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Fouled plug(s) and no choke required

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Fouled plug(s) and no choke required

PostAuthor: glegge » Thu Jun 06, 2019 10:16 am

Hi folks, recently purchased an 84 Virago 1000 which needed a bit of work, nothing major, mostly electrical related to the battery/starter circuit. About 50,000 km on the bike (30000 mi) The bike was laid up for a while, but in excellent appearance. I've done the normal maintenance, changed plugs, oil and filter, new battery installed, that sort of thing.

So once I got it running, things seemed pretty good, but I had some backfiring issues when I eased off on the throttle too quick, normal stuff from what I read on several forums. The bike has lots of power and runs smoother than I expected for a V-twin. After about 50km of driving, I started experiencing a miss in the front cylinder. Pulled the plugs and the front cylinder was fouled with sooty deposits. The plug in the back cylinder was greyish color with the insulator being white as new. So I pick up another set of plugs, this time opting to find the proper non-resistor plugs, as some people say the resistor plugs can cause a weak spark. I disconnected and capped the vacuum line running to the MCV, as many people have suggested, and I also tested the carb balance (but I may revisit that). I tossed some Seafoam in the tank as well, crossing my fingers that the problem would cure itself with little help from me. Haven't made it to 50km yet, but I'm starting to feel the missing on occasion once again. The backfiring is reduced though.

Strange thing I found is that in cold weather (around 5 Celsius or 40F), the bike starts easily with no choke applied. I've owned alot of bikes over the years and never had one yet that started without applying the choke at that temperature. Thats sort of suggests that the bike is running rich, when you combine that tidbit with the fouled plug. So I've been tempted to get a carb kit and do a rebuild, but I read so many horror stories on forums about bikes running worse after a rebuild that I wanted to see what others thought.

As for the carb sync, I used 2 older vacuum gauges but the needles move so erratically that pinching the lines off so that they are nearly closed is the only way to be able to get a reasonable reading. The reading was about 3" of Hg. for both cylinders, so it doesn't appear to be an imbalance. I checked the gauges against each other to make sure they are both reading the same, and they are. What i don't like is using a gauge which measures up to 30" to confirm they are balanced at 3", but thats the normal range of most vacuum gauges. So I'm thinking I may put together a hose/oil system which works by measuring the differential in vacuum, rather than the absolute vacuum. Seems to be a more logical way to go, as crude as the hose/oil systems are.

Just wanted to get some input to see if this is an unusual or if anyone has experienced something similar. The choke cable linkage all seems good, no signs of anything sticking. I suppose I should run a compression check as well, just to see if it's a larger mechanical issue, but the bike runs fantastic, up until the point the plugs foul. Install new plugs, and everything runs great again....for a while anyway.

Thoughts appreciated!!

glegge
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Re: Fouled plug(s) and no choke required

PostAuthor: bstig60 » Thu Jun 06, 2019 12:14 pm

Check your pilot screw and see where it is set. It should be 2.5 turns out from a soft seat which is the nominal setting. The further out it is the more fuel it lets in. Also, check the choke on that carb and make sure it is fully closed. Check fuel levels using the clear tube method.
Bill
"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

Please take the time to edit your profile to show your location. City, State/Province and Country. It is easier to help you if we know where you are.

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http://viragotechforum.com/viewtopic.php?f=220&t=31501#p279545

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Re: Fouled plug(s) and no choke required

PostAuthor: glegge » Fri Jun 07, 2019 9:38 am

I'll get a look at this 2nd set of plugs this weekend. As for the pilot screw, I'll look at that as well, but I think the caps are still in place so I will have to pull those out first. Does the choke on these carburetors actually control the air flow by positioning a butterfly valve? I have an XJ700 and the choke controls fuel in a mini enrichment cycle, rather than limiting air intake to the engine. See item 4 and 5 in this diagram. https://www.partzilla.com/catalog/yamah ... -xv1000l-n

glegge
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Re: Fouled plug(s) and no choke required

PostAuthor: bstig60 » Fri Jun 07, 2019 12:08 pm

The Choke just adds more fuel to the air flow through a port in the carb venturi. If I remember correctly, the choke unscrews using a 10mm wrench. Then you can check the movement and the seal. If the pilot screw brass plugs are still in place, that means no one has ever touched the pilot screws. If your bike is completely stock, that's OK, if you have modified the air intake and/or the exhaust system, then you need to adjust the pilot screws to properly tune your carbs. The plugs must be drilled out, but if you attempt this, be very careful not to damage the pilot screw heads or their threads.
Bill
"It´s a friggen motorcycle, it´s not supposed to be comfortable, quiet or safe. The wind noise is supposed to hurt your ears, the seat should be hard and riding it should make you s**t your pants every now and then. "

Please take the time to edit your profile to show your location. City, State/Province and Country. It is easier to help you if we know where you are.

SERVICE MANUAL DOWNLOAD LINK
http://viragotechforum.com/viewtopic.php?f=220&t=31501#p279545

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Bike year & model: 1999 Yamaha Virago XV1100LC Cruiser,
2003 Honda Goldwing GL1800 Touring
2007 Honda ST1300A
1987 Honda TLR200
Sex: Male



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