Old Guys X Autocycle

Just to clarify the 3rd transfer port mill work at the bottom of the cylinder was cut with a 15/16" side mill the end mill was used to make the short upper cut (7/16" wide) above the intake port, to the height of the other two transfer ports. Depth of both 3/16".

After the last post I decided to finish the expansion chamber conversion to muffled status. I had previously cut the back section off, leaving about 3.5" of tube. I then cut most of the pipe off of a stock kit muffler, leaving about 3" of pipe which was then slipped over the short length of tube on the expansion unit. I used a Harley tube clamp to secure the slip jointed pipes after having double slotted the outer tube for the compression fit...it's not coming loose! I'll use the clamp to support the rear to frame with a bracket not yet built.

I tried the pipe with and without the muffler on both the X-celsior Schinn and the Grubee Skyhawk a couple of days ago and the muffler really quieted both well and I couldn't tell that it killed the mid range much at all especially on the Schwinn and so I've flip flopped once again & will mount the pipe on the Schwinn. It felt pretty peppy with the mods I'd made to that point, no speed racer of course. I think it's a great fun little cruiser though...Rick C.

Wonderful complement Wret, BT style has been my major inspiration as well for most of my bike designs, of course I'm not a slave to exact replication, just build in the spirit of a marque and era. 1st. 25 years of motocycles is especially of interest to me, both the road & track versions.

The China girl power plant kit was arguably the initial motivation for most of us older guys to build a motor bicycle, 'kinda like a Whizzer, as an easy inexpensive lark to full fill a juvenile daydream to build one & get it out of our system. I'm one of those and many thousands of dollars later I'll admit I'm hooked and still enjoy building an occasional 2 smoker & I hope to encourage their continued use as more and more good components become available to build reliable, peppy, relatively powerful motors, which are also affordable. Having usable parts on hand is always a big plus & for me it means being able to finally justify my previous design catastrophes & purchasing mishaps while lending an element of logic to building yet another bike to my growing collection.

I built a bike for my daughter in law back in the early Spring this year & she has enjoyed it. Creme tires, bone crusher leather saddle, lots of chrome and polish everywhere & a very pretty CG motor, basically stock internals, Schwinn single spring fork. Very upright riding position & extremely easy to pedal and start or just ride for exercise around the neighborhood. Yesterday my not so young cousin asked if I'd build her one as well. She is in wonderful physical condition but 35 years older so I'm looking at the wonderful stylish ladies step through frames for a base to build around, rear tank or add an appropriately lowered tank & tube.

Just a few of my thoughts. I'll look forward to seeing anything you decide to build & know each will be special.

Rick C.

Thanks for the likes guys. Allen I too thought I was done with the little 2 strokes a couple of years back, but my wonderful riding experiences on them has me still building around them. Since joining the forum on the last day of 2014 I've almost completed 7 bikes, 5 of which are based on the China girl engine. In that same time period I've built six 66 cc motors & have two more engine builds started, which will give me 3 complete motors on the shelf, waiting for the right frame to inspire me to begin another project.

In the last 4 years I've had only one engine failure (lost a ring) but other than replacing the cylinder I was able to reuse the rest of the motor. Since I ride every day that health and weather allow; I'd say dependability has not been much of a problem... 4 stroke or two. I'm a fan of both & will continue to use both in my builds.

I'd say that 80 percent of my riding miles are enjoyed on the China girl bikes so yeah I do enjoy them & hope you all do as well. Rick C.

Just a couple of days riding Sky hawk with the newly modified engine & I'm really liking the way the mods on the 38 MM stroke GT-5 motor feel, so much so that I'm jumping in and duplicating the same modifications on the 40 mm "long" stroke power plant that's mounted in the X-celsior Schwinn bike.

I have an extra cylinder with(40 mm) wide intake studs & a 40 mm reed block with SHA Dellorto clone carb & a couple of new 66 cc piston sets so I'm good to go without putting the X-celsior out of commission to scavenge her parts for modifications...sweet, got something else to work on that's fun.

