yes/No? Now what, back to the carbs to make sure the guy did them right? Continue to look for leaks? Sorry so long just trying to provide as much info as I can to get the best suggestions. Thanks.


  2. #2
    MR-1 X 2's Avatar
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    What year xl1200?

    If carbs. are assembled correctly they normally don't cause air leaks....only gasket, seals or cracks in castings create the problems that are usually not known about until Kaboom time!

    It sounds like you are on the right track but photos would be helpful.

  3. #3

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    2000 XL1200 Limited. Will post pictures tonight of the set up I used. Can you use any one of the pulse line to put air in the engine? With about a pound or so loss in 15 mins do I need to concentrate on the gaskets? I sprayed on the third test and didn’t see any bubbles around the head and cylinder gaskets. Should I tip the engine on the side and spray the bottom of the engine block to check for cracks? Are there other gaskets I should be checking besides the ones from the bottom of the cylinders to the top of the heads? Thanks.

  4. #4
    Predator-x's Avatar
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    I see you only sprayed the gaskets ,but its important to spray the crank seals they are know for causing air leaks.

  5. #5
    When I pressure tested my xl1200 I used a HF-Vacuum Pump,suctioned to 10psi and waited 20min....guage didnt move......Im sure on your situation 1psi is not a air leak if your pumping air into the engine......also check your reeds....that will cause a lean runnaway....carb gaskets as well...........who rebuilt your carbs?

  6. #6
    pokplalya22's Avatar
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    I'm having this same problem, I was thinking a crank seal. I did have a couple of backfires that may have damaged the reeds. This is the first I'm hearing that reeds could cause a lean runaway issue. I thought they would only affect mid/top end. But now that I think of it, if the reeds aren't sealing correctly, or broken, they could be leaking air in prematurely..causing a lean condition.Correct?

  7. #7
    dockwalker's Avatar
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    Had same problem with my XL1200.My carbs were rebuilt by OsideBill(God rest his soul) so I knew they were right.Found a rear seal leaking.If your's didn't leak with 10 lbs, I don't think its a seal or the bottom of the block.My guess would be carb gasket or reeds or possibly a pulse line sucking air.I'm not a mechanic, just a guy who stayed at a Holiday INN last nite!LOL

  8. #8

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    Jun 2012
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    Put 8 pounds of air in the engine tonight and sprayed soapy water over every gasket, pulse line, hose that I could see and no noticeable bubbles. Checked after 8 minutes (as someone recommended 8 pounds 8 minutes) and lost maybe a quarter pound or less after 15 mins the same as before a pound loss. The carbs were built by a local guy here in Glen Burnie Maryland who has a jet ski shop. This was before I knew about this forum or I would have mailed them to Bill. They noticed there was no gasket between the base of the carb and the mounting bracket so they added them and said they rebuilt the carbs with Mikuni rebuild kits. I guess my next test will be to remove the plates/brackets and check/replace all the gaskets. After that take the carbs apart to see what they look like. So does it look as if the engine gaskets are good? And I need to concentrate on the carb area? Thanks for all the suggestions, advice and even a laugh I can use it.haha.

  9. #9
    With the pressure test as you described, I would forget about the seals, they are fine.

  10. #10

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    All thanks for the advice. After multiple pressure tests and your input I'm going to say it’s safe to assume (I hate that word) the engine is holding pressure and it’s time to move on to another area. But first since I blocked off the carbs at the plate would it be safe to say the reeds or the O type gasket that goes around the reeds and the reed plate are good since there was no leak in those areas and the engine held pressure? Any other areas that could cause my lean runaway? Going to do a search to see what I can find about carbs and other areas that cause a lean runaway.

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