10 Go-Fast Tricks

One strong thumper pilot.

Here's what Scott Summers and his mechanic, Fred Bramblett, do to his XR600Rs to make them more competitive. These ten tips can be applied to any production thumper, but the jetting specs are for recent-model XR600s only.

1. To increase airflow, remove the airbox lid and use an aftermarket air filter. Do not remove the backfire screen from the cage. Removing the screen changes the intake velocity and causes the bike to have poor throttle response at low rpm.

2. To increase exhaust flow, Scott replaces the stock muffler with a White Bros. Megalloy system, with an open end-cap for closed-course competition. Scott says, "Please don't use the open end-cap for trail riding, as it is way too loud to use on public land." He also recommends sealing the muffler to header junction with high-temp sealant - they use Hondaline Hondabond H.T.

3. Check the header pipe where it mounts to the exhaust manifold. Sometimes the welds are overdone, and the extra material can restrict airflow. Grind away the protruding material to increase flow, but don't overdo it to the point of making the area weaker.(br>
4. With these mods, Scott uses the following jetting:
   Jet   Stock   Mod
  Main   152     155
  Pilot   62      68
  Airscrew       2.5 turns out
Scott says, "Most four-strokes come jetted on the lean side and must be richened when you increase intake and exhaust flow."

5. To make the race bike run cooler and extend clutch life, they mount an XR250R oil cooler to the steering head and remove the headlight for more airflow.

6. For better cooling they sometimes wrap the header pipes with exhaust wrap made by Thermo-Tech to keep heat from being transfered back into the cylinder and head by airflow.

7. If a course or trail isn't going to be too muddy, they trim 4"-5" off the back of the front fender to allow more cooling air to reach the cylinder.

8. Scott recommends against the use of plate-type skidplates. You got it, he feels they restrict air flow and trap engine heat.

9. Run good pump gas with an octane rating of 91 unless you have a modified high compression engine. Scott runs a stock engine because "the increased compression braking throws off my timing."

10. Keep your valves and valve decompression systems adjusted properly! This is extremely important for any thumper.

Last Updated Feb 7, 1996

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