I have changed my exhaust piping configuration on my A15, and to my horror, the fuel consumption has climbed to abt 35% more. To make things worse, i can feel a significant amount of powerloss.

These were the setups ( before & after ) on my stock A15.

Before
- 4 ->1 extractor ---->center straightflow mid bullet ---> tailpipe. ( the entire tubing size from the extractor to the tailpipe is 1.5in )

After
- 4 ->1 extractor ----> S-Flow center muffler ( right before the axle ) -----> tailpipe. ( the entire tubing size is 1.78in )

I changed to this config to eliminate the loud noise from the tailpipe, which apparently is successful...BUT didnt expect such high fuel consumption and powerloss.

Please help me to pinpoint where did i g o wrong guys.....thank u.

Did you touch the carb after this exhaust change?
You may now be running too lean.

I would expect the fuel consumption to go up a bit with the larger exhaust diameter 35% is a lot more than I would have expected. At speed for optimum fuel ecomony you will now need different jets in the carby.

Are you keeping the RPMs exactly the same as before, or revving it a bit higher now that it is quieter? Higher RPM exponentially increases consumption.

Ang95451, - For your info, im not using the stock OEM Hitachi carb. Im using a different model ( changed abt 5 yrs ago, way before i changed my exhaust config ). Ok, back to the story..so after i found the consumption was bad, i made it leaner a little more, but there was not much changes at all. The plugs' color are slightly on the lighter tan region. Hmmmmm...how shall i say it...in WinXp, open My Computer ->it's the folder's default color...

ddgonzal - The rev's are same as before, where i dont go more than 3k most of the time. Fuel consumption when cruising at 3000rpm on 5th gear @100kph is about 1.5Liters/10km

None of the other settings such as valve clearence / distributor timing were altered. No leaks were detected on the fuel linkages...and im quite confident that the carb is still in its best condition.

15L/100km . why not bolt the old system back on and see how it goes? at least you may eliminate the exhaust if no improvement is found.

Good idea. But for experimental purposes, guess i'll just change the S-flow muffler to a straight flow and observe the consumption. If it's still as bad, then i'll revert back to 1.5inch piping diameter size.

Anyone else have better suggestions?

Goddamn silent Ass-Flow muffler !!!

I cannot think that a exhaust can make your fuel consumption go so bad. Something sounds wrong.
Take it to a mechanic that has a gas analizer machine to see what it says about the exhaust gases.

My main suspicion is exhaust instead of other things since this issue happened immediately after i changed the exhaust system. Within the next 300km after i changed it, i noticed the difference. It was real good before that, 9L/100km....and what else could go wrong during an exhaust setup swap ?...yeah, before anyone would ask, i'll clarify that there are no leaks found from the extractor till the tail pipe end....

There's no visible black smoke from the tail pipe too. Even signs of a healthy engine ( tiny water droplets from the tailpipe during cold start ) is there.

I asked about the carb because I'm assuming that maybe the new exhaust flows a bit more than the old and now your mixture is not right. I think you may be too lean.
I recently played around with my carb jetting to try and get my fuel consumption to go down. I had adjusted it a little leaner and everything was fine. My fuel consumption went down. When I continued to adjust it lean, I lost quite a bit of power and my fuel consumption went up.

or,
now that I think about it some more, that super quiet muffler may also be more restrictive than the old one.

"""When I continued to adjust it lean, I lost quite a bit of power and my fuel consumption went up."""""

Wow...can that happen? I mean, power loss is something normal. But, how it can make the consumption go high is quite a puzzle.

So, shall i make it richer now?