Read My Plugs

[Paul Sutton]

When I sorted out my carbs I put in new plugs and they just would not color up at all (81 SH). The heat line on the ground strap was good and there were no issues with performance relating to a lean mixture. I did keep a check on the center electode but it retained its sharp edges and there was no sign of metal erosion or insulator melting - so I stuck with it.

 

[DirtyErnie]

Drove to work last Thursday, mileage was disappointing in the high 30s. Looking at pilot jets.

What's the sweet-spot for # of turns out on these EX500 carbs? 2? 1.5?

Anyways, left side plug: this one has the strap facing the intake and the gap facing the exhaust.​

 

[DirtyErnie]

Right side plug: this one the gap points up to the top of the chamber, and there's an air leak around the throttle shaft.

 

[DirtyErnie]

Thinking I'm going to try dropping the pilots from #45 to #42 and try again. Either that or I need fatter needles, but I don't think that's it & I have the #42 jets. Needles are one notch down from stumbles.

Left side carb mix screw is maybe 1 turn open. Right side is more open, but has an air leak on the throttle shaft.

I'm seeing the swirl bias I ground into the intake ports when I look at these plugs; they're both darker on the intake valve side, lighter on the exhaust. Tells me the mixture is rotating forward past the plugs, using the plug nose as a flame-holder, and getting hotter on the exhaust side. I was reading a lot of Larry Widmer's stuff when I did these heads. (Unless everyone else is also seeing this on their bikes, in that case I'm just talking to myself again ;-) )

 

[Brassneck]

I like your attention to the fine details...I could use your patience with tuning my race bike. Unfortunately, I'm of the camp that feels if it pulls hard, idles well, and doesn't look like it's melting the plug...run it until something happens--ha ha. Thoroughly enjoyed reading this thread.

 

[DirtyErnie]

This is going to be a cruising & commuting bike, so it should be getting a lot better than 36mpg. That's actually a dangerous amount of fuel for these, kinda running the risk of washing out the rings at present, but I'll take that for a little while rather than getting a sudden hole in the piston. Getting closer to done with the Ninja Carb Swap!

Gotta remember, they only run their hardest when tuned RIGHT.

 

[DirtyErnie]

Update: the #45 pilots had left side about 3/4 turns and right about 2.5 turns on the mix screws. Throttle shaft air leak would explain that. Dropped in #42 pilots, will see how that works. Probably going to end up putting a #45 on the leaky side

 

[Paul Sutton]

On my 81SH I found that light grey color on the insulator disappeared by reducing the pilot screw by 1/8 turn. If possible repair the leak on the seal - One less variable to consider. With the SH and stock carburetors I was always getting between 60 - 70 mpg based on Imperial Unit, but then I was never pushing the bike hard.

 

[DirtyErnie]

Can't repair leaks on EX500 carbs, there are no seals. We'll see how the mileage goes with this change, and then probably lower the needles a notch after. I'm expecting 52+ MPG US. after things are tuned, that's what it did before.

 

[DirtyErnie]

How to lose a whole bunch of time chasing your tail:

Put in the #42 on the good left-side carb, still wouldn't tune with the mix screw until just before the screw seated shut. Well, damn... there goes about two weeks of tuning... plugged air jets...
break out the carburetor cleaner, shoot down both pilot air jets, now the bike is way lean on the very bottom. So, that didn't work. Switched back to the #45 jets on both sides, and now it pulls from a low idle. Pretty sure the #45 is the right pilot at this point. After knocking the timing pick-up as late as possible, I'm getting good color lines on the ground strap. Both sides are showing just a bit late on timing, so I might adjust that up a little.

But I have one concern: neither side is more than about 1/2 of a turn out from seated on the mix screws to run right, and that sounds pretty wrong.
Mileage is still in the mid 30's.
Full set-up:
Pilot: #45, 1/2 turn on the mix screws
Main: #145 (same pilot and main jets as the BS34's?)
Needle: HKK, #3 position. I've tried lowering the needles, but it just starts getting weak in the midrange.

Next Steps? I have a half of a mind to go with #42 pilots and thinner needles, but I think that's the wrong way if I look at any of the tuning charts. 1,200RPM and a barely cracked throttle is well below where the needles will pull fuel, right?
I think it's time to order fatter needles. HKL is the next step on the PWK28 needles map, and it's pretty much my last & only choice to pull fuel out above the pilots. 'H' taper is definitely what this bike wants.

