Spark problem. Pls help.

[Muscle racer]

Like most old 750s, mine has its shares of problems. Thanks to this site, I always fix them. Now I have another one. Everything was running fine, when the bike felt like it was losing power. Like it was running out of gas. I had a  similar problem before, but it was a bad ignition coil.

After riding, I felt that the first 3 pipes were hot but #4 wasn't. So i know it's not the coils. When I ride, I can see blue spark going from the plug boot to the engine block on #4. Is it a spark plug problem??? I replaced all 4 spark plugs with new ones 4 months ago. It turns on fine and runs fine above 45mph.

I hope it's an easy fix.  

Pls help.

Thanks guys

[Bobber0071]

Have you checked the carb to see if it has a dirty jet or a small clog. If you are getting good spark I would goto the carb on that cylinder and check it. My 360t did this on the right cylinder cleaned out the carb and I was good to go.

[Buster]

If you're seeing a spark while riding, the wire/boot is bad.

[sgtslag]

Since it is still running well, "above 45", I would suggest using a fuel cleaner, like SeaFoam, added to the gas tank.  It is inexpensive (around $9 for a 16 oz. can), and if it fixes your issue, nothing more to be done than invest the money, and a small amount of time.  Add the correct amount to the full tank of gas, run it for a while (around the block is sufficient), then let it sit overnight, and ride normally thereafter.  This has fixed many a bike over the years.

If it does not fix your problem, then pull the carbs and clean them manually.  The SeaFoam will not harm anything:  it dries out fuel; stabilizes the gasoline for up to one year; it dissolves varnish deposits, in the gas tank, and in the carbs.

Add it to the crankcase to dissolve varnish and carbon deposits within the engine, and the transmission, as well.  Follow directions:  check the color or your oil before adding it, then check it often thereafter -- change the filter and the oil when the oil turns black.  You will only need to do this once every 30,000+ miles?... (Probably never need to again, with modern, high detergent oils and regular changes...)  Great stuff!  Cheers!

Oops!  Mis-read your comments about the blue spark jumping from the cap to the motor...  Thought you were commenting that you were testing the spark on that wire.  Bad wire/cap.

[TOOLS1]

I'm with Buster. You need a new boot, or plug wire. I would start with new boots. I like the NGK ones. To install them, you just kind of screw the old ones off. Trim a 1/4 inch off the wire, and screw the new one on.
TOOLS

[Muscle racer]

It's not the carbs bc I had them synched recently and I just used sea foam on it.  I rode it yesterday and it was running fine, and I didn't notice a spark.

It's strange how it comes and goes.

Now I have another issue. My petcock is dripping gas. 1 drop every 5 secs. Is there a way of sealing that or do I need to replace the petcock?? There $60 on eBay.

Let me knOw.

Thanks

[TOOLS1]

A bad plug wire/boot will make the spark jump when wet, or the wire is within a cretin distance from a ground. Just because it stopped does not mean it has all healed up. Have, you tried to tighten the petcock? They will work loose if you are bumping/moving them while working around them.
TOOLS

[shinyribs]

Im with Tools on the plug boot.If you saw it leaking voltage once it needs replacing.Yeah,they dont heal.  Errant sparks and a gas leak.....sounds like fun!   Im just picking.Good luck with your bike

[Muscle racer]

You guys were right. It was working fine 20 min ago, now it started again. I look down and see that stupid blue spark. So it is the boot. Do they sell them individual or I gotta get all 4?

The bike is my daily transportation. So I don't like problems. Thanks guys

[TOOLS1]

You can get them individual, but I would go on, and replace all 4. It only takes a few minutes. Also the whole set only costs $20.00. I like the NGK ones.
TOOLS

[Piute]

  There every where's  
 http://www.parkeryamaha.com/sparkplugboots.aspx
 
  Just to give you an Idea $only Yama Ha Ha shops in my town

[fasteddie55ca]

sounds like the plug boot might be default ( NGK) change the wire and boot and try it when its dark out this way here you can see if your spark is arking