Do these plugs look LEAN to you?

From a twin, two of the left hand side and two of the right hand side.

They don't look lean to me. Realize though, looking at plug color doesn't mean that the mixture is good throughout the engines operating range. The engine could be lean on the bottom and rich on top, or visa versa, but if the engine isn't run in those ranges much it won't show up on the plugs. For this reason the best way to judge mixture strength is by doing plug chops or tuning on a dyno where the exhaust gas is checked while under load. If you can maintain that same color throughout all the different operating ranges of the bike THEN you are all set.

Nessism wrote: They don't look lean to me. Realize though, looking at plug color doesn't mean that the mixture is good throughout the engines operating range. The engine could be lean on the bottom and rich on top, or visa versa, but if the engine isn't run in those ranges much it won't show up on the plugs. For this reason the best way to judge mixture strength is by doing plug chops or tuning on a dyno where the exhaust gas is checked while under load. If you can maintain that same color throughout all the different operating ranges of the bike THEN you are all set.

I confess, though i have a Kawasaki Twin, these plugs are from my 77 XS650 pictured below. The OP put HOOKER exhausts on (from the 70s - they sound great) and dabbled with the jets. My issue is light popping on deceleration AND sometimes when im riding.
Its a great bike, just want to make sure i dont burn up a piston. See pics below

Light tan (digestive biscuit colour) is what you want, so those plugs don't look far off, but as mentioned you need to kill the engine at higher speeds to see if you are weak on the mains.
If you took those plugs out after coming to a normal stop it only indicates that the low end fueling is pretty close to where it needs to be.
If you were very weak higher up though, enough to do damage, there would be visible evidence of blistering on the electrodes which wouldn't be masked by the tan of a normal low end stop.

zed1015 wrote: Light tan (digestive biscuit colour) is what you want, so those plugs don't look far off, but as mentioned you need to kill the engine at higher speeds to see if you are weak on the mains.
If you took those plugs out after coming to a normal stop it only indicates that the low end fueling is pretty close to where it needs to be.
If you were very weak higher up though, enough to do damage, there would be visible evidence of blistering on the electrodes which wouldn't be masked by the tan of a normal low end stop.

Thats very helpful. Cheers.

I took those plugs out this morning after the bike sat all night. Just to keep on top of the engine temperature, I bought one of these Thermo-Dipsticks. It arrives tomorrow.

JWKZ750 wrote:

Nessism wrote: They don't look lean to me. Realize though, looking at plug color doesn't mean that the mixture is good throughout the engines operating range. The engine could be lean on the bottom and rich on top, or visa versa, but if the engine isn't run in those ranges much it won't show up on the plugs. For this reason the best way to judge mixture strength is by doing plug chops or tuning on a dyno where the exhaust gas is checked while under load. If you can maintain that same color throughout all the different operating ranges of the bike THEN you are all set.

I confess, though i have a Kawasaki Twin, these plugs are from my 77 XS650 pictured below. The OP put HOOKER exhausts on (from the 70s - they sound great) and dabbled with the jets. My issue is light popping on deceleration AND sometimes when im riding.
Its a great bike, just want to make sure i dont burn up a piston. See pics below

NICE YAMAHA! I buy those bikes too! I have a 76' project sitting. Cooler than a 750 twin Kaw (Sorry 750 twin owners)

Decide for yourself, for me the plugs color looks near perfect

z1kzonly wrote:

JWKZ750 wrote:

Nessism wrote: They don't look lean to me. Realize though, looking at plug color doesn't mean that the mixture is good throughout the engines operating range. The engine could be lean on the bottom and rich on top, or visa versa, but if the engine isn't run in those ranges much it won't show up on the plugs. For this reason the best way to judge mixture strength is by doing plug chops or tuning on a dyno where the exhaust gas is checked while under load. If you can maintain that same color throughout all the different operating ranges of the bike THEN you are all set.

I confess, though i have a Kawasaki Twin, these plugs are from my 77 XS650 pictured below. The OP put HOOKER exhausts on (from the 70s - they sound great) and dabbled with the jets. My issue is light popping on deceleration AND sometimes when im riding.
Its a great bike, just want to make sure i dont burn up a piston. See pics below

NICE YAMAHA! I buy those bikes too! I have a 76' project sitting. Cooler than a 750 twin Kaw (Sorry 750 twin owners)

i have to agree. The Yamaha XS 650 (at least the 1977....earlier years had lots of problems, and its widely agreed that the 1977 bike was the best of them all) is a much more fun bike than the Kawa KZ750, and the Yamaha is faster too.

Scirocco wrote: Decide for yourself, for me the plugs color looks near perfect

Thanks for posting. Yep I agree its close to perfect, but the bike will only start with choke on for a while, and it makes these strange intermittent bogging noises when running, and has a very low sounding popping noise in the exhaust from time to time.

Here is another shot of it

Thanks for posting. Yep I agree its close to perfect, but the bike will only start with choke on for a while, and it makes these strange intermittent bogging noises when running, and has a very low sounding popping noise in the exhaust from time to time.

Without specific carb info the choke issue could be normal, the other symptoms could point to the beginnings of a carb tear down and clean/rebuild..... Plugs look good I wouldn't worry about a lean condition

ezrider714 wrote:

Thanks for posting. Yep I agree its close to perfect, but the bike will only start with choke on for a while, and it makes these strange intermittent bogging noises when running, and has a very low sounding popping noise in the exhaust from time to time.

Without specific carb info the choke issue could be normal, the other symptoms could point to the beginnings of a carb tear down and clean/rebuild..... Plugs look good I wouldn't worry about a lean condition

Its really cool to have knowledgeable guys like you and others in this post helping out. The bike (to me) is gorgeous and I really dont want to melt a piston. Im going on a long trip this weekend so maybe the constant fuel flow will clean out the carbs (I plan to do about 75mph for at least 1.5 hours on a 200 mile trip). I also noticed there is a bit of RUST in the tank....