Pocket Bike Engine Project

[lowracer]

I added another smaller sausage muffler to quiet down this little monster & it definitely has helped although it looks weird. I will probably do something similar once I get the expansion chamber pipe I'll be ordering this week. (see pic)
-Lowracer-

 

[LS614]

Wow, that is a really cool build! Looks unique but also fast and mean

 

[cannonball2]

Hey Lowracer, is that one of the engines off ebay. I have seen 2 versions? 51/52cc and 54cc. Advertised Hp of 4.2. Same emgine? Getting ready to pull the trigger on one for my friction drive currently tunning the 31cc 4stroke. Should bolt right on.

 

[NEAT TIMES]

I would highly recommend the metal rewind & cover, it may have better internals also. There is a big difference in sound and power between my 49cc and the cag with the 52cc kit. thinking the cag motors have a full cylinder shroud with factory installations. Mine did not run long, then they would not run any more!! did not mess with them much to find probs. Maybe this fall/winter.

Lowrider, can you post your belt maker and part number ? Am thinkin of the cogged driver and thin belt with a wheel rim pulley like you. Mite install a section of flat belt in the rim channel. Thanks

Ron

 

[lowracer]

Cannonball2,
I did get it off eBay for $129. It is the Stage 2 51cc. I didnt see any difference between the Stage 2 & Stage 3. Maybe the compression is different but I didnt want the higher compression one in case of reliability issues?
I did take it for a high speed run today & definitely hit 50mph. Cant wait for the expansion chamber to arrive...

Neat Times,
The engine pulley is a STD V-Belt pulley & the belt is an AX (X=notched). Just order the correct length on eBay, they run about $12.
-Lowracer-

 

[lowracer]

What ratio of Gas to Oil do you all recommend? I started out running around 32:1 & just added some extra oil to get around 25:1. I dont see any blue smoke coming out of the pipe, so I just wanted to make sure I wasnt doing anything wrong.
Thanks
-Lowracer-

 

[cannonball2]

Id break it in on 32:1, then run a good synthetic at 50:1. 24:1 is too much in my opinion. Think of the poor weedeaters, out of the box to WOT on 50:1.

 

[lowracer]

Cannonball2,
Thanks for the advise...I'll do the next gallon @ 32:1.
I noticed something strange today (similar stuff happened to my Robin EH035).
I plugged up the tiny hole in the fuel cap since fuel was jumping up & out at high speed.
Then when I went for a ride, the engine died a few times. I opened the cap (heard a little exhale) & screwed it back on, then she started right back up. Plugging the cap doesnt allow air thru & it must starve the engine?
I got home & unplugged the cap. My new fuel tank is enroute from Dax & I hope it has a better fuel cap breather design.
-Lowracer-

 

[cannonball2]

You had a vacuum lock, you heard a little inhale. I dont know what kind of cap you are using. Some have valves that only allow air in. I guess I am going to order one of these engines tomorrow. Should wake up one of my FDs. I wish I could use a pipe but the engine is facing the wrong way on the FD, have to use a can type muffler.

 

[lowracer]

Cannonball2,
The cap is just a cheap one that came with the small white tank I bought to use for something else. I ordered a bette larger tank but wanting to get this project on the road quickly, I rigged it up. The cap has nothing inside it but a small hole (real cheap stuff here)...lol
I ordered an expansion chamber pipe today that I'll probably have to cut & use some piece of the flex pipe I currently have to make it all fit correctly. I have been known to use scrap pieces of aluminum seatpost & even ceiling fan drop pipes to fashion exhaust that goes the correct way. Maybe you can still hook up & route an expansion chamber?
I know from experience that it can add a bunch of power especially if the current exhaust is restrictive (Had a Yamaha QT50 moped that went 28 mph stock & then 50 mph adding just an expansion chamber & large holes in the airbox.) I hope to get 5 mph more on this engine since the current exhaust flows very freely.
Definitely get one of these engines off eBay, I am pleasantly surprised how bad**s it turned out & may get another if reliability proves itself. I'm hardly excited to wanna ride the Subaru Robin anymore, but that little 4 stroke is super reliable.
-Lowracer-

 

[cannonball2]

Hey Lowracer, ordered the engine today from ebay. I splurged an extra $15 for the 54cc stage 3 in silver, had wanted blue, but were out. I also ordered from Dax the cannister muffler and top mount fuel tank. After I get it up and running, thinking of going to a 1 1/4 roller. If the little dude will spin 11K thats a top end of 40. Not bad for an FD! May later order the expansion chamber if I think I can fit it. Heck for $39 it not tooo big of a gamble.

