Sportsman 80

GoldenMotor.com
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sportscarpat

Bonneville Bomber the Salt Flat record breaker
Jun 25, 2009
1,839
471
83
california
Hi Guys,
I built up a pedal bicycle as a boardie and it's a cool bike, great for bombing down hills as a gravity racer, but eventually I have to pedal and pedaling a boardie for a tall guy like me is difficult. The pedal bike is a 110mm Sportsman Flyer frame with a single speed coaster brake hub. These frames are built from .090" wall tubing and are perfect for the smaller four stroke engines.

Here is the starting point. Last day as pedal bike and time for some four stroke power!

Sportsman 80 by Sportsman Flyer, on Flickr

Here's the engine I am using. This is a Harbor Freight 79cc four stroke. As shown here I have already stripped down all the unnecessary components like stock gas tank, intake, carb, and exhaust. I have added a custom intake and exhaust manifold and 19mm Mikuni carb. I also removed the internal engine governor, plugged the governor holes left in the case, and trimmed off a piece of casting I didn't need. Oh, I also stuffed in a nice fat cam from AGK and some stiffer valve springs.

Sportsman 80 by Sportsman Flyer, on Flickr

On this side of the engine I had to drill through the side cover casting to add the oil fill point cap. Drill through, tap 1/2" NPT, then add a 1/2" NPT by hose fitting and a brass hose cap. Intake and exhaust components are all tig welded stainless steel with laser cut 1/4" stainless flanges.

Sportsman 80 by Sportsman Flyer, on Flickr
 
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sportscarpat

Bonneville Bomber the Salt Flat record breaker
Jun 25, 2009
1,839
471
83
california
Here is the AGK cam and valve springs. Shane gets credit here for making these parts available for the HF79cc engine. Very cool!

Sportsman 80 by Sportsman Flyer, on Flickr

Inside of the little beast. New cam installed on the right. Crank is in the middle and the space on the left is where the engine governor plastic gear used to reside. Those are now gone and the holes plugged. Nothing better than throwing a nice fat cam into an engine! I didn't get a picture, but up top I added the stiffer valve springs and readjusted the valve train.

Sportsman 80 by Sportsman Flyer, on Flickr
 
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sportscarpat

Bonneville Bomber the Salt Flat record breaker
Jun 25, 2009
1,839
471
83
california
Sportsman Sprocket Adapter being installed. Normally I don't need to modify the bend on the coaster brake arm as small engine builds don't require a lot of sprocket offset. This build is different. I run the sprocket as far to the left as the frame will allow. That's a 44t sprocket and once combined with my reduction drive pedal crank I will have proper street gearing.

Sportsman 80 by Sportsman Flyer, on Flickr

Here is the sprocket mounted up. I like to leave it loose and make the final offset adjustment with the wheel in the frame.

Sportsman 80 by Sportsman Flyer, on Flickr

Here is the key to the whole drive system. This reduction drive pedal crank assembly gives me the necessary engine side gearing reduction while leaving the bicycle side pedal system intact and fully functional. All this when combined with the engine mounted centrifugal clutch means no drag while pedaling, and once you wind up the engine past about 3000 rpm the pedal side freewheels and the engine takes over.

Sportsman 80 by Sportsman Flyer, on Flickr
 
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hsvmick

hsvmick

Member
Mar 23, 2011
234
6
18
hobart tasmania australia
G'day Pat,
another beautiful tame little machine you got there with a great colour too,can i ask how doe's the front drum brake work on these bike's are they 90mm drum's or 70mm and stop pretty good as i looking for a good front braking set up without going disc
 
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culvercityclassic

Well-Known Member
Sep 27, 2009
3,115
177
63
Culver City, Ca
Great looking bike, I keep on looking and talking myself out of one. I ride a motorbike to work everyday and I think people are tired of hearing my two stroke ****. Got a built 99cc, wheels, fork, clutch... Now all I need is a email from Pat with an offer that's hard to refuse...hint hint
 
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sportscarpat

Bonneville Bomber the Salt Flat record breaker
Jun 25, 2009
1,839
471
83
california
hsvmick said:
G'day Pat,
another beautiful tame little machine you got there with a great colour too,can i ask how doe's the front drum brake work on these bike's are they 90mm drum's or 70mm and stop pretty good as i looking for a good front braking set up without going disc
Click to expand...
Hi Mick,
I would call the brakes adequate but not exceptional. Just the nature of the beast. I have always leaned toward the vintage look so I feel a disc brake would look out of place. Maybe not.
 
