FOX Dynamark Mini Bike Information and Chronological Guide.
I buy and collect Fox minibikes. 04/01/23. Email:

Overall Fox History and Info.

    There isn't much history on the Fox Corporation (Janesville WI), so details are a bit thin. But I'll try and fill in what I know, and hopefully add more info to this page in the future.

    Fox Corporation started just after WWII in 1946, selling motorized vehicles. Mostly stuff like farm carts and golf carts and later snowmobiles. But in 1958 Fox got into the go-kart market selling their "Go Kart" brand of fun carts. This fad seemed to fade a bit and by 1965 Fox was making minibikes too. Their first bike seemed to be the 1965 Fox Little Gen and it's 2.5 or 3hp motor (probably Lauson.)

    In 1966 Fox started to get more serious about minibikes and introduced their "Sport Bike" (2.5hp Lauson) and "300" models (3 or 4hp Briggs) mini bikes. The 300 model had 6v lights, full suspension, jackshaft, fancy fenders and gas tank covers, centrifugal clutch. This can be seen in their Fox catalog #6, along with their go karts.

1967 Fox Campus Mini Bike from catalog #7.

    By 1967 Fox really got serious about mini bikes. Their Fox catalog #7 showed their "Campus Bike", which was basically an upgraded model 300 from the prior year. It was available in a variety of formats from a no motor version, to a 5hp Briggs model with lights. The Campus mini bike had 6" solid wheels and full suspension (front and rear), and the top model had a funky gas tank plastic cover, giving it a sleeky 1960s look. Fox also sold lower minibike models like the Sprite, the Trail Bug, and the Doodle Bug (no relation to the China-made Doodle Bug DB30 of the 2000s). The Sprite had 4" wheels, and the Doodle Bug used 6" wheels. Most mini bike models used a jackshaft. Note that in 1968 and 1969, as seen in the Fox catalog #8 and Fox catalog#9 (looking for a full Fox catalog 1969, or a good scan of it), the models didn't change.

1970 Fox Street Scamp mini bikes from catalog #10.

    With 1970 Fox completely changed their mini bike models, as seen in their Fox catalog #10. This probably came about because Rupp changed their models significantly, and Fox wanted to compete. The big change was spoked 10" wheels on all models (except for the Doodle Bug, which still used 6" solid wheels.) These 10" spoked wheels were not available from any U.S. manufacturer, so they were imported from Italy (originally used for Italian scooters), which was what Rupp was doing too. Also all minibike models had chrome gas tanks and fancy exhausts (except the Doodle bug's was painted, but it used the new gas tank design too). Also new to Fox was Kelsey-Hayes rear disc brake used on the rear sprocket for all mini bike models (even the Doodle bug minibike). Some Fox mini bikes had disc front brakes too.

    Starting in 1969, first for Fox (and something many others followed) was the 20 degree slant motor mounts and a jackshaft (but no jackshaft on the Doodle bug, but it too had the slant motor mount). This 20 degree motor mount was known as the "tilt power plant" and was a first on the Fox 1969 models. Tecumseh was the motor of choice too, and frankly was leaving Briggs and Straton behind as the go-to mini bike engine. With the 20 degree mounted engine, the gas tank could not be mounted to the carb (as was done on Briggs engines.) Hence Tecumseh made their HS40 model #55266A engine specifically for Fox and the 20 degree motor mount. This was the early version of the HS40 with a slightly different head pattern (head gasket #32643), and a diaphragm carb (a float bowl carb was not ideal with a 20 degree slanted engine.) At this point it became obvious that Tecumseh was serious about supplying engines to mini bike makers, and that Briggs was a has-been. Hence Briggs got out of the mini bike engine supply chain, with Tecumseh taking over for just about every U.S. mini bike maker. Whether Briggs was forced out of the market, or just did not want to be in the market, is unclear.

    In 1969/1970 Fox single speed bikes used centrifugal clutches, and dual speed minibikes used a 2-speed automatic clutch system, which utilized two centrifugal clutches (one on the motor and the other on the jackshaft.) This set up used a centrifugal clutch with two chains going to the jackshaft.

    In 1971 Fox again changed their mini bike models, probably to follow Rupp's changes. A Fairbank Morse torque converter was the norm for most models (the 2-speed automatic centrifugal clutch set ups were gone). This dramatically increased the power of the bikes, as the Fairbank Morse converters were a very good design. Suspensions were bulked up too, again probably to compete more with Rupp. The Tecumseh diaphram carb was no longer used (a change Rupp made too). Instead a slant intake manifold was utilized to keep the float bowl carb level (because the 20 degree motor mount.)

Fall 1972 Fox/Dynamark catalog showing the Thunderbolt models.

