New used race motor. Need help

[Ztank]

So my son is getting board with his 2002 Polaris 120. Already have different gearing, dial a jet the v stack on carb and different governor spring. I have a lot of questions for an upgrade. I’m hopping someone with some experience in theses little motors can help me out.

I traded a few snowmobile parts for a Honda gx 120 motor. It was advertised a mini champ motor. I wasn’t sure what I was getting. Its written on the recoil cover “has adjustable cam valves float ( not sure what that is) 18.25 hp needs new valve springs.” Guy said when he bought it from hay days the seller said it was bored. I don’t have a set of calipers to measure, so who knows. Can this engine really get 18.25 hp? I’m thinking not.). I got it from a snowmobile junk yard that bought it from hay days with a bunch of other things. The guy also throw in a junk parts motor.

So I brought it home. It was in a box with 5 or 6 bags of parts and screws. The head has had work on it. Intake and exhaust has been ported. The governor has been removed. It has reinforced rocker arms and the springs in the valves are really thick. i took the cover off the parts motor and the springs are thin. There is also a set of springs in the box that are in between the two. I want to replace the springs but want to put back what is currently in there. What lbs do I go with? The box includes a carb, but it look stock and never used. Where the intake has been ported, it doesn’t match what I have. Can anyone tell me what I need to buy. I know somewhere they make board carbs for these motors. I’m assuming that is what was on it. Also what do I need to get for the muffler and pipe? Do I need the wedges to mount this Motor? I know for the hind clone motors you need them. With the governor eliminated, what is going to prevent me from blowing up the engine?

 

[thedude306]

It's a 4 hp motor stock so I would think that it could get into the 10-12 hp range pretty easy. 18hp is pretty aggressive but prob possible.
If it's pushing that HP you are going to want some pretty stiff springs. I am guessing in that 30lbs plus range but that's just a guess. You would need aftermarket push rods and arms for sure going that high.

I know on my clone motors there is a transition piece between the carb and head. It's plastic and matches the carb profile to the head profile. I am running a bored out honda carb and it's the same profile of the the clone carb. My guess is the transition piece is missing. Put the stock carb on for now, then look at bigger carb.

I've got a straight pipe and a muffler for the motors. It's annoying loud with the straight pipe. My guess is that It's more of a heat issue then a flow/performance issue (well I guess they are related) with the exhaust. Go for some kind of can on it IMO.

motor needs to be higher in the back. Wedges make that happen. I just blocked mine but it doesn't get the full support of the pan so I am going to monitor for bending.

with the governor removed the only rev limiter is the throttle thumb. With a well built motor they should take 6500rpm for a long time. You can also adj the cable so you can't get full RPM or put a throttle block behind the thumb lever. I would do it more for your kids safety if they are not ready for full throttle over worrying about the engine.

a couple of places that I have used for parts are recmotors and nrracing

 

[Ztank]

Thanks for the info. I was looking more at this motor and comparing it to the stock parts motor. The head is shaved and there is a valve releaf cut in the piston. I did find a plastic plate the goes in between the carb and the motor that does change the profile. Also found a volosity stack to go on the other side of the carb that has had some work done to it too. I also noticed that there are welded reinforced rocker arms on it too. what would be the heaviest springs they make for this motor? From what the comment above said, this really could be a 18.25 hp motor. I traded some snowmobile parts for it. Looking like I get more than what I bargained for but my son is going to love it. Defiantly will have to change the drive sprocket so I don’t rip up the track.

 

[Ztank]

Also what is the stock bore of a carb and how big of bore should I get?

 

[Ztank]

Another question, what kind of gas do I need for this thing?

 

[thedude306]

I would call and ask the guys at nrracing.com about the carb and fuel requirement. They have the springs as well.

I'll get a picture of my carb specs for you tonight.