Help! Backfiring/Fouled Plug

[Hogchain]

Greetings,

 

I am at an end. I do not know what is wrong with my motorcycle. I have a 2006 RSTD with 8500 miles, and a few months ago I noticed a little backfiring when riding (mainly coming out of the right muffler.) It progressively got worse. I decided to change the plugs and noticed that the rear right cylinder plug was fouled (completely black.) I changed all the plugs, the problem persisted. In fact, after just a 20 min ride it fouled the new plug on the Right Rear Cylinder. My local dealer suggested to run some Techron through the bike, did not help. Also, there is a strong gas smell when running the bike. I checked the plugs and they are getting fire.

 

I read on the forum that it might be my carbs, I bought a Carbtune 2 and synced the carbs (they were not even off that much.) No Change. A friend suggested to change the plug wire, but I quickly found out the plug wire is molded to the coil.

 

I am not a mechanic, but I have done minor repair and maintenance on my bikes through the years. I am at a total loss. The owners manuel says that a black plug means a defective engine (I sure hope this is not the case.) Your help would be much appreciated.

 

God Bless,

 

Matt Powell

My bike needs a good doctor

[k9cottage]

i would guess a flooding carby with the unburnt fuel igniting in the exhaust pipe try giving the offending fuel bowl a few taps with a screw driver handle

[dacheedah]

does the cylinder heat up when running, same as the others??

[mbrood]

I am with Kevin... on a cold bike... start it up and run for 30-45 seconds and shut her down... now reach in near the heads and compare the heat on each exhaust pipe... odds are that the right rear is much cooler (not firing right). The unspent gas going into the exhaust would be a prime setup for backfire!

[RSTDdog]

One plug in photo looks very rich. The other looks lean. How long has your bike been sitting??

 

Looks like right rear carb is flooding. Try draining all four float bowls. You'll need lots of rags for this to catch the fuel. Withthe drains out turn key on (DO NOT START) to cycle the fuel pump and flush float bowls and lightly tap on them as suggested. Look for signs of varnish and build up onthe ends of the drain screws.

 

If that doesn't clear it up, my guess is the float is stuck open to the bottom of the carb from varnish. If bike has been sitting, you will need to clean and overhaul carbs to get it to run correctly. You will also need to change the oil and filter anfter carb overhaul since the oil is probably fouled with gas.

 

RSTDdog

[Cougar]

Looks wet, right rear coil..I am thinking. been there done that.

Is that plug firing? also if so, does it have a good spark?

Jeff

[V7Goose]

A black plug like that is either running extraordinarily rich or the plug is just barely firing. A super rich jug on this engine is not common, but could be caused by a choke plunger stuck all the way out or something really odd like a pilot jet falling out. A stuck float, maybe, but that should also cause lots of gas to flood down the inside of one of the front lower fairings.

 

The only engine problem that could cause that is oil fouling or possible total loss of compression - either would be generating massive amounts of white smoke on the right side at all times.

 

The fact that it is black is proof that there is SOME spark, otherwise there would be no soot. A normal burn is hot enouugh to co9mpletely consume all fuel and not leave any soot. A very weak spark might be unable to consistently burn all the available fuel, much like having way too much fuel. Most likely cause on this engine would be a high resistance plug cap. Did you check that? Anything over 10K is bad.

Goose

[GeorgeS]

Does the same thing, backfireing. Or maby just call it a lot of " popping "

Its supposed to be caused by the Air Injection System . Or AIS system.

 

Part of the poulution control junk .

 

It fairly easy to overide it, so no air is injected into the exhaust pipe.

 

I have not done it as yet, but plan to. There are several postings on this site as to how do overide the system.

[V7Goose]

Does the same thing, backfireing. Or maby just call it a lot of " popping "

Its supposed to be caused by the Air Injection System . Or AIS system.

 

Part of the poulution control junk .

 

It fairly easy to overide it, so no air is injected into the exhaust pipe.

 

I have not done it as yet, but plan to. There are several postings on this site as to how do overide the system.

This information could not be more wrong. Popping or afterfire on this engine is ALWAYS caused by either something wrong with the fuel mixture or combustion process, or an exhaust leak. The AIS NEVER causes this problem. It is true that disabling the AIS can HIDE an existing combustion problem, but it dos not SOLVE it.

 

As I have sated in MANY older threads discussing this problem in great detail, the 2nd gen bikes will NEVER pop or bang on decel in totally stock trim UNLESS there is a problem that needs to be fixed. Disabling the AIS is not fixing anything, it is simply hiding an existing problem because you do not want to be reminded it is there.

