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Post by minnesota750 on Apr 6, 2015 11:54:51 GMT -5
Hi Everyone, My Winter engine teardown and rebuild for my 73 is finally done. I spent this last weekend working on getting her to fire up, but am having some issues with the point gap and timing. I have some questions, which are probably pretty elementary to those of you who have years of experience with this, but for me it's baffling. Please correct me where I am wrong. 1. From what I've read the points are supposed to stay closed, except when it's time for one of the cylinders to fire, then they open, interrupt the charge and the spark is sent to the cylinder. 2. For the TX engine, the cylinders fire at different times, right first, then left. I have a diagram below of what I've worked out to be the correct Intake, Compression, Power, Exhaust sequence for the engine. Again, if I'm wrong, please let me know where I've made mistakes. 3. The points are supposed to be closed and only open once per side (Left and Right) when the cylinder needs to fire for the top of the power stroke. 4. The left and right side points will open/fire at different times, otherwise they are supposed to be closed. 5. When I set the points and turn the engine over it appears the points are opening at random times, and not just when the cylinder is on the compression/power stroke. Right now I'm frustrated beyond belief and just want to hear this engine fire up after all of the work I've put into it. Any advice/suggestions/public shaming followed by solutions is highly appreciated. Thanks. MnTx  |
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Post by farmrjohn on Apr 6, 2015 15:47:34 GMT -5
The points cam is driven by the oil pump shaft that rotates at 1/2 the speed of the crank. If you look at the points cam, you will see that it will close one set of point or the other but both may be open at the same time due to the shape of the points cam. When the points are closed, it completes the circuit through the primary ignition coil, allowing it to charge the secondary coil to high voltage. When the points for that coil open, it causes the charge to collapse, and the secondary high voltage discharges through the spark plug. You will also see that one set of points is mounted directly to the points plate which is adjusted first, then the second set of points is on a "floating" mount that is mounted to the points plate. This one is adjusted after the first is set. This link shows the procedure: tx750.proboards.com/thread/2/ignition-breaker-points-maintenance |
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Post by minnesota750 on Apr 6, 2015 23:03:44 GMT -5
Hi,
Thanks for the info and the link. That helps solidly that what I'm doing is indeed right. If there are other suggestions for helping time the engine I would very much appreciate them. I have the Yamaha manual as well as two additional manuals, but am still having issues with timing. I can't seem to get it to fire up despite my best efforts. Any suggestions on the 360 degree twin firing order? I think I have it right in the diagram but want to make sure.
Thanks.
MnTx
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Post by scotttx on Apr 7, 2015 18:33:07 GMT -5
Man, you just made my brain hurt!
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Post by argo1974 on Apr 8, 2015 16:34:22 GMT -5
You can imagine a 360 degree four stroke twin being 2 separate single cylinder engines. While adjusting ignition timing, only concentrate yourself on that particular "engine" and its ignition points. If you can get it firing at the end of compression stroke, great. If not, valve cam or points cam may be out of phase. Valve cam timing is incorrect in some service manuals, so check with service bulletin #302. In case points cam is 180 degree out of phase, the governor is misplaced. There is a 3mm pin on the shaft that goes in either way. I suppose the timing marks are correct on primary drive/oil pump gear.
Generally spoken, TX engine fires once every revolution, either left or right cylinder.
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Post by minnesota750 on Apr 12, 2015 0:06:51 GMT -5
Hi, Thanks for the advice everyone. I finally got it fired up today. I'm still having an issue with it running and then not wanting to start again like there is no spark. I ran it for about 30-45 minutes today on and off working to set the carbs and static timing. Then suddenly it killed and wouldn't start again, just like before, as if there was no spark. Any known electrical issues this could be caused by?
Also, on the eccentric cam there is a small mark on the edge on one of the lobed end where it connects to the oil pump shaft - is that mark supposed to line up with anything?
I was so close and heard it run only to be frustrated again by this crazy lack of firing acting like there is no spark.
Thoughts?
MnTx
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Post by farmrjohn on Apr 12, 2015 10:58:39 GMT -5
If it was running then your points cam should be on correctly. That is an index Mark to get it on in the correct orientation. If you have lost spark after having it there could be an issue with either the kill switch on the handlebar or the. Ignition switch. Does the electric starter turn the engine over when there is no spark? If so that would rule out the kill switch. It would also be worth checking all the connections including the plug wires at both the plug and coil. Also make sure the points themselves are clean and can ground the circuit when they are clocked.
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Post by scotttx on Apr 12, 2015 17:33:35 GMT -5
This may be rudimentary, but, if you are still dialing in the timing and carbs, pull the plugs and make sure they aren't fouled, and the gap is still good, from personal experience, i fouled a few plugs when i was first dialing my beastie in, and i also swapped my wires and coils, then invested in a timing light, it is a real sanity saver
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Post by minnesota750 on Apr 12, 2015 19:24:05 GMT -5
Starter turns and everything seems to be in working order. I re wrapped the entire harness when I put everything back together and did continuity tests.
Going to try plugs next - any suggestions on replacement coils? I had thought about replacing them, but didn't have any idea on what to replace them with?
TxMnTx
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Post by minnesota750 on Apr 12, 2015 19:25:18 GMT -5
Really appreciate all of the advice btw.
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Post by farmrjohn on Apr 13, 2015 9:37:40 GMT -5
www.mikesxs.net/product/17-6805.html These are a straight replacement. I'm working on changing over to a dual output coil/wasted spark system and will post that up if it is successful. If you replace the coils I would use new wires, caps and plugs. The ends of my original plug wires were not making good contact at either end.
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Post by minnesota750 on Apr 20, 2015 11:34:41 GMT -5
Replaced the coils, wires, connectors, and plugs. Runs like a champ now! Thanks everyone - very grateful for this site and the brain trust here.
TxMnTx
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Post by scotttx on Apr 26, 2015 6:49:09 GMT -5
Glad you got her running,i know i love riding my beastie, she's alot of fun,hope you enjoy it as much as I do
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