Re: Back firing

Posted by mitchberry on Sep 06, 2010; 11:41pm
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/Back-firing-tp1270157p1429727.html

i'll admit i didn't read everyone else's posts, but i will say that back firing does not have anything to do with carbs...

 a backfire is caused when the valves open at the wrong time, or the engine ignites at the wrong time...

 this is generally caused by timing...  in other words, you probably need to either adjust the timing chain or replace it.

 
Backfiring isn't caused by the amount of air going into the carbs... though with that said, you should make sure to jet for altitude as well as modifications to exhaust and air filters...

if it's all stock, use the stock jets.. if you have custom exhaust and air pods on it, then change the jetting.

the other thing that will cause backfiring is bad valve shims.. i assume there are shims in these motors.. i've never cracked one open...  but i can say that i don't recommend doing that yourself unless you really know wtf you're doing..

shims are spacers that adjust the space between the valve buckets and the cams within .500ths or more of a mm....   if they are off, the valve may not open or close as much as it should / BOOM  backfire....