Posted by Max on October 17, 2001 at 20:15:14:
In Reply to: Heat, muffler discoloration, engine damage? posted by Fella on October 17, 2001 at 01:43:07:
Any restriction in the air entering or leaving the engine will change the total air flow some when it is changed. The muffler is one of the restrictions. Carb piston, intake manifold, air cleaner, valve size and passage area when open another, and don't forget the smallish ID of the stock exhaust pipe. The carburetor allows fuel to flow because of the air pressure drop whe the air travel through a restriction -venturi effect. The fuel control parts, needle and jet, can only flow a specificed amount of fuel for a given pressure drop. We change the amount of fuel by enlarging the jet or raising the tapered needle in that jet thus makig the effective size larger. The Savage makes is somewhat easy to change raise the needle allowing a slightly greater fuel flow by removing the white spacer. Other carburetors had a series of grooves and clip and we could change the A/F (air/fuel) ratio up or down. As you can see by reviewing the forum writers experiences there is a wide variety of tolerances and some bikes do not benefit from the additional fuel they have the correct amount after the exhaust change because the may have been slightly rich on fuel before that. Mine has a pilot jet change (unkown size as it wasn't on the work order) as it was so rich when I bought it used from a previous jet change it would soot the plug in 20 miles. After the SuperTrapp muffler change I tried the spacer trick and put it back in as I was still runing to rich at cruise. Mine seems perfect now with larger than stock headpipe and 84 DB HD muffler. You can get an idea if you need to add fuel by running the bike a cruise warm about 50 and carefully add in some choke, if it runs better and stronger, then more fuel would be helpful, if it doens't change or runs slower it is OK. This only checks the speed you were running at and does not substitute for a dyno check of A/F ratio over the whole speed range. Do this only when there is no traffic around and the road is wide enough to not run off it while you are focusing on the gentle adding in some fuel. "Tuner beware".
Any bike shop will be very reluctant to change the emissions from stock as the EPA/CARB can fine up to $10K and a year in jail for anyone who should know better tampering with the emissons. Actually now you know better and could get nailed if they had the resources to get you. Max