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Discussion Starter #1 (Edited)
Hey all! I finally just got done building my chopper and I’m having an odd issue. One cylinder seems to be running different than the other, drastically if you look at the spark plugs. I’ve followed all of S&S’s recommendations for “pre-adjusting” the carb. And then did my best to find tune it. It seems to idle good and drive good. Judging by my pictures, what do you all think?

S&S 113 Evo motor
  • Pro-R Hyper Charger (uses vacuum from back of carb to operate butterflies)
  • V&H big radius 2 into 2 exhaust, no baffles, but I did install cones.
  • Super G Carb (just did full rebuild) .031 intermediate jet, 0.078 main jet
  • NKG iridium spark plugs 0.04 gap
  • New plugs and wires
  • Crane hi-4 ignition (timed at 32° at 2500rpm), semi advanced spark, no VOES, no retard or advance on rear cylinder
  • 93 octane gas with small bit of sea foam (about half recommended sea foam ratio)
  • Compression tests and leak down tests are perfect.
  • no detected exhaust leaks
  • Have not yet did the WD-40 test on intake manifold to test for leaks
9F4138D2-62D0-4E15-9B3F-9FD33A37097A.jpeg
A0F4E48F-3B85-4D88-886B-E74EA3592167.jpeg
 

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Both cylinders rarely look exactly the same due to engine configuration. The front cylinder always runs cooler. Check and verify compression is same or within several pound of each other. Check for intake leaks very well. If all is good just run it
 

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Discussion Starter #3
Compression is exactly the same at about 172psi. Passes leak down test also. I will try spraying some wd40 or carb cleaner where the intake meets the heads and where the carb mounts to the intake. The yellow on the plug is what threw me for a big loop. Haven’t seen that before.
 

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Like I said they are never the same. Is this a new build or older motor? Valve stem seals could be weeping throwing things off on the color as well possibly. That's about all I can think of. If all checks out I wouldn't worry.
 

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Your compression ratio is arround 11.75
(11.75 * 14.696 (psi at sea level) / 1 = 172.678 psi compression)
You risk pre detonation with that low octane fuel, and it will happen first at the hottest rear cilinder.
Then, with modern bio fuels 5 or 10% ethanol, it gets harder and harder to read spark plug colors. The ethanol will 'wash' the color off. Your sea foam probably does the same.
Get yourself a premium high octane gas and try again. Or lower the compression.

Edit:
Forget my reply. Just found your octane numbers are not the same as ours.
"In Europe, the octane rating on the pump is simply the RON figure. America, uses the average of the RON and the MON figures, called the AKI (anti-knock index). Thus, 97 octane “super unleaded” in Europe is roughly equivalent to 91 octane premium in the United States "
 

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Hey all! I finally just got done building my chopper and I’m having an odd issue. One cylinder seems to be running different than the other, drastically if you look at the spark plugs. I’ve followed all of S&S’s recommendations for “pre-adjusting” the carb. And then did my best to find tune it. It seems to idle good and drive good. Judging by my pictures, what do you all think?

S&S 113 Evo motor
  • Pro-R Hyper Charger (uses vacuum from back of carb to operate butterflies)
  • V&H big radius 2 into 2 exhaust, no baffles, but I did install cones.
  • Super G Carb (just did full rebuild) .031 intermediate jet, 0.078 main jet
  • NKG iridium spark plugs 0.04 gap
  • New plugs and wires
  • Crane hi-4 ignition (timed at 32° at 2500rpm), semi advanced spark, no VOES, no retard or advance on rear cylinder
  • 93 octane gas with small bit of sea foam (about half recommended sea foam ratio)
  • Compression tests and leak down tests are perfect.
  • no detected exhaust leaks
  • Have not yet did the WD-40 test on intake manifold to test for leaks
View attachment 264637 View attachment 264638

Keep in mind that intake leaks regardless of where they are will affect both cylinders equally. Even if this engine does have an intake leak, it would not be attributable to the differences you see on the spark plugs.
 

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They look OK to me. But the gas we have today has corn juice in it, so the plug will have soot as a normal condition as well as a lean showing strap. And can be way off or right on with the same look.

If it runs well and holds soot on the strap, I would put some miles on it. Maybe have a look at the pistons tops after 500 miles just to sleep better.

But with what that motor cost, getting some numbers off a set of wide bands would be cheap insurance.
 

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Discussion Starter #8
They look OK to me. But the gas we have today has corn juice in it, so the plug will have soot as a normal condition as well as a lean showing strap. And can be way off or right on with the same look.

If it runs well and holds soot on the strap, I would put some miles on it. Maybe have a look at the pistons tops after 500 miles just to sleep better.

But with what that motor cost, getting some numbers off a set of wide bands would be cheap insurance.
Thermodyne, Thanks for the reply! What do you mean by numbers from a set of wide bands? Are you talking about putting it on a dyno?
 

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Discussion Starter #11
  1. How many miles on the Motor? Ride it till its broke in, check the plugs then.
    5,000 miles on motor. It sat almost 10 years inactive. I ordered some more jets so I’m going to go up a size on the jets and see where that gets me. Meanwhile I’ll try to rule out any intake leaks. As long as it seems like it’s running good, I’ll just put some miles on it like you said and break it back in. Then re-evaluate. I wouldn’t mind getting one of those wideband oxygen sensor setups though. That would be pretty cool to have.
 

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Thermodyne, Thanks for the reply! What do you mean by numbers from a set of wide bands? Are you talking about putting it on a dyno?
Dyno would work. Wide bands are O2 sensors the operate over a wide range of fuel mixtures. 10:1 out to 18:1

You can also get stand alone wide band setups with a meter that you can read on the road.

If your pipes have 18mm bungs, you can just screw them in and wire it up. If not, then you'd need to weld the bungs in.
 

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Discussion Starter #13
Dyno would work. Wide bands are O2 sensors the operate over a wide range of fuel mixtures. 10:1 out to 18:1

You can also get stand alone wide band setups with a meter that you can read on the road.

If your pipes have 18mm bungs, you can just screw them in and wire it up. If not, then you'd need to weld the bungs in.
do they have dual ones where you can read both cylinders at the same time but individually? Or do you just have to get two different modules and use one for each cylinder?
 

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do they have dual ones where you can read both cylinders at the same time but individually? Or do you just have to get two different modules and use one for each cylinder?

Look a the link I posted above. Lots of options to include systems with dual sensors.
 
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