Jump to content

Stroked XR200 Motor


Recommended Posts

I have a 1982 XR200 motor in my CR125/XR200 conversion. I had Powroll stroke the crank. I bored the cylinder and put in a Wiseco piston.

It's running with a 1995 ignition system, 1995 stock exhaust, 30mm Mikuni knockoff carb and atc200 head (larger fins). Stock XR200 cam.

I finally have it jetted reasonably well. I get great low end torque, but the power drops off pretty quickly as it revs and it won't rev very high.

What's the next step to get more out of the top end? Do I need an aftermarket cam or would I get more from an exhaust?

Thanks for the help.

- Brad

Link to comment
Share on other sites

I just did a simular rebuild on a 97 engine and encountered some tuning issues. I know this is a long post but there are so many variable in an engine build its hard to zero in on one issue. Our engines are different, so here is a list of my mods along with some comments:

1. Stoker crank

2. Powroll's big bore 11:1 piston because it was already clearanced for the crank, got my choice of compression ratio, and it included gaskets; making it as cheap or cheaper than using Wiseco. Both pistons are forged, the OEM is cast. The stroker bumps the CR by 1/2 point so a 10.5 piston for a stock engine will be 11:1 with the stroked crank.

3. Head is mildly ported, I don't know if it was done correctly or hacked.

4. XRsOnly SS header because Powroll no longer makes a pipe for this engine/chassis, but their CRF230 pipe fits.

5. Supertrapp IDS2 muffler with 8 discs because Powroll says this povides the best power without being too loud.

6. Powroll Torque cam. Powroll claims the high lift cams makes a big impact on moded engines. The Torque cam provides a better idle than the stock engine with awsome bottom end; Powroll claims this engine build produces 10% more torque than a stock dry sump XR250R. A stock cam may close the inlet too early for use with compression ratios above 10.5:1.

7. Stock carb, stock jetting except one up on main but I may test a stock main.

The high compression ratio makes the engine very sensitive to ignition timing and the problem is these engine don't make obvious ping noise during detonation, hard to hear over the other engine noises. The second problem that I encountered was ignition advancers not within spec because of wear.

The "F" mark on the flywheel is 10 degrees, the two full advance marks are 28 and 32 degrees. The spec for the advancer is 20 degrees which fits with the timing marks on the flywheel. I've checked stock xr200 engine and found them to be running 34 degrees total which is way too much, I've also found advancer that had 24 degrees of advance instead of the 20 degree specified. Both situation may be ok in a stock engine but don't work well in a modified engine. Powroll says 29 degree max for total timing, if you have too much total advance the top end power may be limited by too much advance, or detonation.

I'm currently running 8 degrees initial and 28 total with slightly shortened springs on the advancer to delay the start of mechananicl advance (eliminated mild ping 2000-2300rpm).

Link to comment
Share on other sites

Wow, I'm very impressed Chuck. I just had the basically the same conversation with Dave Miller on Thursday, which was how do you make a motor rev higher. And one of the points he was talking about was exactly what you said. The at higher RPM you need the ignition to fire later, combined with a cam with lobes separated, duration etc. for correct scavaging, pipe and on and on. I really need to recored him, so I can write this stuff down. I'm getting too old to remember things five minutes later, but I did mange to get a few things out it. Manly a combination of everything on getting more fuel in the cylinder. But to the original post, strokers need the proper cam, exhaust, carb, ports, valve sizes, timing and ignition curve. Some people say strokers don't rev, but Kitaco 11mm stoker XR100 kits rev past 14k. But a reverse cone megaphone type exhaust and cam will do wonders. When I put a Meg on my old 200 conversion, I got 1500 rpm more rev out of it. But I was using it on MX tracks, not woods, so I needed more rev. It wasn't like a XR100 or my CRF150RB, but much better.

Edited by socalxr
Link to comment
Share on other sites

The Honda 200 is especially restrictive when stroked. It was based on the old SL100 engine with maxed out bore and stroke. That's why you can only bore to 67mm, there's no more room between the cylinder studs left for sleeve. Anytime you add displacement you have to increase air flow proporionately just to maintain the rpm potential before modification. I wouldn't expect much rpm or hp from a 200 without a major port job.

Link to comment
Share on other sites

I was hoping to hear "you have to do this one thing and it will really fly." But thanks for the great feedback. It sounds like I have to do quite a bit more to get the power out.

I'm riding hare scrambles, so I don't have much opportunity to rev it high, but it would be nice to have it available.

