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Toro Zmaster 25CH Keihin Carb problem

Discussion in 'Mechanic and Repair' started by chilipeppermaniac, Jul 23, 2006.

  1. chilipeppermaniac

    chilipeppermaniac LawnSite Member
    Messages: 3

    I have owned a 2nd hand Toro Zmaster with a 25 Hp Horizontal Kohler Command motor for about 3 yrs now. This spring I had troubles starting it.
    The 1st area of concern I pinpointed was my Keihin Carb which appeared to be starving for gas. I noticed that gas was not pumping inside the carb when the linkage was operating the accelerator pump on the carb. Also fuel would leak up the shaft thru the rubber boot outside the pump assembly.

    After removing the bottom cover on the pump section I discovered several tears in the rubber diaphragm. I ordered a new accelerator pump kit which should have done the trick I thought. Once I put the new assembly together and started up the mower it seemed to work fine for the few minutes I had it running. 2 hours later I went to cut the lawn and it ran poorly and was back to hard starting again. To my dismay I not only found gas leaking out the shaft again, but the new diaphram was torn too. Has anyone had a similar incident or can offer advice on what to do to avoid repeating the same thing again after I buy another new part?
    I cannot afford to keep ripping these mesh filled rubber pumps to the tune of $36 for 30 seconds of running time.

    1 further question on this rubber pump which is basically the size of a quarter. The carb housing has a significant recessed grooved circumference to it, while the removable cap bowl has none and is flat. In assembling the parts, the rubber circle has one side with a larger ridge than the other, so I assumed that ridged side should be oriented with the ridge fitting into the carb base while the flatter side faces the cap and has the spring pressing on the diaphram from the cap side. Thanks.

    Also, my part number is Kohler 24 757 08-s
  2. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    Hmmm, I have never ran into this situation.
    Could be a blocked or partly blocked passage causing the engine to try pulling fuel thru the diaphragm causing it to suck a whole in it ? If I did run across this I would do a complete tear-down of the carb. then spray choke cleaner thru all passages and jets followed by compressed air, Then reassemble and try it again.

    Below is a break-down in case you need it.

    CH Carb..jpg
  3. chilipeppermaniac

    chilipeppermaniac LawnSite Member
    Messages: 3

    RestroRob, Wow, that sure is a nice diagram. That was much beyond any of my expectations as a response to my problem. I will try as you say to do with cleaning out the carb totally. Thanks
  4. viper00085

    viper00085 LawnSite Member
    from NC/VA
    Messages: 237

    also just as a side note, (prolly not your issue) but make sure the accel pump linkage is hooked up correctly, it can be put on reverse and cause it to squirt on deccel instead if acceleration. I have seen it 3x this year with exmarks and scags that the landscape companies mechanics tried to work on the carb. It will cause the eng to act like its flooding out at idle and bog when engaging the pto.
  5. chilipeppermaniac

    chilipeppermaniac LawnSite Member
    Messages: 3

    I called and my part is in. I am hoping everything goes smoothly and I can get the carb totally clean and hopefully have all my bases covered before the initial test to see if all is well again.

    I am not sure how to get the linkages backwards, but in my experience with this mower I believe I do have the linkages etc all in their proper order.

    Thanks again Viper.

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