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Thread: Temp variation in cylinder...Use temp for rough fuel jet setting? I'm lost.

  1. #1
    Join Date
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    Travis AFB, California
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    Default Temp variation in cylinder...Use temp for rough fuel jet setting? I'm lost.

    Hello all, I've been doing a restoration of a 79' GS550e. Work completed thus far...Body Engine de-greased and detailed, Body dents pulled, Air Filter replaced, Air box sealed, Air box boots deplasticized, valves shimmed, new tires and tubes, all carburetors dipped and rebuilt with all new o-rings and gaskets, tank evaporusted, fuel cock rebuilt and tested, Ignition system replaced, intake boots replaced with new vitron rings, magnetic ignition contacts installed, plugs replaced, clutch cable and clutch mechanism replaced, fuses and grounds checked and replaced...now for the final carburetor tuning. My question has to do with the individual cylinder temperature. According to my clymer manual and Bikecliff's page, The fuel pilot should be between 3/4 to 1 1/2 turns out after bottoming the screw. When rebuilding the carburetors the PO's didn't keep track of the factory fuel jet settings but I followed the instructions per many mechanics before me put forth. My bike feels weak and seems to be missing out especially at low speed and idle. It lacks power. Cylinder one gets to 210F, Cylinder two gets to only 158F, Cylinder three gets to 330F, and cylinder four gets to 190F at standard running temps after a quick twenty minute ride. Using the fuel pilot screws, I've brought down the temp on cylinder three to 280F but I'm way beyond the factory/forum recommended fuel pilot screw settings at 2 1/2 turns out. (My air pilot screw is set at the standard 2 turns out on all carbs after gentle bottoming out)

    My question: Is it wise to use the fuel pilot screws to try to tame the possibly lean/rich fuel mixtures to even out temperatures? I've tried vacuum syncing the carburetors but the pilot air screw didn't seem to change the reading. My cylinder 1 & 2 exhaust smell rich, whereas my cylinder 3 & 4 does not. Plug readings have told my nothing BTW. The bike runs too rough to get a standard reading. Am I barking up the wrong tree?

    Also there is the dreaded ghost idle issue but that comes after step one of getting it running fair.

    Any help would be appriciated!

  2. #2
    Join Date
    Mar 2005
    Location
    West Slope, OR
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    Yes, you are

    1. You don't sync the carbs with the mixture screws. The adjustment screws are on top, under the top cap
    2. Fuel screws shouldn't be more than 1 turn out. If it's still lean, go up a step on the pilot jet
    3. I'm guessing #3 is hot because you didn't cap the vacuum port?
    4. Plug reading will always tell you what your issue is

    If by "ghost idle" you mean the idle is increasing, it's telling you there's a air leak.
    Also, while temperature is only a guideline, that guideline is saying your carbs are still not clean
    1978 GS 1000 (since new)
    1979 GS 1000 (The Fridge, superbike replica project)
    1978 GS 1000 (parts)
    1981 GS 850 (anyone want a project?)
    1981 GPZ 550 (backroad screamer)
    1970 450 Mk IIID (THUMP!)
    2007 DRz 400S
    1999 ATK 490ES
    1994 DR 350SES

  3. #3
    Join Date
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    I capped the vacuum port between the 1&2 and the 3&4 carbs. I used the old caps as they wern't dry rotted and seemed to fit tight. I'm pulling the carbs again to swap with a new set I've found online that haven't been messed around with. The mixture pilots and needle seem new and I suspect they are the chinese garbage parts. I have a junk yard set in the mail that I'm just going to clean up. Thank you for your help. Back to the factory settings once the new parts come in...

    Quote Originally Posted by Big T View Post
    Yes, you are

    1. You don't sync the carbs with the mixture screws. The adjustment screws are on top, under the top cap
    2. Fuel screws shouldn't be more than 1 turn out. If it's still lean, go up a step on the pilot jet
    3. I'm guessing #3 is hot because you didn't cap the vacuum port?
    4. Plug reading will always tell you what your issue is

    If by "ghost idle" you mean the idle is increasing, it's telling you there's a air leak.
    Also, while temperature is only a guideline, that guideline is saying your carbs are still not clean

  4. #4
    Join Date
    Mar 2005
    Location
    West Slope, OR
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    Default

    Okay, the ports between 1&2 and 3&4 are vents and should be open
    The one you need to cap is on the inside of #3

    If that's not capped, or connected to the fuel tap, there's your leak
    1978 GS 1000 (since new)
    1979 GS 1000 (The Fridge, superbike replica project)
    1978 GS 1000 (parts)
    1981 GS 850 (anyone want a project?)
    1981 GPZ 550 (backroad screamer)
    1970 450 Mk IIID (THUMP!)
    2007 DRz 400S
    1999 ATK 490ES
    1994 DR 350SES

  5. #5
    Join Date
    Apr 2017
    Location
    Travis AFB, California
    Posts
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    Default

    Ah, same page, but different book. Those vents...sorry. Yes both on the outside of the carb are drain hosed to the ground. The #3 is attached to the pet cock. The two I was speaking of were the flow through tubes between the carbs. They are two, 1/2" pieces of hose between 1&2 and 3&4

    Quote Originally Posted by Big T View Post
    Okay, the ports between 1&2 and 3&4 are vents and should be open
    The one you need to cap is on the inside of #3

    If that's not capped, or connected to the fuel tap, there's your leak

  6. #6
    Join Date
    Mar 2005
    Location
    West Slope, OR
    Posts
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    Default

    Does your bike still have points?
    1978 GS 1000 (since new)
    1979 GS 1000 (The Fridge, superbike replica project)
    1978 GS 1000 (parts)
    1981 GS 850 (anyone want a project?)
    1981 GPZ 550 (backroad screamer)
    1970 450 Mk IIID (THUMP!)
    2007 DRz 400S
    1999 ATK 490ES
    1994 DR 350SES

  7. #7
    Join Date
    Apr 2017
    Location
    Travis AFB, California
    Posts
    15

    Default

    No it has the Dyna S ignition that was recently installed.

    Quote Originally Posted by Big T View Post
    Does your bike still have points?

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