couple mods im interested in


New Member
Dec 19, 2008
ny long island
Okey i have ton of experience with 2-strokers ive owned a derbi senda which is a motorbike in spain and i rebuilt that motor and did pretty much everything from port polishing polishing/matching, polishing inside the crank chamber, reeds, pipes, carbs jetting. there area few things i haven't done.
one of those things is increasing compression, now a method i know of is to take the head of the cylinder and with sand paper on a flat surface start polishing it with oil to decrease volume only slightly. and therefore increase compression.

Another thing i want to know what size carb normally comes with these whizzer type engines. and what type/size carb people used and got away with.

Any one know of racing/performance crank bearings out there, anyone use them, how are the results.

Again i was looking for reed mod, i know there are different thicknesses of these and i was looking for a carbon fiber one.

Last but not least mod, if i take the piston connector rod and sanding it down to decrease weight. was wandering if anyone has done this and how much sanding would i get away with without compromising strength.

Off the topic
how long do people break in their engines for. and is there reason to re-tighten the cylinder bolts after couple hundred miles.

Thanks guys.

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
up north now
I'll say this- if you look around, and do some searches, you will find threads about all the stuff you are talking about. I know folks have done reed, pipes, ect.

Don't know what the size is officially of the carb, but I think it's around 15mm, 18 being used by some people (aftermarket).

I wouldn't sand the rod, it will ruin it.

Finally- break-in is done within the first 30 minutes (rings, if done right) to 150-200 miles (some just break in and run smoother after about a gallon of fuel) Vary the throttle amount and engine speed a lot during this time period, especially the first 30 minutes.

Don't be afraid to let it rev, and don't run the engine below 10 mph.