 

In this particular case, disabling the AIS cannot ever have any affect whatsoever on the combustion process (is is simply air induction into the exhaust), so it will have no effect at all on the fouled plug. It MAY stop the banging, and it may simply allow the unburned fuel to build up to the point where an explosion splits the muffler.

 

My recommendation is that you always find and fix an existing problem instead of just finding a way to stick your head in the sand.

Goose

Edited September 23, 2012 by V7Goose

[Hogchain]

Checked plug cap resistance it is 21.3K on all four plugs. What does that mean? Is that where it should be?

[mbrood]

The resistance from the inside of the plug holder to the ignition fues should be ~23K, 13K for the secondary of the ignition coil and 10K for the plug holder internal resistor. Unscrew the plug holder from the wire and recheck the end of the wire to the fuse... I would guess modified plug holders. But that IS on a 10% tolerance of the spec but to have them ALL in that region is rather odd.

[Cougar]

This is why I always have spares of these coils from pinwall.

 

Not sure if it is a hard job or what the cost is the replace the

end (cap) for these coils. I just replace them myself,.there

pretty cheap , not sure if this is your problem or not. kind of

looks like what has happened to me in the past. those rear coils

are up-side down in the rear and get ALL the elements of the

weather , not sure why Yamaha did this on the placement of them.

 

I also have sent my coil to the Goose and he did confirm that mine was bad (not the coil) just the cap.

however there a one piece unit. so I replaced the whole darn thing.

 

http://stores.ebay.com/PinWall-Cycle-Parts-Inc/Venture-Royal-Star-/_i.html?_nkw=Coil&_fsub=3669171014&_sid=12458664&_trksid=p4634.c0.m322

This link is taking you to all the coils. click Yamaha on the left and then you type bike.

Good Luck.

Jeff

[frankd]

Checked plug cap resistance it is 21.3K on all four plugs. What does that mean? Is that where it should be?

 

 

I would say that all the plug caps, wires, and coil secondaries are fine. All 4 on my 1st Gens measure virtually identical. Over 10K ohm is bad for the plug cap itself, but when you measure them with the coil attached, you are also measuring the coil secondary. For both of them 21.3Kohm is fine.

 

I don't see where you've checked that cylinder for spark. Pull the plug cap off the bad cylinder, and temporarily install a new spark plug into the wire. Make sure the base of the plug is grounded and start the bike, and look at the spark. If it's a nice strong, blue spark, you have something else wrong. Fouling like you have comes from excessive oil in the cylinder, a rich mixture, very weak spark, or a real cold spark plug. You know you have the correct spark plug installed, so cross that off. If the spark is strong, cross that off also. Leaves a rich mixture (high float, leaking needle & seat, or starting jet stuck open, jet falling out) or oil contamination. Does the bike use oil (I mean like a quart every couple of hundred miles or worse)? Probably not. Then you have a carb problem.

 

As RSTDog said, after it's fixed, change the oil. But don't ride it like it is because oil thinned with unburnt gasoline will cause the motor and transmission to wear quickly.

 

Frank D.

[V7Goose]

Checked plug cap resistance it is 21.3K on all four plugs. What does that mean? Is that where it should be?

I would be VERY suspicious of those readings - even if all the caps are good, they would almost certainly not read identical resistance - generally they will be somewhere around 9K, but that can vary by as much as 20%. I suggest you check your meter against a know good value.

 

You did measure them off the wire, right? You also mentioned that you had taken the caps apart to clean them - I hope you did NOT try to clean the resistor in any way! Those are a thin film resistor on a ceramic core, and even the lightest rubbing will destroy them.

 

A plug cap that measures 12K - 14K is bad, but generally will run OK. Any cap that reads 20K is total trash (unless internal cleaning can bring it back down to 10K, of course). I will also mention here that you CANNOT measure the secondary coil resistance as shown in the shop manual - that is just one of the meany errors in that book. The coil is completely isolated from ground.

Goose

Edited September 23, 2012 by V7Goose

[Trader]

This information could not be more wrong. Popping or afterfire on this engine is ALWAYS caused by either something wrong with the fuel mixture or combustion process, or an exhaust leak. The AIS NEVER causes this problem.

Goose

 

VGoose, you probably have forgotten more about these bikes than I know....but if the AIS is Cracked or has a seam leaking air, would that not cause too much air into the mixture?

 

I know having the air box off causes it to run like junk...because of too much air.