 

[lowracer]

Cannonball2,
Awesome!
Now we'll have more to talk about once you get your screaming little monster.
I took it out today for a ride & when I got back I noticed some wetness under the carb bowl. I cleaned it off, tightened the screws & went around once again. Got back & more wetness under the bowl. I'm guessing the bowl isnt sealed real well (gasket perhaps) & there are only 2 screws that hold the plastic bowl on. When I received this engine, they sent me a spare carb & I was a bit curious why I got 2 carbs (identical). Maybe one for spare parts??? LOL. I also noticed the 4 head bolts weren't as snug as when 1st received & checked. This high compression, high rpm engine probably loosens all its bolts & if gone unchecked, will lead to problems. I plan on breaking out the Red Loctite to secure these bolts that get loose. I noticed that the spark plug even got slightly loose & will sparingly hit the threads closest to the outside of the engine with Blue Loctite. No Dax fuel tank or Expansion chamber in the mailbox today
-Lowracer-

 

[cannonball2]

The old trick of torqing everything when hot might help. Things some times loosen after a few heat cycles, but will hold torque after that. Was looking at the pipes gonna be hard to do on the FD.

 

[LS614]

Torquing while hot is the absolute BEST way to strip threads out of your engine, loctite is the way to go if you don't want to waste time AND need to buy helicoils...

 

[lowracer]

Cannonball2,
I just went for a blast thru the neighborhood & am still amazed how much power this little puppy makes on top (without the expansion chamber). I then came home to do a rollout test to figure the correct gear ratio I am currently running (no better way to do it than a rollout test).
I double checked myself to make sure I got the same count. For each 1 full revolution of the driven wheel (with my weight on the bike to squish the tire), The crankshaft spins 15.6 times, so I am running a 15.6:1 ratio. At 10,000 rpm's the bike will be moving at 47.8 mph, assuming this engine can run @ 11,500 rpm's without exploding, the bike will be moving at 55 mph. I need to either get paced or radar detected since I dont have a reliable speedo or GPS device. I can imagine my wife's reaction to my request when I ask her to pace me in her minivan...LOL
-Lowracer-

 

[cannonball2]

Wow Lowracer, that a pretty low ratio, but maybe the little dude needs something like that to let it wind out. Its probably a PITA to do so but if you dropped it a point with a bigger engine pulley you might see 60! Aw, probably shouldnt go that fast any way. They say these make 4hp, I bet all at the top too which is where you need it at those speeds. Wind resistance begins ro increase dramatically over 45.This is just way cool! Hope mine runs as well.

 

[lowracer]

Cannonball2,
I had a few MB's that I geared lower & missed the engine powerband altogether....what a drag...literally.
I got lucky with this one since it goes nice off the line without the need to pedal & can hit close to 55 which is perfect for just one gear. I live in the lowcountry (flat), so I dont have to gear it for any hill climbing. I have owned many recumbents including two that were fully faired. Its amazing what wind resistance & aerodynamics will do for a body in motion. Hmmm....Now you got me thinking again about an aero cafe style front fairing for this machine....Got to come up with a new name for it too I guess.
'The Beast' morphed into 'The Screaming Little Monster'...lol
-Lowracer-

 

[lowracer]

I received my Dax fuel tank today, installed it, filled it, rode it & took a few pics. Looks good & holds more fuel than the little temporary tank I installed (just to get riding). I'm going to need to look into a better fuel cap since both tank caps spit fuel out of the top when things get moving. Unfortunately the only caps I have that work well are on my Subaru Robin & Lifan 2.5 neither of which have the same cap threading.
Any ideas?

 

[cannonball2]

Hey Lowracer, that head on the stage 3 is the other one I was talking about, looks like the cooling fins bolt on with 6 bolts, as I remember from looking at it else where still has the removable combustion cone. The cranks in there engines look really nice. Its the stage 3 kit that has the offset crank key. Wonder if its in this engine? Got notification my DAX stuff is on the way. Got the FD all disassembled and am just waiting for stuff. Plan to pull the head and look stuff over the RL the crap out of the head bolts. From vids I have seen these little dudes seem to wind forever.

 

[lowracer]

Cannonball2,
I thank you for your input on fixing the fuel cap spitting all over me. I'll get to work on it asap. I did get a chance today to take it out @ WOT for a taste of what it will do going 'Ludicrous Speed'. I definitely believe it will turn 11500 rpm's and has so much power on top. I am eagerly awaiting the expansion chamber I ordered as that should complete the package & then I'll get my wife to pace me in the van & figure out top speed. After the engine cooled down, I removed the slightly loose head bolts one at a time to apply Red Loctite.
Since going 2-stroke, I haven't looked back...LOL
-Lowracer-