Thought I would post a quick review of the 250 sport. I have been testing one for about 3 months now. Overall very impressed with frame,suspension,and overall quality. I have installed 14 tooth front sprocket and rejetted carb several times untill i was happy with overall performance. Im 6"3 and 240# and it pulls me around great. I have rode this bike very hard and except for a broken chain it has held up very well. I have done big jumps with this bike and has done very well. One of the nicest suspensions out there on chinese bikes. I would like to see grese zerks added to swing arm and dog bone. Itook mine apart and packed with grease. Also better wiring I rewired some of mine with 10 gauge wire instead of 14 like they used. also took off foot shifter and redrilled and tapped to fit grove better. I made my own oil cooler gaurd out of rock crusher screen (woven stainless steel) If you rejet,change sprocket,regrind exhaust ports,readjust valves,and double check all fastners you will have a great bike. As with all bikes I will find a way to make it better. Im also testing a 150 and a 90 jetmoto. Hope to get a review posted soon. I have talked alot to Eugine at Jetmoto and he has been excelent to work with. Likes to hear the good and bad about the bikes and come up with ways to make them better.

 

Thanks for the review!

 

Thanks for the info man. "regrind exhaust port and readjust vales" Could you explain a little more in-depth what and how you did this? I'm not sure how to adjust a valve, or what tools I would need to do that. How much and in what manner did you open up the exhaust port?

Thanks
-JNY

 

Sorry i didnt explain better. When I set up my 250 it was running crazy lean. First i lowered the clip on needle to bottom notch. Still was running lean and had to choke to start. Rejetted carb with 107.5 main and 38 secondary jet. I have since drilled both out 3 more times. not sure of final size yet. When i get a chance i will take the bits i used and match them up to jet sizes. Take your valve cover off and 9 times out of ten the valves will be very tight. I think i adjusted mine to .004 on intake and .007 on exhaust side. If you need an exact number let me know . All you need to do is raise back wheels,take off valve cover,take out spark plug and use something soft to stick in spark plug hole on top of piston. Dont use a screwdriver it will scratch. I use rubber fuel hose. When the piston gets to top dead center you can adjust your valves. As far as the exhaust goes where the exhaust pipe bolts to the head i took mine off and there was extra metal around the exhaust port on the head. I took a plastic plug about the same size and pushed it up inside to block off the exhaust port. Before you start grinding put a thick coat of vasiline around the plug so later on you can just wipe out any metal flakes. I used a die grinder to put about a 45 degree angle on the port. I did the same thing on the pipe side. Makes the exhaust flow 100 percent better.

 

Man! Thanks for the info on that! I'm new to ATVs, and 4 strokes in general. I've not any valve adjustment before. I need to find a book or website that explains how to do it.

EDIT: Apparently all the valves need to be closed (duh) so the engine must be TDC on the compression stroke. In order to measure the valve clearance, you need a feeler gauge which seems to be a little piece of metal. hrms... I think I understand now, but what exactly are you measuring?

Anyway, You use the rubber hose to tell when the piston is TDC by spinning the wheels while in gear?

I would love to see before and after shots (or just afters) if you have them. I plan on doing this as well as an intake port and polish soon after getting mine (8-11 days from now I think.)

You might want to shoot an email to john at racewayatv.com for info on what jets to use. He has spent a good deal of time on this guy.

-JNY

 

I talked to eugine at jetmoto about jets and he was the one that sent me the 107.5 and the 38. The 38 secondary is not bad but after drilling it got better. The 107.5 main is way off if you want to ride hard. I wont know untill i match up my bits to the new jets but im guessing im close to a 127. Just starting to run rich at full throtle. Will put a uni or k /n on and should lean back out. Eugine said they need to redyno 250 because of the larger primary exhaust pipe.

 

I've had to adjust the exhaust valve clearance several times. I even cleaned all parts with carb cleaner and Loctited the adjuster. It came loose 2 more times. The last time I adjusted it seems to have stayed put. I have no idea what the actual clearance is set at, but I have had no further problems with it. I never have had a problem with the intake valve clearance.

I'm going to look at the exhaust port too. I took the endcap off the muffler and removed the piece of screen wire, ie. spark arrestor out. I noticed the baffle looks to be restrictive seeing how one end is reduced down. I turned it around with the reduced end now in the header tube. I also filed away some rough areas in the aluminum endcap. Changed the sound big time, and with leaning the carb down it has a much quicker throttle response. What is your elevation? I'm in Indy, and it is about 800-900 feet here. As soon as my parts get in, and I can ride it I will run it, and read the plug to see if I am too lean.

I've always wondered if it would run better with a slightly smaller carb on it. It sounds like it bogs because the intake velocity is too slow if you suddenly open the throttle all the way. It's obvious JetMoto built this quad for speed, with the high gearing and all. A 250 thumper should be able to be lugged around all day with no problem. Torque baby, give me torque!

BTW, here is the oil cooler guard I fabed up. Nothing special, but it works.

 

I would be interested to know the exact valve clearance this thing needs. I've read all engines are slightly different, so my perfect setting will likely be off just a little? I'm really not sure. As soon as I get it here, I'm going to take the filter to get a K&N replacement. I've been told that isn't going to increase airflow because the stock one is pretty good for a dry filter. Then we are going to rejet the carb and replace the spark plugs with NGKs. Change the oil.

While I'm riding the crap out of it (before I mess with porting the intake/exhaust) what should I look/listen for to tell if the valves are too tight or loose?

After I port and polish the intake and exhaust, should I go ahead and trailor it over to the local powersports place so I can buy jets until I find some that don't run lean? I have read how to tell if the top end is lean/rich, but how do you test the secondary (pilot?) jet? Do you just let it idle and then kill it and read the plug?

Thanks,
-JNY

 

I set my valve lash at .004 intake and .007 exhaust. That should get you real close. Most bikes i see are to tight. They start hard and run like crap. If they are loose they make alot of noise and horsepower is low. As far as the jets go I use carb drill bits and drill them untill i get what i want then match them up to a new jet. I lowered my needle clip all the way and drilled out my jets. For main jet ride around untill you get up to operating temp. then stop and put in a new plug. then ride wide open for about 15 seconds up a small grade if you can to load engine. then kill engine,chop throtle and grab clutch. then pull your spark plug if it is white or blistered too lean light brown or tan your good on main jet.

 

Forgot the pilot jet. Set idle 10 percent higher than normal and turn fuel screw right or left about a half turn untill you get the highest revs then readjust idle. Take it out and ride about 1/4 throttle it should maintain a constant speed without hunting. If it is hunting or surging your lean. Also lean if you hit throttle and backfires and spits through carb. Also backfires through exhaust when you let off. Running rich if idle is rough or you have to blip throttle to return to idle.