Back firing

Posted by Andyt59 on Aug 22, 2010; 3:36am
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/Back-firing-tp1270157.html

Restoring an '81 CB750C Custom. I'm having issues with it backfiring. I don't know much about these carbs. That doesn't mean I am ignorant of how carbs work, but multi-carb set ups kinda scare me.

I've put the stock air box back on. The carbs have been cleaned. According to my local Honda dealer, this bike had 125/68 jetting and that is what is in it. I have a set of smaller 102 jets out of another set of carbs. I also installed stock exhaust.

It runs OK until it warms up. It makes no difference of how it runs if I choke it or not. After it is warmed up, the performance takes a dump. Literally. It's totally gutless up to ~5000RPM. It's got some cahonies above that. I have checked and rechecked the timing. Oh, and the idle is screwy too. After it warms up, the idle doesn't want to drop. It stays around 3000 RPM.

Any help would be great. I'm trying to have this bike ready for a CMA Fastlane Rally in Kamiah, ID (268 miles one way) the end of next month. Ultimately, I'm building this for my wife. I've been really lucky on the bright work (chrome) and am having the '81 tank custom painted.

-Andy