After years of screwing around with what the previous owner started with, a DynoJet kit, I decided to go to a hotter spark plug (NGK 5531 or the NGK DPR6EA-9, stock plug is the DPR7EA-9). First ride today and it actually runs better today (40 mile test ride with hotter plugs) than it EVER HAS! For the first time I have a dark brown plug in back and a more tan colored plug in front! The power and crispness of the throttle is so much better. I'm using a lot less throttle to do the same stuff and when I go to start the engine, it fires up immediately! My gut says I will also get better mileage.

Let me give you some history....I have a 2000 RSS. Barons BAK, Freedom Performance Racing 4" duals, Barons Ported Intake Manifold (I really ported it and rounded the corners so there is a very good smooth radius close to the size of a dime). I've been told that this porting will richen the mixture. Well it does from what I've experienced. The PO has changed pipes, BAK and DynoJet jet kit. Well it popped, it back fired, it coughed, you name it it did it! Plugs were black!

So I tried to move back to stock and slowly change things. I purchased all Mikuni jets and adjustable needle kit from SS Custom. I started with a 170 main and stock pilot, still rich. So I slowly reduced my main down all the way to a 162.5 and now I'm on the third clip from the top needle slot with the donut and a washer under the clip. Still running rich. I've trimmed the choke knob, checked my coils, adjusted the accelerator pump, rebuilt the carb, checked the float level, I run 87 octane fuel, cleaned the air cleaner, even run it without an air cleaner, put new plugs in. Last week my rear plug started fouling. I got to the point that I may call SS Customs and get their HSR42.

One last ditch try, my plugs had about 200-300 miles on them when the rear plug started to foul. I started reading on the NGK Spark Plug Website about spark plug heat ranges....see below this came from the NGK SPARK PLUG SITE. So I decided to go one step hotter on my plugs!!! It helped hugely. Here's my thinking... I have a modified engine, pipes intake and exhaust, the stock plug doesn't run hot enough to correctly burn the mixture that is being delivered. And I don't ride like a GrandPa! Well like I said the hotter plug has given my bike new life! Yes, I am aware of issues of going too hot, but one step hotter is all I did.

DISCLAIMER...your mileage may vary, I don't guarantee this will work for everyone, and it could actually screw up your engine if something else is wrong and you misdiagnosed the real problem and went with a hotter plug. #1 this makes a lot of sense if you modified your engine to flow more through the heads as I have. Anyway I hope this helps some guys that have had similar issues that I have had.

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FROM THE NGK WEBSITE
https://www.ngksparkplugs.com/about-ngk/tech-talk/spark-plug-basics

CAUSES OF CARBON FOULING
*Continuous low-speed driving and/or short trips
*Spark plug heat range too cold
*Air-fuel mixture too rich
*Reduced compression and oil usage due to worn piston rings/cylinder walls
*Over-retarded ignition timing
*Ignition system deterioration
Pre-delivery fouling:
Carbon fouling occurs when the spark plug firing end does not reach the self-cleaning temperature of approximately 450°C (842°F). Carbon deposits will begin to burn off from the insulator nose when the self-cleaning temperature is reached. When the heat range is too cold for the engine speed, the firing end temperature will stay below 450°C and carbon deposits will accumulate on the insulator nose. This is called carbon fouling. When enough carbon accumulates, the spark will travel the path of least resistance over the insulator nose to the metal shell instead of jumping across the gap. This usually results in a misfire and further fouling.

If the selected spark plug heat range is too cold, the spark plug may begin to foul when the engine speed is low or when operating in cold conditions with rich air-fuel mixtures. In some cases, the insulator nose can usually be cleaned by operating the engine at higher speeds in order to reach the self-cleaning temperature. If the spark plug has completely fouled, and the engine will not operate correctly, the spark plug may need to be replaced and the fouling cause identified.

Do you know if the bike ever had a HC on it? If so someone may have changed the air jet due to the HC instructions. Also does it have a Dyna aftermarket ignition box on it? There shouldn't be any reason the change to a different plug. IMO you only fixed the symptom and not the problem.

Dave J....all stock ignition. No high compression. Whats weird though

What I've read is that when you port the intake you change the flow volume and you get a more fuel and hence a rich condition. It makes sense when you change the air cleaner, the intake and the exhaust the entire systems flow has changed. All I know is I continue reading about guys that have done similar changes that have rich conditions. What NGK put on their site about heat ranges makes sense. My anology is a foggy day, when more fog (fuel) moves in it takes more sun (spark) to burn it. The hotter plug creates the self cleaning which is now required due to high flow.

