My CFmoto 250 build

[toomanytoys2]

I’ve been doing a lot of research and gathering parts for my CFmoto 250 engine in my new to me 2007 Joyner SV. The few times I have driven it, it seemed to be really down on power. It also seemed to be rather high geared. The first thing I noticed was that the engine wouldn’t top out in high range. I figured that the engine was on its last legs, so I did a compression test. I got 120psi for the pressure, which would normally seem ok. However, I had located two different manuals on the CF, and one said the pressure should be 1,300Kpa (185 psi) and the other stated 1,400Kpa (213psi). So that would seem to back up my worn out theory, unless the specs are wrong.

I was able to locate the CFmoto distributer in China, so I ordered a complete genuine CFmoto head. Since on any engine, the most power gains are in the head, I took the head to my favorite engine guru to get some pointers on where I should concentrate the porting. He builds engines anywhere from alcohol burning Briggs & Stratton to world of outlaw sprints. Before looking at the head, he wanted to test some new loads for his 243 Ackley Improved, so we went to his private range in an orchard, I helped him setup his chronograph, and we fired off some rounds. Afterwards I took him to lunch and picked his brain. He then said “let’s go port your head”, I wasn’t expecting that. We went back to his shop, and for the next couple of hours he worked on the head, while I watched and asked questions. For giggles, he wanted to flow it, but I didn’t bring all the parts that he needed to do it though.

During lunch he asked me what they of carb, cam, and exhaust I was planning on using. I am using a pumper / slide carb off of a Honda XR250L. The throat measures 31.6mm, but the venturi is a taper bore, which acts like a small carb at small openings, but flows like a big carbs at WO. The down side to this carb was that it was produced during the “smog” era. That means that the pilot jet was a fixed, pressed in design. So I had to take some extra pilot jets that I had and turn them in the lathe, so that they would match the dimensions of the stock jet. This means tuning will be a little time consuming, since I will have to pull the carb, to swap the jets.

As far as the exhaust, I felt that the 1-1/2” aftermarket exhausts are too big to achieve good scavenging. I told him that I was thinking of going with a 1-1/4”. After doing the head, he recommended that I go 1-1/4” for the first 10”, and then go 1-3/8” after that. The head pipe that I am using is from a Honda CRF250X. It starts at the head at 1-1/4”, then steps up to 1-3/8”, 12” later. However, the “bushing” that goes into the head’s exhaust port was too large, so I cut the pipe before the first bend, chucked it in the lathe, and turned it down.

[toomanytoys2]

For the muffler, I will be going with one from a Yamaha WR250F dirt bike. Those bikes were rated at around 30HP, so it should flow good for this motor, and be really quiet. If I feel like it is too restrictive, there is an internal baffle that is easy to remove, yet doesn’t increase the noise that much.

When I tried to install my carb into the stock intake manifold, I ran into two problems. 1st the throat of the carb was too big. 2nd the angle of the manifold caused the carb to hit the coolant connections, so time to make a new manifold. So scrounging through my metal scraps I found some good flat stock, and some pipe that had the same ID as the carb throat. So with a hole saw, pipe cutter and welder, I fabbed up a new intake manifold. Don’t look too close at my welds, 80% of my welding, I do outside, so I use a modified Harbor Freight flux core welder. To join the carb and the intake manifold, I am using a piece of radiator hose. However, the output side of the carb is a little too large for my taste, so I chucked the carb in the lathe to reduce its size. However, since the intake side and the output side are offset, I had to use my 4-jaw chuck to get it square. For the air cleaner, I had to use a 90 degree elbow for clearance, and I also had to flip the elbow around to match the OD of the carbs intake. To mate the air cleaner to the elbow, I got a short piece of exhaust tubing that they can both clamp to.

You may be wondering why I am doing all of this external stuff first, especially on a worn out engine. That is because I am waiting on a cam. Tom at SYC Powersports is grinding a cam for me. I will be kind of a guinea pig for this new cam, so I am trying to get everything else done before it comes in, and I tear the engine down. More to come…..

[jmansracerocket]

To many, those r actually good welds, espically for flux.

[toomanytoys2]

Man what a difference. Since I am waiting on my cam, I decided to get all the work done on the intake and exhaust systems. Finished them up, and it feels like a totally different engine. Remember that my engine is a very tired stock unit, and it only has 120 lbs. of cylinder pressure instead of the 200 lbs. that it is supposed to have. Previously the engine would not even begin to top out in high range. Now it scoots up to about 8,200 as indicated on the tach. I can only hope that it makes as much of an improvement on the finished engine.

