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Discussion Starter #1 (Edited)
I have a 2007 Honda shadow spirit VT750DCA w/Vance & Hines exhaust. Upon purchase 1yr ago ran great, 21000 miles. About 3months ago started experiencing deceleration backfiring, was told that w/V&H exhaust, carbs needed re-jetting. A Dyna jet kit was installed by local bike shop, carb boots replaced, 3return trips cleared up issues of poor acceleration, backfiring idling/deceleration. Two wks, deceleration backfiring reaccurring, if I pull the choke out -just a little bit,1/4”-5/16” - seems to lessen the deceleration backfiring. Can anyone please advise me the common cause/re solve to fix this problem? Not a professional but can wrench & follow instructions for repairs/replacing parts. Please send advise for resolving this frustrating situation. My advanced thanks & appreciation. JB
 

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1983 Honda vt750 Shadow
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1983 Honda vt750 Shadow
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Here is the single carb model if that is what you have.The mixture screw in below.
The dual carbs have the mixture screw on the side.
You can find a manual here
 

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1986 VT1100c
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153 Posts
Both on the carb,,,😉 might be best to look at some pictures and exploded diagrams to understand the instrument,,,

Thanks Swifty😊 you have incredible patience and great skills at information presentation! I'm not that patient with folks that don't approach problems methodically or do minimal research before expecting miracles,,, good on ya!🎉
 

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1983 Honda vt750 Shadow
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Thanks.
I always think back to when i was a new mechanic and if you could get an experienced tech to help you in the right direction, it would save going in circles and throwing parts at a problem. Then it is up to you to learn how to research.
 
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1986 VT1100c
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I can't remember that far back,,,😉 my excuse is absorbing too much carb cleaner!! Seriously these forums have so much available information, both in past threads and tech manuals that I actually enjoy teasing the folks that ignore alll that and just ask "why?" Being reminded that others have experienced similar problems and did research to help solve them first is important too,,, no free rides in my book, and more appreciation and respect of dedicated folks supplying information learned by experience is something these questioners??? need to learn too.😝

I only draw that hard line because I've read and studied a hundred manuals, thousands of threads on forums,, and most casual "questioners" don't even thank the techs that supply them with the necessary information to solve their mechanical problems. It's only polite to give something back,, it's not admitting anything other than inexperience and is kind of arrogant from my perspective to "think u got it all goin on" because nobody knows it all,,,✌
 

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1995 VT1100C2
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Take a look here: 1182.001.qxd (dynojet.com)

Dont confuse idle thumb screw with A/F mixture screw. Your service shop should have given you your old jets and the instructions and indicated how many turns. It takes a bit of patience to adjust the decel popping out so most shops won't do it since it runs up a bunch of hours )($$$) and results are not guaranteed. Look on thhis site for decel popping and you will find an accurate procedure
 

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1986 VT1100c
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Yup, shop labor for an incomplete job $100 per hour,, priceless technical advice and information on forums, free! Thank you guys for helping, it's a cooperative effort!!!!!

My 86 Shadow is ancient, it ran ok when purchased last year but after doing a high speed shut off test it was running lean according to plug color. I removed and cleaned carbs and enlarged both main and pilot jets. It took 3 times off to get it right, no problem with air cutoffs, mixture screws set close to original settings. I did replace rubber intake tubes as they were hard and heat damaged. The key to carb tuning is the high speed shut off test(plug chop) it shows what the plugs look like under load. Honda CV carbs are precision instruments and proper jet size and perfect condition of diaphragms as well as air cutoff valves is essential to proper function. It's not rocket science,, it's motorcycle science!! Idle mixture screws don't have much to do with performance at speed, but if grossly misadjusted can influence low and mid range. It is a tiny jet that primarily controls idle. Even reputable shops can produce less than satisfactory results in carb tuning processes.
 

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+1 on the air cut valve. My '95 VT600 had backfire on decel ever since I got it. When I examined the carbs I discovered they were completely missing! I guess a PO had removed them because he like the sound!?
 

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1995 VT1100C2
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... Idle mixture screws don't have much to do with performance at speed, but if grossly misadjusted can influence low and mid range. It is a tiny jet that primarily controls idle...
The critical thing in decel popping is you have likely rolled the throttle back to an idle position so the pilot jets and A/F screws are playing a critical role. At idle, a slight incorrect adjustment may not be noticed but rolling off the throttle will cause the popping. In fact, slight popping means the engine is tuned well but some owners find it annoying so like to run slightly richer when decelerating.
 

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2001 Shadow Spirit 750
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I like the decel popping. One more thing to help be noticed. (y)
 

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1983 Honda vt750 Shadow
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My 1983 750 is before they started putting on the air cut valves and it pops a lot.
I even fattened up the pilot jets and it still does it.
Maybe even more than before. I am used to it and call it my signature sound.
"Loud pops save lives".
 

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I cured the decel popping by putting 2 6mm flat washers under the needle's permanent collar.
Popping gone, my bike is a single carb, and I lost some mileage though by that enrichening.
Just something easy to try, you don't have to remove the carb(s) just pop the tops off.
worked for me,
 

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2002, Shadow Spirit 1100
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I had a bike which never decel popped, then it started decel popping. I went to a shop and they told me the petcock screen was probably dirty. I went home, drained the tank, cleaned the petcock screen, filtered and poured the cleaned gas back in and no more decel popping. Something cheap and easy to do. Even if it doesn't work at least you eliminated fuel flow from the tank as an issue
 

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1995 VT1100C2
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I had a bike which never decel popped, then it started decel popping. I went to a shop and they told me the petcock screen was probably dirty. I went home, drained the tank, cleaned the petcock screen, filtered and poured the cleaned gas back in and no more decel popping. Something cheap and easy to do. Even if it doesn't work at least you eliminated fuel flow from the tank as an issue
In that case you aren't getting enough fuel to fill the float bowls, you would also noticed lack of acceleration. Did you have poor acceleration?
 

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2002, Shadow Spirit 1100
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In that case you aren't getting enough fuel to fill the float bowls, you would also noticed lack of acceleration. Did you have poor acceleration?
Actually the acceleration was ok. One time when my fuel flow was hindered at high speeds I would get a thumping/ high speed miss. In that case I changed out the fuel filter and it resolved the issue.
 

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Based on my experience with my 02 Shadow Spirit and 1975 CB550F. I would say its running lean. Too much air. I know, i know, the first thought is too much air right? But usually its the opposite. Pull a plug and see if its oily and wet'ish "too much fuel" or burnt "too much air." It should be a tan to light brown when normal.
 
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