sue23
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Post by sue23 on Nov 23, 2008 12:45:41 GMT -5
It looks like there should be a whole forum just on starting but we have a problem with it kicking back that nobody seems to have asked before. It's a '78 SR500 and always been hard to get started although it didn't kick back before. We rebuilt the carb and some stuff and got it starting on the 1st or 2nd kick nearly every time. It didn't seem to have a lot of power and the spark looked weak but it was so easy to kick that I sometimes started it with just sandals on. It ran fine all summer until the
stator burned out. It's the coil that powers the CDI or something like that. A new stator costs a lot more than the bike did so we installed the points, coil and another side cover off an XT500 on ebay. Now it has a much stronger spark but kicks back so hard we can't get it started anymore. The timing is correct, it sparks at the F point on the flywheel just like it's supposed to and nothing else is changed but we can't start it now. When the starter gets down to the bottom of it's strike there is a loud bang and it trys to break my leg or throw me off! I guess the spark was so weak before when the stator was going out that it wasn't able to kick back so my question is when you replace the stator or the CDI with a new one or install points like we did and you can get a good spark how do you start it without having it kick back and throw you off?
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nsman
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Post by nsman on Nov 23, 2008 13:04:09 GMT -5
MeThinks you have it timed 180 degrees out.
Time it old school,find TDC with the valves closed.Back it up 6-8 degrees and that is where you should have your points opening.
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Post by solo2racr on Nov 23, 2008 13:23:49 GMT -5
MeThinks you have it timed 180 degrees out. Time it old school,find TDC with the valves closed.Back it up 6-8 degrees and that is where you should have your points opening. Same answer I was thinking halfway through the original post. 180 degrees out. |
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sue23
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Post by sue23 on Nov 23, 2008 15:09:46 GMT -5
We haven't actually checked the points against the valve timing. Is it possible to put everything together according to the manual so the marks all match up and still get the timing off by 180 degrees?
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nsman
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Post by nsman on Nov 23, 2008 18:31:39 GMT -5
The T mark is in the correct position twice, one time when the piston is at TDC with both valves closed(comp stroke)and again 180 degrees out.If you have the spark timed 180 out the plug will fire the mixture when the piston is in the wrong position causing a kick back.
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sue23
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Post by sue23 on Nov 25, 2008 11:55:28 GMT -5
The T mark is in the correct position twice, one time when the piston is at TDC with both valves closed(comp stroke)and again 180 degrees out.If you have the spark timed 180 out the plug will fire the mixture when the piston is in the wrong position causing a kick back. Those marks are on the crankshaft so they come around every revolution but the gears that drive the points have the same ratio as the cam and only come around every other time at TDC on the compression stroke if the marks are lined up which is when the white mark is visable in the window on top. We checked and the points are in time with the cam at the correct TDC on the compression stroke when the valves are closed. Actually everything seems fine except the points gap was a bit too wide, about .030" instead of the very small .012-.016" called for in the manual. It seems like it should be able to start OK except nobody had been able to work up enough nerve to give it a try. |
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pcnsd
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Post by pcnsd on Nov 25, 2008 13:14:38 GMT -5
Assuming the ignition is correct;
When you kick the bike over, there is a disconnecter pawl that is part of the kick starter assembly. It disengages the starter mechanism at the bottom and the top of the kick stroke if properly installed and undamaged. Kick the start lever forcefully all the way through and pause at the bottom of the stroke, (stand on it) before returning the lever to the up position. If it still kicks back that would indicate the disconnecter pawl is broken and needs repair. You should also check for the broken piece if the above is true, before it finds its way into some mischief.
PC
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sue23
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Post by sue23 on Nov 27, 2008 19:25:00 GMT -5
If you mean that piece of metal bolted to the inside wall of the crankcase above the starter, yeah a chunk of that broke off a while back. The loose piece was removed from the bottom of the crankcase when we were putting in the points. That looks like all it does is stop the petal from going down and hitting the foot peg though. As hard as the thing kicks back I'm surprised the whole started hasn't broken already. Where can that broken piece be purchased for a reasonable price? Online stores like Cheapcycleparts.com only go back to about 1986 and don't have 30 year old parts.
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Post by chew652 on Nov 27, 2008 19:50:15 GMT -5
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Post by aero on Nov 28, 2008 5:13:37 GMT -5
If the engine is kicking back usually this is a sign of over advanced ignition timing. The points gap will affect the timing and the dwell angle. Set the points gap to what it should be first. Check the advance unit also. My XS650 used to play this sort of of game and that was down to the auto advance unit being shagged. (springs were tired and there was a lot of wear on the mechanism) The SR ignition is basically an electronic magneto, so the spark will appear weak when kicking it over. Most SR starting problems are caused by the carb diaphragms or jetways getting blocked  |
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sue23
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Post by sue23 on Nov 28, 2008 8:35:54 GMT -5
The static timing is correct but since nobody has the courage to try and start it again we don't know about the advance.
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pcnsd
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Post by pcnsd on Nov 30, 2008 16:21:44 GMT -5
You could push start with a friend. Kick into 2nd gear after you are at a run speed (7-10 mph) use the compression release to allow the motor to start turning. You can also pull with a vehicle using a tie-down strap etc and the same compression release technique. After it runs you can check timing and advance with a timing light.
Regarding the disconnector pawl (what I call it) It serves a couple of functions including preventing kickback. They are available from Thumperstuff and Yamaha. Please trust me... you need it.
PC
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sue23
New Member
Posts: 8
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Post by sue23 on Dec 5, 2008 10:31:34 GMT -5
We ordered a new part to replace the broken piece so hopefully that will fix it.
Well, we got the replacement for the broken piece and put it in and it seems to have fixed the starter so it will disengage at the bottom now but the engine still won't start because there's no compression. I wonder if all the kick backs and backfires could have damaged the engine?
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