Spark plug color and jetting
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Tourer
Joined: Jul 2006
Posts: 298
Likes: 12
From: Villa Rica, Georgia
Spark plug color and jetting
My bike is a 98 fxdl. I just got my engine rebuilt by Hillside cycle, stage 2 head porting, cylinders bored, woods 8 cam, and some S&S goodies. It also has a mikuni 42 hsr with a k&n foward facing intake and a dyna 2000 igntion module and coil set up for single fire. Right now there is no VOES cause I discovered it was leaking and the module is on curve 2.
The timing was done as per the dyna instuctions and the carb has a 25 pilot, 165 main and the needle is in the stock location. 1 1/2 turns out on the air screw. I got ngk spark plugs ( dont recall the number) that were supplied from Hillside with the engine. What I'm seeing when I checked my spark plugs is they look like they are almost clean, as if they were just taken out of the box. From what I've read about spark plug color is a light brown/tan/chocolate color is ideal.
According to the butt dyno the engine runs great. I'm getting mid 40's for gas mileage with a high of 46. Starts up cold easily but to me it feels like its running a little on the hot side, with in approx. 30 seconds I'm already feeling heat from the heads and exhaust. The engine just turned 1000 miles so I'm ready to really see what this thing got. My question is why do my spark plugs look like there almost not firing? The engine was first run with a 20 pilot then a 22.5 now it has the 25 in it. Could my 25/165 jetting be too lean causing the heat? Forgot to mention I also got new screamin eagle spark plug wires.
Before the engine was rebuilt I ran the same jetting and the last set of spark plugs was dam near black. I would think that my new engine combo would need more fuel. Any advice would be greatly appreciated as I am still learning this engine and determined to get it straightened out. Thanks guys !!!
The timing was done as per the dyna instuctions and the carb has a 25 pilot, 165 main and the needle is in the stock location. 1 1/2 turns out on the air screw. I got ngk spark plugs ( dont recall the number) that were supplied from Hillside with the engine. What I'm seeing when I checked my spark plugs is they look like they are almost clean, as if they were just taken out of the box. From what I've read about spark plug color is a light brown/tan/chocolate color is ideal.
According to the butt dyno the engine runs great. I'm getting mid 40's for gas mileage with a high of 46. Starts up cold easily but to me it feels like its running a little on the hot side, with in approx. 30 seconds I'm already feeling heat from the heads and exhaust. The engine just turned 1000 miles so I'm ready to really see what this thing got. My question is why do my spark plugs look like there almost not firing? The engine was first run with a 20 pilot then a 22.5 now it has the 25 in it. Could my 25/165 jetting be too lean causing the heat? Forgot to mention I also got new screamin eagle spark plug wires.
Before the engine was rebuilt I ran the same jetting and the last set of spark plugs was dam near black. I would think that my new engine combo would need more fuel. Any advice would be greatly appreciated as I am still learning this engine and determined to get it straightened out. Thanks guys !!!
Road Captain
Joined: Aug 2012
Posts: 625
Likes: 102
From: New Albany, Ms.
I think you've answered your own question.
Sounds like your on the right track, so richen that puppy up before you burn a hole in the piston.
Better to start off rich, & work your way to lean.
Safer that way.
Little tricky to tune without a air/fuel gauge or Dyno.
Ride Safe,
Harold
Sounds like your on the right track, so richen that puppy up before you burn a hole in the piston.
Better to start off rich, & work your way to lean.
Safer that way.
Little tricky to tune without a air/fuel gauge or Dyno.
Ride Safe,
Harold
Grand HDF Member
Joined: Apr 2007
Posts: 3,727
Likes: 3,072
From: Brighton, MI
I think you're real close. Today's modern fuels really don't leave much color on the plugs if you're tuned properly. Getting color on your plugs is putting you over towards the rich side. But having color is also a good way to tell that you're not to lean. (Cheap insurance)
As long as you're not getting any black specs like pepper or metal specs on the porcelain and you're not getting any ping I say you're pretty damn close. I think your engine temps are indicative of a fresh rebuild and the engine is still wearing in. If you do bump up the Jets only do it slightly. Again I think your jetting is really close to being on the money. YD
As long as you're not getting any black specs like pepper or metal specs on the porcelain and you're not getting any ping I say you're pretty damn close. I think your engine temps are indicative of a fresh rebuild and the engine is still wearing in. If you do bump up the Jets only do it slightly. Again I think your jetting is really close to being on the money. YD
Seasoned HDF Member
Joined: Aug 2008
Posts: 5,081
Likes: 2,159
From: Ohio
If you have a W8 installed from Hillside then that engine has some compression set up in it, will have some more noticeable heat when idling. Without a AFR reader and a warmed up Evo, it is best to play in the safe area as heat isn't your friend in a break in period.
Plug reading is getting harder with today's gas but richen that low speed jet to get some slight color, sqeezing MPG ism't a goal with a warmed up set up. From reading a Mikuni with a AFR reader the idle air screw richens the low speed deeper into RPM's than a CV. I can't remember which way richens a Mikuni but it is opposite of a CV, may want to richen that screw some until you make your jet change and put it back after making the jet change.
Plug reading is getting harder with today's gas but richen that low speed jet to get some slight color, sqeezing MPG ism't a goal with a warmed up set up. From reading a Mikuni with a AFR reader the idle air screw richens the low speed deeper into RPM's than a CV. I can't remember which way richens a Mikuni but it is opposite of a CV, may want to richen that screw some until you make your jet change and put it back after making the jet change.
Seasoned HDF Member
Joined: Mar 2010
Posts: 21,116
Likes: 7,640
From: Poolville
I am very familiar with Scott's work. I suggest you get it to a dyno. Jetting a stock Enjoy is not an issue but when you get a W8 build its a hole new ball game. Don't cheap out... That build should get you to near 95/95. Good luck...
One question did you send him the whole bike or just the parts and you did the assembly?
One question did you send him the whole bike or just the parts and you did the assembly?
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Tourer
Joined: Jul 2006
Posts: 298
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From: Villa Rica, Georgia
I sent just the parts. He returned it with the cylinders and cam installed, I put the heads on and installed it in the bike. This morning I changed the jetting to 27.5 pilot and a 170 main. Also I forgot to add that I have a RB Racing pro stock pipe on it if that makes any difference. I'm thinking about replacing it with a D&D fatcat. That RB pipe makes a hell of a noise just riding around! I'll update this as soon as I can. Again I really appreciate all of you guys help and advice on this matter.
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Seasoned HDF Member
Joined: Nov 2009
Posts: 15,705
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From: Farmington ,MS
Most "spark plug color charts" are still from the days of leaded gas...and you will never get a plug with today's gas to look anything like the plugs on those charts.
For the color to mean anything, you have to do a full throttle run and then shut the motor off, or run a steady state on a dyno.
If you really want it correct, an AFR reader is the only way to go.