Honda Shadow Backfire/Afterfire on Deceleration? – DIAGNOSIS

First of all let's point out the facts :
- BACKFIRE is a sneeze, or cough, popping or little bit of flame coming out of the carb or intake.
- AFTERFIRE is popping out of the exhaust.

So we're going to tackle "afterfire" first:

If your bike is afterfiring, your pilot circuit is too lean. Start by adjusting your air fuel mixture screw(s). If that doesn't fix the problem, the answer is in this VIDEO!

This issue could also be indicative of an exhaust leak, a valve adjustment being out or potentially a vacuum leak (rare).

If your carb is coughing, that's also an indication of a lean condition. TJ explains and gives more details IN THIS VIDEO – so WATCH NOW!!!

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[mrkapusta]

I love that this keeps popping up (no pun intended). To anyone who sees this LISTEN TO TJ DAMMIT! I had this issue after removing that gheeeey Honda intake (velocity stacks now)and putting the gorgeous backdraft exhaust on my bike. I was told different things from, “it’s what you get with no baffles”, “you’re chasing gremlins dude!” Etc, etc. In a last ditch effort I listened and READ what TJ said to do... my 750 ace was all set for a trip to my mechanic. I purchased the largest set of jets off of TJ’s site. Double shimmed my float needles. Wallah! Bike runs incredible not ONE BACKFIRE on decel or hard downshifts etc. I was so shocked that I expected to see a unicorn cross the road on my test drive back home. My wife saw the huge smile on my face and immediately thought I cheated on her. THATS HOW GOOD IT FELT fixing that annoying problemo. Ride on my friends....

[itsreallytom]

Finally someone who properly defined afterfire and backfire

[plumblevelsquarebear]

Best description of a backfire/after fire I can find on the interwebs.

[stevefavela]

I actually like the backfire pops specifically downshifting before a bridge and letting it pop and then gunning it 👌

[jeffwest]

TJ - Thanks for the videos. They are always informative and entertaining. I too, thought my VT600 was running lean because of the decel afterfires. When I rebuilt my carbs I discovered the air cut off valves were both missing!. When I replaced them, no more afterfire.

[casparzimmermann]

Most often decel poping starts when the stock muffler is replaced with an aftermarket piece. The SAS (Secondary Air System) is designed to let air into the exhaust the help the Cat burn unignited fuels properly coming from the enginge. Aftermarket mufflers increase the airflow through the pipes, therefore nothing is timed to stock anymore. Loosing the SAS should solve the problem. Make sure to fit a dongel to not get any errors on your board computer.

[boomerguy]

My 1988 Shadow VT600C VLX did this when I first bought it with 8400 miles on it when I went downhill from my house with no throttle in second gear. It was really as much a "backfire" as it was just a random "popping" sound which I thought was cool. However, to be on the safe side I synchronized the two carbs because I NEVER needed the choke to start it, no matter how cold the engine was. I gave it a full tune up with new air filter, spark plugs, fluids, etc. The spark plugs were clean so I figured the air/fuel mixture was OK -- not that I could adjust them anyway because they are sealed. After I sync'd the carbs, I noticed four differences:
I needed the choke to start it
The "popping" sound was gone
The idle speed needed to be reduced (I still keep it at high idle as recommended by the service manual.)
More power (This is subjective: my butt-meter says I have more torque and I definitely have more power going uphill and a higher top speed which I reach quicker.)
Problem solved with just a simple tune up and synchronization which required a manometer and turning one screw. I love it!

One extra note: Since synchronizing the VT600 requires removing the fuel tank, I discovered my petcock was bad. It didn't leak when riding but it would not close completely when I removed the tank and dribbled all over the engine when I pulled the fuel line off the discharge tube. This was an easy fix with an aftermarket petcock. So I extra fixed a safety hazard. I love this

[YNTGUNS]

I have this backfire, that happens sometimes in downshifts. Not all the time tho. on my injected 07 zx10r. Valve adjustment was done already and there all in spec

[FirstLightAdv]

Thanks for explaining it in straightforward manner!! Very helpful!!

[fastcar]

I adjusted my 1100 just as he said and no more popping. Works!

[RobertMertensPhD]

Now it played. I don't why two other times it didn't. I haven't changed anything except the day I played it. But I still have, not afterfire, but an afterfire after shutdown, inside the pipes. So that suggests leftover fuel in the pipes. I've retuned these carbs five times and they still seem to be out of sync, even thought I've also synchronized them, using pressure gauges and all. I know at tone point these was a vacuum leak, but I think I fixed that (just a loose manifold screw or a poorly mounted carb).
There are instructions for setting the air-fuel mixture, and I've also done that several times. I think you have a video for that, but that one is one of those I can't seem to play. I only have this problem with a couple of channels.

[Tacbi]

Hey bro my motorcycle backfired only when I turn off .. just like switch off and 4 seconds pum 💥!!! Only one time after off ... what u think ???

[bryanmiller]

I used the jet calculator and it calls for smaller jets that are in there now. Mixture screw is 3. Still popping like hell

[jacobrice]

Thanks 🙏 Simple and too the point. My “after fire” Is so loud it scares the hell out of me 😬😅

[Youngphoenix]

Thanks for this advice I put a new carb on my 250x honda sportrax and it's fine in first gear but when I switch to second when I let off gas it after fires. It very well could be a valve adjustment issue. It prolly needs done so I'll do that after I adjust the fuel air mix screw

[TorbenVestergaards]

Hi TJ!!
Greetings from Denmark, overseas!
I just bought one Blaked out mean VT 600 Bobber Split Lane, with a lot of TJ’s candy on it! Paenut tank, v.stacks with Long Air fuel min screws etc etc.
I just love it. I seems to have a litlle backfire from the pipes though, when i let off the trottle to fast, ore going down hill a bit.
The iddle seems ok, but it stopped for a few times though. Even when riding at low speed it stopped between a gear shift yesterday.
I may run a little to slow in iddle, i recon.
My Q is: Do i just turn both fuel screws both sides the same way? And wich way?
Right side shows number 2 upwards- left side (need unscrew a little cover)seems to have the nr. 1 pointed backwards!
Besite that its running like ”a bat out off Hell”
I only got it a week now and i F… love it. And people Ask about the sticker with the white ”cross” on the site..🤣Tj Cus!’
Thx
Torben

[seanriddell]

Hi quick question

Got a honda shadow 600, when mid way through the revs it started to burble and no accelerating.

It's only happy low to mid range in the revs


Is this too much air probs or fuel probs.

Many thanks
Sean

[marc-andretheriault]

Do you have a video where i could learn how to ajust the air fuel mixture on VT750C ??

[pappydanny]

Changed my pilot jets today. Got rid of the back fire but front cylinder is making a putting noise through the exhaust. Seems to run ok

[Justiceisforgotton]

Is this the TJ that is Ken to Shane just curious