Kill Switch Won't Work When The Engine Runs Aaway

Street Ryderz

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Oct 14, 2016
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I saw a video today about a two stroke motorcycle engine that was doing the same thing. Apparently it was getting too hot due to an air leak and was dieseling. I need to learn how to check the crank seals for leaks. I have zero idea how to do that. People just say "behind the magneto" and "behind the clutch cover" but I don't see anything there. Is there a video somewhere or a post somewhere that describes how to do this? I've checked the intake (both ends) head gasket and base gasket multiple times. No leaks that I could find.
If the kill switch works every time other than that one instance then it's probably fine and dieseling as you said, crank seals will do that, and may only leak slightly while at higher rpm and temp and be fine while cold and at startup. Pulling the covers will reveal seepage if they are bad but wont show anything if it's the above, they are not that hard to replace and pretty cheap too, I'm sure there are YT video's showing how to do it, it can be any engine as the process should be the same.
 

Cisco

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Pulling the covers will reveal seepage if they are bad
When my engine started racing, I opened the mag cover. The seal had come completely unseated. You can see the seal after removing the mag coil and magnet. Lubricate the inner seal lip and shaft before inserting the seal. Be sure the inner seal lip slips over the shaft before seating the seal, or the inner seal lip may pucker out, and the seal tensioner spring may pop loose. I used a 19mm deep socket as a drift to seat the seal.
 

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Street Ryderz

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Oct 14, 2016
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When my engine started racing, I opened the mag cover. The seal had come completely unseated. You can see the seal after removing the mag coil and magnet. Lubricate the inner seal lip and shaft before inserting the seal. Be sure the inner seal lip slips over the shaft before seating the seal, or the inner seal lip may pucker out, and the seal tensioner spring may pop loose. I used a 19mm deep socket as a drift to seat the seal.
Yeah it happens quite a bit with these, using a deep socket for the installation when still assembled is how I do it as well, though I'm sure there is a tool for it the socket or going around it with a punch is the only way I've ever done it while assembled. Other wise when the crank is out and the case half's have just received new bearings they get pressed in with the arbor press same as the bearings, then it's real easy.
 

Zak

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Mar 21, 2019
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So whats the problem now? Your plug is looking pretty good. Is it still lean surging?
What do you mean by lean surging? I was thinking of my air/fuel (still a new bike in break in) when today I was admiring how smooth my engine was at a cruising speed. But when the engine got hotter it would surge forward while I was trying to just cruise. Full throttle, no surging. Kill button pushed with throttle open and no surging. Just when the engine gets hot. Is this lean surging?

My inexperienced two cents: While getting this build's bugs worked out, I put my needle all the way lean. I got about 5 minutes into my ride and my bike took off on me, kill switch didn't work. Luckily I wasn't going too fast and was able to slow down and dump the clutch to kill it. That is the only time my kill switch didn't work. Minutes before that happened I was feeling the bike wanting to take off on me and I would kill have to kill it. This was one of my first rides on this bike. I am not offering medical advice. I am not a lawyer.
 

Chainlube

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Jan 5, 2020
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What do you mean by lean surging? I was thinking of my air/fuel (still a new bike in break in) when today I was admiring how smooth my engine was at a cruising speed. But when the engine got hotter it would surge forward while I was trying to just cruise. Full throttle, no surging. Kill button pushed with throttle open and no surging. Just when the engine gets hot. Is this lean surging?

My inexperienced two cents: While getting this build's bugs worked out, I put my needle all the way lean. I got about 5 minutes into my ride and my bike took off on me, kill switch didn't work. Luckily I wasn't going too fast and was able to slow down and dump the clutch to kill it. That is the only time my kill switch didn't work. Minutes before that happened I was feeling the bike wanting to take off on me and I would kill have to kill it. This was one of my first rides on this bike. I am not offering medical advice. I am not a lawyer.
It sounds like you need to tighten everything up once you get it warm. The heat will make it expand and you'll get an air leak causing the surge.
Ride it around and get it warm then tighten everything, put the clip back in the middle until it's broke in, hate to see you burn a hole through the piston from too lean then get it even leaner with the heat expansion.
 

Zak

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Mar 21, 2019
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It sounds like you need to tighten everything up once you get it warm. The heat will make it expand and you'll get an air leak causing the surge.
Ride it around and get it warm then tighten everything, put the clip back in the middle until it's broke in, hate to see you burn a hole through the piston from too lean then get it even leaner with the heat expansion.
I got it one notch from full rich right now. Runs great except for that surging when it gets running temp. But I'm at 4,000 feet... I checked for a leak around the intake with carb cleaner, none. I'll spray around the cylinder and case seals. My bikes from years ago I had to run really lean at this altitude.

Edit:. That's a good idea to tighten it up when warm. I'll do that this weekend.
 

DAMIEN1307

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My bikes from years ago I had to run really lean at this altitude.
Yeah...That doesn't sound right to me that you have it that rich...Im at 4500 ft just an hour or so away from you and even my new Bofeng carbie is at full lean on the "C" clip on the needle and runs perfectly.
 
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