The carburetor worked really well, and my guess on jets was pretty close. Right now it’s on the rich side, and that’s where I want it. I did have to come up with a solution for the throttle cable though. Due to its location on the carb, I had to get a long universal cable that had a 90 degree bolt on connection on one end, so it would clear the head. One feature that I really like about the carb, is that the choke is an automotive flap style, with a built in fast idle cam. This makes starting a breeze, and I can use it if I think that the jetting is lean at the tuning stage. I had to trim a little off of the intake manifold, then the carb and filter fit like a glove. I ended up with about 1” clearance from the back of the seats.

To activate the choke, I went low tech. I am using the throttle lever and cable from a lawn edger. I will be mounting it on the left side of the shifter bracket, with the lever down, choke off, pull up, choke on.

The exhaust pipe took a little fudging, but it worked out pretty close to where I wanted it. At the head pipe, I have about 10” of 1-1/4” tubing, and it then transitions to about 5” of 1-3/8”. Then there is a slip fit junction of 1-1/2” that goes to the muffler. I went with a slip fit because the motor is mounted by rubber mounts, but the muffler is mounted to the frame. The slip fit will allow the pipe to have some give due to the different flex points.

The muffler is also rubber mounted. I welded a bracket to the frame and one to the wing. I went with two mount points because I felt that the muffler’s weight might put too much stress on the head pipe. On the rear muffler strap, I got lucky. I used a generator strap from an old VW bug, and it worked perfectly. The muffler is very quiet. In fact, there is far more intake noise, then exhaust noise.

I will probably be on hold for a little while until the cam comes in. I do have to replace the front spindle / A Arm bushings, and just a bunch of little stuff, but I also have to do some things around the property. Plus I just bought my wife a new dirt bike and it needs to be stripped down on gone over before we do our annual Easter trip

[SYCARMS]

The Joyner is an excellent buggy, I have a few. The problem is they are the heaviest on the market. That same engine is used in the later hammerheads, about 100+ lbs lighter with much better performance.

[toomanytoys2]

The reason I wanted the Joyner was mainly for the front suspension. I just feel that the strut design has too many limitations.

[SYCARMS]

They are good riding buggies.

[Daugela]

First post on the forum. Great write up! Just picked one up too that I'm restoring... May shoot you a PM

[toomanytoys2]

Well, I finally got to put the Joyner through its paces, and it held up great, except for the last 100'. It was a 40 mile round trip in the desert. I know that most of you are back east, but I'm out here in CA. I ride dirt bikes as well, but I grew up on four wheels (had my own sand rail at 16), so lets just say that a sand wash littered with boulders is what I like. In my opinion there is nothing better then steering with the throttle, and lets just say, my foot was buried most of the time. Tom, I want to give you a GREAT round of applause. The cam specks that you came up with are perfect for a Joyner. I've built a lot of engines, 2 stroke, and 4 stroke, and your cam was right on the mark for a heavier buggy like the Joyner. I bet it would be even better on a lighter buggy, such as a Hammerhead.

Speaking of Hammerheads, it didn't make the trip so well. There was multiple failures with it. The person driving it was my son's best friend. He was more accustomed to dirt bikes then 4 wheel vehicles. I told him that you never let a tire rub against a rock, well you know how that story goes. He did, we found the closest camp site, and they put a huge patch on the outside of the tire, aired it up to 40 psi and said go balls to the wild to get home. 10 Miles from camp The Hammerhead died. It was almost dark, so I did minimal troubles shooting, then said screw it I'll tow you home. So I hooked up a tow rope, ( I'm prepared for problems), put the Joyner in low gear and started to tow him home.

Then when we all most back to camp (100') max, the Joyner died- What the hell. There was a lot of confusion, should we drag a truck out to pull the buggies up? I yelled, give me a flash light, and I discovered that the retaining screw on my carburetor support had backed out and fallen out, so the carb fell out of the intake manifold, more redesign is needed, on my part.

The Joyner was great. Even though it took a while to get a cam from Tom, it was well worth the wait.

The reason that it has taken me so long to post, is what happened the next day. Lest just say that I am the leader of the pack. I understand maps GPSs, and have a very good since of direction. The following day we did a dirt bike ride from 3000', to 7000'. There was one section, 50 yards max that was pure ice. There was no option because it was blind curve, so you turned right, and you hit the ice. On a dirt bike, you can not stop on ice. I take that back, I was the only one who didn't stop. Everyone else stopped by eating it. I am old (papa is older them me though), but I still have the technical skills. However, as I was going down, I was thinking, "OH ****" we have to climb this on our way back to camp.

