[Astor123]

I had this problem last year when I replaced the mufflers, it started to backfire on the right side only. The simple fix was just a spark plug replacement.

This time around I was working on the bike and it was out of commission for about 2 weeks, replaced the front tire, did a rebuild on front brakes, and changed the oil.

Most of the backfiring is during deceleration but it also does it slightly while idling in neutral. I did check the exhaust manifold and the muffler on that side and it seems to be just fine. One thing that I didn't rebuild is the air cutoff valve. Could that cause it to backfire only on the right?
BTW, I did replace the spark plugs on that side again, just in case. Last time I had this problem I triple checked the timing belt and the valve clearance so I know that is ok.

Update: I rode the bike today on the freeway, came back and took the plugs out and both sides were running lean. I need to pull the carbs out anyway to replace the plenum gaskets and I'll do detail inspection and a clean up but I was thinking about another thing that might cause the problem, K&N air filter with a combination of short almost open exhaust pipes?

 

[drmcmtru]

If plugs took care of it last time,then i'm thinking plug wire or plug wire end (at the plug).
No way the air filter doing this,feeds both sides,right? What's up with the plenum gskts.?
Are you doing the carb's while they are off? Seems like a lot of work if you don't. If lean condition was the cause i would think you would have misfiring on both sides.Good luck with it,take your time.

 

[Astor123]

drmcmtru,
took care of the wires and sparg plug connection a while back, and I did check up on it just in case. But I will spill my stupid ass so others can learn.
Had a center plenum gasket leak during January (cold for Houston) and it was a gasket I did not replace when I did the carbs. Bought one from Randakk and he was a gentlemen that he sent me the complete set for each of the carbs attaching to it but my lazy ass needed to ride so I improvised w/ silicone. Now, the big plenum gasket is no big deal but there is a small o-ring that goes with it, tra la la...with silicone behind it. The only other problem is that I'm painting my house and my trusted Honda lawnmower decided to talk to me today, what the f.. is next on the menu?

 

[Astor123]

After 5+ months I finally figured out the backfire issue. While trying to readjust the new points after 500 mil. I noticed a tiny little black spark mark on the side of the spring. There is a article recommending that the points from a CB450 work better since they have a dual ground strap so I had them installed. Well, the left side works perfect but the one on the right is a little different than the original. It has a different mounting plate and it brings the spring "real" close to the mounting screw, close enough that when heated it would connect. To solve the problem I had to replace the screws with a smaller head screws and grind the hole on the mounting plate to move it further away from it. And that did it.

 

[budoka]

You're a patient man Astor123, that's alot of fiddling with small stuff. I was going to suggest a re-jet since the pipes are different but you would have likely thought of that already. What's the deal with the mower? The main issue we have here at the shop is either pooched fuel and dirty air filters/carbs.

 

[Astor123]

I got it re-jetted and it's running perfect. I should have paid attention the first time I installed these CB450 points. After removing the originals I just tossed them in a spare parts box and never looked back. The new points screwed right on so I adjusted the gap and that was it. Maybe if I would have had the bike up on the stand it would have been different, working on a pair of tired old knees creates a different perspective.

Oh, the lawnmower, Honda's Harmony 215, great machine except they probably got the plastic housing that holds the air filter from some plastic manufacturer located in the mountains of Albania or Bangladesh. The actual mold was distorted and it never had a proper fit against the carb intake and it constantly needs to be cleaned.

 

[Chopin]

Kudos ! Astor: Whether you accept the position or not, you are the top notch mechanic/ repairman/ etc. for the 1200 riders here. I ride an 1800 so all I can do is lurk .

 

[Eric]

I have messed with air in, air out faster and sometime you need to change the spark plugs heat range, you may have all ready covered this. Just a thought. Eric