79cc 4 stroke frame mount build

Discussion in '4-Stroke Engines' started by cspaur13, May 11, 2009.

  1. cspaur13

    cspaur13 Member

    i just got my engine from harbor freight yesterday.
    in store price was $109 and i matched it to online price of $99 dollars and i had a 20% coupn and it rang up to $80 dollars and i got the 1 year warrenty for $11. i took it home and noticed the gas tank and muffler would have to come off to fit in the frame. so i took it all off and the engine fit like glove in the frame. couldnt ask for it to be any better. im gonna use my gas tank form my 2 stroke kit and i'll weld a straight pipe to the back or i'll weld a straight pipe to the back and pput the stock muffler on it. im gonna use the grubee v-frame mount. it looks like th esame mount pattern and im gonna use the hilliard extrem duty centrifuegal clutch at northern tools and i'll be al set.
    i do need some help with the gearing. i know jpilot has his gear ratio calculator but i dont think the speeds are at all accurate since you only put rpms and not hp or bore measurements. if i can use the pedals i'd be fine with a starting off speed of 5-10mph. but if they have to come off then im gonna have to do from 0 mph to w/e my top speed would be. can some one help me out with that.

    heres some pics of the engine. its a realy beauty. for the price i got it for it built really nice and it looks really good quality. i'll have to fire her up in a couple days. i cant wait to start on this build. any help please.





    P1030467.JPG dose any1 know how do bypass this and remove the govern/rev limiter



    P1030472.JPG the black one is the one im using. the red one will probally be moterized another day

    Last edited: May 11, 2009

  2. BeachBum

    BeachBum New Member

    I'm guessing you want to bypass that governor spring? Want to know how they do it on golf carts where I live?

    Ziptie/cable tie. Put it through the spring and zip it together. Not too tight, but it will stop the spring from opening as much. Works like a charm on a 14hp golf cart engine, don't see why the same thing won't work on a bike engine.

    If you want I'll snap a shot of my golf cart later to show you exactly what I mean.
  3. cspaur13

    cspaur13 Member

    i just want to bypass it , dont really matter how its done. i'll give it a try. it cant hurt anything. yea a picture would help.
    thanks beachbum.

    also can i use my throttle cable from my 2 stroke kit or am i gonna have to go to the lawnmower shop and get one for this engine or get one off a go kart site
  4. ZnsaneRyder

    ZnsaneRyder Member

    You may have to set up a custom throttle. To bypass the governor, just remove the gov arm, and throttle lever from the top of the engine, and set up your throttle cable to go straight to the carburetor.

    I can't wait to see this new build!
  5. s_beaudry

    s_beaudry Member


    I know I for one want to see more progress updated from you on this project. I am going to buy this engine as well as soon as I am on the other side of town where the HB store is.

    As far as I know, you will be the first one to frame mount this engine, and I am SURE there are many many more on this forum interested in doing the same.

    Please keep us updated...
  6. BeachBum

    BeachBum New Member

    Here's a shot of the engine on my golf cart. This is the way they do it around here. (Then again I also had my mechanic swap gears so I could get even more top end at the cost of some torque. 28 MPH isn't bad for a golf cart)

    Attached Files:

  7. HoughMade

    HoughMade Guest

    How many teeth are on the clutch?

    The gear ratio calculator gives a theoretical top speed if you are able to get the engine to turn that speed under load. The engine is rated to about 3600 rpm, I'm guessing, but attached to a bike, with weight to carry, friction losses and wind resistance, it will not be able to get to that engine speed in every circumstance.

    That is why you need to gear the engine (with 2.5 hp) to peak no higher than about 40 mph. If you do more, you will have lousy acceleration and may not even see top speed because the engine will not get into its power band.

    You can always gear it for less and get better acceleration with a lower top speed.

    For instance, with a 10 tooth clutch sprocket (no other reduction) and a 56 tooth rear sprocket, you will have a theoretical top speed of about 50 mph, but you probably will not get to that speed.

    With a 10 tooth to 68 tooth (rear sprocket), you get a theoretical top speed of about 40 mph at 3600 rpm...probably about right.

    With a 9 tooth clutch sprocket to a 60 tooth, you get about 41 mph at 3600 rpm.

    With an 11 tooth to 74 tooth, you get about 41 mph.

    If you want better acceleration and do not need a 40 mph top speed, you will need an even bigger rear sprocket or some other reduction.

    The good news is that at 79 ccs, you likely have a wider power band than my 49 cc 4 stroke, so gearing for a 40 mph top speed may provide decent cruising at a lower engine speed...but that's just a guess.
  8. ky biker

    ky biker New Member

    This is how I did it on my side pusher and trike.

    I had to get a longer cable at the local bicycle shop,but you can use yours if it is long enough.

    I added a spring to help the throttle return an bolted a bracket to the muffler cover to guide the cable

    Attached Files:

  9. cspaur13

    cspaur13 Member

    the govern arm looks like it might move something inside the engine. but i guess it dosent. im gonna take it off tonight. thanks.

    am i really the first to try to frame mount it. wow. i hope you go down soon and get one.i have a feeling these things could be the next new item moterized bikers want on there bikes. better than those cheap 2 strokes. if it cant be frame mounted in my bike i'll just have to do a rack mount but i hope i can do the frame mount. im pretty sure i can.

