98 replies to this topic

[Dwight_Rudder]

I have been dialing in my modded XR200R. Love the way it handles with the 1987 suspension with Race Tech Emulator fork kit and Progressive suspension fork springs and the Works Performance Heart Transplant. I had to split the cases due to the engine jumping out of gear under a load so I had Wee Racing in Alabama and Powroll , mod the engine with a stroker crank, 66mm 10.5:1 piston and the FULL RACE cam. We built a 1.25" header and are using the stock muffler with the large diffuser insert (ATC250R). Wee Racing specially degrees the Cam advanced to improve the low end and midrange. Powroll says it won't work but Chuck and Brad at Wee Racing have been doing this for many years with great results. They claim it is reliable also. We are using the stock carb. So far I have had to drop the main from the 130 they installed to a 122 and may drop to a 120. Stock needle in the middle position. Right now I have the stock 38 pilot but my fuel mixture screw is set at 1/2 turn out and probably can go in more so I will change to the leaner 35 pilot. It still has a bit of a blubber at 1/4 throttle. I think this is due to the engine now (with stroker and BIG cam) drawing hard on the smallish carb at low throttle openings. I currently am running stock 13/47 gearing but will be changing to 14/47 as it feels way too low geared now. I am running stock rear wheel with the stock IRC Ve33 tire which works great. I will keep y'all up to date with testing and how it works. This is my Post Vintage Race bike, Backup modern race bike and Enduro work bike.

[mikewrf18 TT Gold Member]

Dwight_Rudder said:

I have been dialing in my modded XR200R. Love the way it handles with the 1987 suspension with Race Tech Emulator fork kit and Progressive suspension fork springs and the Works Performance Heart Transplant. I had to split the cases due to the engine jumping out of gear under a load so I had Wee Racing in Alabama and Powroll , mod the engine with a stroker crank, 66mm 10.5:1 piston and the FULL RACE cam. We built a 1.25" header and are using the stock muffler with the large diffuser insert (ATC250R). Wee Racing specially degrees the Cam advanced to improve the low end and midrange. Powroll says it won't work but Chuck and Brad at Wee Racing have been doing this for many years with great results. They claim it is reliable also. We are using the stock carb. So far I have had to drop the main from the 130 they installed to a 122 and may drop to a 120. Stock needle in the middle position. Right now I have the stock 38 pilot but my fuel mixture screw is set at 1/2 turn out and probably can go in more so I will change to the leaner 35 pilot. It still has a bit of a blubber at 1/4 throttle. I think this is due to the engine now (with stroker and BIG cam) drawing hard on the smallish carb at low throttle openings. I currently am running stock 13/47 gearing but will be changing to 14/47 as it feels way too low geared now. I am running stock rear wheel with the stock IRC Ve33 tire which works great. I will keep y'all up to date with testing and how it works. This is my Post Vintage Race bike, Backup modern race bike and Enduro work bike.

Sounds like a great build! Where's the pics?

[KDXIdaho TT Member]

Looking forward to the build Dwight. I have an 87 XR200 with a 96' CR250 forks/disk and the motor will need a rebuild this winter, so I'm looking for tips.

KDXIdaho

[Dwight_Rudder]

KDXIdaho said:

Looking forward to the build Dwight. I have an 87 XR200 with a 96' CR250 forks/disk and the motor will need a rebuild this winter, so I'm looking for tips.

KDXIdaho

I wanted to keep the stock front end with the 1986-90 suspension so I can keep the drum brake to be able to use the bike in Post Vintage AHRMA Competition.
The stock drum works pretty damn good. I have the stock front end working as well as my 1997 XR250R forks I used on my CRF250F (formerly 230) project.
The bike actually looks stock. Same bike as in my Avatar.
Dwight

[chuck4788]

Thanks for the post on the project, I'll have to try the ATC250R diffuser (insert).
As a side note the 84-85 XR250R mufflers fit the 86-02 XR200 frame, have less back pressure than the 200 muffler, a 1 1/2" inlet and mid pipe, and the XR200R diffusers fit.

[Dwight_Rudder]

chuck4788 said:

Thanks for the post on the project, I'll have to try the ATC250R diffuser (insert).
As a side note the 84-85 XR250R mufflers fit the 86-02 XR200 frame, have less back pressure than the 200 muffler, a 1 1/2" inlet and mid pipe, and the XR200R diffusers fit.

Don't know if it will fit my 1.25" header.

[Dwight_Rudder]

Just installed a 120 main jet and a 35 pilot. A/S set at 1 turn out. Needle in # 3 or middle position. Runs great. I also installed a 14T sproket on front pulls it fine so far. I will ride some more this weekend.

[Dwight_Rudder]

Dwight_Rudder said:

Just installed a 120 main jet and a 35 pilot. A/S set at 1 turn out. Needle in # 3 or middle position. Runs great. I also installed a 14T sproket on front pulls it fine so far. I will ride some more this weekend.

Pulled the 14T fine in the lower gears but spaced to wide in the upper gears.
Going back to the 13T and maybe a 46T rear instead of the 47T.
Disappointed in jetting. Still blubbers badly at 1/4 throttle. Pilot is as small as it can go with the 35Pilot . A/S set at 1/2 turn out. Needle in the # 3 position. Tried #2 but it started overheating. Main is now a 118 and I think I will drop it to a 112 or a 115 and see how it runs. Now it runs good when cool but quickly starts blubbering when it heats up.

