Testing the 79 & 99 CC HF motors

Discussion in '4-Stroke Engines' started by Quenton Guenther, Dec 18, 2011.

  1. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    It certainly has been a busy year, but we still managed to design the Q-Matic drive to fit the latest motor from Harbor Freight. We produced a fair number of drives for the 79 CC and finally had time to test the drive on the current 99 CC HF motor. Many parts are interchangeable between the motors, and the drive side bolt pattern is also the same.
    Some things are surprising, including the 5/16 fine thread bolt used on the 99 CC in place of the 8 MM on the 79 CC. The 79 CC was rated to use 89 octane, however the 99 CC wants 87 octane. The "foot" bolt pattern is very close on both motors, however the 99 CC uses a staggered system, meaning the boltholes are closer on one side than the other. The bolthole centers are 102 MM on one side and 104 MM on the other. This was first discovered when we noticed the extra mounting [foot] plate holes didn't line up, if we rotated the plate the holes lined up. Next we noticed the crankshaft on the 99 CC is over size, and requires the pulley I.D. size increased to fit.

    The 79 CC is 80.7 CC and the 99 CC is 98.5 CC a difference of 17.8 CC. The 79 CC has the same size 15 MM carburetor, but loses the air/fuel mixture screw on the 99 CC motor. The motors produce very similar power, however the 99 CC is slightly slower in stock form. The 79 CC has a higher top end with identical drive ratios, but the 99 CC pulls harder on the way to top end. After a few minor modifications, the 99 CC will pull harder and reach a higher top speed.

    Blue or black? My test bike is blue; the 79 CC motor housing is blue. The 99 CC used to have black covers and didn't match my blue bike. The used test 79 CC motor now has black cover & black rope start, whereas my 99 CC test motor now has blue cover & blue rope starter assembly.....this means they are interchangeable.

    After the few minor modifications to the 99 CC motor and some break-in time, here are the facts.. Easily hits 6000 RPMs, pulls very hard, can pull a harder ratio [gig her top end, slower start]. With the ratio of 11.55 X 1 the following numbers were the results 3000 RPMs = 20 MPH 3600 RPMs = 24 MPH, 4500 RPMs = 30 MPH, and 6000 RPMs = 40 MPH.

    If I can find a little extra time I will try changing the Q-Matic ratios and see what happens at 9.52 X 1..... Should easily pull the numbers and should look like this:
    3000 RPMs = 24 MPH
    3600 RPMs = 29 MPH
    4500 RPMs = 36 MPH
    6000 RPMs = 48 MPH
    6155 RPMs = 50 MPH

    Way too fast for a bicycle, and I am sure no one will want to go that fast. BTW I had the test bike at 6300 RPMs several times during testing using the 11.55 ratio drive.

    Have fun,


    Attached Files:

    Last edited: Dec 18, 2011

  2. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    More pictures

    Have fun,

    Attached Files:

    Last edited: Dec 18, 2011
  3. Stoney

    Stoney Member

    All the pics are mini???
  4. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    Hi Stoney,

    Thanks for letting me know they were small. I just "upsized" them all. Let me know if anyone needs any more pictures.

    Have Fun,
  5. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    Changed the primary ratios yesterday. At 8.5 X 1 it was too tall and stopped the motor from reaching the same 6300 RPM level. The top speed was also lower as the motor simply ran out of power under the harder load. The bike was only able to reach 46 MPH @ 5100 RPMs.
    I reset the adjustable pulley to a slightly lower size and found the bike with a quicker take-off and higher top end speeds. The current ratio is 9.87 X 1 and produced a top end of 49.3 MPH @ 6300 RPMs

    Final conclusion:
    Ratio should be 11.55 X 1 for heavy riders or hilly areas [or both].
    11.55 X 1 is supplied by using a 2.5" primary pulley on the Q-Matic drive.

    Using a 3" primary pulley on the Q-Matic drve supplies a 9.53 X 1 ratio. 9.53 X 1 is good for average riders on slighty hilly roads. The 9.53 X 1 ratio allows the motor to run at lower RPM levels at crusing speeds.

    Light weight rider or flat ground travel can use a ratio of 9.876 X 1 on the Q-Matic drive. The adjustable primary pulley was set at 2.90" to cause the 9.876 ratio.

    Happy New Year and Have fun,
  6. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    Just completed another round of ratio tests on the 99 CC HF motor, and will share the results. The following ratios are used on a 26" bicycle, AX series belt, with a 56 tooth rear sprocket.