    28mph. wow i've only been able to do 15 tops on the gold coarse. thats awesome.

    the clutch has 10 teeth. yea i doubt i'l be doing 3600rpm alot. mabey once in a while for a minute.
    i have a 36 and 44 tooth rear sprocket. i was hoping i would be able to use one of them and not have to buy another sprocket but probally not.
    i just want to do from a complete stop to at least 30. but i wouldnt mind a top speed of 40.
    its always windy down here and i could probally deduct 5 mph when im doing atleast 25mph. so my top speed wont be to high.

    ky biker

    my cable is long enough. nice setup. im gonna go work on it tonight. i'll see if i need to use a spring for it.

    thanks every1 for the help.
    i still might need some help with gearing. houghmade did do a very good job of explaning. idk if i might need a jackshaft or if it would just be cheaper to get abig sprocket like 56-62 teeth sprocket form andy. also do they make these centrifuegal clutches with a 9 tooth sprocket.

  10. Gen3Benz

    Gen3Benz Member

    If you look at page 17 of the engine manual
    Part #60 is a gear driven off the crankshaft
    When the throw weights driven by this gear are thrown they push out a cup that pushes on part #61.
    Which rotates a lever that moves the #88 rod going to the throttle.

    I yanked off the side cover of my new 2.5 and took a pic...

    So...you can either remove the gear or the #88 rod to remove the governor.
    I'm guessing if you remove the rod you would have to secure the lever so it doesn't hit the crank.
    Or try the spring like the others

    On my 6.5 I took off the flywheel and used a punch to knock out the pin the gear rides on, then used a set screw to plug the hole.
    Just like the you-tube vid.
    Last edited: May 13, 2009
  11. cspaur13

    cspaur13 Member

    thanks Gen3Benz. i just thought u had to diconect the govener arm on the top of the engine. this really helps. i'll try taking it off today
  12. cspaur13

    cspaur13 Member

    my dad took the govern off. just have to seal up the hole with soem jb weld or something. its a pain to get that govern off. he spent an hour trying to get it off.
    now i can run my thrrotle straight to the carb.
    heres some pics of the govern. its smashed up from the plyiers. i should of got a pic of the inside of engine after i took it off.




  13. Gen3Benz

    Gen3Benz Member

    Well, thats one way to do it:grin5:
    I think I will just remove the rod going to the throttle.
  14. macarollo

    macarollo Guest

    I remember the feeling when I finally got my governor off my 6.5HP engine. Feels good to FIX that problem the designers engineered into their design!

  15. cspaur13

    cspaur13 Member

    thats probally the way to go. less time and hassle. but taking off the rod dose it fully disengage the govener or dose it still kinda work cause the actual govener gear and everytihng is still in there. but idk. it will probally work just fine.

    you would think they would make it easier to take off seeing as every1 dosent use these motors for generators and small equipment. its one less thing to have to worry about.

    but im starting to think that a frame mount on my bike is not possible. the grubee v-frame mount might have to be mounted higher up on the bike then i thought and then the engine wouldnt fit. not to sure. im gonna hav emy dad make sure before i order it. if it dosent i'll have to buy there rack mount setup instead but i would rather have the frame mount.

  16. Youngbird

    Youngbird Member

    Man....if the motor fits in the triangle....weld a plate in there and get on with it!:cool2:
  17. Gen3Benz

    Gen3Benz Member

    The governor would still operate...but it wont adjust the throttle.
    Just have to make sure the lever arm doesn't move enough to hit the crankshaft.

    Haven't looked at my bike to see if the engine will fit my bike...been kinda busy with other stuff
    If it does I might do what youngbird suggested and weld in a plate.
    Then run a JS to drive the pedal sprocket like a sick bike parts shifter kit.....I dunno yet
    Last edited: May 15, 2009
  18. cspaur13

    cspaur13 Member


    i should take it to my grandpas house. he'll weld a plate on there for me. it would sure be a he** of alot cheaper than buying a mount. plus it would be probally better.

    yea so its pretty much not there. but atleast i dont have to worry about it anymore. you can just cut the lever arm out of there. then you dont have to worry about it hitting the crankshaft. i know it dosent slip out. have to use bolt cutters or w/e to cut it out cause of the curve.
    yea if not you can always do a rackmount. i know alot of people get jackshafts or make them. but where dose every1 get them or do you have to make them. sory i dont really know what all you would need to make agood one unless you can buy them already made. might need a small one so i can have the gearing just right.
    plus you will have to take the gas tank and muffler off for it to fit in most bikes unless you have a chopper bike with alot of room or a custom made frame.

  19. ZnsaneRyder

    ZnsaneRyder Member

    I'd recommend gearing that engine LOW. I know it says 3600, but it like to be at 4000 in my experiences.

    40mph is way too fast. My bro's tall gearing gets 38mph flat, 43mph on a downhill. And we still want to lower the gearing for better takeoff. It's a powerful engine, but it doesn't have a lot of torque.
  20. cspaur13

    cspaur13 Member

    will the #40/41 or #35 chain work on my sprocket from my 2 stroke kit. its 415 chain. its probally the same but idk. would i have to get a gokart/minibike sprocket. well im gonna have gear it low. from takeoff to w/e it will top off at. i'd like a 25-30 mph cruising speed. so topping out at 32-38 would be fine.
    and did you remove the govener. or dose it usually run 4000 rpm with it on.