> Does anyone know what the needle jet insert part number is? Same as a PWK28? Maybe I'll grab a pair of those as well (and some #148 mains to be sure I'm maxed out on fuel)

 

[5twins]

Mid 30's mileage is bad and could indicate either your mains are too big or your needles too rich. BS34s by the way, had 132.5 mains. The most any 650 carbs ever had were mid 130's mains. It's easy to over-jet CV carbs because they work on engine demand. The slide doesn't open all the way when you whack the throttle open, only as much as the engine can use.

 

[DirtyErnie]

Mid 30's mileage is bad and could indicate either your mains are too big or your needles too rich. BS34s by the way, had 132.5 mains. The most any 650 carbs ever had were mid 130's mains. It's easy to over-jet CV carbs because they work on engine demand. The slide doesn't open all the way when you whack the throttle open, only as much as the engine can use.

You're right, but my combo:

• Pocket-ported heads (cleaned up the bowls really well)
• Shell #1 Hoos mis-grind (exhaust 5° early, so lower overlap)
• Pods.

The BS34's ran best with a #45 or a modded "#46" pilot and a #145 main & Heiden needles with the Heiden 2-1 exhaust and a cherry bomb muffler.

I have switched to a stock exhaust and the EX500 carbs, otherwise everything is as above.

 

[DirtyErnie]

Original build thread

 

[DirtyErnie]

Well, hell...

What do you do when you're heading off into the weeds tuning carburetors? Go back to basics.

• Are the passages and jets clean?! Sprayed them down, they're good.
• Check fuel level? Bluddy hell... 2.5mm high.

Re-set the floats to 17mm, got the fuel back down to the top of the bowls, rather than 2/3 up the serial numbers...

Took a 50 mile ride after that.

• Taper is too lean now, so back to a 'J' taper.
• Waaay too much pilot, and then lean needle diameter above that. Back to 'J' diameter, and step things down to a #42 pilot.

It's amazing what you can compensate for when you thought you did something right the first time.

 

[DirtyErnie]

Got a few rides in this weekend.
#45 pilots @ right fuel height = 1 turn out on mix screws.
#42 = 1 1/2
#40 = 2

This seems ok now, not sure if it wants more or less fuel until...

JJJ needles back in. Started at #3, there was some roughness. Raised the needles a notch and it got worse. I'll lower them 2 slots next ride.

Sudden WOT below 1,500RPM and it would fall on its face.

 

[DirtyErnie]

Took a couple more rides, did a little more fiddling. Dropped the JJJ needles from #4 down to #2 and things cleaned up pretty well, still a little weirdness down low. Swapped I. The JJK needles at #2, and it seemed better. Will post up mileage after I get back from work.

She's a bit cold-blooded with the JJKs, the pilots have enough fuel to make the cold engine want to go, but the needles fall on their face below about 2k. I might try stepping down to the #38 pilot and the JJJ needle.

 

[DirtyErnie]

Yesterday to-from work = 44.5 MPG, so something was a step in the right direction. Still getting a little rumbley vibration as I roll the throttle closed, and a tiny bit of a chocolate ring around the tips of the plugs. I'm thinking it's time to step down to the #38 pilot; that would get my mix screws open to about 2 1/2 turns, which is starting to sound appropriate.

I did take a ride last night after raising the JJK needles up to slot #3, and the choking as it transitioned to the needles below 2,000rpm seemed better, but I'm really betting on the #38 pilot and the JJJ needle being closer to the right set-up.

 

[DirtyErnie]

New month, new needles. Probably shoulda sent this order in June, but I didn't wanna.
Anyways, wouldn't pull clean WFO @1,400, and was getting horrible mileage while showing symptoms of running lean. Picked up JJH and JJG needles. Playing with JJH now, Position 4 and 3 gave me black plugs, but 3 was less black than 4. Set to 2 and rode to work this morning. Feels good. Will pull and get more pics after work. Likely will have to go down a size on the pilot now.

 

[DirtyErnie]

Right side. Pilot looks good, but there's leaky throttle shafts here. Black stain halfway down makes me think I could lower the needle a notch.

 

[DirtyErnie]

Left side. Dark around the nose, maybe drop the pilot a size, after checking idle mix and clean jets. Still a bit dark down the nose, drop the needle another notch?

I'm seeing both sides wanting lower needles, and maybe adjust the mix screws a bit.

This was a 50 mile day, to/from work, 2/3ed of that was 70mph freeway. 38mpg.