The Backwards Engine Experiment, 1939 Colson

bairdco · #1 12-04-2009, 05:01 PM

here's a before and after of my bike. just finished it today, and it rides super friggen awesome.

the build-up process is detailed here: http://motorbicycling.com/f38/rustor...off-13144.html

yeah, the motor's on backwards. that's part of the reason i'm making a new thread here. i'm gonna list the pros and cons, performance, etc... as i go along.

for now, i just got it running today, and besides the "hot foot," it works perfect.

i'll update this later. i need to ride it to the liquor store to get a soda, and that'll probably take me a few hours...

nowramfg · #2 12-04-2009, 07:07 PM

I was wondering why you reversed the barrel....I think I'd rather have the carb at the back...

bairdco · #3 12-04-2009, 07:58 PM

good for you. keep it that way..

i just got back from my first ride, about 20 miles. this thing screams. when i say "it screams," i mean, i blew past a guy on a 50cc scooter, and he couldn't catch up with me. i was riding down Newport Blvd, a 45mph zone, with traffic. keeping up with them no problem. and i still haven't completely opened it up yet.

don't worry, i'll post proof when i can get a buddy to pace me with a video camera.

there's NO four stroking or sputtering at all. none. not even once.

my set-up is:

66cc Grubee Starfire GT4 reversed.

you have to spin the jug and the piston, and match the transfer ports on the case. i also smoothed them all out as far as i could into the jug, and very carefully smoothed the burs at the cylinder ports.

the head and the jug were both lapped on a glass table, probably lost a millimeter on each to increase compression.

the intake manifold was cut down so the carb would clear the frame, which also gives a performance increase by having a smoother, shorter path for the fuel mixture. i also match ported the intake manifold to the jug as much as i could.

the exhaust pipe was straightened and ported, and the baffle and it's internals have been left alone.

the NT carb has been cleaned and polished inside and out, and the burrs and step downs have been smoothed and polished. air cleaner is still stock.

NGK BH6S plug, with filed tip, gapped to .025

solid inner wire plug cable and new boot.

Opti-2 oil at 60-1 ratio

the motor is brand new, and i'm not baby-ing it at all for break in. (if this develops any more power after break in, it's gonna be really scary...)

30 tooth sprocket on 24" wheels.

i'm 135lbs, and can ride this bike off the line without pedaling (but i do anyway.)

the bike itself is a little squirrelly, due to it's smaller size, but i think it has to do a lot with the crappy Duro tires. they came with the bike, i normally hate whitewalls, but they look pretty good on this one. another problem with them, is the whitewalls aren't straight, which gives the illusion of the wheels being bent while they're spinning.

more later...

dmar836 · #4 12-05-2009, 12:19 PM

You might be getting a ram air effect from having the cyl reversed. This was experimented with by Yamaha on GP racers back in the late 70s.

bairdco · #5 12-05-2009, 02:28 PM

Quote:

Originally Posted by dmar836

You might be getting a ram air effect from having the cyl reversed. This was experimented with by Yamaha on GP racers back in the late 70s.

i was thinking that, too. it might be another psyche-out, but it almost sounds like it's sucking in air, like my old mikuni sidedrafts did on my honda racer.

there's really no openings in the air cleaner, though, except for the ones in the bottom.

i think that just the way it's not crammed up into the engine helps, too. it's not affected by the heat, and air can flow into it better.

one problem, which has nothing to do with the orientation of the engine, is the crappy plastic petcock in the carb leaks if it's in a certain position, or if you wiggle it around. it's an easy fix, i'll just take it out and make a block off plate. i don't need 2 petcocks anyway.

just got back from a 30 mile ride. the speed trap radar sign in front of the high school clocked me at 41, 43, and 46mph, in three consectutive runs.

my speedo registered about 3-5 mph faster. i'll need to calibrate it using a crazy method i concocted (it's in the "quarter mile time" thread.)

i'm working on getting a video camera set-up, so this doesn't end up being the usual b.s. about how fast i think i'm going, how fast i claim i'm going, and how fast i'm really going.

still need to work on the "hot foot" problem. checked out some header wrap, but didn't want to pay 30 bucks for a roll, when i only need a little bit. my vintage usa made converse are getting toasted.

otherwise, the heat isn't bad at all, it's just when my shoe rubs on it when i pedal.

that's all for now.

**2door** · #6 12-05-2009, 08:53 PM

Don't pedal.
Tom

Motor Boys · #7 12-06-2009, 09:41 AM

I love it and thanks for the PM's on how to do it I have started making one for my chopped out banana seat bike should look cool.

MotorbikeMike · #8 12-06-2009, 11:30 AM

Hi Baurdco, I have "Pedal Extenders" for standard 1-piece cranks, they will jack your feet out a full inch, PM me of you like

Mike

bairdco · #9 12-06-2009, 02:37 PM

thanks mike, but i think i've got a plan.

i can bend the exhaust closer to the frame almost an inch, and i'm working up some heat shield designs.

fixed the leaky petcock at the carb today, just switched one out (good thing i have another carb,) took the bike out and it wouldn't fire up. sputtered, bogged, and stalled. looked down and saw gas flowing out of my air filter, and out of my exhaust pipe.

knew right away the float was either stuck or filling up with fuel.

yup. took the carb apart and the plastic float was full. changed it out (again, good thing i have another carb) and left the petcocks closed, pedaled around, dropping the clutch, letting it sputter and die a few times to blow all the fuel out of the case and the pipe.

fired it up and rode a 40 mile trouble free trip.

there's some really nice straightaways with a bike lane, and one with a gradual downhill slope. with the 30 tooth, i floored it down the hill, never exceeding the RPM limits (but close,) and was paced by a guy in a pickup, who pulled over to talk about my bike, and he claimed he had me paced at 50mph.

i really need a video camera. (i know, "downhill doesn't count," but c'mon, it felt awesome...)

at whatever fast speed i was going, the engine still ran ultra-smooth, not like my other one, where rapping it out caused the whole bike to vibrate like an old electronic football game (kids, ask your parents what that means.)

i gotta do something about these crappy, out of round tires, though. gives the bike this "whump whump whump" feeling. not bad enough to be dangerous, but it's friggen annoying. probably order some monday.

one new problem, is after riding flat out for 30 minutes or so, i stopped at the store, had a smoke, and after the bike cooled for 10 minutes, it took me ten minutes to start it. choked, unchoked, tickled, fast-pedaled, etc... finally, it fired up and was fine the rest of the 2 or 3 miles home.

gotta check the plug later, make sure it's still cocoa coloured.

oh, one more thing. i've been championing the coaster brake only, no front brakes forever, and i just gotta say, i love having a front drum. it's not grabby enough to skid or toss you, and it works great for just slowing down. still love the coaster, and the two combined work really great...

bairdco · #10 12-06-2009, 03:27 PM

i forgot, and i'm sure some of you are wondering if the carb would suck up any water.

i rode through a mini lake-sized puddle and splashed the whole bike (it's nice having fenders.) the carb got pretty wet, but there was no surging or bogging. don't know what'd happen if it was raining, but hopefully i'll be inside when that happens...