Trials and Tribulations: A Build to Remember


Local time
12:49 AM
Aug 6, 2008
Some say that ambition leads to experience through trial and error. Well, I suppose for me it's true. This has been one **** of an ambitious project and I gained a respectable amount of experience fixing one problem after another.

I attribute most of this to the fact that the engine kit (a so-called 80cc Chinese engine from Powerking - Nice guy by the way) was definitely not designed for the type of bicycle I chose to mount it on (an Army Recon folding 21 speed mountain bike from Rietti - another Ebay project), however, there were several issues - most not serious as it was due to the cheap hardware included with the kit and a couple of serious issues due to an inherent design flaw in the engine casing (I cover this in detail on this thread - chain keeps bunching up... (help) ). Also I had fuel leaking from every stud on the fuel tank and from that cheesy aquarium tubing meant to be a fuel line.

I suppose I'll format this essay in a problem-solution style beginning with my first mod to the last. Here goes the story:

1. The engine is designed to be mounted on a V-frame styled bicycle. Problem is that my bike is not a V-frame but has a single fat tube that connects the front wheel to the rest of the bike and it has a hinged latch in front of the seat so it can be folded.

Solution was to get a 12" section of a 3/4" ID steel water pipe and a 12" X 3/8" carriage bolt. I just happened to have a Cummins 7 X 12" mini lathe just sitting in my apartment so I used it to cut the threads off the pipe and face the surface to make it smooth and shine. I also used it to round that square part of the carriage bolt just beneath the head so it will fit into the pipe. I rounded the edges of 2 nuts so they would fit inside the pipe as well to keep the bolt centered within it. There is a small V section where the pedal crank is. The large section supports the seat and main part of the frame. The small section has just the crank derail mechanism attached to it. I drilled a hole about an inch above the weld through both parts of the V. I formed fender washers around the frame pipes for where the carriage bolt enters and exits the frame. I also cut a piece of tire tube rubber and glued it to the frame (handy since my bike came with a hole in the tire tube. had to get a new one). I figured the rubber would help prevent water from getting to the holes I drilled into the frame and rusting.

Once I put it together I now had an appropriate place to mount the engine to.

2. Main part of my bike's frame way too big to attach the engine to.

Solution was to buy a piece of 3/4" X 1/8" steel bar and make a mounting bracket. I drilled 4 small holes and one large 3/8" hole into the bracket. 2 of the small holes are for the studs that mount the engine to the frame. The other 2 holes are for securing the bracket to the frame to prevent the chain from becoming misaligned due to the torque from the engine. The 3/8" hole is for a 2 1/2" carriage bolt that mounts the bracket to the frame. Also, I formed another set of fender washers around the frame where the bolt enters and exits. These washers allow me to really tighten the nuts on the carriage bolts without collapsing the frame.

I admit I screwed up 3 times by drilling 3 different needless holes into my frame while finding the appropriate place to mount the engine. I just wrapped tire tube rubber around all 3 useless holes and put carriage bolts in them to fill space.

Yay! Engine is mounted!

3. Problem. Unable to mount the fuel tank due to the large fat diameter of the frame.

Solution was to form 2 new brackets from 1/2" X 1/8" steel bar around the top part of the frame. I drilled 4 holes in each bracket. 2 for the tank's studs and 2 for mounting the bracket to the frame from the top. I didn't want the brackets to wrap around the frame because it would obstruct the Army Recon logo.

4. Problem was that my bike has handle bar extenders and I like them. The throttle won't allow me to reattach the extender on the right side.

Solution was to cut the end off the throttle so that an inch of the handle bar extends beyond it so I can attached the extender.

5. Problem was that FUEL TANK LEAKS FROM THE STUDS and from the hose at the carb nipple.

Solution was to get some fuel tank sealant and a real fuel hose. I bought some Northern Fuel Tank Sealant and some acetone. I rinsed the tank out with acetone and let dry. I poured about 3 ounces of the pretty navy blue sealant into the tank and swished it around to coat the entire inside then I let the excess drain out where the petcock screws into. Not only did this stop the leaks now I don't have to worry about my tank rusting and fouling up my carb. Here on California's north coast it's quite cool and wet for a good part of the year anyway.

As for the fuel hose, why the **** do they send that **** to use? I bought a real hose, a real in-line filter and some clamps. I forced the hose and a clamp onto the brass nipple. No more leak.

6. Problem was that front suspension on the fork allowed the frame to lower enough that the front wheel to knock off the spark plug cap off the plug and even let the tire rub on the cooling fins of the engine. There is a gap of about 1 1/4" between the engine and the tire so the frame sinks at least that whenever I apply the front brakes.

Solution for the spark plug was to cut off the boot and make a small one out of JB Weld.

As for the other issue. Well, It became a serious problem when some ******* made a right turn in front of me and I hit the bakes hard enough that the front wheel jammed against engine and locked it up sending me over the handle bars and the bike on top of me. As I lay there in the hospital emergency room waiting for the X-ray results that showed I had 2 fractured ribs, a fractured wrist, and a fractured elbow I came up with a solution. I pulled up the little rubber boots on the front forks and measured up an inch and put 3 screws in each side to prevent the front suspension from going any lower than an inch. It won't allow the tire to rub on the engine now.

