Right cylinder Backfiring

L

lhemrick

Active Member
I recently did a top end rebuild on my 1970 Honda 350k. I Had it running great and then broke the bike down for powder and paint. I have it looking "PRETTY" again but it now is backfiring slightly on the right cylinder. I have already cleaned the plugs and points. Checked timing and the gaps. I swapped the plugs and the new caps from one side to the other. I made some carb adjustments but its still doing it. What gives?

Thanks!
 
Either you're running a bit lean (dirty carbs?) or you might have a bit of an exhaust leak near the head. Did you replace the copper crush gaskets when putting the exhaust back on?
 
I carbs had a rebuild and were clean and running good. They sat on the counter for a couple of months while I did the other work. I don't understand if it is them how they got out of adjustment just sitting there. I did take the right one off and open it up and check just to make sure. Now the exhaust leak is other thing entirely. I did use new copper gaskets and I don't see any evidence its leaking at the head but now where the pipes connect to the mufflers is another story. Both joints are leaking like crazy there. Could that be it?
 
If the carbs have been sitting a few months, it might be worth the peace of mind just to clean 'em out again.

As for the leak at the mufflers, that's not likely to be the issue.

Were the carbs synced after you got them on the bike? Also, do you notice the backfiring happening at a certain time (throttle position, decelerating, something like that)?
 
I think if i remember correctly (got tired of fooling with it and walked away) its when I let out of the throttle.
 
Sonreir said:
As for the leak at the mufflers, that's not likely to be the issue.
Click to expand...

Depends on the length of the muffler, extent of the leak, etc. I wouldn't be so quick to dimiss this option, or at least rule it out. I had rejetted my carbs (a bump up) a week before I did my exhaust. It was running great and pulling through all the gears. Plug chop looked good after 3 sets of new plugs and multiple ranges.

After putting some Emgo shorty exhaust on (attached at te headers) I rode t around town for a little while with a smile on my face annoying the neighbors. When i took it out on the highway to test some top end for a few miles (ie: pushed her and really got te engne hot) I started to hear some backfiring. By the time I looped it back toward the house the low to mid had a fairly constant backfire.

The increased heat of really getting on it had caused the slip on to expand creating a leak where i thought I had a good seal. Not having a welder I pulled my muffler clamps shimmed the slip ons (AGAIN) with some aluminum flashing, and then wrapped over the joint and muffler with "tiger tape" a fiberglass and tar based muffler repair bandage.I then put placed the clamps on over the tiger tape. The bandage is black and not horribe looking, although i will be re-wrapping my headers to the muffler in the future eventually and it will be hidden.

Having now pushed the bike on the highway again since the Fiberglass bandage. Between the added shimming and the tiger tape it has eliminated the exhaust leak. Backfiring is gone now. Not sure of your setup but this is an easy and cheap thing to rule out even without a welder. Then you are at least closer to the true problem if it doesn't correct the issue.

Gary
 
Thanks Gary! I'm just gonna start at the front and make sure the exhaust is sealed from front to back. When pulling my mufflers I noticed I still rock one the pipes on the head even though the clamp nuts are tight. Its not the side thats giving me the problem though. Is there anything wrong with using two exhaust gaskets?

Thanks
 
On second inspection its backfiring on the throttle up and feels a little sluggish with maybe a slight miss involved. Its not an exhaust leak because I sorted that today. The battery is new and I swapped the coils from one side to the other with no change. Anyone got any other ideas?
 
Someone could be following you around with fire crackers. Are you ridding the bike near a play house that is practicing west side story....wait was there guns shots in west side story? Do you live near a natural fault line? I'm outta ideas
 
With all the new paint and powder the coil bodies didn't have a good ground! Jumped a wire off them to the ground on the wiring harness and it runs perfectly!
 
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