Off set key

[butre]

7o miles per hour I could see being possible without anything drastic like a big bore if you're revving it to death down a grade. I know 65 is possible on a motor that hasn't been bored out because I've done it, it just didn't last long spinning 11000 RPM, even with good high end bearings and good studs and whatnot. what ended up killing it was the ring retainer wiggling out of the piston and into the cylinder wall, ruining all my good port work. not much you can do to prevent that other than find a better piston. that bottom end lives in a drawer in my tool box now, it'll see a new top end as soon as I can scrape together the cash to get a bored and sleeved cylinder and some half decent pistons and rings. maybe I'll even go 50mm bore and case reed, who knows.

 

[45u]

77.1 kmh I got I don't see it getting much better unless you want a piston in the face.

Guess you will never know unless you try one.

 

[45u]

7o miles per hour I could see being possible without anything drastic like a big bore if you're revving it to death down a grade. I know 65 is possible on a motor that hasn't been bored out because I've done it, it just didn't last long spinning 11000 RPM, even with good high end bearings and good studs and whatnot. what ended up killing it was the ring retainer wiggling out of the piston and into the cylinder wall, ruining all my good port work. not much you can do to prevent that other than find a better piston. that bottom end lives in a drawer in my tool box now, it'll see a new top end as soon as I can scrape together the cash to get a bored and sleeved cylinder and some half decent pistons and rings. maybe I'll even go 50mm bore and case reed, who knows.

What you do 7o falling off a cliff? If not must of been a very steep hill. If I ever get one to do 70mph I will have a video and documentation for sure. My biggest concern going that fast would be if the tires are going to hold up!
Thanks
Jeff

 

[butre]

I didn't do 70, 65 was the best I ever got on flat land. the tires hold up fine, it's the rest of the contraption that dies

 

[45u]

Up date found out about the timing on these little motors. There is so much slop in the key and rotor you can do some timing changes with out a off set key.

 

[Deleted member 12676]

good squish velocity only allows a timing change of retarding it a couple degrees. I get this info from a research paper I paid $26 for.
But these engines don't have enough compression or RPM to require a squish band (whose main job is keeping the piston cool).
45u, make a graph of your bikes timing (RPM vs timing) and then compare it to the correct timing curve I show on my site from a Jaguar CDI.

 

[45u]

Gonna be hard to check, there are no points to check it with. All you can do is run it and use a plug fired timing light. Most automotive lights won't work. I have a xenon spark fired light I save for these motors. Dim, but it works when nothing else will.

Steve

Here you go.

 

[Diamond Back]

Timing advance is a crutch to get over slow combustion. If you can speed up the combustion, you don't need so much advance. Pressure, heat and turbulence tend to speed up the combustion. RPM and increased throttle opening tend to increase these and help to pick up the pace, so less advance is needed. A tuned exhaust pipe increases the pressure substantially so often some sort of timing retard mechanism is needed once you go tuned exhaust. Improved squish will also necessitate less timing advance.

An offset key will do the job and has been used for years as a timing tool. Many of the CDI coil conversions for older engines come with a stepped key for the flywheel right from the engine manufacturer. Timing advance is normally conservative on a stock engine so a few more degrees advance will liven a stock engine. Raise the compression or otherwise modify it and you risk detonation.
Steve

Where detonation starts on a Happy Time motor:

I dont get what your saying,, one quote you say retard (which would mean turn magneto clockwise,,correct??))) if you have a pipe and performance head,,, then you say advance will liven it up,,, so which one,,, I have a GT5 engine (i think) ZAE 80 connect rod and short piston with wristpin in center,, does this mean I have the 38mm stroke engine,,, I have a banana pipe expansion pipe, RSE thin round HEAD, and a nice custom built 66cc volume Boost bottle,,, I get some four stroking alittle bit sometimes, but if I run it wide open under slight load it clears up,,i went from .70 main jet stock NT carb to a 67 main jet with needle in top leanest slot,, but spark plug is still gray/black,,, also whats weird is powerband dont kick in to real high revs and if i twist trottle wide open it kinda bogs and if i back off a hair it runs a little better,,, am i still running rich?? so i have an off set key, which way should i turn it ????

 

[Deleted member 12676]

wrong! Timing advance is not "conservative" on these engines by any stretch of the imagination. Look on my site to see the stock timing curve and what timing curve works better.
Just click on my signature link. The stock timing is very advanced which is what is needed for the stock low compression. Unfortunately it doesn't retard much with high RPM and so serves as a way to limit RPM. (that and the unbalanced crank)

 

[Deleted member 12676]

Diamond, it sounds like your jetting is a little rich at open throttle and very rich at medium throttle. Before I put a good carburetor on mine I fixed that by fattening the needle by melting solder onto it. That leans the mid range without affecting top end. You also need a leaner main jet. See my site for details.
If you want the powerband to be at lower revs then you need to lengthen the header. Try 2 or 3 inches.