Porting

August 8, 2007

Finally! I have a moped that gets up to speed! Well, not up to a great speed, but it now does 25mph instead of a measly 5. The cause of the prior sluggishness? A completely blocked exhaust port. I took the engine apart today on a whim and noticed a block spot with a tiny hole in it. Looked on the other side where the hole came out and realized that it was actually my exhaust port. Ouch. Soaked the deposit in PB Blaster (still my favorite solvent ever) for a while, and then took to it with a small hammer and a screwdriver, chipping away at the carbon.

Thirty minutes later and it was starting to actually look like a proper port.

Fifteen minutes thereafter I had it roughly opened up to the correct dimensions.

A full hour after finding the blocked port and it is clean. With no exhaust attached (still getting it cleaned up at the time) and no oil in the reservoir I stomped down on the kickstarter to see how the bike sounded.

VRUP VRUP VRAP VRAP VRUP VRUP Vrup vrup vrm….

Hooray! Let me play you a clip of how it sounded before clearing the port:

PFT PFT PIIFT PIF PIF POF pft pft puuf prm…

VRUP! vs PFT There is no mistake: Vrup will always win.

Trying to figure out how to delimit my Iowa model moped now that it can get to speed (Iowa models were limited to 25mph). There are a few concepts of what could possibly be the limiting factor, but there hasn’t been any definitive “This causes it” discoveries. What I do know is that by rounding out the exhaust port (the ’82 Urban Express Iowa has a flat port) I can add about 3mph. Additionally, I could upjet the carburetor (putting in a larger size jet) to add significant speed, but that would mean finding a jet that works. It also means I need to find out what size jet I am using right now. Upjetting could net me anywhere from 5-15mph. I’m hoping for the upper range, but expecting the lower.

On the tentative list for the bike:

  • New oil! Probably the first new oil in it in the past 5 years
  • New spark plug
  • Put the rear fender on
  • Battery. I NEED a battery to get the bike lights running correctly
  • New, larger jet (I think a #75 or #85?)
  • New fuel lines and filter
  • New plates
  • Touch up paints
  • Shine and condition the wonderful leather seat
  • Custom exhaust? Sure, why not.

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