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Q: At what point does retarding my timing become dangerous? Based on the assortment of scratches on my flywheel and my own bumbling attempts at timing my first rebuild, I believe my points are opening around 13-14deg BTDC. My woodruff keys don't fit the race crank I bought, so the flywheel is too crooked to hit 17deg like the manual says, but I was planning on retarding anyway and the bike is actually running pretty well. I am running a 15 bing 82 jet 19T front sprocket on a 50cc. My idea was to jet/gear/time it for top speed and try to recover some of the low end with a hi hi comp head from treats and my pipe. There's no flames coming out of the exhaust, but if you squat you can see fire in the header when someone gives her a bunch of gas up a hill. Is this thing going to explode on me? The plug is wet, sometimes, but she's not four stroking and I'll probably try an 80 jet once the break in is over. I'm under the impression that A) Advanced timing + high revs = grenade. B) Richer runs cooler. C) Retarding moves heat out of the cylinder and assists with exhaust velocity/scavenging at high rpms. Correct me! 
ArgoATX fucked around with this message at 05:13 on Dec 29, 2015 |
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Dec 29, 2015 05:09
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UnkleBoB posted:Hey guys. I have a few motorcycles, but was thinking of grabbing a moped for fun. What do you think of this? That's an awesome price, buy it right now.
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Dec 29, 2015 23:59
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 Taking a breather after the inaugural ride of the Shanks MC, deep in the heart of ATX. 50cc Maxi GPS'd 41mph at ~7.8k rpm with even more go left to get, I'm pretty pleased with the old bitch. Hit me up if you feel like riding in Austin, crews are getting hard to find since ACR went on hiatus!
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Dec 31, 2015 05:33
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How! posted:Thats pretty far advanced actually. Most hardware stores sell various sizes of woodruff keys. You can get one that is close and sand it down till it fits. 13-14deg btdc is advanced? If stock according to the manual is 17deg, wouldn't, say, 20deg be "advanced" in the sense that the spark is firing even more ahead of tdc? The header thing was an exhaust leak, good call 8) I'ma point a laser thermometer at her tomorrow.
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Jan 6, 2016 01:22
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OlDirtyBehrmann posted:Yeah, 13-14 degrees isn't advanced at all. It is very tame. The best thing to do us run a cdi with a curve. For example my hpi mini is set at ~35 degrees btdc. Thanks for confirming! I've done my reading and "13deg btdc is too advanced you'll blow it up!!" really didn't sound right. Have you ever read anything about ignition timing curves? http://www.dragonfly75.com/motorbike/timingcurves.html is what I was going off of, if you want to over rev a 50cc the only way to do it seems to be a matter of pushing the timing way back and puking enough fuel through your main jet to be hitting the right mixture at higher than stock speeds. There's a dyno graph on the above site that demonstrates 4deg timing retard putting out an extra 1000rpm with the right pipe.
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Jan 6, 2016 02:49
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OlDirtyBehrmann posted:A cdi with a curve, hpi mini being my choice, will allow you to both advance the timing to get more punch down low and retard the timing enough up top to keep your temps down and rpms up. That being said, you can get plenty of rpms and not blow up with a nice pipe/carb/kit and a stock ignition. My hobbit still runs points and does 60 thanks to my MMM Destroyer pipe/21mm phbg/Dr kit. The cdi simply lets you blast over the entire rpm range rather than just in one area. Ahhhh, I am now seeing the appeal to paying $300 for a good cdi rig. Is the setup for a cdi just a matter of dialing in a number for the top and a number for the bottom of the curve? Does a 50cc ever need a multi-stage carb or is a fancy timing module the next step?
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Jan 6, 2016 04:25
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