    Primary pulley set at 2.95" [total corrected ratio = 9.7 X 1]
    Primary pulley set at 2.90" [total corrected ratio = 9.87 X 1]
    Primary pulley set at 2.85" [total corrected ratio = 10 X 1]
    Primary pulley set at 2.80" [total corrected ratio = 10.24 X 1]
    Primary pulley set at 2.75" [total corrected ratio = 10.45 X 1]

    I will only list the speed at 2500, 3500, and 5500 RPMs on the various ratios

    9.7 X 1:
    2500 RPMs = 19.9 MPH
    3500 RPMs = 27.9 MPH
    5500 RPMs = 43.8 MPH

    9.87 X 1:
    2500 RPMs = 19.5 MPH
    3500 RPMs = 27.4 MPH
    5500 RPMs = 43.1 MPH

    10 X 1:
    2500 RPMs = 19.3 MPH
    3500 RPMs = 27 MPH
    5500 RPMs = 42.5 MPH

    10.24 X 1:
    2500 RPMs = 18.9 MPH
    3500 RPMs = 26.4 MPH
    5500 RPMs = 41.5 MPH

    10.45 X 1:
    2500 RPMs = 18.5 MPH
    3500 RPMs = 25.9 MPH
    5500 RPMs = 40.7 MPH

    The ratio choices can be expanded by replacing the AX series belt with the 15 series wedge belt.

    26" wheels, 56 tooth rear sprocket, 3" primary pulley, wedge belt:
    9.748 X 1:
    2500 RPMs = 19.8 MPH
    5500 RPMs = 43.6 MPH

    26" wheels, 56 tooth rear sprocket. 2.5" primary pulley, wedge belt:
    11.96 X 1:
    2500 RPMs = 16.17 MPH
    5500 RPMs = 35.57 MPH

    Hope this infomation is helpful.

    Have fun,

    After several more tests and some high winds, I have determined using a 3" primary pulley is too much. It works well on flat ground, no wind, and a light rider, which isn't the average riding conditions. Simply dropping the 3" pulley to 2.90" made a lot of difference, however if hills or rider weight are considered, the primary pulley should be reduced to 2.75" as this ratio will keep the bike within acceptable limits.

    Have fun,
  7. jbcruisin

    jbcruisin Member

    I ordered one of these 99cc engines from Harbor freight. Too much good talk about them to pass it up. :) It's going in my blue bike.

  8. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    Hi Jay,

    It appears the HF 99 CC 4-stroke is the motor of current choice.

    We have done a lot of research and testing on both the 79 CC and the 99 CC, and have lots of information if anyone needs it.

    Have fun,
  9. jbcruisin

    jbcruisin Member

    my blue bike should really run with the 99cc
  10. MotorbikeMike

    MotorbikeMike Member

    Harbor Freight Q-matic choices

    Hi all, well I have a quandary, I have both a Big Blue Dog (greyhound) and a Black Predator.
    The choice is, I have a drop-loop Model 08 Simpson Racer, chopped to a bit radical in the front end, Worksman Wheelset, 60 tooth Maniac Mechanic rear.

    Looks like my adjustable pulley should be at about 2 3/4, ax 25 belt, BUT, shall I try Blue, or Black????

    Sadly, the blue MIGHT go well with the proposed blue paint for the bike, BUT the 99 might haul my big self better?

    This should be fun?

  11. wzuccarello

    wzuccarello New Member

    Just swap the shrouds around. They're interchangable between the 2 engines!
    Last edited: Jan 9, 2012
  12. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    Hi Mike,

    I had the same problem with the factory test bike. It was a nice blue with the 79 CC Greyhound motor which as you know is also blue. I simply exchanged the covers and rope starter assembly and ended up with the 99 CC Predator motor in blue. If you use the 99 CC motor with the flex pipe be sure to drill the main jet out to .031", otherwise it will run too lean.

    I agree the 2.75" primary pulley should be ideal with your H.D. [heavy duty, not Harley Davidson] frame.

    You can use the motor mounting plate from the Predator as the pattern to drill holes in one of the stock 4-stroke motor mount kits. Be careful as the motor "foot" pattern is staggered on the 99 CC and not the 79 CC. One set of holes is 102 MM and the other is 104 MM. The side mounting holes use 8 MM bolts on the 79 CC motors, whereas the 99 CC motor uses 5/16 X 24 threads [not a common thread size].