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sportscarpat

Bonneville Bomber the Salt Flat record breaker
Jun 25, 2009
1,839
471
83
california
culvercityclassic said:
Great looking bike, I keep on looking and talking myself out of one. I ride a motorbike to work everyday and I think people are tired of hearing my two stroke ****. Got a built 99cc, wheels, fork, clutch... Now all I need is a email from Pat with an offer that's hard to refuse...hint hint
Click to expand...
Hi Jeff,
I also ride to work and have been riding my cruiser version of this machine. Same frame and engine package. Engine internals are bone stock, governor disabled but not removed, and it cruises comfortably at 37 mph. That 99cc engine you have sounds pretty cool. I was late to the small four stroke game so never had the chance to buy a 99cc before they were discontinued. Now when you see them people want too much money.
I do have a 212 Hemi Super Cruiser in the early stages, but that's another build for another day......
 
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sportscarpat

Bonneville Bomber the Salt Flat record breaker
Jun 25, 2009
1,839
471
83
california
So I had some time and bolted the engine in. Still lots to do but I was excited to see how it would look. Man, I really like how this bike is coming out. So much like the 200cc bikes I have built but much simpler and lighter. After mounting the engine I finished hooking up the fuel line and controls so I could fire it up. With the added cam it completely changed the sound of the engine compared to a stocker. If it runs as good as it sounds it will be a little monster.

Sportsman 80 by Sportsman Flyer, on Flickr

Another view with it's stable mate, my cruiser version of the same basic bike. Between the wife and I these two will get lots of use. I still need to install the clutch and primary chain, throw on a cycle computer (I really need to know mph to keep off the local radar), and finally mount up some 26 x 2.5" Maxxis Hookworms. On these bikes I left the stock pull start covers for added flywheel protection and ease of starting. I am working on a bump start system for the centrifugal clutches, but really it's not necessary. These bikes are easy to start.

Sportsman 80 by Sportsman Flyer, on Flickr
 
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sportscarpat

Bonneville Bomber the Salt Flat record breaker
Jun 25, 2009
1,839
471
83
california
Finally out on the open road. I added some better tires, Maxxis Hookworms in 26 x 2.50. They are a tight squeeze but clear everything. They also give me confidence when running at 40 mph.

Sportsman 80 by Sportsman Flyer, on Flickr

Closeup details. The 5/8" centrifugal clutch is working nicely and dialed in for 3000 rpm lock, this way it feeds in just as the engine starts to build torque and stays engaged on trailing throttle which is important while cornering. You can also see the added top engine mount. On bigger 200cc engines I run three mounts, but these smaller engines seem fine with just two.

Sportsman 80 by Sportsman Flyer, on Flickr

Country road cruising. Nice to live on the edge of town! So these two bikes are basically identical chassis, one set up as a cruiser and the other a board track racer.

Sportsman 80 by Sportsman Flyer, on Flickr

By the way I did have a few teething issues with the orange bike. It was hard to start at first and running rough. The factory coil to flywheel gap was way too wide and once I figured that out it ran much better, then took a turn for the worse. Powder coating shop again got grit into the gas tank which crudded up the carb. Cleaned it all out and smooth sailing after that. It was a quick fun build that will now see plenty of hard miles.
 
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runnermike

runnermike

Member
Nov 18, 2012
936
0
16
Sanford, FL
Pat

Beautiful...simply beautiful! The more I look at this bike the more I realize how not beautiful my bike is...lol!

As the orange bike sits, with everything on it, including the engine upgrades, what would it cost someone to purchase/have you build and ship?
 
silverbear

silverbear

The Boy Who Never Grew Up
Jul 9, 2009
8,325
670
113
northeastern Minnesota
Pat,
You've built a lot of great bikes including the one's which end up at Bonneville, gutsy machines that have morphed from bicycles into record setting performance motorcycles. For normal riders looking to have a good time and dependable transportation this one is just right. Not too powerful and not under powered either. Even stock that engine has a lot of torque. With the modifications you have made it must have really wakened up! Nice job!
SB
 
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sportscarpat

Bonneville Bomber the Salt Flat record breaker
Jun 25, 2009
1,839
471
83
california
Hi Silverbear and Mike,
Thanks for the comments. These 80cc bikes, my cruiser and boardie, have proven very useful machines, and as you say Silverbear, the engine sizes seems just about right. They can pull a decent hill and comfortably cruise at 38 mph. They can reach 44 mph on flat ground with no head wind. I find it very convenient to retain the stock rope pull flywheel cover. So easy to start and ride, and legal in California, too. My wife and I have been riding them EVERYWHERE without worry. We do a lot of exploring and she keeps wearing a small back pack crammed full of goodies so I have a surprise for her. I need to test them first to be sure they are safe.

Panniers for the cruiser!

Sportsman 80 by Sportsman Flyer, on Flickr
 
hsvmick

hsvmick

Member
Mar 23, 2011
234
6
18
hobart tasmania australia
PAT,
panniers for the cruiser?your wife must pack same goodies if you wanting more room in her backpack ,good thinking amazing goodie's you come up with and the sportsman 80 must be a flyer great little machine well done
 
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