HF 79cc Push Trailer

Discussion in 'Push Trailers' started by Wheres my dog, Mar 4, 2011.

  1. Wheres my dog

    Wheres my dog New Member

    The ever versatile HF 79cc has found life as a new form of motorized bicycle!

    I bought the engine a few weeks ago and have been tinkering with her for a project, and I just started one this morning... a push trailer

    Going for a very small, sleek, and refined look for a pusher... no large frame or overhang, no fancy style, just as plain and simple as I can possibly make her

    If my numbers are correct here, she should top out at 25.7 miles per hour... 12 tooth centrifugal clutch driving a 60 tooth sprocket with 12 inch tires, and the engine running at 3600rpm's

    Trying to keep total pusher weight with engine at or below 50 pounds

    Will update this thread as I make progress... planning to be finished and test riding her by Wednesday the 9th...

  2. Wheres my dog

    Wheres my dog New Member


    The HF is on the shelf for the time being.... would you believe I had it idling bolted down to the trailer I made with no throttle hookup on it and all of a sudden that thing just wound out and almost took off on me!!!!

    Fuel tank was about half full and it had been idling nicely for about 3 minutes or so and just like that it wound itself out!

    Too scary for me right now..... the good news though is that the same trailer is noiw being retro-fitted with the TITAN 50cc

    More to come
  3. MikeJ

    MikeJ Member

    No throttle hookup? None at all? If that butterfly carburator plate drifts open with nothing holding it back, yeah, that engine will wind up to really high RPMs.
  4. Wheres my dog

    Wheres my dog New Member

    Mike.... original engine linkage was in tact

    I meant that I did not have an additional throttle cable tied into the engine linkage!
  5. Wheres my dog

    Wheres my dog New Member

    Spent some time with the engine today checking the springs and linkage and see no problems what so ever...

    I had it running about 20 minutes or so with full gooses and she slowly came back down to idle with no issues.

    More investigating tomorrow...
  6. Gen3Benz

    Gen3Benz Member

    Yank the side cover and hack the rod out and cap the hole with a set screw
    Rev that little f'er to the moon haha
    I have one of these engines i wanna mount to a bike since i have a 6.5 pusher, if i would only find the time :grin5:
  7. Wheres my dog

    Wheres my dog New Member

    Anyone have any pictures of how they hooked up their throttle to a HF 79cc???

    Looking for a better way or more ideas
  8. MikeJ

    MikeJ Member

    Hey Wheres -

    Attached should be some photos I took of my HF 79 cc throttle linkage. The sheet metal piece bolted to the engine started out as a 3 inch-by-4 inch piece of wood fence plating from Ace hardware. I bent it using a vise to a 90 degree angle and enlarged some existing holes. In the last photo, you see it bolted to an engine mount point. In another photo, you see a cable eyelet (for lack of better term) holding the cable from the twist-grip throttle control to this plate. (any bicycle wrencher worth his pay knows instantly what that eyelet is). The larger spring is an auto carburator spring from most any auto parts store (buy in a package of 5). I chose this one and adjusted its length so that it will pull the throttle handle back to full stop; the throttle handle grip has no spring in it. The little wimpy spring is from the stock engine. It is connected to some point on the seat post so that by default, it will pull the carburator plate full open if not balanced by the much stronger auto carburator spring. It has been a while; I think the angled steel piece used to be on the governor; make sure it can rotate back and forth freeley. You can see the governor has been totally disconnected. The linkage is all stock parts and pieces. The cable clamp is a bicycle brake cable clamp. If you can show a wrencher what this is, he should recognize it right away. I cut the wire cable to a shorter length after these photos were taken.

    The advantage of this set up is that the throttle cable is in one long gradual arc from throttle grip to eyelet. There are no sharp bends. The strong spring returns everything to an idle state that you adjust to. It will take a little jockeying back and forth to make it happen.

    When you start the engine, an idle set screw on this engine's carb will determine minimal idle speed. My engine will now remain running in the mid 1300 rpm range because it has been somewhat broken in and "loosened up". It used to run at 1800 rpm when brand new.

    I hope these photos help.


    Attached Files:

  9. autowood

    autowood New Member

    A new twist on the push

    Got a new twist on the pusher trailer concept. I got the same HF 79cc motor. I have on order a 24v 10si Delco alternator. Going to mate the two and have two 12v batteries(SLA) that will be charged mounted on a trailer. I have several 24v bicycles that this will hook up behind and totally expand the limited range of an electric powered bike. I have thought about putting a hub motor on the trailer and then it would become a pusher too. The advantage of this system is that it can be run without the gasoline engine running in Politically Incorrect places such as the boardwalk, but fired up to recharge when appropriate. :D