[V7Goose]

VGoose, you probably have forgotten more about these bikes than I know....but if the AIS is Cracked or has a seam leaking air, would that not cause too much air into the mixture?

 

I know having the air box off causes it to run like junk...because of too much air.

No, the AIS cannot affect how the bike runs in any way. Its sole function is to simply allow fresh air into the header pipes when conditions are right to reduce unburned hydrocarbon emissions without causing exhaust problems.

 

Think of it this way - it is the functional equivalent of a street sweeper walking behind a horse in a parade. If the sweeper is drunk and sick, it makes no difference to the horse at all. Of course the marching band coming along next won't particularly appreciate the horse apples, but the horse still does not care.

Goose

[Trader]

Wonderful illustration!

[Hogchain]

OK, I finally figured it out. Thank you all for your help!

 

So heres how it went down:

 

1. I first noticed a fouled plug so i changed all of them (it was time anyway)

2. Back left plug fouled again almost immediately (so i changed it again...i know, stupid)

3. Bought Carbtune II to synced carbs (they were not really off much)

4. Checked the plug cap resistance...it was fine (i said it was 21.5ish but that was still connected to coil rookie mistake )

5. Took plug caps apart and cleaned them (this made no difference whatsoever)

6. Decided it had to be a carb issue (I have never touched a carburator)

7. Downloaded service manual (Even though the information on the pages looked like a combination between cave art and hieroglyphics to me, it helped)

8. Opened the vacuum chamber covers (three looked fine, even though i did not know what i was looking at )

9. Left rear vacuum cover came off and exposed the plastic screw, a couple of springs and washers, and part of the needle laying in the chamber (I am assuming that caused the carburator to flood out the back left cylinder and foul the plug)

10. Put all that stuff back together

11. With everything apart, i cleaned the carburator (I HATE ETHANOL GAS!!! )

12. As per service manual, i blew out the carburator parts with air compressor

13. Put it all back together, and started the bike

14. Re-synced carbs

15. She is purring like a kitten (no more backfiring, and she is running smooth)

 

I still don't know what I am doing, but learned a lot on this project. Thank you all so much for your help. Feel free to correct or critique my list; I am no mechanic (my degrees are in Sociology and Theology...needless to say, this was a learning experience) Thank the Lord for this forum!

 

Matt Powell

[GeorgeS]

This information could not be more wrong. Popping or afterfire on this engine is ALWAYS caused by either something wrong with the fuel mixture or combustion process, or an exhaust leak. The AIS NEVER causes this problem. It is true that disabling the AIS can HIDE an existing combustion problem, but it dos not SOLVE it.

 

As I have sated in MANY older threads discussing this problem in great detail, the 2nd gen bikes will NEVER pop or bang on decel in totally stock trim UNLESS there is a problem that needs to be fixed. Disabling the AIS is not fixing anything, it is simply hiding an existing problem because you do not want to be reminded it is there.

 

In this particular case, disabling the AIS cannot ever have any affect whatsoever on the combustion process (is is simply air induction into the exhaust), so it will have no effect at all on the fouled plug. It MAY stop the banging, and it may simply allow the unburned fuel to build up to the point where an explosion splits the muffler.

 

My recommendation is that you always find and fix an existing problem instead of just finding a way to stick your head in the sand.

Goose

 

I just bought the bike " New " 10 weeks ago. ZERO miles on it, I first heard the popping on the 25 mile drive home from the dealer, first tank of gas !!

 

Pops a little on low speed, and mostly on decelleration going down fairly steep hills.

Other then the popping the engine runs like a Swiss Watch !!

 

I don't consider it a " Problem " as such, just sort of annoying !! Especially for a New Bike !!

 

I ran my 1989 1st gen, for 88,000 miles, and never heard so much as " One Pop " out of the exhaust !

 

Sorry, but can't agree with you on this one, as I have read reports by to many people discribeing the same thing with the 2nd gens.

 

And many reports, of disableing the AIS system, and guess what? No more popping !!

 

But, I am going to do a Carb Sync, ( have new tool ) and will replace plugs with, Irridum plugs.

 

MPG has been running about 40 MPG Average, 38 around town, and 41 to 42 pure freeway driveing. Engine starts, idles , and runs perfect except for the occasionaly popping from the exhaust.

 

Usually only happens, when Slamming throttle closed, from a higher engine RPM, for whatever reason it is necessary to do that.

Obviously this causes, the Vaccume, at the AIS sencing Point, to " go high " !!

 

You say I should be looking for a problem , perfect running new engine, 40 MPG, starts great, makes gobbs of power, what should I

be looking for as to a problem ???

