More Horsepower

Not being able to leave well enough alone,  we tried a few simple performance modifications on our Bajaj Legend.

Don't ask us for step by step instructions and details of how we did these things.  There is enough information here for the experienced mechanic, and only those who know what they are doing should try any of this.

The Bajaj engine  is considerably detuned and designed to perform reliably in countries where fuel and oils are not up to U.S. standards.  We feel there is enough reserve in the design to accept these conservative modifications without significantly reducing the engine life.  Be aware that performing any of these modifications will void any warranty coverage.  None of these modifications affected the emissions profile for the engine, if fact, the increased compression ratio reduced the HC emissions a little.

Don't try to remove or disable the emissions control system.  It is required to meet passive emissions regulations and to remove or disable it will not improve performance in any way.

Disabling of the TRICS ignition system

The Throttle Regulated Ignition Control System was introduced by Bajaj Auto to insure that, when under full load conditions, and low quality fuel was being used, pre-ignition would not occur.  When the throttle is advance beyond 1/2, the ignition timing is retarded.  With the better quality fuel available to us, we can disable this feature and gain a little more horsepower.  We have put a lot of miles on our test Bajaj, using regular 87 octane fuel, without any signs of pre-ignition.

Simply unplugging the TRICS connection on the CDI will perpetually retard the ignition and adversely effect performance.  Pins 7 & 8 of the CDI must be tied together to bypass the retarding of the ignition.  See the Tech Notes for CDI pin locations.  Either remove the plug and solder pins 7 & 8 together, or cut the wires near the plug and solder the Orange/Brown and Brown/White wire together.  Insulate the joint to avoid grounding.

Here is what happens:  When starting the engine, the timing is retarded to 16 degrees before Top Dead Center.  After the engine speed goes above 1500 rpm, the timing is automatically advanced to 30 degrees before Top Dead Center, and stays there.

Exhaust System

We installed Phil Waters POC exhaust system.  This too gave us a little more horsepower.  Go to The Argo Company Car page to see the modification we made to quite it down.

Milling the Head

i machined .040" off of the head.  This gives a conservative increase in the compression ratio.  Stock cylinder compression test was 182 psi, with the milled head it went to 208 psi.  I still use 87 octane fuel without any indication of overheating or pre-ignition.

Using a fuel/air ratio meter, we found that we needed to richen the fuel supply.  We didn't need to increase the main size, we just lowered the clip on the main jet needle to its lowest position.  Using a fuel/air ratio meter is the ONLY way you are going to get it right.  Simply adding more fuel to the fire is no guarantee of better results.

With the above modifications, I now achieve a top speed of 64 mph indicated.

My preference is to leave the carburetor and cam timing alone. I like having good low end and mid-range torque.  It's fun to squeeze more horsepower out of a small engine, but these few conservative changes gives me plenty of power for the kind of riding I do.

Al Kolvites