popping out of exhaust

deadchef

deadchef

xsbobblehead
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hey guys, need some help. i have a video below demonstrating a popping out of the left hand exhaust. this started mid-ride a few days ago and almost seems to slowly get worse. this has not been an intermittent problem.



bike- 81, 47.5p, 137.5m, canadian needles and jets, uni's, shorty exhaust, pamco

background- bike has ran well so far this summer (and past several summers for that matter). i did recently open the mix screws to 3.5 turns out to get rid of 'small deceleration pop when coming to a stop sign' issue on right hand side. ran great afterwards. added a digital voltmeter this summer. charging system all good.

things i've checked- went through the usual, pulled the carbs and completely cleaned them out with carb cleaner and compressed air. i changed the throttle shaft seals a few years ago. changed the rubber manifolds around the same time. put on a new set of plugs with no change. also swapped the plug wires with no change. checked the float level on the left carb with a rubber sight tube and it was fine. i didn't check valve clearances but i did open the left intake valve cover just to make sure the lock nut hadn't come off.

really just kinda at a loss at the moment. weird to have this all of a sudden manifest and nothing has changed. any ideas would be appreciated. thanks!
 
It's not unheard of to have the idle mix screws at slightly different settings....mebbe turn the left back to its previous setting. Of course, the dead cylinder method would be the ultimate for those settings.
For a leaky exhaust gasket you could blow some smoke up at the clamp and look for disturbance.......I found one like that. Still smoking cigarettes?
 
My guess is that the exhaust header gasket leaking. I finally fished mine out and installed new ones - no more popping or backfiring. An amazing transformation for a simple repair.

Pete
 
thanks for the suggestions! i tried adjusting the mix screw in the left hand side and it didn't help.

luckily i quit smoking cigarettes over 5 years ago so i can't try the smoke trick but do i have some new header gaskets i'll pop in. worst case scenario i have a few sets of carbs that i can swap with just in case i overlooked something there...
 
it appears this gasket was passing exhaust.
IMG_1926.JPG
IMG_1927.JPG


it looks like i might not have squished down the gasket enough. how squished is enough?

IMG_1928.JPG

IMG_1929.JPG


i'm gonna pop in the new gaskets and report back. thx
 
deadchef said:
it looks like i might not have squished down the gasket enough. how squished is enough?
Click to expand...
Mine closes up more than a lot of them. Comparing the thickness of a used donut to a new one, there wasn't any difference... If there's a torque spec for the flange bolts, that would be your answer. I would try snugging it down good using the old donuts first. Clean it all out good, and have the other muffler bolts loose when you do that.
 
swapped in new gaskets to no avail. if anything it seems to be getting worse. tried to ride up the street and the left cylinder is cutting out upon acceleration. popping and small backfires.

i don't think it's electrical or timing related as the right side runs fine and doesn't miss a beat. i also swapped plug wires and the issue remained on the left side. so i'm guessing it's gotta be somewhere in the fuel/air delivery. i sprayed some wd40 around the manifolds and carb searching for an air leak but heard no change (not sure if i should use wd40 when i do this test, just hesitant to use starting fluid as i appreciate my eyebrows ;)). i use a manual petcock so i have a cap on the brass barb on the left manifold. i removed the cap while it was running and it really didn't sound any different at idle which i thought was odd. i put my finger over the barb and it also didn't make any change. i do have another set of manifolds i can try which will be my next step before i try another set of carbs...
 
This may be an old wives tale, but sometimes grease will prevent it from binding as you tighten/ torque it down. The grease burns away, shortly after.
There is a very slim margin where the face of the head and the pipe face are parallel, so as xjwmx mentioned above, the muffler should be loose, or removed completely to allow the faces to seat properly.
With that said, mine backfires on both sides when decelerating. Any suggestions?
 
I'm thinking I had some decel pop after putting some aftermarket mufflers on using adapters to make the fit. After a bit of riding some carbon built up around whatever leak there might have been and now no issues....I'm thinking.
 
My SH used to pop on the left during deceleration. Increasing the mixture screw by 1/8 turn solved it. Another time I had popping and it was because the header gasket was not tight enough. On the SH the mufflers are welded to the headers so I had to loosen the muffler mounting bolts also when tightening the headers.
 
well just tried a new set of rubber manifolds and that didn't change anything.

to reiterate, this is more than just a decel pop. if you see in the video it is popping during idle and also sputters during accel.

next plan is to try a different set of carbs. if that doesn't cure it then i'll try a different set of headers/mufflers. grrrr.......
 
Just a thought, sounds a bit like my bike 100 yards from home when I forget to turn the fuel tap on. Have you checked that fuel is freely flowing to both carbs? I guess that when you swap carbs that will drastically narrow down where the problem lies.

Best of luck.
 
yeah paul, i checked the fuel straight away and it was all good. since i only have the one petcock it seems it would do it on both sides but this issue has been isolated to the left hand side only.

so i swapped in a working set of carbs, closely jetted to what i have (wasn't there a thread here about too many xs's? :cool:). it was a major improvement, however, there seems to still be a slight stumble on the left hand side at idle. it also has a small decel pop. could be a coincidence that this replacement set of carbs needs a good sync and cleanup/fine-tune or it could still be some other underlying problem. it's at least very rideable right now.

not sure about the original carb set though. seems entirely odd that mid ride it started this problem about 30 miles ago and continually got worse. i closely examined the carb and did notice some wetness around where the shaft seals reside. maybe they are to blame even though they have been replaced just a few seasons ago.

i'm also under the impression that my crap exhaust isn't helping anything either. cut-off stock headers with shorty mufflers that are poorly mated. i do have another set i might swap on... :lmao:
 
interesting update

since this issue originally started, i have swapped in the following-
new boots
cleaned carbs thouroughly (which had new oem throttle shaft seals installed about 4-5 years ago)
new plugs
tried swapping plug wires
new exhaust gaskets
different exhaust
checked valve clearances
different carb set (synced using homemade meter)

only after changing to this other set of bs34's did things improve, but not completely resolved. at idle, the left hand side has a slight intermittent miss. right hand side seems to run fine and doesn't miss a beat. previously i had tried using wd40 to spray around the throttle shaft seals on the original carb set and didn't hear any difference. this time i used starting fluid. now i didn't try it with the original set but with this current set i am noticing when i spray starting fluid around the left hand, outer and inner throttle shaft seals the miss goes away. i tried this test several times and the miss goes away each time.

so now i'm convinced that the shaft seals are no good. what is interesting though is that i also changed the seals on this set of carbs about 4-5 years ago. has anyone else replaced these seals and got such a short life span out of them? i bought these seals from the local yamaha dealer and they looked rather new, not like they've been on the shelf for 30 years. is there another alternative that i should look at?
 
now for some closure...


i replaced the butterfly shaft seals and all seems to be well with the world. frustrating though since i replaced them about 4 or 5 years ago. i did observe that the old seals seemed to be looser on the shaft then the new ones were. the old ones were still very pliable if not more than the new replacements. i'm not sure if maybe the fuel over time had destroyed them. :shrug: i didn't see any rips or tears.

here is a pic of light shining thru the old seal.
IMG_1937.JPG


here is a new seal.
IMG_1939.JPG
 

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