I plan on riding the Sky hawk a lot over the next few days & hope the rings seat in quickly. I can't wait to run her up a bit. It should be quite sporting! Rick C.

Had a reminder why having more power on tap is great. A pit bull attack that I was just barely able to pull away from on the Schwinn. I was very fortunate to injury as I had to first slow down to keep from hitting the animal,then accelerate away to avoid jaws...he tore my pant leg but missed flesh.
Had I been on the Sky hawk no problem. Really confirmed my decision to complete the reed valve mods to my X-celsior Schwinn. It is true that it's better to have power & not need, than to need &..... Rick C.

Yeah guys I relate to your stories of dogs and bikes. I so like the critters but just won't suffer a vicious animal and it's been several years since the last for real attack. Dogs generally like to chase/race bikes accompanied with much barking and no evil intent. I've no problem with that, but this was different.

At any rate I'm going to tear down the X-celsior Schwinn today & start the cylinder mods. I am going to have some power on tap! I also intend to stay with the 1" diameter piston window. I read the plug on the modified GT-5 engine and the .70 jet is running rich but not fouling and that's how I like it. Running continuously at 25 mph and higher will like the richer mix. Expansion chamber use requires a higher jetting also. I'll play with both engines till they tune in, but let rings seat before change of jets.

I'm running a rocket CDI on the Sky hawk And stock kit CDI on the Schwinn. From the material I've read on the difference between stock CDI and aftermarket ignitions and my use of the Huffy D., Jaguar, Lightning and Rocket (pill bottle) units; I'm convinced they all perform better than stock. I have an extra Jaguar & it will also end up on the X-celsior Schwinn. The stock CDI I use initially on all my new builds, if I suspect the ignition is causing a problem it's cheap and quick to swap out and check. On some bikes I just stay with stock, but if the build is performance enhanced I opt for one of the custom boxes. Up to 5,000 rpm or so the stock timing advance type CDI which continually advances as rpm's are increased is ok. 4 stroke engines preform well with this type of advance, two strokes not so much, after mid range rpm is reached on a 2 stroke higher rpm performance is enhanced through a relative reduction of advance. As the rpm increases (especially on piston port engines) the continued retarding of timing helps prevent detonation caused by the ignition firing before optimum fuel/air mix and piston to head position occurs. Power is reduced by this premature ignition of course & destructive heat is created. Higher compression ratios of performance engines make the forces involved even more violent. Also the rotating assemblies take a beating when detonation occurs while they are out of position to absorb the forces generated. Smooth is good on any engine. When power is increased the value of smooth is exponentially increased. An engine out of harmony won't live long when asked to produce more than half it's power.

My mix on the modified GT-5 Sky hawk is at 30 to 1 for now. I thought 20 to 1 a little thin. Rick C.

I'll be putting the modified parts on the 40 mm long stroke motor for the X-celsior Schwinn today, along with the reed valve and a modified slide Dellorto SHA clone carb, also jetted .70; this combination should work well with the muffled expansion chamber, but I've been wrong before. The same mods on the GT-5 38 mm stroke motor (without expansion chamber pipe) feel stronger during each ride as the rings seat and the new reed petals start to really flex, they too require time to break in. I may also try a modified reed plate to mount the Dellorto in the offset position if more clearance is required for carb/air cleaner to frame fit.Rick C.

Thanks Jeff & a lot of us want to see you keep on building 2 or 4 strokes electrics all good.

Forks are Sunlite and ,lol ,the springs are bigun's but the wheels are little one's 24". My thoughts were and are to find the shorter springs. I may eventually go to 26" wheels also, but right now I'm having a blast riding the little guy, man is it quick and sporty...not yet fast but feels like a small cafe racer compared to Harley fat boy, really begs to lean into the corners...hard to explain exactly why, so I won't. I'm reluctant to change things that are fun, even if they look a bit off... till the new wears off.

