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ArgoATX
Dec 10, 2014


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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How!
Oct 29, 2009

ArgoATX posted:

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! :allears:

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.

Richer doesnt run cooler. All youre doing by up-jetting is introducing more oil/gas. It is possible to seize if you're tuned poorly and have a bigger jet than you need. Cold bikes are mostly about timing and airleaks.

You're right about A though!

Edit: fire from your header is not a good sign man, fix those airleaks and timing or you're gonna be bummed.

How! fucked around with this message at 17:36 on Jan 4, 2016

Rev. Dr. Moses P. Lester
Oct 3, 2000

How! posted:

Richer doesnt run cooler.
Pretty sure it's a well established principle of all engines, 2 strokes especially, that richer does run cooler. But simply upjetting may not solve overheating issues. Oil mixture changes fuel mixture, too, don't forget that. If you got more oil in the gas then you got less gas going in with the air and therefore a leaner fuel mixture.

More ignition advance generally does run hotter. I don't believe it has any effect on exhaust or charge flow to speak of. It just changes when the peak pressure of the combustion happens. I would run stock timing unless you're really tuning for performance. And then I might want to do test runs with some kind of temperature sensor on the thing to make sure it's not gonna melt.

How!
Oct 29, 2009

Rev. Dr. Moses P. Lester posted:

Pretty sure it's a well established principle of all engines, 2 strokes especially, that richer does run cooler.

Yeah, I think you're right about all that. I was just trying to make sure he doesnt solve tuning problems by just using larger jets.

ArgoATX
Dec 10, 2014

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.

Richer doesnt run cooler. All youre doing by up-jetting is introducing more oil/gas. It is possible to seize if you're tuned poorly and have a bigger jet than you need. Cold bikes are mostly about timing and airleaks.

You're right about A though!

Edit: fire from your header is not a good sign man, fix those airleaks and timing or you're gonna be bummed.

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.

OlDirtyBehrmann
Jun 19, 2002

Just A Little Bit Closer...
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.

OlDirtyBehrmann
Jun 19, 2002

Just A Little Bit Closer...
Hello, double post.

ArgoATX
Dec 10, 2014

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.

OlDirtyBehrmann
Jun 19, 2002

Just A Little Bit Closer...
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.

ArgoATX
Dec 10, 2014

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?

OlDirtyBehrmann
Jun 19, 2002

Just A Little Bit Closer...
The curve is not adjustable in any way. It is programmed in the cdi box itself. Different cdi boxes have different curves, though the hpi is different and the box can't be swapped out with different boxes that aren't made for it specifically as it functions slightly differently. A carb with multiple circuits and swappable needle allows for more precise tuning which you will want when running an upgraded ignition anyway. I would ditch the 50cc cylinder, personally. It will be way easier to get much more torque and higher rpms from a larger cylinder.

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Sandbagger SA
Aug 12, 2003

Giant Thighs.
Painted Threads.
Just Off the Highway.
My dad found a website.

treatland.tv

He's thinking about upgrading to 60cc bore/piston on his project Honda express bikes since one of them needs new rings anyhow.


I'm kinda interested in seeing how well it works.

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