    In 1972 Fox (now also marketed as Dynamark) released many new models including the Thunderbolt line of mini cycles. All the Thunderbolt models are using Tecumseh 3.5, 4, or 5hp motors. Here's the 1972 Dynamark/Fox catalog #12 which shows many of the new Thunderbolt models.
Fall 1973 Fox ad from a NY department store catalog.

    In 1973 the Fox/Dynamark line had mostly spooked wheels mini cylcle type bikes (Thunderbolts.) This is seen in their Fox minibike catalog 1973. In addition to the Thunderbolts, they also offered a Tecumseh mini cycle with lights and a speedometer (Thunderbolt 200mc). The Thunderbolt 125 used a 3.5hp Tecumseh and only had front suspension and a clutch. The Thunderbolt 150 had front and rear suspension, a 4hp Tecumseh motor, and torque converter. In 1973 the Thunderbolt 198mc was introduced with a really cool leading link front suspension, 5hp Tecumseh, and torque converter. The Tunderbolt 200mc was top of the line and really a full motorcyle with a Tecumseh 2 stroke motor (though no gears, used a torque converter.)

The Fox Sundowner. The early models had spoked 10" wheels. The later models like this one had Speedway 10" wheels.

    As an interesting side note, Fox Corp bought out Speedway in the spring of 1974. Speedway rose from 1970 to 1973, and then died (Speedway was a Division of Taylor metal products.) I'm not sure what benefit Fox got from this purchase, as their models are different than the big wheel Speedway mini bikes. Here's the news bulletin on this:

      Snowsports Dealer News - April 1974, Mansfield, Ohio. Snowsports Dealer news has learned that Speedway Products, Inc. has been sold for an undisclosed amount of cash to Fox Corporation, Janesville, Wisconsin, according to Bill Graff, a Fox spokesman. The company acquired "the entire Speedway line and most of the company's assets". John Morrow, former Speedway president, has also moved to the Fox Corporation and has been named Vice President of operations.

    The 1969, 1971 and 1974 Fox mini bike catalog(s) have largely escaped me (does anyone have a copy they call sell me or at least let me borrow to scan???)

The Fox Tracker. Essentially the same model as the Desert Fox but with lights and white in color.

    About 1974/1975 Fox downgraded their minibike line to basically only two stroke models. This included the Sundowner (intially released in 1973), the Desert Fox and Tracker models (essentially the same model, but the Tracker had lights and was white.) By 1978 Fox sold off all their remaining bikes and parts to Manco. For this reason you can find the Fox Sundowner with Manco labeling (and Speedway rims!)

    Below are some pictures of these bikes I personally own, restored, or have seen. Fox was definitely moving to more mini-cycles than mini-bikes with many of their models, increasing the wheel size to as large as 14" diameter. Again this followed what Rupp and Speedway were doing at the time. Their Thunderbolt and Desert minibike/minicycle models were the new flagships of the mini bike model lines. Note most models had "TC" and "4HP" round stickers on the original torque converter covers, signifying their proudness for the 4hp Tecumseh motors and Fairbank Morse torque converter. But by 1975 Fox had moved to Comet brand torque converts (probably price dictated that move.)

The 1971 Fox AM Scrambler mini bike model. This is a great minibike with 10" wheels,
rear disc brake, Comet torque converter, 4hp HS40 Tecumseh motor

The 1972 Fox Thunderbolt 170 mini bike model. Awesome minibike with 14" wheels,
drum brakes, torque converter, Tecumseh motor (non-original carb/exhaust).
Torque converter cover is not original on this bike (a commonly damaged part.)

The 1973 Fox Thunderbolt 198mc mini bike model. This is really more of a mini cycle with
front "Earls" leading link suspension, 16" front wheel, 14" rear wheel, drum brakes,
Comet torque converter. Note the torque converter cover is not original on this bike (a commonly damaged part.)

The 1974 or 1975 Desert Fox mini bike model. Another minicycle more than a minibike.
Again front "earls" leading link suspension, 14" wheel rear wheel, 16" front wheel,
drum brakes, Comet (or Fairbank Morse?) torque converter, and a two-stroke AH817MB
134cc (8.17ci) Tecumseh motor and diaphram carb. Preston Petty Products "mini mudder" front
and rear plastic fenders. Unfortunately this bike is not mine.

Here's another Fox Desert Fox, circa 1974 or 1975. This bike is mine. Not as
original as the prior Desert Fox, but it runs well. Adapated a 19mm slide carb
to the motor with a custom intake. This really helped the Tecumseh AH817 engine performance.
But to be honest, a Tecumseh HS50 would have been a better motor for this bike!