What Dave is saying, is we have hundreds of members who have opened up their intake and exhaust and have jetted their bikes richer to accommodate the increase in air flow. You are still running rich enough to think you need to go to a hotter plug, after going so lean on your jetting and needle, your bike shouldn't even be running properly. Something isn't adding up.
One solution, is if somebody had a Hypercharger on the bike before, and changed the air jet per instructions, that could be the source of your excess fuel. The bigger air jet, makes for a richer Pilot. Since the Pilot never stops adding fuel, it creates a rich environment across the board.
Another place may be the float level. If it's set a bit high, it'll create a rich condition. I was fouling plugs on my Springer, and when I dug back into it and starting double checking, I noticed the float was about 3 or so mm above max. It doesn't take much.
The CV carb adds fuel according to the air flow, if you increase the aitflow and you aren't to lean on the jetting and needle, it'll add fuel because of the Venturi action in the carb throat.
The fuel system works by air flow(or vacuum)sucking fuel out of the bowl. It pretty much self regulates. You can be to rich, but if you're to lean, the bike should buck and snort and run like crap.

SKWEARpeg wrote:
What Dave is saying, is we have hundreds of members who have opened up their intake and exhaust and have jetted their bikes richer to accommodate the increase in air flow. You are still running rich enough to think you need to go to a hotter plug, after going so lean on your jetting and needle, your bike shouldn't even be running properly. Something isn't adding up.
One solution, is if somebody had a Hypercharger on the bike before, and changed the air jet per instructions, that could be the source of your excess fuel. The bigger air jet, makes for a richer Pilot. Since the Pilot never stops adding fuel, it creates a rich environment across the board.
Another place may be the float level. If it's set a bit high, it'll create a rich condition. I was fouling plugs on my Springer, and when I dug back into it and starting double checking, I noticed the float was about 3 or so mm above max. It doesn't take much.
The CV carb adds fuel according to the air flow, if you increase the aitflow and you aren't to lean on the jetting and needle, it'll add fuel because of the Venturi action in the carb throat.
The fuel system works by air flow(or vacuum)sucking fuel out of the bowl. It pretty much self regulates. You can be to rich, but if you're to lean, the bike should buck and snort and run like crap.

SKWEARpeg That could be, that makes sense, my PMS did nothing last time I adjusted it, but it use to work...no one has ever mentioned the "air jet". To my knowledge, I don't think there was ever a hypercharger on the bike, but you never know. The PO did put the Baron's BAK on it, but he's not the first owner. I've checked the float bowl level and it's OK, if anything it's at the gasket surface level and not 4mm above, but I'll check it again. Frankly I've never heard of the "air jet". Seriously, I'm tempted to leave it the way it is, it's running so well right now. No pop on accel or decel, no cough's, great acceleration. I use less throttle than before. Like I said before I'm tired of screwing with it and just want to ride with no issues.

Thanks for the input.

It just seems odd.

You're getting fuel from somewhere.

Does the bike start properly with the Enricher?

If you're interested the air jet in question is up below the diaphragm and the stock size is 2 mm's. Hypercharger included a smaller jet or 2 which would make the mixture very rich. The secondary air jet is at the mouth of the carb toward the bottom. Put your finger over this with the engine idling and if there's no difference then it's probably plugged up which would also drive the system rich. This secondary jet is shut off when the decel valve is working.

If any part of the pilot air jet system is plugged then the bike will run really rich. Even with the stock pilot jet.

This seems to be a trend primarily in 99 models. Per Factory Pro web site, 38, 39, and 40mm Mikunis were known at one point for wearing out the needle orifice in the emulsion tube. If it is worn oblong, the needle never seals the gap and would allow constant flow from the main, past the needle. Nobody has looked for me yet, but I know of at least 5 99 model owners chasing rich conditions downhill with smaller mains than the norm. A signature seems to be an ineffective PMS screw, where you can close it all the way up and it won't make the engine die, which it should if everything is right.

I read that once years ago so I bought another emulsion tube at about 35,000 miles. Well I found out they don't wear out on our bikes. The emulsion tube is made from bright hard steel. The ones that would wear out were made from brass.

The needle in mine has always had a little play but no more one way than the other. And the engine will idle just fine without flow from the main with the needle removed.

jd750ace, thanks I've heard about the Needle Orifice but couldn't figure out where or what it was to replace it. I don't see the needle orifice or an emulsion tube? Are you referring to #14 in the carb parts breakdown?

By looking at the parts diagram of the carb, looks like #2 is the Air Pilot Jet being referred to???

Here's a link to the carb parts break down:
http://www.cheapcycleparts.com/oemparts/a/yam/50044381f8700209bc78f006/carburetor