Edited September 25, 2012 by GeorgeS

[frankd]

Hogchain,

 

You need to add step #16....change the oil.

 

Glad you got it running good....

 

Frank D.

[V7Goose]

I just bought the bike " New " 10 weeks ago. ZERO miles on it, I first heard the popping on the 25 mile drive home from the dealer, first tank of gas !!

 

Pops a little on low speed, and mostly on decelleration going down fairly steep hills.

Other then the popping the engine runs like a Swiss Watch !!

 

I don't consider it a " Problem " as such, just sort of annoying !! Especially for a New Bike !!

 

Sorry, but can't agree with you on this one, as I have read reports by to many people discribeing the same thing with the 2nd gens.

You do have a problem with your brand new bike, wether you want to admit it or not. And it is not uncommon with sloppy setup work at the average dealer.

 

As far as agreeing with me - you are free to agree with whomever you want. In my opinion, out of the two opinions you are evaluating (me and the "other guy" who has a problem and doesn't care to fix it - well, one of us don't know squat. I cannot elaborate on what I think of the "other guy's" approach 'cause all I do is insult people when I talk plainly.

 

I will say that disabling the AIS is one of the most extraordinarily UN-intelligent things I have seen done to these bikes. Those who do it without understanding what is going on are just making a poor shade-tree mechanic decision. But if they have found all the information on this subject that is available on this site and STILL make that decision . . . well, let's just say I would be deliberately insulting them if I finished that thought.

 

And many reports, of disableing the AIS system, and guess what? No more popping !!

 

But, I am going to do a Carb Sync, ( have new tool ) and will replace plugs with, Irridum plugs.

 

MPG has been running about 40 MPG Average, 38 around town, and 41 to 42 pure freeway driveing. Engine starts, idles , and runs perfect except for the occasionaly popping from the exhaust.

 

Usually only happens, when Slamming throttle closed, from a higher engine RPM, for whatever reason it is necessary to do that.

Obviously this causes, the Vaccume, at the AIS sencing Point, to " go high " !!

 

You say I should be looking for a problem , perfect running new engine, 40 MPG, starts great, makes gobbs of power, what should I

be looking for as to a problem ???

And if your engine is leaking, parking over a rug hides the puddle. But only a fool would think they were "fixing" the problem.

 

On a new bike there are only a couple of things that will typically cause this problem. Many of them have an exhaust leak at the Y pipe - this was especially common in 05 and 06. The pipes are crimped, not welded, and the crimp leaves two large gaps that can suck in fresh air. When this problem is present, you will typically see a gray film on the chrome heat shields of the lower pipe right around the Y joint. The film wipes off easily, so you won't see it if you have recently washed the bike. You can usually even feel the exhaust pulses with your hand if you hold it behind the Y joint. The fix for this problem is warranty replacement of the Y joint.

 

Other typical causes are any vacuum leak, carbs not in sync, and incorrectly set mixture screws.

 

Irridium plugs won't do anything for you. In my opinion, they are a complete waste of money UNLESS your only goal is to not change them for 50k-100K miles.

Goose

Edited September 25, 2012 by V7Goose

[V7Goose]

OK, I finally figured it out. Thank you all for your help!

 

7. Downloaded service manual (Even though the information on the pages looked like a combination between cave art and hieroglyphics to me, it helped)

8. Opened the vacuum chamber covers (three looked fine, even though i did not know what i was looking at )

9. Left rear vacuum cover came off and exposed the plastic screw, a couple of springs and washers, and part of the needle laying in the chamber (I am assuming that caused the carburator to flood out the back left cylinder and foul the plug)

 

Matt Powell

Good to hear, Matt. I don't know what a "vacuum chamber" is, but it is clear that you found the problem and got it fixed. I'm glad for that.

 

Be careful with that service manual - there are LOTS of errors in it (some real significant). It is a great tool to have, but I do suggest you read all you can find on this site about any particular service procedure before just diving in with that manual.

 

I hope you took the time to properly set the float levels while you were in there. We haven't discussed this for a while on the site, so for the benefit of the newer members, I'll mention it here - 100% of these bikes come from the factory with the floats set WAY too high. I do not know why, but my statement is based on the difference between the actual setting and the shop manual spec.

 

Having the floats too high generally results in an overly rich mixture at speed. The idle mixture can still be set correctly with the screws, but you would need to lower the slide needle to compensate for it at high RPM. After setting the floats properly, the average bike seems to get about a 10% improvement in MPG.

 

Ride safe,

Goose