exhaust back pressure

nq50KillingSpree · Post by **nq50KillingSpree** » Wed Aug 20, 2008 2:45 am

I have 2 1986 honda spree's one runs like a scolded dog at 35 mph all stock moter..and the other is in real ruff shape....i paid 300 bucks for both of them..so i cant complain...I want to know if i remove the stock muffler....and replace with a straight pipe(aluminum ball bat is perfect size) How do i know how much(if any) back pressure is needed......because i want to increase power not diminish it....i have removed the rear fender/air box and replaced the stock filter with a high air flow cone filter...it seemed to do alot of good.....i have yet to open the air intake. or open the exhaust port any...
any help would be nice......esp a web site to order aftermarket parts...like carburators and racing gears and such.........plze help.....thnx

Clivester · Post by **Clivester** » Wed Aug 20, 2008 2:58 am

See these two threads for previous discussions:

http://www.hondaspree.net/phpBB2/viewto ... 694c421e05

http://www.hondaspree.net/phpBB2/viewtopic.php?t=5707

Clive.

keithw · Post by **keithw** » Wed Aug 20, 2008 7:30 am

The Honda Spree carb jetting is very sensitive to intake and exhaust mods. Most anything you do to open things up will require a bigger jet. If you don't jet it properly and run it lean it will burn up the cylinder and piston. I'm up to an 85 jet from the stock 65. Sorry, the answer isn't to just throw an 85 in it and you're good to go. You need a selection of jets and pick the one that's correct for your engine. The sizes that I've found from Honda are 62,65,68,70,75,80, and 85. The Spree engine will turn around 12k rpm, up from 8k stock, and stay in one piece if derestricted and jetted properly.

keithw