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lots of popping/backfiring through exhaust on deceleration

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lots of popping/backfiring through exhaust on deceleration

PostAuthor: oldgreyxv750 » Tue Aug 13, 2019 1:24 pm

as the title says, i am getting lots of backfiring through the exhaust on deceleration.

the bike is a 1982 xv750.

the carbs have been thoroughly dis-assembled/boiled/cleaned with aerosol carb cleaner. spark plugs are new and gapped to spec. good spark on both cylinders. air filter is not new but backfiring occurs even with it removed. compression is 150 on both.
i have not checked timing ... haynes says it is non-adjustable.
there appears to be an aftermarket exhaust on the bike ...stamped "s&s headers". otherwise stock (the numbers on the jets match up with the numbers in the haynes manual).

i am focussing on the pilot screws (idle mixture screws ?). i am used to working on hondas which use a tiny washer and o-ring after the spring. i don't see these here so i am assuming that yamaha doesn't use them ??? (can't seem to locate these screws and springs on the exploded parts diagram). i have also been assuming that they are metering fuel, not air, since they are on the engine side of the carb. this would mean that screwing them out enrichens the idle mixture and screwing them in leans the mixture out.

if i am wrong on this, or if you can shed any light on the topic please chime in.

thanks
joe

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Re: lots of popping/backfiring through exhaust on decelerati

PostAuthor: mark75 » Tue Aug 13, 2019 3:46 pm

don't over-look exhaust leak, make sure it's all tightly sealed.
:ider:
what's the old saying?
b/f through the carb = too lean.
b/f through the exhaust = too rich?
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Re: lots of popping/backfiring through exhaust on decelerati

PostAuthor: Cusstout 1100 » Tue Aug 13, 2019 4:20 pm

Yes, Yamaha uses the tiny washers and O rings. If yours are missing you have an air leak at a critical location.
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Re: lots of popping/backfiring through exhaust on decelerati

PostAuthor: oldgreyxv750 » Tue Aug 13, 2019 5:06 pm

no wonder i was tearing my hair out over this machine !

mark ... i had it wrong ... i thought backfire through exhaust meant "too lean".

cusstout ... thanks for the info re : washers and orings, but am now wondering did you mis-state it when you said i have an air air leak due to those being missing. wouldn't it rather be a fuel "leak" without them ... as in waaaay to rich ?

finally, can anyone help me locate those washers and orings on the parts diagram. as i said in the OP, i can't see them no matter how hard i try.

thanks for the feedback, guys ... feeling a lot more sane now !

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Re: lots of popping/backfiring through exhaust on decelerati

PostAuthor: Flyingdog » Wed Aug 14, 2019 1:40 pm

oldgreyxv750 wrote: help me locate those washers and orings on the parts diagram. as i said in the OP, i can't see them no matter how hard i try.


Hitachi innards.PNG

Pilot Assembly.PNG

Carb components.PNG
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Re: lots of popping/backfiring through exhaust on decelerati

PostAuthor: Jake » Wed Aug 14, 2019 4:21 pm

_______________________________________________________________________
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It’s what you know for sure that just ain’t so.”

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There is an old Chinese proverb - "Man with one watch knows the time. Man with two, not sure."
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Re: lots of popping/backfiring through exhaust on decelerati

PostAuthor: Cusstout 1100 » Wed Aug 14, 2019 8:12 pm

There should be engine vacuum at the point the pilot screw enters the carb body. If it's not sealed with the o-ring, you would have a vacuum (air) leak causing a lean air/fuel mixture.
My Ride, '97 XV1100, +14, 10" over forks, progressive rear, Jardine forward controls, cobra slip-ons, K&N Filter, Dyno Jet Stage 1, Kuryakin grips, heat demon heaters, custom fabricated seat, chrome side covers, bullet signals, risers, custom modified rear fender with modified FZ1 tail light, sectioned and reversed front fender, custom paint...

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Re: lots of popping/backfiring through exhaust on decelerati

PostAuthor: oldgreyxv750 » Thu Aug 15, 2019 12:05 am

yes, "c" and "d" are the little devils that are missing ... and i know it wasn't me because i was looking for them during dis-assembly and was surprised to see that there was nothing there except a needle and spring.
anyhow, we have gotten to the meat of the matter and i thank you all for your help (still not finding a part number for those things though).

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Re: lots of popping/backfiring through exhaust on decelerati

PostAuthor: Flyingdog » Thu Aug 15, 2019 2:27 am

oldgreyxv750 wrote: (still not finding a part number for those things though).


And...you won't in the manuals. You'll have to pay attention to what you have vs which one a person orders. Ones with the groove for 0-ring can usually be gotten separately thru places like "Jets R Us" or the other style, as in pic, seems to only be in rebuild kits. They maybe sold separately someplace, have never look around. My 1000, using Ver 2, Hitachi..doesn't list them. Bout the only fiche listings seems 86-87/1100, when they still used Hitachi before switching to Mikuni. Just gotta search..look..and compare. Sometimes ya get lucky. Guess, I just don't find it's worth it tracking down 1 part and hope that's the only part ya need. For what ya get, kits are cheap.
https://www.amazon.com/Yamaha-81-83-Vir ... B077SQHS57
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Re: lots of popping/backfiring through exhaust on decelerati

PostAuthor: mark75 » Thu Aug 15, 2019 4:34 pm

oldgreyxv750 wrote:no wonder i was tearing my hair out over this machine !

mark ... i had it wrong ... i thought backfire through exhaust meant "too lean".




hmmm... you may be right.
my memory keeps getting me in trouble here lately. :ider:
a 2nd opinion is always good. :):
"Over the Mountains of the Moon,
Down the Valley of the Shadow,
Ride, boldly ride" ... E.A. Poe


Time flies >>> whether you're having fun __ :bike: or not :fan: ---

Any day above ground is a good day.
so Laissez les bon temps roulez. just roll safely --- Semper Vigilans...always watchful

"I hear and I forget, I see and I remember, I do and I understand." ... Confucius*

If you don't read the news you are not informed.
If you read the news you are misinformed.
... Mark Twain


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The views, opinions, and experiences expressed in this post are mine and may not necessarily represent views and opinions of other VTF members, so feel free to agree, disagree, or ignore them.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
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Re: lots of popping/backfiring through exhaust on decelerati

PostAuthor: Flyingdog » Thu Aug 15, 2019 5:12 pm

OK..here's another opinion...

Rich..backfires thru exhuast (excess/unburnt fuel go'n thru the exhaust valve)
Lean..hickups, sneeze'n, cough'n, spit'n thru the carbs.

:bg:
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Re: lots of popping/backfiring through exhaust on decelerati

PostAuthor: bstig60 » Fri Aug 16, 2019 3:38 pm

oldgreyxv750 wrote:yes, "c" and "d" are the little devils that are missing ... and I know it wasn't me because i was looking for them during dis-assembly and was surprised to see that there was nothing there except a needle and spring.
anyhow, we have gotten to the meat of the matter and I thank you all for your help (still not finding a part number for those things though).

Many times the O ring will be stuck inside and you will have to use a piece of small stiff wire with a hook, in the end, to get it out. I have seen the washer stuck to the O ring. If they are really missing, they are available in the K&L rebuild kit and are also available on eBay.
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