The stock Xr70 is as reliable as a rock but a bit down in the power dept for the trails we ride. It just didn't have enough beans to pull the gap between 1st and 2nd on much of a hill and gearing down made 1st gear less useable. My son was pretty frustrated with the performance although he didn't know what was holding him back.
After looking at the alternatives to his present bike such as a kx60 or 65 and a klx 110 or a small wheel ttr125 we decided that improving the power of the XR would satisfy the present need and allow him to continue improving his skills with confidence.
After doing some research I contacted Powroll and they suggested a thrust chamber and a big bore kit.
Step 1) We installed the thrust chamber which is a spacer that increases volume of the silencer and tested. It does not interfer with the stock spark arrestor and is neighbor friendly quiet. I thought I noticed a modest increase in torque but my son said he could not tell the difference. The next weekend we went on a campout and rode about 20 miles of tight singletrack first day and I noticed that he was holding second gear throughout most of the rides which was unusuall since I generally am encouraging him to shift up. The next morning I pulled the chamber without his knowledge and we rode the same loop and he was back to his usual first gear screaming along the trails and he was complaining his bike wasn't running right. We cut the loop short and rode back so i could reinstall the thrust chamber and he immediately noticed a difference. We concluded that the thrust chamber is good for a modest increase in torque although it is sold as a device that will extend the rev range.
Step 2) Big grin time! Installed the 80cc piston in the rebored stock cylinder and rejetted per recomendations. After break in jetted for power and noticed a dramatic difference. The bike easily holds 2nd gear on most every hill and pulls through 3rd gear. It now accelerates a 180 lb test rider (me :) ) up a test hill in 3rd gear where before it would barely hold 2nd and pulls stronger through 2nd as well. My sons summary was that it pulls as hard in second as it used to in 1st and 3rd as it used to in 2nd. We are using the stock intake, carb and air cleaner and throttle response and starting is very good and the power profile is very friendly. There are none of the burps or glitches in part throttle delivery that plague some setups.
I wouldn't hesitate to recommend this setup to anyone who is in a similar situation. Powroll has a revised cam grind for the bike and we are looking forward to give it a go. We'll let you know how it goes!
:)
After looking at the alternatives to his present bike such as a kx60 or 65 and a klx 110 or a small wheel ttr125 we decided that improving the power of the XR would satisfy the present need and allow him to continue improving his skills with confidence.
After doing some research I contacted Powroll and they suggested a thrust chamber and a big bore kit.
Step 1) We installed the thrust chamber which is a spacer that increases volume of the silencer and tested. It does not interfer with the stock spark arrestor and is neighbor friendly quiet. I thought I noticed a modest increase in torque but my son said he could not tell the difference. The next weekend we went on a campout and rode about 20 miles of tight singletrack first day and I noticed that he was holding second gear throughout most of the rides which was unusuall since I generally am encouraging him to shift up. The next morning I pulled the chamber without his knowledge and we rode the same loop and he was back to his usual first gear screaming along the trails and he was complaining his bike wasn't running right. We cut the loop short and rode back so i could reinstall the thrust chamber and he immediately noticed a difference. We concluded that the thrust chamber is good for a modest increase in torque although it is sold as a device that will extend the rev range.
Step 2) Big grin time! Installed the 80cc piston in the rebored stock cylinder and rejetted per recomendations. After break in jetted for power and noticed a dramatic difference. The bike easily holds 2nd gear on most every hill and pulls through 3rd gear. It now accelerates a 180 lb test rider (me :) ) up a test hill in 3rd gear where before it would barely hold 2nd and pulls stronger through 2nd as well. My sons summary was that it pulls as hard in second as it used to in 1st and 3rd as it used to in 2nd. We are using the stock intake, carb and air cleaner and throttle response and starting is very good and the power profile is very friendly. There are none of the burps or glitches in part throttle delivery that plague some setups.
I wouldn't hesitate to recommend this setup to anyone who is in a similar situation. Powroll has a revised cam grind for the bike and we are looking forward to give it a go. We'll let you know how it goes!
:)
