Bonneville America Forums Forums Technical Forums Exhaust stop the pop!

865 with stock headers and cross over still intact, with two tail pipes fit with identical baffles in each spaced exactly the same, rejetted both carbs bench synched and both f/a screws 2 turns out, plugs show great burn...

Sitting at idle the left side pops every or every other time it fires.

Pulled the carbs checked everything over and put them back on, and regapped the plugs, checked for airleaks, none.
Turned the f/a screw slowly fatter to 1 turn making the pop slower but louder, did the same the other way and it just got quicker.

What the hell is going on here?

Don't think its a sync issue, the carbs never came off the rack and I checked the butterfies spacing and its right on.

I also have a procom, played with every setting.. no dice there.

K&n pods both clear
No fuel delivery issues to the carb.
Running 87 vrs premium this tank but there's no way preignition is that bad.
I'm starting to think I have a burnt valve or something horrid

Rest well knowing it's not a burnt valve.. that be the case you would have a dead miss as that would prevent the cylinder from building compression.

Just spit balling here but did you use sealer when you put the exhaust back together? I use hi-temp RTV sealer at the header to head seal as well as where the headers connect to the mufflers. A leak at either place can cause similar issues.
I'm sure you have removed the air injection from the bike but I felt that was worth the mention just the same.
Now.. the "pop". Remember that these bikes, like every other vehicle these days uses the "waste spark" method of emission control. The bike fires once at or around top dead center and again on the exhaust stroke to burn any excess fuel before returning it to mother nature.. at this point the exhaust valve is open and it actually ignites in the header which can cause a pop if the mixture is too rich on that cylinder... or the ignition timing is slightly off... again possibly a procom induced thing.

Would be nice to try a stock igniter if you could lay yoour hands on one.

I think it may be a procom thing. I'm going to change the o plugs and wires today. Needs to happen anyway so I can cross my fingers and hope... I know that not the issue though

A.I. is removed and my only non cdi idea is maybe my valve is hanging? Again thinking out loud..
And no my exhaust is clapped on with only the copper exhaust crushies on... ill adress a frew things and get back.

How much worse will 790cams make it? The 865 is a trasplant, carbs cdi, everything came from my 790...

790 cams are preferable, I wish I could find a decent set.

fuel level in the float bowls? i know mine did that on one side and usually when i was in a turn to that side of the bike , apparently the float bowl filled up to much with fuel....not sure this has anything to do with it but sometimes i get lucky, so there it is. :-)

Its possible. I doubt that mine is that out of wack, I know they seat well.. ill rip them apart again

Took it apart, reset everthing, put back together and pop pop pop. Tured the screw out 4 times out on that one side and it went away, my plugs showed a tad rich at 2.5 turns... somthings not right here

You say you had the carbs apart? You didn't accidentally leave out the needle guide bushing, did you? It's easy to do, don't ask me how I know.

That the pizza top looking thing? Haha I took my carbs apart 4 Times today, last time to verify that both jets are the same haha oh man I hate this bike right now...

So true to form I said f this and decided to fit my scrambler pipes on it. It's now really open pipe, now I have to re tune this turd. And make a baffle or two cause its lean with 150s and k&ns....

2.5 turns out isn't extreme, but I'm thinking exhaust leak.

Pizza thing? I'm not sure what the heck that is. I am referring to a small Bronze (I think) bushing that centers the needle above and into the jet. They can fall out during disassembly and you might not even notice, until you try to ride it.

Well first, I'm an idiot, the copper head gasket had the slightest leak. Not bad for being reused 3 times now.
Eddy, I have pods, a fuel line and one throttle cable in my way, I feel like you might have a lot more in yours! Haha

Ryk... you got me scared now. These puppies the little guys that protrude above a little from the bottom?

The plastic pizza top thing that keeps the box top from hitting the pizza = the plastic thing in the slide hold the spring in my head

And thanks guys for following me down the rabbit hole of common sense.

^^header gasket

Three times tightened up? Probably not a lot of squish left in those puppies. All you have to do is overtighten the header pipes once and you may have to replace them. Always use the torque spec and they will theoretically go a few more cycles off and on.
Matchmarking and being sure to replace them in the same orientation should help them acquire a reseal as well. Or just squeeze a bunch of Red Goo Silicon in there, your call anyway. I have a Ironworker friend who thinks that a bolt should squeak twice and that is properly tight, ok for structural steel, maybe, not so with mechanical things. I have helped him out, with 3 Heli-Coils now.

Hahaha nice. Yeah got my new copper just gotta get the goo