Problem with Crastsman TL1000 (Intek 20 OHV V-Twin) - OVER-REVVING/SURGING

[panshovelmike]

Hello and thanks in advance for any information. I did search before posting but couldn't find anything to help me with this particular issue. I have an older Crastsman LT 1000 riding mower with the Briggs Intek 20-hp OHV V-Twin. The mower was not running when I got it, but I got it to run well after changing oil/filter, replacing the battery, spark plugs (gapped at .30), fuel line, and cleaning the carb multiple times. It was running perfectly - choke knob operational, throttle lever (slow-fast) working properly, charging system good, etc. I used the mower for about 20 minutes to cut part of my back yard and it worked great for that time until the end. I dropped the speed to idle and put the mower in neutral to move a few things in the yard, and when I did that I noticed the idle was surging up and down, which it hadn't been doing before. I wanted to finish up so I put it back at full throttle and it seemed to be working properly (was no longer surging). I was mowing at full throttle when all of a sudden the engine seemed to over-rev quite a bit faster than it was already running at while set on full speed on the throttle lever. At the same time it did that I noticed some sparks shooting out from the front near the muffler. Tried to throttle down, and the throttle lever had no effect. Could not get the throttle speed to come down at all, so I shut it off and let it cool down. Upon restart it immediately goes to over-revving again, with the throttle lever having no effect up or down. I checked the linkage on the end of the throttle cable and it moves back and forth when I work the throttle lever up and down. I'm guessing that the throttle cable is going to some kind of a governor, because it doesn't attach directly to the carb but rather to a cylinder type thing which is under the carb. Behind the cylinder are some actuating arms with springs on them. It's dark out so I haven't had a chance to investigate further but I need to get back on it in the morning. Any ideas?

UPDATE: Looked at the carb and throttle linkage with a flashlight. I don't know much about this particular carb but I'm familiar with motorcycle and automotive carburators so I know a little about carbs. On the top right corner of the carb is an adjustable phillips head screw with a spring underneath it. This screw is what I would normally assume to be an idle adjustment screw, so with no throttle being applied (or with the throttle speed lever set on low), the rotating throttle cam on the right side of the carb should have a tab which contacts this screw. At least thats what I'm used to. What I've noticed is that this cam does NOT come close to touching the screw no matter where the throttle lever is set at. Looks to me like something is mechanically holding the throttle open. I can manually shut the throttle on the carb with my hand, but it's under spring pressure and opens again immediately when I release it. The spring putting this tension on it goes to an arm on the bottom left side of the engine. At the bottom of this arm, it clamps to a shaft that goes into the crank case. What the heck is this thing?! I can see that the throttle isn't being allowed to close. I don't understand what could have changed here while I was using the mower. Looks like I can bend a tab or rotate the arm on that shaft going into the crankcase so that I can get it to where the throttle on the carb will close while relaxed... but I'm really not understanding what caused this issue in the first place when everything seems tight and there are no broken springs...? Am I on the right track here? If not, can some point me in the right direction?

 

[ILENGINE]

From your description of the problem I would consider two things. One the arm has slipped on the rod going into the engine. that is the governor control arm in your quesions. it is what slows the engine down, and pushes against the springs your talked about. Two the governor gear inside the engine has broken, which at that point there is nothing to push against the springs.

while moving the throttle on the carb to the wide open position watch which direction the rod with the clamp turns. Loosen that clamp, move the throttle to the wide open position, and then turn the rod in the direction that it turned in the previous explanation until it stops. then tighten the clamp down securely. See if that fixes the problem. if the engine then still overrevs, most likely the governor gear is broken, which will require removing the engine, and removing the bottom sump to replace the gear. then you will have to go through the previous adjustment procedure above again.