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Thread: boiling fuel in left carb!!!

  1. #1
    kimrpaige
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    boiling fuel in left carb!!!

    Hello again everyone,
    I have been having a problem with my carbs leaking gas on my 81 R100RT. I replaced both floats, needle valves and pivot pins. Now my left one is still leaking intermittently. Mostly after the eng is warmed up and at slow speeds or stuck in traffic. I do the normal thing, pull over, shut the gas off, remove the bowl, shake out the old gas, hold the float up, turn the gas on, release the float to clear out any debris, and re-install the bowl. Everything seems to be perfect! I do have inline filters installed below the petcocks. Now this happened to me yesterday afer I parked the bike to check my mail at the PO. When I removed the bowl the gas was boiling!! Could the bike be overheating? I have not checked the timing recently. Could the float level be a bit too high? I adjusted them to shut off when parallel to the carb flange. I did just move to Orlando from Maine and the temp here is just a wee bit warmer, but I owned a /5 years ago while in Jacksonville and never had this problem. So what's up? Any insight? P.S. The right one is fine. I know this is not rocket science but it is getting the best of me. Thanks in advance. Kim

  2. #2
    Liaison 20774's Avatar
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    Hard to believe that the carbs could get that hot. When this happens, does the left carb feel much warmer to the touch than the right? You might want to check the valve settings as this could lead to a bad running situation if not set correctly. Again, hard to believe heat could be that much different.

    For the 40mm carbs, you could verify the float setting in a slightly different way. Turn the petcocks on for about 10 seconds, then turn them off. Drop each float bowl. Is the height of fuel in each bowl the same? The height could be about 25-26mm when measured to the small well in the center.
    Last edited by 20774; 09-27-2009 at 02:27 PM.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  3. #3
    kimrpaige
    Guest
    Kurt,
    I really do not think it is heat either, as my feet seem to be the same temp and my left foot is not roasting as it should be if that side is running warm. The valves were adjusted probably about 1000 miles ago, and were normal. I'll try your method of measuring the fuel height this afternoon and update you. The bike runs perfect and the carbs are in sync, valve adj was fine, the only thing I have not checked during tune-up is timing, and it should not change with electronic ign, and it starts perfect also. But I can drag out the light , if I can find it, LOL not used one in years, LOL. I have been a mechanic for years, and these bikes are so simple, but this one has me puzzled! Kim

  4. #4
    K Bikes Complex by Choice cjack's Avatar
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    The shop here had a leaker...no matter what we did or checked and it ended up being the outside of the float needle seat. It was seeping around the side of where it was pressed in. They ordered some seats from Bing...you have to tap and pull the old seat out...then press the new one in. After that replacement, the carb was dry.
    R1200GS LC Rallye
    Jack Hawley MOA and RA #224, KE9UW ("Chuck")

  5. #5
    Didn't somebody just find a cracked tube inside a bing carb on this site??? Sounds like the same problem.
    "Wow I didn't know BMW made motorcycles, Yeah I think Honda does too."

  6. #6
    kimrpaige
    Guest
    Kurt,
    I got home this afternoon, and dropped the bowls and measured. The results are the left carb is at 27mm and the right is at 29mm. So I need to adjust the tangs to achieve 25-26mm. I rode it today and no leakage, so I'm hoping I got all the crap out of the needle valve seat. Kim

  7. #7
    Liaison 20774's Avatar
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    Kim -

    I was going from memory...here's what Snowbum says on his page for height of fuel:

    For the 32 mm carburetors, use 24 mm fuel height.
    For the 40 mm carburetors, use 28 mm fuel height.

    http://bmwmotorcycletech.info/bingcv-2.htm

    So, looks your carbs are right where they need to be. Too high and you'll run a tad rich; too low and you'll run lean. It's hard to adjust them any finer than what you already have.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

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