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Old Nov 04, 2012, 09:16 PM
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United States, VA, Charlottesville
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engine wont shut off

i have an super tiger 45 abc engine and it takes for ever to kill the engine if i close throttle completely and place me finger over carb it still takes about 7 seconds to kill engine what could cause this
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Old Nov 04, 2012, 11:51 PM
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United States, IA, Muscatine
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Small vacuum leak. Try sealing the oring at the base of the carb.
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Old Nov 05, 2012, 07:50 AM
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United States, MI, Waterford Charter Township
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Yup, it can't run without air, so it's safe to assume you have a leak?
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Old Nov 05, 2012, 09:38 PM
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Canada, ON, Windsor
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If there is no air leak at the carb base or rear cover then likely the air is coming in past the front bearing. In a lot of cases there is an oil return passage milled into the bore behind the front bearing that can be filled with JB weld or Loctite metal epoxy to minimize the air leak.

GMS and their TT clones were notorious for this one and that was the only solution. Even a rubber sealed RS type bearing would not work that well.
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Old Nov 06, 2012, 11:02 AM
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United States, TX, Weatherford
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Don't rule out a loose back plate either. But for sure it is an air leak. I would not attempt to seal off front bearing oil return passages, to much of a mess and really not a big deal. Carb leak or a back plate leak is a significant leak. Check the o-ring on the high speed needle valve too. Some leakage is inevitable but sounds like yours is a little bit more than normal.
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Last edited by Chip01; Nov 06, 2012 at 11:02 AM. Reason: typo
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Old Nov 06, 2012, 11:08 AM
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I think fuels with a little higher oil content helps seal the front.
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Old Nov 06, 2012, 12:09 PM
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As I mentioned, I went through this with GMS and TT motors in the 45-52 range and there are threads regarding the problems if you do a search.

I tried several solutions, including swapping to OS carbs, with no success. Sealing that oil return was successful in several instances.
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Old Nov 06, 2012, 09:30 PM
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ok cool ill give that a try
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Old Nov 17, 2012, 08:57 PM
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OK so finally had a chance to seal up the motor and all is still the same i don't know why but this thing just doesn't want to cut off
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Old Nov 17, 2012, 09:03 PM
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What specifically did you seal?
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Old Nov 17, 2012, 09:14 PM
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i sealed the back plate and i replaced the carb mounting oring and also added some red rtv to it help seal it
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Old Nov 17, 2012, 10:48 PM
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Only thing left is what I described about the oil return passage behind the front bearing. Don't forget that to run a 2-stroke motor must get fuel AND air into the crankcase, to then be fed through the porting to the combustion chamber. If you sealed the rear cover and carb effectively there really is no other location for it to enter.

On that note, if there is play in the bearings, especially the front which on the GMS and TT clones were smaller than most other motors I've seen in that class, any eccentricity translates to wear in the casting bore, (and perhaps scoring of the crank itself, visible when you rotate the crank and look through the carb throat) and a corresponding increase in any air leak. Unfortunately that is one that is not curable, but a sealed rather than shielded front bearing is about the only option at that point. Before the bearing is installed remove the inboard seal with a straight pin or other sharp pointy tool to allow some lube to get at the rollers.

Having said all that there is one location that is not common, but can still create some problems. A loose fit between the carb housing and barrel can allow some air to leak through from the throttle arm side and draw in fuel along the way.
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Old Nov 18, 2012, 06:44 AM
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Another place for air leaks is the draw bar that keeps the carb in place. Ideally there should be an o-ring below the drawbar too, but few engines have this.
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Old Nov 18, 2012, 07:12 AM
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That through clamp is a rather inelegant method to retain the carb, but two screws through the sides of the bore really is not much better for leak possibilities. However, the instances of leaks were minimal and on other engines would still allow the carbs to close and shut down the engine(s). I was trying to cover what I found specific to the GMS and TT motors. His ST motor exhibits the exact same behavior.

It has been recommended to ensure the nut side of that clamp bar be to the throttle arm side to torque the carb deeper into the housing when tightening. I have never found this really necessary if the carb is held down during clamping. The bigger problem is overtightening as that can damage or deform the carb base diameter.
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Old Nov 18, 2012, 08:43 AM
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Yes tightening the draw harder will not achieve anything. It is indeed poor engineering for what it should do. I'm referring to a leak around the bolt and the nut on the draw bar. You can check for leaks here by closing the carb completely, then wet the draw bar in oil and turn the crank back and forth.
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