[Vulc98]

Anyone have this issue, with the engine popping and almost acting like she's starving for fuel. But if I accelerate hard, it evens out until I let off the throttle. Current set-up is:

Modified air cleaner cover with K&N filter
Dynojet stage 1 carb kit and Vance & Hines exhaust. New plugs as well as fresh oil.
I have read through forums about similar issues.
Any advise?

 

[aforman40]

Same as my problem, mine it was battrey that was dead causing weak spark due to low voltage, if is not the battry, clean carb and ajust float level to factory level as per manual, check air leak on you inlet, put back plugs you removed, but according with my experience this common problem on vulcans caused mostly by spark , its weak spark or one cylinder its not firing properly , check battrey, coils, lastly Ic igniter

 

[JBTrickle]

Check that all vacuum lines are in place and attached correctly as well. Check the lines behind the airbox too.

 

[MotoMedic1]

Hi Vulc,

• The next time you are riding and this issue occurs, use the choke (actually an enriching circuit) to see if the problem gets worse, goes away or remains the same.
• If it gets worse or goes away or improves then you have a fueling problem.
• If there is no noticeable change then you may have an electrical issue as suggested by aforman40.
• Also carry a spare spark plug with you. If the engine stops running, you can quickly check if the ignition system is still functioning.

 

[Vulc98]

Thanks motomedic👍, it always happens when the hwy is busy and difficult to find a safe moment to pull over, lol. Good excuse to get out of the city and find a quiet section to mess with the choke.

 

[Vulc98]

Does this look a bit on the lean side?

 

[MotoMedic1]

• No.
• Your plug indicates a low end rich condition with a slightly rich mid and good upper range fuel mixture and a proper heat range.
• I would inspect the gap. The electrode (anode in the ceramic) looks a little mushroomed. Too wide a gap can cause localizing of the spark and it works its way around the anode to find the path of least resistance which intensifies electrical heating of the anode at those localized spots.
• Try lifting the main needle two positions (= lowering the clip on the needle). If you are unfamiliar, Go to DynoJet web site and look for download instruction for that jet kit.

 

[Vulc98]

Rear plug...

 

[Vulc98]

Looks like the rear cylinder isn't burning like it should. Strange on a single carb engine, that it can do this. Maybe a weak coil or fouled plug.

 

[JohnnyV]

Motomedic is incorrect, your front cylinder is certainly lean. The rear cylinder looks rich. I'd bet that you have a vacuum leak somewhere that is allowing fresh air into the front cylinder which is causing the rear cylinder to get all the fuel. You need to look at the carb boot and intake manifold and see if there is something wrong. My guess is it's your boot. It can be a pain in the butt to get on and off and that's why a lot of people make mistakes when installing them.

 

[Vulc98]

Thanks for the input folks. I started taking it apart and have the carb left to remove. I'll post an update if I find anything obvious.

 

[The rider]

Didn't get to much anti seize on that rear one did you?...could be an optical illusion.
Anyway..plugs are cheap...check the wire..toss in another plug ..see what happens...On a single carb application with proper ignition color variations of the plug usually relate to cylinder health.
It sounds like the plugs haven't been in there very long..on that rear plug it looks like there is a layer on the rim of the plug but not dull in color is why I mentioned the anti seize..antisieze can contaminate the plug...causing the current to travel along the insulator and back to metal inside the plug..although the plug may appear to work fine by bench testing...it may not perform well in a hot turbulent environment with fuel vapor
Also to consider we have less compression at cruise than opened up as the throttle is highly restricting the air..thus why sometimes a cylinder may operate with increased throttle position vs cruise throttle position.

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[Vulc98]

Thanks Rider,

I learned early on, to not use antisieze on plugs, for that very reason, lol. Im going to go over all vacuum lines and connections, verify float level is correct and move the main needle up a notch. Going to test the plugs loose and see if maybe a weak coil, etc. It's strange, as the bike works great below 100 km/hr. It may be the plug breaking down at higher constant rpm, or also the coil. I'll try all the troubleshooting tips you guys mentioned and keep you posted. Thanks for all the suggestions 🍻

 

[MotoMedic1]

• Not sure why JonnyV is attempting to mislead you. Your front cylinder is not lean.
• How do I "read" a spark plug? - NGK Spark Plugs
• The rear cylinder IS rich AND the plug is carbon fouled. The rear cylinder is likely not firing at this point.
• You should do a compression check on the rear cylinder and check the exhaust for obstructions.
• Also it may be time to replace spark plug wires and caps.
• As a test you can swap the ignition coils and see if the issue follows the coil or stays with the wire and cap.
• To be clear: The rear cylinder is carbon fouled. Under normal circumstances this would indicate a rich mixture.
• A rich mixture IS NOT the problem!
• You have either an ignition issue or compression issue at the rear cylinder.

 

[The rider]

Thanks Rider,

I learned early on, to not use antisieze on plugs, for that very reason, lol. Im going to go over all vacuum lines and connections, verify float level is correct and move the main needle up a notch. Going to test the plugs loose and see if maybe a weak coil, etc. It's strange, as the bike works great below 100 km/hr. It may be the plug breaking down at higher constant rpm, or also the coil. I'll try all the troubleshooting tips you guys mentioned and keep you posted. Thanks for all the suggestions

You can use anti sieze..just a very small amount....what you have left if the threads of the head will be enough.

If you have an intake leak that large it should trash the idle....which

Brings us back to that cylinder either having weak ignition or poor health .

Single carb right?
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[Vulc98]

It is a single carb, yup. I am leaning towards weak ignition, whether it be the coil or the plug wires or plug. The plugs are new, with just over 1000 km on them. The bike doesn't idle rough or sound like it is misfiring or running on one cylinder, so it must be breaking down at higher rpm?

 

[MotoMedic1]

• After a closer examination of your rear plug pic, it appears wet or oily
• Does the cylinder smell heavily of raw fuel?
• Does the plug feel oily?
• You may have an issue with rings or valve stem seals.
• I would lean towards rings since that would also cause low compression and incomplete burning and carbon fouling.
• A low compression condition from valve gap on it's own would cause dry carbon fouling which has a sooty deposit.
• The oil would be coming from valve guide seals or piston ring blow by.

 

[Vulc98]

If it were the rings or seal, that cylinder would smoke or at least smell of burning oil. Investigating tonight, hopefully

 

[JohnnyV]

• Not sure why JonnyV is attempting to mislead you. Your front cylinder is not lean.
• 
  
• A rich mixture IS NOT the problem!

A white strap is a lean cylinder. It's an acceptable(but not optimal) lean IF both plugs were the same. It isn't acceptable when the front is lean and the rear is rich, especially on a single carburetor. Which is why he needs to look for an air leak between the carb and cylinders, assuming his ignition system is properly functional. A bad seal at the boot or intake manifold will let fresh air in to whichever cylinder it is closer to and cause that cylinder to run lean while the other runs rich. I'm not going to argue but the front cylinder 100% isn't rich like you said it was, it is lean and the cylinders are not balanced. Once again, assuming the ignition system is functional and the cylinder is healthy, the problem is an air leak.

 

[The rider]

Looks like I see a layer of semi solid material similar to carbon...but not..in the circled area a chunk looks like it came off while removing the plug...can you confirm

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