Thanks for cluing me into the ignition timing. I'll have to play around with it to see what difference it makes.

- Brad

Link to comment
Share on other sites

I agree and you probably will never be able to make a 2 valve 200 breathe like a 4 valve or even a CRF230 but do you want a road race motor or a trail motor? Have said that I've looked at dyno charts of CRF230 and XR200 motors that show a stock 200 with more peak power and bottom end than a CRF230, in other words a flatter wider power curve. But the 200 does this with a higher CR and a more aggresive cam.

The restriction issue may be why Powroll uses a 1 1/2" header and although they used Mikuni carbs on some of their engines they recommend the stock Keihin with the Torque cam. Also the torque cam has a lot of lobe separation which broadens power.

I doubt if even one percent of my ride time is at peak power so my goal is power where I spend most of my ride time which is why the stroker and torque cam, all of the extra HP is just a bonus because the bike now pulls in sixth gear like the stocker did in fourth.

Link to comment
Share on other sites

Stroked XR200 engines can be made to rev with the two valve head to a point they won't stay together well......no problem. Powroll can sell you the parts needed .......... and the repair parts you'll be needing also! Has to do with piston speed, con rod ratios, con rod angles etc.. The torque cam brings power in at a much lower rpm needed for the stroked engine to live. Not as much peak power, but excellent delivery for slick, tight, technical, conditions. If you want to rev a XR200 stroker motor, you better have lots of money and be prepared to do lots of wrenching. Ran into to this also on XL125s' back in the 70s'. If you need or like high rpm, you need a engine that was designed for it from the ground up...........like CRFs'.

Old School Al

Link to comment
Share on other sites

I'm not looking to make it into a high revving motor. I'd much prefer that my motor holds together. It's great for it's main purpose which is riding New England hare scrambles.

It's just that right now, the motor is all low end. If I try to ride a wheelie, I run out of rpm before I can get the bike balanced. It just seems like I should be getting a little more out of the top end.

I appreciate the input.

- Brad

Link to comment
Share on other sites

Mine revs, not as good as my stock engine but it sure puts out a lot more power. I found an old Powroll brochure on another website that showed an engine build like mine had a power peak only 500rpm lower than a stock engine. What I think are the differences between our engines are the cams, exhaust/muffler, carbs, and possibly compression ratio.

So I think you need a cam and some time fussin with ignition timing. I have an 82 XR200 engine that outpulls my 90 engine on top end so there may be differences in head flow between early and late engine, and I've been told early heads flow better than later heads, I have a 200X head on the shelf but I'm clueless about how it flows.

I gave up using a timing light because of all the oil splash from the inspection hole, what you can do with a timing light is verify that the timing marks on the CDI Sensor and the Advancer line up at idle and at high speed (above 5k). Then you can do the timing static and avoid all the oil spray.

Link to comment
Share on other sites

Stroked XR200 engines can be made to rev with the two valve head to a point they won't stay together well......no problem. Powroll can sell you the parts needed .......... and the repair parts you'll be needing also! Has to do with piston speed, con rod ratios, con rod angles etc.. The torque cam brings power in at a much lower rpm needed for the stroked engine to live. Not as much peak power, but excellent delivery for slick, tight, technical, conditions. If you want to rev a XR200 stroker motor, you better have lots of money and be prepared to do lots of wrenching. Ran into to this also on XL125s' back in the 70s'. If you need or like high rpm, you need a engine that was designed for it from the ground up...........like CRFs'.

Old School Al

Excellent point. I built SL100 engines in the 70s that would wind 15k+ but they ate parts frequently. First it got bored to a 125 and the aftermarket started putting CB550 pistons in for 145 then strokers put them to 175. Honda took it to 185 then 200. Powroll upped it to 220 with another stroke. A acquaintance of mine made his own stroker cranks that took them to around 240. That's pretty heavy loads to be put thru a basically unchanged bottom end. Even the 125 started to show signs of limited breathing. The 200 is just an evolution of the same motor. If the displacement is doubled the rpm will be halved .. at least. Not to mention piston speed, etc you mentioned which can take that down further. What the 200 is, a really torquey 100, especially with a stroker. Revs just keep falling the larger any motor gets. When I look at the cam specs for the cams other than the torque cam I shudder to think of the useful life a 200 would likely have with everything needed to take advantage of them. I'm thinking transmission parts would become a fusible link at somewhere around 20 hp if the rider wasn't very careful how he used them. These are good low rpm motors that you shouldn't expect a whole lot more from.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

×
×
  • Create New...