The more and more I look around, the more and more I realize that a 36mm should just be too small for a 650cc bike. 36mm carbs are on 400cc 4-strokes and 250cc 2-strokes. I even saw a 36mm flat-slide on a 125 smoker. 650cc is over 50% bigger than a 400 - so why exactly should I be using a carb that's the same size?

I'm about the drop the hammer on a carb right this second but I'm really thinking it's the TM40 I should be getting - not the TM36. Unless someone can make a real good argument, I may just have to get the 40.

A 36 or even smaller would work on this low tech low HP engine and get better mileage. For a larger carb to work as intended you need more air flow higher lift and longer duration cam, open exhaust and more rpm,higher compresion.  At lower rpm a big carb does not work as well as a smaller one due to the venturi effect and fuel atomization.

This engine already has a very short intake, a large carb would just make this worse. Small and long intake runners produce more torque along with small diameter header pipes.

I cant see much advantage of a big carb on this engine without lots of expensive mods....i have a ninja that takes care of my need for speed.

Did you read what i said....look up the basics of an ICE, what i said was correct. If you want to go fast get another bike, wanting speed from this bike is like cutting steak with a butter knife....far better tools for the job.

If you did not want opinions why ask the question? No reason to be rude to someone answering your question.

The carb needs to be sized to work with the engine.  This includes port size, valve size, cam duration and lift, exhaust flow, etc.  If you have an engine that flow lots of air - then it can use a larger carb.

The Savage has a very mild cam, relatively small ports and valves, a restrictive exhaust system, mild compression, and it is designed to run smoothly at cruising speeds.  This means that the air flow is relatively low most of the time, and a smaller carb is better because the airflow through the smaller carb is at a high enough speed to create a nice vacuum and pull fuel out of the jets well.

If you put too big of a carb on without making other changes to improve the flow of air through the engine - then the speed of air flow through the carb becomes low and the carb does not work well atomizing or metering the fuel at low throttle settings.  The carb may work well when the engine is revved up - but that is not where the cam, valves, ports, exhaust are designed to work well on the Savage.  Too big of a carb....and you will end up with an engine that runs badly until you have the engine running at full speed.  It will be a very frustrating bike to ride.

With a stock engine the 36mm is supposed to be best, and with modificaitons you can move up to a 38mm.

Drifter wrote on 11/08/12 at 04:12:27:


Kind of like buying a 100hp John Deere tractor and 20' bush hog to mow a 1/4 acre yard then......... The only way to make use of the extra  size and power is to expand the yard........by several acres   !

ZAR wrote on 11/08/12 at 06:11:56:

Because wanting to maximize volumetric efficiency is EXACTLY like mowing your lawn! Didn't you know?!

*facepalm*


Thank you to Dave and Gyrobob. I think I'm gonna dig into the motor a little bit - most likely with a bunch of Lancer parts.

LANCER wrote on 11/09/12 at 05:37:25:



I agree,...  with a sense of awesome totalness.  I would speculate, though, that for a VM carb to be so responsive, getting the jetting (I made a rhyme, eh?) spot on is a perty big thang.

I'm not willing to spend $100 on something that I know I'm going to want to change out shortly - it's not like I can get that money back. I also want a flat-slide. Most likely I'm going to get the TM40-6 pumper and start saving for Lancer's 97mm bore kit and cam.