Introduction: Increase Power and Mileage

I have an old motorcycle which i love. It does not have any self start. So why waste money on a self start if you can change the way of starting the motor in a stylish and more of a genuine way which no other motorcycles possess.

So I am starting... This is my first instructables, and I thought this is a good idea to be shared. Treat me as a minor.

The motorcycle I have is 1999 model Royal Enfield 350cc Bullet. It has a very good, designed from heart-Motor. Wherever I go with this motorcycle most of the people around even other Royal Enfield riders, look at this very cycle in a wow face. This makes me happy and pride. Everyone loves Bullet. Every part of this motorcycle has got a masculine feel to it. So i thought of converting this conventional single spark engine to a twin spark engine.

In theory this modification enhances the combustion of air-fuel mixture and might require only less amount of the mixture for maintaining the rpm of old motor. Also we can get an immediate response for throttle. So lets start..

Step 1: Remove the Tank and Cables

First we have to remove the gas tank so as to remove the engine head. While removing the tank make sure that you first 'cut off' the fuel supply and remove the fuel lead to carburetor. After that carefully remove the throttle cable attached to the carburetor, by removing the top cover of carburetor. While removing carburetor, if you are a starter, make sure that you take pictures of parts so as to make sure that everything goes into place when refitting.

Also remove the decompression cable and decompression unit. To remove the decompression cable, pull out the top plate. To remove the decompression unit undo it using a spark plug spanner or a 21 dia ring spanner

Step 2: Remove Carburetor and Engine Head

Next step is to remove the carburetor and engine head. While removing carburetor, remove the filter leads also. Remove the two nuts on either side of the carburetor, and now you can simply remove the carburetor and its gaskets and auxiliary air screw mechanism. Place the removed components in a clean and ordered way.

Now its time to remove the engine head.

First remove the rocker arm covers by removing 8 long nuts. Now remove the rocker arms and place it on a clean surface. Now u can pull out the two push rods easily.

Also remember to remove the 'y' shaped oil pipe.

Next undo the remaining nuts on top to remove the head. Before pulling up the head, make sure you have removed the exhaust pipe from the frame.

Now use a wooden plank to pull out the head of engine. Care must be taken since the fins around the head are likely to break or bend under stress. So try to avoid hard hits, and use of screw divers on removal.

Make sure that any dust or foreign particles fall into the bore underneath.

Step 3: Decarbonising Engine

On removal of Head, you may find a lot of carbon deposit in head and top of piston. Then it is time to decarbonise the engine. If you are comfortable in not doing so, then go to next step. But it is a very good practice to decarbonise since you have opened the engine. You can also regain the pressure back so that there is a tight isolated chamber without leak for a good combustion.

Use a scraper to scrub out the deposits. Do not use any chemicals for this purpose. Just use plain water to clean, and dry it under the sun.

For decarbonising the piston, remove the bore(cylinder) also. By undoing a single nut. You can pull out the bore simply pulling out through top. Now there will be a ring lock at two sides of the piston. Remove this small ring using a small scew driver and nose pliers. After that push the rod from the opposite side of the piston. Now you can just simply pull the piston out. Remove the piston rings with hands. Do not use pliers since it can harm the piston.

Now decarbonise the piston and clean it. Clean the bore too using a clean cloth. Now apply oil on piston and inside the bore. Slide the piston from top of the bore. If it slides and reaches the bottom slowly with slight resistance, you are good to go. If you feel the piston slides without any resistance or there is some space between the piston and bore, then you might have to change the settings.

You should now buy a new oversize piston, and increase the the cylinder size to match it. Or you could buy a new bore and put it by cutting a sleeve. Both these can be done in a lathe workshop.

If you are going with a new over size piston, you could get more power, but a with a decrease in mileage.

On reassembling the piston, make sure u position it to the standards, and put the rings as specified. The three rings must be put as their openings mutually 120 degree to reduce the leakage.(Please make sure you refer the workshop manual before doing so. They contain many points to be followed, or you could simply ruin the motor. Workshop manuals a available online, just search for it).

Step 4: Adding One More Spark Plug to the Head

Next step is to add an additional spark plug to the head. The new plug can be added diametrically opposite to the first plug. Now there is a decompression unit in this position. The trick is to reposition this unit so we can use this position for the new plug.

