New Exhaust, Not Much Performance

I recently installed a Weak-Ends exhaust on my Tomos ST. I put in a bigger main jet - 66 to replace the stock 55. It seems like I've gained a little power, but my top speed only went up from 25 mph to 27ish.

Today I messed around with the air/fuel mixture quite a bit, but it didn't seem to do much for my performance. According to the spreadsheet, there are people pushing 40 mph with just an exhaust upgrade and upjetting.

Any thoughts on why I'm not seeing much of an improvement? I weigh about 225. Maybe I need to stop eating so much pizza?

Re: New Exhaust, Not Much Performance

Brent Bublitz /

Have you opened up the air flow? Remove the air box and get a high flowing filter or screen. The stock box/filter could still be choking it off quite a bit. You have to have enough air going in to get the power out.

Honestly, your weight might be a factor, but you should still be seeing more improvement than you have.

Re: New Exhaust, Not Much Performance

Darrell Gabbard /

your engine is restricted to comply with your State laws on speed. I would look at a bigger intake manifold ID and port the engine intake or buy a big bore kit. now by buying a nice pipe and expecting to blast just proves PT Barnum correct.

Re: New Exhaust, Not Much Performance

I would say your jetting is far too rich for just a pipe. The stock intake is not that restrictive, you should get speed. You likely would only need to go to somewhere around a 58-60 jet. Look into that.

Re: New Exhaust, Not Much Performance

could have crazy short gearing, some tomos came with very low ratio gears

so many other things that could be wrong, its tough to say. probably should have figured out what was wrong before adding a pipe to the equation

Re: New Exhaust, Not Much Performance

Super Tightpants /

new exhaust requires proper jetting as well as higher flow air filter.... if after all that has bin taken care of no difference is made, then you my friend might just have gotten the wrong pipe for what your looking to get out of it .

Re: New Exhaust, Not Much Performance

Thanks for all the suggestions. I think I'll start by putting a higher flow air filter on and trying out some different jet sizes to see what kind of difference it makes.

The ST comes with 26x28 gearing, which limits the speed to somewhere around 25-30 out of the box. I bought a 22T for the rear, but I haven't put it on yet. Don't want to mess with too many variables at once...

Re: New Exhaust, Not Much Performance

Cylinder head temp gauge is your friend. You can watch the temps when you re jet. If its too hot up jet too cold jet it down.

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