7. Problem was that the carb would not fit onto the engine because of the angle of the frame the engine is mounted to.

Solution was to cut off part of the intake manifold at the bend and use JB Weld to glue a 3/4" 90 degree copper street fitting to it. I used JB Weld to attach the carb to it as well. I drilled a small hole for a screw to secure the carb to the fitting as well. This solution allowed me to ensure that the carb was reasonable level when the bike is on level ground.

8. Problem was that the clutch lever sent with the kit was complete ****. It was so loose that it wouldn't even hold the cable in place.

Solution was to order an alloy (pot metal) locking clutch handle from Ebay. I removed the locking pin and used my lathe to make a little lip on it. The vibration from the engine kept popping the clutch in gear so this mod prevents that.

9. Problem was that the chain links jumped the sprocket inside the engine which locked up the back wheel. First time I tried to start my engine I had the full force of my weight going downward onto the crank when it locked up. I thought I may have broken my ankle but it was just a bad sprain.

Solution was to form 2 pieces of 1/2" X 1/8" steel bar around the sprocket held in place by JB Weld. Due to the angle the engine is mounted to the frame I had to file down part of the case. Chain never gave me any more problems.

10. Problem was that bike has kickstand mounted on rear wheel axle. Could not fold the bike without it falling on the engine.

Solution was to get a double sided kickstand. Works great.

11. This isn't a result of a problem but built an intake resonator. I did some research on intake resonators for 2 strokes and supposedly they work pretty good at enhancing performance on the low end of the throttle and also improve HP as well as efficiency. If you look at the pics I attached to this post you will see the 10" by 3/4" copper tube I painted black attached to frame under the fuel tank. I soldered end caps and a 3/8" nipple to attach a hose to a nipple soldered onto the 90 degree street fitting attached to the carb. The theory behind the resonator is to give space for the back pressure in the intake manifold to go to when the reed valve or whatever closes. Imagine that the air inside the intake manifold has a certain velocity to it as it flows into the crankcase of the engine and when the valve closes the air still has that velocity. That causes the air to 'bounce' backwards like a ball thrown at a wall. Carbs will carburet in both ways so it become enriched with fuel twice at low rpms. The resonator prevents the air from flowing back out of the carb (See Boost Bottle for more info on this). Also since the back pressure oscillates in waves the resonator has to be tuned to the engine. I tuned mine by matching the volume of the copper pipe plus the volume of the connecting tubing to the displacement of the engine. I measured the volume by filling up a 10cc syringe with water and measured out 80cc. I never ran the engine without this setup so I have nothing to compare it to but what I can say is that I have enough torque to accelerate up a 5 percent grade hill from a stop. In the clear tubing there are beads of condensed oil that oscillate back and forth at idle from the direction of the back pressure as it enters and leaves the pipe.


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Local time
12:49 AM
Aug 6, 2008

. I should note too that I have 60 miles on my current tank of gas with a pint still left in it. I can't put a true half gallon in it due to the angle in which it's mounted so I'd say the resonator is working. A commercially built kit called the Boost Bottle is available on Ebay. I don't know how well they work though some others swear by them.

Safety is important to me. I'd rather be riding my bike than lying in the emergency room so I invested in some cheap add-ons like a speedometer, a brake/tail/turn signal light with a horn, a mirror, and a cushy spring loaded seat to fit my fat butt comfortably. Some gel-padded bike gloves should be used to dampen the vibration. And most important of all is a US-DOT approved helmet which is required by law in this state.

Last but not least I do wish to protect my investment. I have a cheap motion detector bike alarm and a bike cover to deter thieves and protect it from the wet environment we have here.

Well, this has been a somewhat long winded post however I hope that my experiences and solutions will help others with their projects. See attached pics for clarification.

Thanks and safe riding!

P.S. I did take the cover off the clutch side of the engine to find no grease in there! I put just enough to cover the teeth on both gears to reduce the whine noise.


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Local time
12:49 AM
Aug 6, 2008
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Sounds like you went through heck on this build. I salute your refusal to give up, and applaud the ingenious methods you came up with to overcome the obstacles. And that resonator sounds like a good idea.


Local time
12:49 AM
Aug 6, 2008
There is a commercial version of the resonator on ebay called the Boost Bottle.

I get so many people here that walk up to me asking where they could get a bike like mine. The surprised looks on their faces when I tell them the motor comes separate as a kit makes me feel better as they think it was commercially built with it. I did it right.

It's been 300 miles or so since I built it and the only serious issue so far was a blown intake gasket and replacing that crappy cheap stock spark plug with a real one.



New Member
Local time
3:49 AM
Jun 26, 2008
Congrats James!
You certainly paid your dues on this one, hope you've healed up Ok.
Local time
1:49 AM
Jul 15, 2008
Thanks (or maybe tanks) for the info on your build. I've just bought a Hua Sheng 4-stroke kit from Mike Simpson and am in the first stages of putting it together onto an old Trek mountain bike. One of the first things I saw was how cheap the gas tank and fuel line set was, and the four bolts coming out of my tank were going in 4 different directions when I pulled it out of the box. I've been fretting about leaks, and was thinking about testing it before mounting, but think now I'll just take your lead and buy some of that tank sealant. Why screw around with a wad of gas sitting in a cheap metal tank right in front of my you-know-what? I already planned to replace the fuel line with some real stuff from the auto parts store, but wondered if I was just being a wanker. If I am, there's two of us anyway.

Hope you heal fast and get back on that ride.

Bill Leif (Vishnu Tensleep)