[KDXIdaho TT Member]

I'll throw out a few thoughts...

Sounds like it's rich at 1/4 since it's a hot misfire. If it were me, I'd leave the main at 118 or 120 (or richer) and drop the needle. IMO, I'd be careful on running the main lean since it can make you think you fixed a part throttle issue but end up making it run hot and detonate at WOT. That race cam with all that overlap and duration is gonna make it a bear to get that thing jetted right at partial throttle. Depending on how duration/overlap the cam has, part throttle jetting is gonna be a compromise anyway. Have you talked with Powroll on jetting that cam?

Another thought... If you think the cam is a little too hot and messing with your carburetion too much, try adding a two or three thousands clearance to the intake and see if it goes away. It's an easy way of reducing duration/overlap to increasing vacuum signal to the carb. That would be my last option if you can't get the jetting cleaned up. Good luck and keep us up to date.

KDXIdaho

[Old School Al TT Silver Member]

Interesting project.:thumbsup:

I'm thinking along the very same line as KDXIdaho.

Old School Al

[Dwight_Rudder]

I have a friend who is running similar setup but not the stroker crank. He is stock pilot and needle and one up on main from stock.

[Dwight_Rudder]

Been talking to Chuck Elam at Wee Racing and he is thinking my exhaust is more restrictive than what they usually build. Also the smaller header. They usually use a 1.5" header. Mine is 1.25". I have ordered a Torque Cam to try. Chuck says that with his setup that if I install the Torque cam normally that it will be slightly retarded so that will be good for more overrev.

[Old School Al TT Silver Member]

Dwight,

I would think your smaller header would only hurt top end with the full race cam. Usually a smaller header is used to improve low to mid ............. where you're having trouble. Although here I bet all duration and overlap of the full race cam is overiding the effect of the small header.

With a torque cam you're going to the other extreme. One thing to keep in mind is that stroker motors don't like to be reved. The torque cam brings the power in at a lower rpm to stay out of the danger rpm area of the stroker. I don't know how much mid to top you can tweak out of a torque cam. I wonder if you're going to like the torque cam ....... even though the stroker will.

Old School Al

[Dwight_Rudder]

Al, I am normally a short shifter / torque rider. I raced the stock engine to good effect. I used torque cams and stock cams on my XR315 and XR440. So I don't think I will be disapointed. Chuck and Brad like to really feel the power coming on. That is why they like the hotter cams. Me , I like a lot of bottom end power and drive off corners. I shift for speed. On my XR315 and XR300, I used a short duration cam high lift cam. I like the way they perform better than a long duration cam. Easier to jet also.

[Swiss TT Silver Member]

Dwight, it will be interesting to see your opinion on the difference between the Torque cam and the RPM cam. Of course, the 1.25" pipe is fairly small for a 200 with a stroker at 217cc. Wouldn't hurt to go for a bigger diameter pipe.

Swiss

[Dwight_Rudder]

I think the stock header is 1 1/8" . This header is 1.25" and Wee Racing has in the past used 1.5". I want to keep the strong low end response but perk up the midrange more.
I will let you know when I get the cam in.

[Old School Al TT Silver Member]

Dwight,

If you can live with short shifting and not reving you may be able to live with the torque cam. A little past mid it starts to flatten out and dosen't get much done ....... ready for the next gear. Right off the bottom to mid is where it makes it happen. The real plus side of this cam is the engine will stay together. Interesting to see what it does tweaked. I'd try the pipe you have. We run the larger 1.5" ...... but with a insert.

Al

[chuck4788]

An easy bump up in header size is to use the XRsOnly header (1 3/8"od at the end), you can pull the inlet gasket on the 200 muffler and use a bit of RTF for a nice fit. Or if you can find a 84-85 XR250R muffler (1 1/2" inlet) make up a bushing from sheet metal for the end of the header.

A while back I did some comparison tests on 200 exhaust systems and demonstrated that larger head pipes help bottom end throttle response, so do larger mid pipes but with more noise. So I think you are on the right track. The best bottom end power, and the noisiest, was the XRsOnly header and a 84 XR250 muffler wo insert (1 1/2" midpipe). This combo was impressive and pulled the baseline bike 1 1/2 lengths in the bottom of second gear.

I'm currently running a XRsOnly header on my stroker with an IDS2 muffler (1 3/4" core) with a 1 3/4" mid pipe. Changing discs helps with tuning and reducing noise is still a work in progress, currently I'm trying a 1 1/4" stinger to reduce noise.

I feel your pain on jetting; when its wrong it is frustrating. I also started out rich and worked leaner, it is now stock except the needle is one grove rich and the main is a 112. Yogi also had a stroker motor but with a Big Gun exhaust, you might check with him on jetting.

If you are a short shift rider you will like the Torque cam, always puts a grin on my face.

Looking forward to your comparison of the torque and race cams.:thumbsup:

[chuck4788]

Bump

Dwight; Any news on the new cam?

[shrubitup brap]

chuck4788 said:

Bump

Dwight; Any news on the new cam?

Seems he has written much on his new Husky WR150 which may have caused him to lose interest in the XR. :busted:

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