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I have a 98 vn800b My rear plug was always running a bit darker than desirable. I read Russian wolfs wright up on switching from the cr7e to the hotter Cr6e he says that lots of people have done this and no one has had any issues, I haven't been able to find any one that can conferm actually doing this just qouting Russian wolf. Is switching both plugs safe for the motor, I don't want to burn up my bikes motor. Has any one made the switch to Cr6e plugs and how has it been.


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Hi!
When I bought my bike, I found out that the previous owner did that. But even after that both plugs were in terrible condition. Burned black with wrong gaps and never maintained. I adjusted my valves, cleaned and adjusted my carb, and actually switched back to CR7E. To be honest, I have no problem since that and I see no reason not to follow the original service manual. In my opinion if everything is OK there should not be a big difference what spark plug is being used in a second cylinder. Yes, it's a little bit hotter, but both plugs (CR7E and CR6E) should have no problem with those second cylinder temperatures.
What to say, just test Yourself, what is better for You. You can not burn Your engine anyway: )
 

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Discussion Starter #5
Hi!

When I bought my bike, I found out that the previous owner did that. But even after that both plugs were in terrible condition. Burned black with wrong gaps and never maintained. I adjusted my valves, cleaned and adjusted my carb, and actually switched back to CR7E. To be honest, I have no problem since that and I see no reason not to follow the original service manual. In my opinion if everything is OK there should not be a big difference what spark plug is being used in a second cylinder. Yes, it's a little bit hotter, but both plugs (CR7E and CR6E) should have no problem with those second cylinder temperatures.

What to say, just test Yourself, what is better for You. You can not burn Your engine anyway: )


I switched both plugs out to the hotter plug, it's warming up better and seems to be running fine. I just don't want to burn up the motor and I get paranoid about those things. Especially since money is super tight and getting a new bike is not an option


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Installing hotter plugs just "covers up" an existing problem.
It ran fine for the first 15 years of its life without them, and so it should continue.
 

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With the original plugs (CR7E), I had always problems with the rear one.
Since 3 or 4 years, I have changed the rear one to CR6E => no issues anymore.

Maybe we cover an existing problem, but fact is that the engine runs well and plugs color is OK. Could be something wrong in design ?? ..... too many VN800's has this issue.
 

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The hotter plug is covering up two problems:

1. Fuel tap that is leaking, or
2. Carb that need work, or
3. Both.
 

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Well... OK...
Just found something on this issue.
See where it says "The spark plug in the rear cylinder fouls every so often. What's up with that, and what's the solution?"
in this link.

The rear cylinder in all of the Vulcans (except, of course, the inline twin 500) runs a trifle richer than the front. The closest anyone has come to explaining why is that the rear cylinder runs a bit cooler than the front; mainly because with the radiator in front of it, the front cylinder doesn't get the benefit of cooling air, whereas the rear cylinder does. I've always been told that the "cooling fins" on the Vulcan line (hell, on all liquid-cooled motorcycle engines!) are strictly cosmetic, and provide no cooling affect. However, this is the only theory anyone has offered that even comes close to making sense...

In most cases, that doesn't seem to matter; but in some, this causes plug fouling. The best solution that has been found by the Vulcan community is to go up one step in heat range to the next hotter plug; in the case of the 800, the NGK CR6E. Literally noone who has installed a CR6E in the rear cylinder has had this problem occur again. It does no harm to put a CR6E in the front cylinder as well, just so you don't have to order two different plugs, and especially if most of your riding is either highway or hard mountain running (like me!).

Very few dealers stock the CR6E, so you would have to have them order it. A good source to simply order your own would be (again) sparkplugs.com. As of this writing, NGK does not seem to offer the CR6E in the Iridium series.
 

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1. First paragraph pure speculation.
2. Put in a hotter plug for highway or hard riding? Does not know what he is talking about.

If it was a design issue, those bikes would have fouled the rear plug out the show room door. Did they?
 

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1. Fully agree, hard to believe that the rear cylinder is running cooler than the front one.
2. Fact is that with CR6E in the rear, the bike is running well. I have checked the color of plug and is good.

Not all design issues come out already at the dealer. It would be nice to be like that.
 

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I was searching info on this issue and found out that some people on V-Twin have hotter front and some totter rear cylinder. If we think logically, there always will be some difference in temperatures, not matter what. For those who have problems, it would be interesting to do some real temperature measurements.
 

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You would have to take combustion chamber temperatures. That determines spark plug heat ranges, not water temperature.
Any other temperatures are meaningless.
 

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Yes and no. If we need precise temperatures, then Yes. If No, there's an easier way to determine which cylinder has a tendency to be hotter. Do a cold start and measure outside of both cylinders while they warm up. In couple of minutes You will feel it even with Your hand.

EDIT
I'm just talking about a tendency and not about precise measurements. In most cases, I guess, it will always be the second cylinder which warms up faster and runs hotter.
 

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I used to have this problem of the rear cylinder not firing occasionally on my (now sold) 1997 VN400 Classic.
It started happening around 4 years ago so it was definitely not a design error.
I cured the problem by doing the following things each time not in the same order and most times not all at once:
* put some carb cleaner in the tank and ride it , usually fixed the problem.
* dry the -wet with fuel- rear plug.
* sometimes problem persisted so I just had to change the rear plug, even used CR6E.

This occurred usually when bike was sitting for a few days so when new owner had same problem I told him to check the petcock (needed replacement) and he also had the carb cleaned by a professional.
Problem disappeared and he stopped cursing me for selling a junk bike to him!
 

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This occurred usually when bike was sitting for a few days so when new owner had same problem I told him to check the petcock (needed replacement) and he also had the carb cleaned by a professional.
!
Faulty fuel tap will foul rear plug every time.
 

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I agree, but to validate this, we need to answer to this question : why the CR6E plug is not fouled ?
Because the CR6E is a hotter plug and therefore more able to burn off any deposits that are formed by the rich mixture that is there for what ever reason.
But, hotter plugs can also cause trace detonation under heavy loads.
 
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