Has anyone ever had, or heard of a flywheel keyway shearing off? I so, what will the engine run like if it does. My son's cuts out after half throttle, I have checked everything known to check or replace, it is still doing the same thing. Idles fine, runs good until he hits half throttle, then cuts out, if he short shifts, he can ride it, but he really is losing alot of power. It has been suggested that I may have sheared the keyway, allowing the timing to slip a bit. I had the valve cover off & looked at the timing marks, they were not exaclty level, but I could see both. If I moved the cam gear to where they were level with the head, the mark on the flywheel was off several degrees, not sure exactly how many. I am not sure if this is acceptable or not, I am thinking of pulling the stator cover off & removing the flywheel to check, but if I am wasting my time, then I certainly don't need to pursue that. Any help with this will be greatly appreciated.

 

I've been a full time tech for over 15 years Rangerrick63. Sure, I have seen lots of sheared flywheel keys on various small engines. Usually they don't run at all, or just backfire. One time I worked on a 250 Odyssey that started hard, and when it started the engine ran backwards!! (sheared key). You can easily tell if the key is sheared without removing the flywheel. Remove the two plugs on the flywheel engine cover, one is to turn the engine over, the other a window for the timing marks. Remove the spark plug. Turn the engine over until the T mark comes up in the window (Not the F or the l l marks). Sometimes it is hard to see so look carefully. When you find it, put a small screwdriver in the spark plug hole and turn the engine back and forth a bit. The T on flywheel should correspond exactly to TDC which you can determine by using the small screwdriver you have in the spark plug hole. Whenever I've come across a sheared key, it's pretty obvious. Once you have determined that T on the flywheel and actual piston TDC match up, inspect your cam timing. There is only one correct position, the one makes the index lines on the cam sprocket as close to flush with the top of the head as possible. Any other position is unacceptable. Be sure you are using the T mark for this. BTW, if you are turning the engine over the way it runs, you will see in sequence l l (advance marks), F (ignition timing marks), and finally T (Top Dead Center).

 

That is the procedure I used to check the timing, when the "T" mark was in line with the pointer, the 2 cam timing marks were not level (or parallel) with the head. One was approx. 1/4" higher than the other. I then moved it forward 1 tooth on the sprocket, & could then only see one mark. I then moved it 1 tooth the other way & could not see the other mark. So I put it back where it was, but that left the one 1/4" higher than the other. I had assumed they had to be exactly level, but are you saying that this is acceptable? Thanks for your help

 

Yes that is acceptable, as long as it is close as possible. They don't always end up perfectly flush.

 

I really appreciate the input, that saves me some time. You seem quite knowledgeable on these engines, what else do you think it could be? I have went thru the carb countless times, I have went up on the main jet to a 135, down to a 130, now back to a 122, no difference. Everything in the carb "Looks" good, (saw nothing obvious). I have cleaned out the tank & strainer. I have tried running with & without the air cleaner to see if that makes a difference, none. Changed plugs, both CDI boxes, the stator & the pick up, no difference. I installed a Cobra exhaust on it, I even swapped it back to the original exhaust. Still no difference. I have not changed the coil, but I am suppose to be getting one tomorrow to swap to see if that is it, but I don't think so, because I was under the impression that a coil either works or it doesn't. But I am going to at least eliminate the possibility. I have went thru all the wiring to check connections, & grounds, all are good. I have eliminated the reverse cable, but I don't think that could have anything to do with it. Since I don't ride this, I am not sure exactly when this started, I heard it cut out on him at the track a couple of months ago, but my son said he didn't notice it, so I am wondering if it has done the whole time we have owned it, he just learned to ride with it. When I installed the Cobra on it, I really could hear it. As you can see I am completely & uterly baffled. If you might be able to shed some light in a direction I have not tried, that would be a great help. Thanks again.

 

My guess is fuel related. However ignition is NOT out of the question. It really sounds like you're at a dead end. If I were working on it, my next move would be to put the peak voltmeter on it, and check the spark plug firing voltage, as I mentioned in an earlier post. This would tell you with a high degree of certainty whether it was ignition, or fuel\air problem. Maybe there is something wrong you're just not catching, ie. wrong jet needle, something like that. Possibly try a known good carb. Beyond that, maybe bring it to a good Honda dealer that does a lot of ATV type work. A good tech can do a lot of troubleshooting and eliminating in an hour or two.

 

Thanks for your help, fuel is the way I am leaning towards. Tomorrow I will be able to eliminate the coil. Also, this friend of mine that owns his own atv shop, has a known good carb & will let me borrow it to see if that is the problem. He is even baffled on this, everything he thought would be the problem has turned out wrong. Again, thanks, you have given me a couple of routes to take, I will check the peak voltage on the igniton tomorrow, before & after the coil swap. I will let you know, when I find the problem, later

 

check the reverse wires on the right side of the case make sure you do not have them backwards or it will spit and sputter at about half throttle
made this mistake and it was like that for almost 3 months
or make sure they aren't loose or cut
and i also didnt realize how old this post was either