When I ride dirt bikes, I wear a rescue vest. It has spare parts, bolts, nuts, and medical supplies. Well needless to say, I had to put all of my medical supplies to use. It took us an hour and a half to get 5 dirt bikes up that 50 yards. I had to create a splint for my son's friends knee, and it has cast some serious doubts whether I should ride again.

To start with I have a bad back, after this escapade I ended up with a serious case of sciatica. It was absolute hell to load up and drive home. To make problems worse, when I go play, I tow doubles. That means I have my truck, a fifth wheel trailer, and my toys in another trailer behind it. In CA, I had to get a commercial license to do this. So my wife couldn't drive home (legally), and she would be scared to anyway. So I had to drive for 5 hours, in extreme pain. Then I was laid up in bed from Dec 31st to Jan 3rd, on a diet of muscle relaxers and pain pills.

Why am I giving all the details of my pain and suffering? Because I am a College Instructor, and used to teach High School. I also want to send an EXTREME message to the younger crowd, that as they go through life, protect your backs at all cost. I didn't have a choice. When I was 21, I was forced off a twisty mountain by a motorhome coming the opposite direction, and was in my lane. I ended up going end over end down a ravine. So for over 30 years, I have had pain as my bedfellow.

I don't want to be a downer, but please protect your backs. You don't want to have pain dictate what style of life you have.

[SYCARMS]

Glad to hear you like the cam. I put one in my Joyner and cannot believe the difference as compared to the performance cam it replaced. Sorry it took so long. I tried to use the local cam shop but the stood me up after about 6 months so I had to use another shop. Just coming up with a new cam design takes time since nobody knows the limits as to how much of a grind you can get away with. You have to make all the measurements as to all the clearances mainly for the lift and overlap. The lift is the easy one but the overlap is tricky so they do a grind then send it back to you and you have to degree the cam in the engine while checking to make sure when the valves pass each other you have enough clearance between the valves as they pass each other. I have a short hill next to my shop only 20' long but about a 60 degree grade. With the old performance cam to make that hill in high gear I would have to get a running start of about 50' and would barely make the hill and the clutch would be smoking hot. In low it climbed it no problem. The new cam I can get right up to the start of the hill and it climbs it without going over 1/2 throttle. My Joyner is an 06 model and is different from the later 07 and up models for my rear axles have a greater pitch to then as compared to the new models which takes 50% more throttle to get the buggy rolling from a dead stop. This new grind solves that problem. 05 and 06 had this design flaw which was corrected in 07. Again I'm glad to hear you are pleased with the cam, and thank you for sharing the results.

[toomanytoys2]

Tom, the funny part is that I have my friend's son begging his dad to find a Joyner (they're scarce out here), and having me set it up for them. The 40 mile trip was from our camp in Dove Springs, to Bickle Camp. Bickle Camp is a semi restored mining claim of a hermit, that is located in the Red Rock Canyon region of the Mojave desert. Since it was a new riding area for us, there were actually two parts to our group. One route is passable by car, if it has high clearance. So my friend drove his truck, with my wife and his and mine daughters.

The other group was led by me in the Joyner, a topical graphical map and dual GPSs. So obviously, we took a different route. Once we hit Bickle's Camp, my friend's son (who has a tricked out Kawi, 250F) said that he wanted to ride back in the Joyner. We threw his bike in his dad's truck, and on the way back I started teaching him the fine art of steering with the throttle in a sand wash (I had to yell of course). I did not hold anything back, the throttle was buried for most of the time (except for steering purposes), and to be honest, I was pretty amazed at what the little 250 engine was capable of. Everyone seems to dump a Polaris engine in these buggies, and I was thinking I would go this route, but after this trip, I'm going to leave just the way it is.

So for anyone that is thinking of hopping up their 250 engines, I HIGHLY recommend Tom's cam. Just as a side note, I am not paid by him, in fact I have never met him, but he has a wealth of knowledge, and has developed a extremely good product.

[SYCARMS]

Glad to hear you like the cam and thanks for sharing your experience.

[EVILWS6]

Originally Posted by SYCARMS

Glad to hear you like the cam and thanks for sharing your experience.

PM the price for one of the cams. It would go on a HH 250SS.

[BEEFKING69]

Originally Posted by SYCARMS

Glad to hear you like the cam and thanks for sharing your experience.

Also interested in price of cam.

[SYCARMS]

Cam for the CN/CF 250 is $265.00

[BEEFKING69]

Originally Posted by SYCARMS

Cam for the CN/CF 250 is $265.00

Ok thx. Id like to get one when i do the bbk on the hh250ss. Have you had any experience with cams or bbk on the linhai/vog 300?