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Discussion Starter · #1 ·
I’m new to this forum and I just bought a vulcan 800. My brother had it for years and couldn’t solve this issue so he sold it to me for almost nothing. It runs like brand new about half the time. Sometimes it has a sputter and it’ll backfire and cough out of the carb. I found a bit of oil in the air breather but not a lot. I’m baffled. I was thinking maybe it’s a fuel air problem but after realizing how it’s only about half the time I’m not sure. Maybe I need new coils? Any thoughts would be greatly appreciated.
 

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Discussion Starter · #2 ·
I’m new to this forum and I just bought a vulcan 800. My brother had it for years and couldn’t solve this issue so he sold it to me for almost nothing. It runs like brand new about half the time. Sometimes it has a sputter and it’ll backfire and cough out of the carb. I found a bit of oil in the air breather but not a lot. I’m baffled. I was thinking maybe it’s a fuel air problem but after realizing how it’s only about half the time I’m not sure. Maybe I need new coils? Any thoughts would be greatly appreciated.
Also I forgot to mention. He said it stalls at times and has a total loss of power but it’s not often. Only every few times out. I have experienced this yet
 

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a backfire out thru the carb is a sign of a lean air/fuel mixture, means A/F mixture is getting more air than fuel, and oil in the breather is from the crankcase, there's a breather tube running from the inside of the top of the rear cylinder to the back of the stock airbox plate (if it's still stock) and that is crankcase blow-by mist that is meant to be recycled back into the air intake for recombustion, on stock 800s there is a hole at the bottom of the stock airbox that drains this excess oil to a tube that runs to a catch bottle at the front of the frame on the lower right side, when it fills up just dispose of the oil and replace the bottle, this is if your 800 is still stock, otherwise that crankcase breather tube might be rerouted to the ground and that oil catch bottle gone
 
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Discussion Starter · #4 ·
I’ll try to adjust the carb here in a little bit. It also backfires from the exhaust as well. I’ve also noticed a bad gas smell out of the gas cap I don’t know if that could cause issues as well I have one coming in a week or so. I just don’t know why it only runs bad sometimes. I feel like if it was just the carb out of adjustment it would run like that all the time. I’m not sure though.
 

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Sounds like carb issue for sure.

These bikes were horribly leaned out from the factory, there are a ton of writeups and videos about adjusting the AF mixture. Also, sounds like the bike sat for a while... Its likely worth rebuilding the carb, or at a very minimum doing a good cleaning.

Check out this video:


I had a similar problem to what you were describing, just intermittent backfiring and stuff. After adjusting the AF mixture a few turns, cleaning jets, and replacing a worn accelerator pump diaphragm solved the issue.
 

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2009 Vulcan 500
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Pull the tank...drain..rinse with a little fuel.
Carb cleaning ..it probably isn't your original problem...but will be a new problem...as its been sitting
Toss some new plugs in there as well..
Service the air filter...at least make sure its not falling apart and getting sucked into the engine.
Not sure if your bike has one of the 'problem ' fuel caps or not..but some don't let the air in proper and are in a vacuum.
Know how you can shake a fuel jug that isn't vented and it puffs out the sides..then goes relaxed again after a while?..It you open that jug with it puffed..then seal it back up the sides will get sucked in on the jug
Imagine your fuel tank being that jug..it gets shook around (as soon as we take off)..vents off the pressure..then when its time to 'relax' it can't suck in the air..might run fine in a couple hours as it slowly let's air back in.
When the machine acts up again..open the cap and see if you hear a big whoosh.
..if so there is your problem

Backfire...almost always from being lean..especially the carb..you can get exhaust backfires as well from being lean..not as common..but an engine that is barely running because of being lean..may not fire the mix in the combustion chamber for a few revolutions ...the when it does hit and is still lean it may not have completely combusted before the exhaust valve opens..now we have an actual flame to ignite what's in the exhaust.
Tackle the fuel issues first as its a given..tracking down an intermediate ignition issue can be a challenge.

Almost forgot...new fuel line...might be fine now..but it might hard and cracked on the inside..the act of removing the fuel line from the tank..bending around on it etc..will have it shedding black specks to your carb...one of those black specks will lodge itself on the needle and your carb will overflow...causing more work.


Sent from my SM-A115U1 using Tapatalk
 

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Discussion Starter · #7 ·
Ok awesome. I have it going to a shop to rebuild the carb and replace a bunch of leaky hoses. I took it apart and realized what all needed replaced and decided to check it in to a shop. I appreciate all the help. I’ll update and let you know if it worked. Hopefully I’ll be on the road in a couple weeks. The thing that always stumped me was how it only acted that way sometimes.
 
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