    You may also need an AX26 belt with the larger primary drive pulley. The AX26 is the same belt used on the vintage Whizzer motors, and you most likely will have one.

    Have fun,
  13. Richard H.

    Richard H. Member

    How many states would these be legal in for road use and which states would that be?
  14. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    Hi Richard,

    Several states don't have any CC limit and limit HP. For example Whizzers are 138 CC and are legal in CA because of the HP limit. There is another state on the east coast that has put the limit at 5 HP [might be CT, not sure].

    We {EZM} will continue to ONLY supply the 49 CC HS 142a motor in our 4-stroke kits, to respect the majority of state rules concerning motorized bicycles. In fact we are making a kit to adapt our Q-Matic drive to several smaller 4-stroke motors for a couple of states that set the limit to 35 CC.

    I live in NC and have titled several of my bikes as MC and have plates & insurance on them. I have a large selection of Whizzers [over 20], and the new edition versions must be tagged, but the vintage Whizzers are "grandfathered" in as antique and can either display a plate or not. Of course NC like many states has conflicting laws, and often difficult to understand. In NC one section limits the speed to 25 MPH and in another section it is 30 MPH. Scooters are in the same class as motorbikes, because a few years ago, a large hardware store chain tried to sell electric scooters and had the part of the law requiring "pedals" removed.

    I would suggest everyone check their state laws, and even carry a copy, as even Law enforcement has a hard time with some of the rules.

    I was once stopped by a NC state trooper and had to listen to him tell me several times I was going 55 MPH. The speed limit was 55 MPH, and the Whizzer had current plates, current safety inspection sticker, a MC endorsment on my lic., and wearing a helmet. He insisted the motor had to be smaller than 50 CC [wrong] and insisted it had to be stamped somewhere on the motor[wrong]. To add more to the story, I had a vintage gas tank on the bike and the original sticker stated "Do not exceed 25 MPH for the first 500 miles", which lead the Trooper telling me "see, you were speeding" [DUH].

    Have fun,
    Last edited: Jan 9, 2012
  15. Richard H.

    Richard H. Member

    Thanks, good advice.
    Last edited: Jan 9, 2012
  16. Gen3Benz

    Gen3Benz Member

    Nice work! Great info from your testing.
    Where did ya find that air cleaner?
    I bought a 79cc back when they started selling them. Took a long break from motoredbikes and think i'm gonna start another project soon.
  17. azbill

    azbill Active Member

    that is a chrome whizzer air filter I believe ;)
  18. Gen3Benz

    Gen3Benz Member

    Thanks Bill!
    Looks like it'll flow better than the original which has to turn 90 degrees to enter the carb.
  19. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    Hi Gen3Benz,

    Many have simply used a "tuna" can. Filled with mesh [from pot scrubber from a dollar store] and drilled holes to affix to carburetor and more holes to allow it to flow more air.

    Of course a little paint to cover up the "tuna" infromation on the can wouldn't hurt.

    I did in fact use a breather from a 1999 Whizzer, and drilled holes to mount to carburetor.

    Have fun,
  20. Quenton Guenther

    Quenton Guenther Motored Bikes Sponsor

    More ratio options on the HF motors using the Q-Matic drive system.

    2.5" primary pulley
    75 tooth rear sprocket:
    2500 RPMS = 12.5 MPH
    3600 RPMs = 18 MPH
    4500 RPMs = 22.5 MPH
    72 tooth rear sprocket:
    2500 RPMs = 13 MPH
    3600 RPMs = 18.75 MPH
    4500 RPMs = 23.4 MPH

    2.75" primary pulley
    75 tooth rear sprocket:
    2500 RPMs = 13.8 MPH
    3600 RPMs = 20 MPH
    4500 RPMs = 24.8 MPH
    72 tooth rear sprocket:
    2500 RPMs = 14.4 MPH
    3600 RPMs = 20.7 MPH
    4500 RPMs = 26 MPH

    3" primary pulley
    75 tooth rear sprocket:
    2500 RPMs = 15 MPH
    3600 RPMs = 21.8 MPH
    4500 RPMs = 27 MPH
    72 tooth rear sprocket:
    2500 RPMs = 15.8 MPH
    3600 RPMs = 22.7 MPH
    4500 RPMs = 28.4 MPH

    Have fun,