200x Racer: The Engine Build

[xrider]

I'm currently in the process of building a 200x race engine and figured I would get a thread started. My goal in this build is to get into the 28 - 30 HP range. The parts list includes a 6mm Curtis Sparks stroker crank, Powroll .395 lift / .395 duration full race cam, Big Al's Titanium valve springs and retainers, Big Al's Copper head gasket, Wiseco .080 over 12:1 High Compression piston, and 31mm oversized Webcam intake valves. The flywheel has already been lightened, and the Rockers are currently out to be hardwelded. I am not sure which carb setup that I am going to use yet, but I have four that I will dyno it with. I have PK racing's 28mm Mikuni setup, Curtis Spark's 28mm Mikuni setup, and DG's 28mm Keihin setup, and soon to add a Sudco 28mm FCR carb. The engine I am using came out of my 200x mxer. It will go back in the mxer for some indoor racing this winter and Trikefest. Then most likely get pulled out and placed in my other 200x project. We have just torn into the bottom end to install the stroker and new kicker gear assembly. More updates to follow.

Thanks, xrider

[seadoo650]

If you're installing a stroker crank, you will more than likely have to have a stroker sleeve put in the cylinder. Also I recommend running at least a 30MM. carb. They like alot of fuel when built that much. You can still buy new ones from Niche cycle supply.

http://www.nichecycle.com/ProductDes...-SPIGOT&key=it

[Dirtcrasher]

2MM over leaves the 200X with very thin cylinder walls. It's my personal opinion that a cylinder should just be cleaned up rather than bored close to or at the max.

Got any pics of the lightened crank?

[shortline10]

sounds good will be keeping an eye on this thread

[xrider]

This cylinder is already on it's final bore and will require the 2mm over, or else I would of went with a smaller bore. It is the flywheel that is lightened and not the crank actually. I have actually ran a 30mm round slide on a previous stroker and had a hard time getting it dialed in, but I do agree that they require a lot of fuel. I still have a 30mm round slide on the shelf that I can give another shot. What jetting did you use when you ran your 30mm? The Sudco fcr carb that I am looking at is actually a 28mm that is bored to a 30mm. It is sold by ct racing for a Raptor 250, (see the attached picture). I think the accelerator pump of the FCR would really help bottom end and starting. Thanks for the suggestions guys.



xrider

[aproudcanadian]

i think that fcr will be a tight fight, probably have to make some frame mods

[Xpress]

If you do the stroker, be sure to put in stronger kicker gears. My last stroker engine fully stripped out the kicker gears......

[xrider]

Yeah the FCR would be a challenge to fit. I'm hoping it will fit in with only minor modification, or a frame notch. If not I'll have to get more creative. I bought a good set of kicker gears with a stronger spring from Shortline for that very reason Xpress. The ones that came out of this engine were already slipping pretty bad. Thanks, xrider

[xrider]

Did a mock up with the stroker crank today to check the deck height. This stroker will require a 3mm spacer plate. Just dropped a base gasket off at a local machine shop for a template for machining the 3mm spacer plate. Forgot to mention previously that this stroker crank uses the stock xr200 rod. Quick question though. For all of you that have built a stroker before, how do you address the cam chain? Can you still get longer cam chains, or what has worked for everyone else? Any input helps. Thanks, xrider

[shortline10]

3mm spacer isnt all that bad and a good used stock length chain should work fine .

Did a mock up with the stroker crank today to check the deck height. This stroker will require a 3mm spacer plate. Just dropped a base gasket off at a local machine shop for a template for machining the 3mm spacer plate. Forgot to mention previously that this stroker crank uses the stock xr200 rod. Quick question though. For all of you that have built a stroker before, how do you address the cam chain? Can you still get longer cam chains, or what has worked for everyone else? Any input helps. Thanks, xrider

[hot125honda]

Where does a guy get them stronger kicker springs? I am also building a racer motor for ice racing. stock stroke for now but 67mm 12:1 piston. I have yet to figure out what i want for valves. I would like a smaller stemed valve around 31-32mm and port the head accordingly. Im gonna run web cams big cam. I have a lightened fly wheel, but was gonna lighten one more for that. Was also throwing around the idea of dual plugs... I've gotta 34mm round slide carb. Was hoping to run it on methanol or corn juice (98%)
Derek

[Dirtcrasher]

3mm spacer isnt all that bad and a good used stock length chain should work fine .

Mike, can't a longer chain be ordered from an industrial supplier with another link versus a used stretched one? I imagine that a new chain is preferred by you,me or anyone building a stroker versus a stretched chain. Unfortunately, unless custom ordered, I'm sure it would have a master link versus an endless chain. Just curious of your thoughts.....

[shortline10]

I know the old Big Al's timing chains from back in the day came with a master link but to add a link dont you think it would throw the whole timing off by 1 tooth ? I have a nos big al's chain in my collection so Ill take a look . I would def much rather have a new chain and would try one first so see if I could get it to work even if you have to do some fabbing on the tensioner system but the easy way is to just pick out a decent stretched chain . I think a low hour pre stretched timing chain is prob the simplest way to go in my opinion .

Mike, can't a longer chain be ordered from an industrial supplier with another link versus a used stretched one? I imagine that a new chain is preferred by you,me or anyone building a stroker versus a stretched chain. Unfortunately, unless custom ordered, I'm sure it would have a master link versus an endless chain. Just curious of your thoughts.....

[xrider]

My problem is that the timing chain that came out of the motor is shot and it is the only one that I have. A new timing chain would be ideal, but anything at this point that would be reliable and fit well would be feasible. I just don't want the timing chain to be the weak link in my setup if possible.

[WilliamJ]

A longer chain would not put the timing out a notch, but you are right that if you relied on standard marks the extra spacer would. When building a race engine you don't time the cam using factory marks, you must make your own set of timing marks and you make the cam sprocket adjustable (if it isn't already) by slotting the holes and utlimately pinning it to the end of the cam. You find both full lift points and start with it 'straight up' or whatever the cam grinder recommends. Then when you have broken in the cam and got the motor running really nicely - jetting timing etc - you advance or retard the cam a few degrees and see what works best.

Bill