Remove the decompression unit, and we can see the thread is compatible with the threads of spark plug. So I took the head to a lathe and adjusted the height(by machining) of the hole to fit the plug. Now you could see a small hole through which the decompression unit exhaled the gas to exhaust. Close the hole using a small aluminum weld.

Now to position the decompression unit, I have cut a small hole(1-2mm dia) at the center of the head an added a threaded position at the top for the decompression. Also added a hole at top of the decompression unit, so that the gases escape through the new hole instead of the old. Make sure you also seal the old hole.

Now its time to see that all the valves are lapped and sealed. Check the inlet and outlet valves, and also the seal of decompression unit.

Step 5: Engine Reassembly

While Reassembly, make sure that you buy new gaskets. Apply a thin coat of silicon, Too much is not ideal. Also make sure you do not close the small holes on gaskets, As they can be oil flow holes!!

It is a good practice to start assembling while you are free from all other activities and make surroundings and tools fairly clean. Before putting each part, Clean them with a clean cloth, so that no dirt or dust enters the chambers or disturb the system.

Change the engine oil completely by undoing the nuts under the crank case. Also make sure to change the oil filter in the timing cover.

While putting the bore back, it is good to have a helping hand to hold the cylinder while the other can push shrink the three piston rings one by one. Make sure the rings are put as top part pointing to top. REFERRING THE WORKSHOP MANUAL before starting would be good.

The engine head and rocker arms should be fairly tight. Do not over tight other nuts and bolts except that of engine holding nuts, as the may lead to failure of threads.

While assembling don't forget to apply plenty of oil on moving parts(piston, bore, rocker arm, push rods, cam wheels etc.).

While fitting the push rods, make sure each rods rotates freely using a finger, while there is no up/down movement, Not even slightly. This ensures reduced rocker beats and increased life of inlet and outlet valves.

Don't over tight the lock nuts at bottom of push rods, it might break(I broke two of them :p )

While wiring two coils have to be introduced and they should be connected in series and clamped directly to the body.

Step 6: Timing

The engine needs to be tuned well for maximum output. For this first we do timing correction.

Remove the spark plug and insert a small screw driver so that on cranking we can know the position of the piston. Care must be taken that the screw driver do not fall into the chamber. Be careful while doing this process. Engage in top gear and rotate the rear wheel anti clock wise by rocking the the Tyre. While doing this the motorcycle should be on center stand and well lifted from ground. When maximum height of screw driver is found, is the top dead center.

The spark is produced after the the point making contact and then releasing. So rotate the wheel clockwise so that the screw driver goes down to the minimum distance visible. If it goes too further down, try again. At this point set the point as just opened. This can be seen through the ammeter.

"The main concept is the point should get just open when the piston just reaches the top dead center."

The ammeter should show negative and then move to center when reaching this point.

Now the engine should start while kicking. Now set the rpm to about 1200 by turning the idle screw of carburetor.

Now turn the idle screw anti clock wise till the engine just dont get stopped due to low rpm. Now the plate on delco unit can be turned by unscrewing two screws.

Try slowly turning the plate to either direction so that the engine rpm if found maximum. Now turn the idle screw and slow the rpm. And continue this until maximum rpm point is acquired.

Step 7: Tuning

Now the part is to have a perfect air fuel mixture for the engine.

For this turn the engine off.

1.Tighten slightly the air screw and auxiliary air screws.

2.Undo the air screw one and half turns(3 Half turns).

3.Start the engine and increase the rpm so that the engine just don't stop.

4,Turn the air screw (anti clock) to a point that the engine rpm does not increase further.

5. Lower the rpm by turning the idle screw.

6. Undo the auxiliary air screw so that the engine rpm increases.

7.Do the above two steps, so that you cannot increase the engine rpm.

This is the final setting of the carburetor.

You can do the timing adjustment and tuning once more if you are doubtful on the perfection.

Now on kicking the kicker slowly will start the engine. If there is more trouble try changing the spark plug, point and condenser, or the coil for better performance.

Car and Motorcycle Contest

Runner Up in the
Car and Motorcycle Contest