Speaking of change; the X-celsior Schwinn motor mods are complete and back on the bike as of late yesterday. I got in 10 minutes or so of riding, started and sounded right, but I can't report any huge difference at putt putt speeds. I'll let the rings seat before I run up the revs much. Also and reeds are typically stiff, read that as low performing, when first installed. The Dellorto fit but only just without the addition of an offset manifold. Carb wouldn't idle down past 2,500 rpm and I suspect an intake air leak which I'll address this morning.

Oh yeah still no clue to the source of the fuel tank leak, but I haven't seen a trace of fuel in the past 4 or 5 days, the leak must be extremely small at this point, but I'd think that riding would certainly make the source of the leak reveal itself. Sounds like politics.

I'm sure having fun!

Bad air leak/lean

Ludwig II said:

Years back I had a Honda 50 to get to work on, it was winter, and our side road was iced over. An idiot dog came out from somewhere and started all the business of barking and snapping as I was setting off. I ust stuck the left footrest down, turned with the power on 180 degrees and chased the dog, which went round the back of me, I did the same trick with the right footrest and it ran off, never to be seen again. I like Honda 50s.

Click to expand...

Your're the man Ludwig!

I'm currently dealing with a runaway 2 stroke motor on one of my bikes , something I'd not seen in many years & which has now reared up once again to perplex me.

2 cycle runaways occur with super lean combustion chamber mixtures , typically caused by a severe air leak at a case seal, base gasket, manifold, carb etc. More uncommon but still a possible cause is a big under jetting of the carb restricting the required metering of fuel.

A true run away (not to be confused with a stuck throttle) have occurred , in my experience, only on single cylinder 2 cycles. A multiple cylinder 2 stroke motor provides enough load with the extra cylinders, even at idle and in neutral to prevent a true runaway situation. Also the possibility of all cylinders running lean enough to "diesel" is also much less likely.

My runaway goes to pretty much full rpm at idle & immediately after the choke is disengaged. When the clutch is pulled. Now that's not good for motors of any type so adding a load (ride off ) buys time to kill the engine. Using the kill switch won't work, pulling the spark plug lead won't work either because the motor is acting like a diesel and the heat of the engine and compression alone are igniting the lean mixture. Best way to stop the runaway is to choke the carb, less effective but of one that sometimes works is to advance the throttle to wide open (that trick didn't work on my current runaway). Of course a handy shop towel stuffed in the carb will also work if the air cleaner has been removed if you are working in the shop.

Runaways used to be quite common in small, single cylinder, carb type out board motors years ago, not so often now but it's still good to know how to handle the situation quickly & without damaging the motor and what the root cause is...this type of trouble shooting not typically covered in the owners or shop manuals!

I'll get back with the cause of my own runaway, but thinking it's a base gasket or blown seal of some sort. Rick C.

Turned out to be the cylinder base gasket, used a bit of Permatex on it this time. Rick C.

A few riding impressions of the modified GT-5 Skyhawk now that rings are seated. Runs well. Easier to start & can't say why, no pedal just push off scooter style and dump clutch... even with cold engine & choke, busts right off. Lots more low end torque...dead stop on even slight incline ease in the clutch and throttle, results in smooth no pedal take offs. With the same stock kit exhaust it's noticeably louder, but not obnoxious. Power as indicated by the hr. meter/tach as a reference only, comes on pipe at about the same as before 6,000 to 6,500 rpm with a great rush again about the same as before going to the larger 1" piston window, but now it's again quite noticeable that getting to the 6,500 rpm point is done much quicker and smoother. Definite gains are in the low and mid range. All of this was using a 48 tooth final drive sprocket on a well balanced and clearanced engine, so it's also smooth running. I will be trying it out with the muffled expansion chamber borrowed from the X-celsior Schwinn bike, which design should produce even more gains from low through mid range (as it has on both bikes, prior to the last modifications), but may not help & possibly even hurt performance at higher rpm's. Not really important to my riding as low to mid is where I live on my bikes. Speed is good but I want to get there, wherever there is, quickly and without pedaling first of all & going fast, for me, is just knowing that I could if I wanted. lol, Rick C.