Topic: Plug Reading on a CB400T - I am so dumb...

[KB02]

Okay, now I can see that it looks like the bike might be running a little lean, but I'm not too worried about that at the moment.

1978 Honda CB400T (Hawk II).
The bike has been running fairly well. I took it out the other day and it had an episode where one cylinder cut out. It was very odd. a couple of twists of the throttle and the engine rev'ed up to the higher RPMs and that seemed to "clean things out" a little bit. I thought it odd, but after stopping for gas, the bike ran great and I headed home. A few days later I headed out again and the same thing.
   So, I got to thinking that it seemed like a fuel issue. I hadn't cleaned out the carbs since I've owned the bike (Two years), so I thought it would be a good idea to pop off the bowls and see if there might be anything in there blocking up the works. There was a good deal of sediment at the bottom of the float bowls, and the plugs look like this:

Plug 1


Plug 2


It's the red hue to the plugs that has me a little interested.

Here's my theory:
The tank is starting to rust out (there are no inline filters... yet...). Some of that rust sediment has made it's way down to the carbs and it's that rust that "stopped up the works" and caused the cylinder to cut out. Could some of the rust be getting through to the cylinder and turning things red?

What do you all think?

[RRRToolSolutions]

Those plugs look fine to me. They are not too hot and they are not oil or carbon fouled - so just about perfect. What you don't want is a white ceramic insulator - or worse a spotted one. The red is from the detergents and additives package is my guess. Here is a most excellent site to study -

I'd say you're on top of # 14 "the best".

Regards,
Gordon

http://www.4secondsflat.com/plug_chart.html

For the record - this is what plugs look like when hooked to a failed Dyna 2.2 coil - these are from my CB750 holes - 1-4.

[RRRToolSolutions]

Let me also suggest that you always install your plugs with anti-seize applied to the threads. I like the sticks, but any will do. I use a torque wrench and 14 lbs/feet whenever possible. If in doubt and I'm not able to torque-check them, I'll go on the light side and add the wrench when I get home.

[KB02]

Those plugs look fine to me. They are not too hot and they are not oil or carbon fouled - so just about perfect. What you don't want is a white ceramic insulator - or worse a spotted one. The red is from the detergents and additives package is my guess.

Well, they look a bit paler in person. But you think the red is from the fuel itself? I've never seen a plug turn red like that.

[Aaron J Williams]

I'm going to have to disagree with the others on this one. The red you are seeing is rust dust on the plug. I have seen it before on everything from Ford pickups to push mowers and they all had one thing in common, rusty gas tanks.

[KB02]

Yeah, theres a little bit of rust on the tank...

Darn it. I was hoping not to have to coat that tank, too. I've done it before with success, but it's a pain in the but.

Well, inline filters at the very least will be going on soon. Probably this weekend as my other bike is still in the shop and the CB is still a pile of parts (that may change a little bit this weekend, too...)

[RRRToolSolutions]

Rust - I've never thought of that. I like the POR 15 product - a lot.

It takes careful preperation and follow the instructions to a T - but the results are permanent and look like new steel when opened.

I would have thought his jets would have long been stopped-up before the plugs could get that much build-up.

I will admit - I've never seen a red plug!

Gordon

[Aaron J Williams]

There was a good deal of sediment at the bottom of the float bowls

I too am surprised that the jets aren't plugged but if the rust is tiny like dust specks then it will flow through the jet and plug it up slowly, over time as the dust settles out every time he shut the bike off. Inline filters would be a good idea and maybe flush the tank out to get any big stuff that may be in there.

[KB02]

Okay, so I finally got the time to dig into this bike and try to figure out what's wrong with it. The first thing I did was to remove and drain the fuel tank. Once I had it sitting nice and secure on a couple of Milk crates, I brought over a gas container and set to draining. Once the tubes were set up the way that I wanted them, I turned on the fuel valve to the reserve position and the let it go. I expected to see a little bit of rust or a gas water mix come draining out, but it all looked fine. I figured that I would open up the filler cap to help it drain a little faster.

 - That's where the flash of my stupidity hit me. -

It's my wife's bike so I don't ride it all that often. Over the summer, the times that I did ride it, I kept hearing a vibration when the engine reached a certain RPM. After searching I traced the vibration down the door over the gas filler cap. As a way to stop the vibration, I grabbed one of those paper towels you get at the gas station and placed it under the door, above the filler cap to help dampen the vibration. This worked well, HOWEVER, Since I had it folded enough times, and it was as tight as it was under the door, it smothered the vent hole on the top of the filler cap, thus not allowing the vent to do it's job which lead to not enough gas getting into the float bowls to run the bike well.

Step A.) Remove the the thing that blocks the tank vent
Step B.) Ride the bike without worrying again.

While I have the tank off, I am going to run a de-rusting solution through it anyway and probably pop the carb bowls off again to see if they are clean (and replace the screws), BUT, I think I found my main problem: My own stupidity. 

[bryanj]

Nothing wrong with a high quality DOH moment now and then, just dont put your waterproof leggings over the air intake!!!