1st mini bike build, motor questions

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Coolcat70

Member
#1
#1
New to site (thanks for having me) I'm building a mini chopper and am putting a HF 212 predator in it. I'm a cross over from the vintage snowmobile community, so I have some mechanical aptitude, but the four stroke is a bit foreign to me. The rolling chassis I have is a bit larger than your usual mini and I am a grown adult weighing in at 190 lbs so I don't think the stock motor is going to get me where I want to be speed wise. When finished I want a bike that I can cruise around on all the county roads by me that can also get up and go when I want it to. After reading some posts here, watching some YouTube vids, and looking at all the go fast parts, my head is spinning.
Here's what I want to do.
Hi flow air filter
Hi flow exhaust header
Mikuni carb ( I love these carbs, have them on all my sleds)
Disconnect/ remove governor

Here are a few of my questions:

Will I be ok to run billet flywheel and stock con rod or should I use billet rod as well?

What valve springs should I use, I seen guys use 18 to 26 pound springs.

If I go with bigger springs should I change rocker arms, and push rods and valves? ( this one I have no clue on)

My tank will be above the carb so it will gravity feed so I'm assuming that I don't need a fuel pump but I'm not positive.

Timing advance?

I think that's enough for now, I'm sure I'll have more as I move forward.
Thanks in advance for your replies and thanks for the site!
 
Boomstick

Boomstick

New Member
#2
#2
Welcome aboard!

Anyway, if you're going to modify the 212, it seems like the general consensus here is to do swap out the connecting rod & flywheel for the billet pieces. This is especially true if you plan on a governor delete & upgrading the valvetrain.
 
OND

OND

#5
#5
Most of the billet flywheels made by ARC have 28 to 32 degrees of timing built in to the flywheel, and thats plenty of timing.
I would do the billet rod for the simple fact the dipper on the ARC rods has a oiling hole built in to it,. to help oil the rod inserts. Make that engine last a lot longer.
18 # springs will work fine, and no reason to change valves, push rods or rockers...unless you just want to.
I would definetly consider a bigger jet, maybe a 32 to 36 range, and a k&n style air filter and billet air filter adapter.
Hope this helps !
Maybe a header to let this thing breath.

Sorry I didn't mean to spend a ton of your money ! lol
 
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Stangrcr1

Stangrcr1

New Member
#6
#6
Just basic mods like posted above will get any mini to a pretty fast speed, depending on gearing. Your weight is low compared to a lot of members here.... I have 20lbs on ya.

My 69730 predator still has its governor(stock rod and flywheel), has the high flow air filter, stock carb rejetted, and a header and will easily get my mini over 40mph, yet easy to ride.

Its all in the gearing and how you ride it. :thumbsup:
 
C

Coolcat70

Member
#7
#7
Thanks for the info! Gearing is another concern. The bike has 10 inch rims and the sprocket that's on the tear right now is a 44t. I'm thinking its a bit to small but I'm not sure. Could someone get me in the ball park here? Also, in the future I may go to a torque converter set up, how does that effect gearing?:shrug:
 
chipper

chipper

#9
#9
As Stangrcr said with intake , header and re-jet the Predator does great and geared right will go plenty fast w/o removing the governor , IMO it's all you need for a great riding bike that'll have plenty of pep ! I drill my jets w/ a #62 bit or .038 and have excellent results ! 6-1 ratio is pretty high for a powerful engine ( wheelie machine ) I'd go closer to 5-1 but wheel diameter has a lot to do with it too . Good Luck !
 
C

Coolcat70

Member
#10
#10
So, I've decided to go with billet parts and NO governor. Ordered my parts on Thursday and the ups guy can't get here quick enough. I believe I read somewhere that when installing an arc con rod that the low oil sensor has to be removed to make room for the bigger dipper. I've removed both pieces (black part from inside the case and part that sticks through the bottom) anyone have suggestion on plugging hole in case, or just snip wires and use orig. part as plug?
 
OND

OND

#11
#11
I have just clipped the wire off on the inside before and had no problems. Or you can tap out the hole for a 1/4 pipe thread and plug it solid, either way will work fine.
 
C

Coolcat70

Member
#12
#12
Yeah, kinda a premature question, I found lots of threads here on the same topic after i posted it. Btw, I'm seeing a lot of places that will sell me a 205/30-10 tire (I'm building a mini chopper and would like to run one on my rear) but have had zero luck finding a rim. Any ideas?
 
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