Engine mods???

Yes.. Cam Timing, not ignition. When I pulled my wifes Jet-Tah's OHV motor apart, I checked the cam timing vs what the Honda CG125 specs where. I found that the timing was advanced about 2'. So I pulled the lower gear off and retarded it to 4'. This was a change of 6'.

What I noticed, is that it does not like low speeds anymore, duh, I retarded the cam. It has a tendency to have a light buck and miss below 2500 RPM's. Above 3K, it is down right nasty compared to my bike. Alot more power, and you can hear the change in the exhaust.

Basically the procedure is to split the case to gain acess to the crank gear. Use a medium sized three jaw puller, and remove the gear off the crank shaft. This is a compression fit, so you may need to use a bit of heat from a propane or MAPP gas torch. DO NOT USE OXY-ACE, you will likely melt the cheesie china cast iorn gear. Mark the gear TDC dot with a good scribe, this part is VERY IMPORTANT!! The dot is only marked with a dot of paint, and will burn off before you get the gear heated back up. Heat the gear up till it just begins to glow red, and press it back on 1/2 tooth counter-clockwise. This is 5-7' as per my degree wheel. Reassemble motor..

I believe the reason the gear is advanced is for emissions purposes. They do this to decrease combustion temperatures at low RPM's. Got idea, but very 70'ish emmisions. But... It may be just the chinese fast assembly line, not truely checking the gear position. This gear is not locked on with a keyway, just compression. Have yet to crack into the Viva to check it. I plan on doing it when I update to the VFR500 clutch pack.

It works well, but not for the faint at heart. Besides the exhaust and carb jetting, I believe this to be the best power improvement for these motors.