Coleman Minibike GX200 Build

[escout]

Hello,
I have a Coleman mini bike with a gx200, and I'm looking to take it to the next step.

What I have:
-Intake, Exhaust, & Carb re-jet
-Billet Flywheel with 8 Degree Advance
-18lb Valve Springs
-Stock Governor

I just ordered a 14cc head for the thing, but I would also like to run a high torque CL-1 cam.


With the addition of the new head, will that cam allow for enough clearance between piston and valves? Also, I will probably make the swap to E85, so what will that take in terms of carb, timing, etc?.....I dont want a high rpm screamer quite yet, just a lot of torque. Also, will my max-torque centrifugal clutch hold that power for a decent bit? I know a torque converter is the way to go, but I may hold off on that for a bit. Anyways, ideas/input is greatly appreciated and will be put into effect right away. Thanks

 

[Davis]

I would shoot for the e85 sounds good to me!

 

[DeadPixel]

The cam should be fine. Its pretty much a stock lift cam with a little added duration. I have the cam and am building almost the same exact motor as you but have not got it together yet. Might even put it in a CT200U.

I would ask a few people but I am going to try out a BSP cast rod before I put in my billet rod. There only about $10 new and might be a cheaper option than a billet piece. The cart racing guys run them. Don't want to steer you in the wrong direction so I would ask some people before you buy one but this might save you $50 if you plan on disabling the governor.

I first wanted to run straight ethanol in my motor but don't know if I could run the methanol carb or if it would be different. E85 should require a slightly leaner mixture than straight alcohol. If you go this rout post your results because I am curious.

 

[escout]

Good enough for me, I'll get that cam on order, ha. Yeah I suppose I should probably look into a better rod here soon. At some point when I do put in the rod, is there a crank that that will work with my ARC flywheel and allow me to run a 3/4" shaft for better clutch options? The current crank has a 5/8" shaft and I'm very limited on clutches....
I'm sure switching to E85 isn't worth massive power gains by itself, but it does open up doors in terms of being able to run high compression and boost. I have a GM 327 that is pushing some limits, and I would rather do my testing on this gx200 and risk failure before I detonate the more expensive engine, ha. Anyways, I will post results as I get time to work on this little project.

 

[escout]

Well, I just ordered a cam, billet rod, and some gaskets....I'll probably get a new set of stock lifters and possibly a crank (3/4") here soon. Does anyone have advice on pushrods? I know the stock ones are aluminum, and I'm fine with running them, if they aren't prone to massive failure with that cam....so if anyone has advice on that, please let me know. I'll wait to order carb jets and the other tuning extras until I have a chance to build it and run it.

 

[SAS289]

Good thinking on getting rid of that 5/8 crank output. That's one of the things I didn't like about the Coleman. However, you do get a better clutch that has a caged needle bearing instead of a bronze bushing. No need for continuous oiling. Pack it with grease and ride. I used a little too much grease and got splatter onto the clutch bell. No biggie.

Check out these crankshafts... One may be for a longer stroke but I'm not sure.

http://boxstockproject.com/cart/index.php?pg=3&l=product_list&c=2

 

[DeadPixel]

Cant say on the push rods but I know the box stock motor I just ordered has molly rods in it and that's for a motor that spins under 6K. It has stock springs and a BSP4 cam in it. I have had a few people tell me the aluminum are just fine though when I asked this a few months back. I want to run the GX160 lifters in my motor. There lighter and cost the same. If you do go molly I would try the 160 lifters. You need a rod that's +.180" which is 5.440" if still running stamped stock rockers. NRracing claims this is good for a combined weight savings of 7% over stock. If you run roller rockers or mill the head a lot the length might be different. The push rods are about $24 a set.

 

[escout]

Well, I've had some time to throw those parts into the engine....not a lot of time to test and tune though. I have some jets waiting to go in, but the rain is hurting progress. Anyways, after initial startup, I noticed that the little beast did sound meaner from the higher compression. I definitely have a lot more low end torque, perfect for the trails I've been taking it on....I can easily break the rear tire loose. After 10 mins of riding with the new head and cam, the spark plug was fouled out, so I'll have to lean things out a bit and see how that goes. Seems like everyone looks at the peak HP #'s when deciding what to build, but for the average 180 lb guy who isn't into all out racing, you'll want a more usable power-band at lower rpm's....So far what this has proven to be. Probably not the setup for someone who wants to live in the high rpm world.

I have a bunch of other little things done, but this is the general way things have gone so far....
Engine Summary:
-Intake and Exhaust
-Carb re-jet
-High compression head (14cc)
-Billet Flywheel (8 degree advance)
-Billet Connecting rod (std length)
-CL-1 (high torque) Cam

 

[SAS289]

Interesting. But I wonder if you would have been better off without the 8 degree advance? Especially if you were looking for more "low end".

 

[escout]

Possibly. Something I'll have to work out when I spend some more time tuning. Thought about backing the timing off a few degrees, but for now it runs pretty decent. I'll Just keep dialing in jets and reading the plug.....tad bit rich right now and the timing looks close, but we'll see I guess