Exhaust blueing problem

[bloodthirstysystem]

Been getting a lot of info from this board, now i finally have a question. This is a 78 standard with pod filters, straight pipes with large washer baffles bolted in.

Left pipe is turning blue, right side is normal. Carbs have been cleaned, rejetted, mix screws set, needles at 3rd slot. Exhaust valve is .006, intake .004. Plugs are tan at the electrode and both sides look the same, ignition timing set with ohm meter.. runs great.

Has anyone else had a problem with this?? maybe the exhaust valve isn't closing all the way? I need to do a compression test but thought i would ask here..

thanks

 

[Tomterrific]

Retarded timing and lean mixture are two of the common reasons for the exhaust being excessively hot. On a twin carb bike the balance can be off enough that one side pulls more and gets hotter.

Set timing with a light at full advance. Anything else is a best guess. Use premium gas or play Russian roulette with detonation and holed pistons.

Points, right? Pull a plug at idle and see how both sides idle. Just pull each plug for a three count (blump-blump-blump). Is one idling higher than the other? Is one side not running? Adjust them both perfect by trail and error or a manometer.

I've never adjusted the carbs on a 73 XS but I do old Triumphs so I have experience. You need to balance the carbs off idle as well. There are several ways to do this but I don't have a favorite. If you don't find an acceptable way ask and I help you figure out a good method.

Tom Graham

 

[bloodthirstysystem]

I set my timing with a digital ohm meter. will a timing light make much of a difference?

i always thought blue pipes = lean, yellow = rich. i searched online and some people were saying this is wrong and it is opposite. can anyone confirm?

my plugs both look good, the reason i'm having trouble.

 

[Sundie]

Question: do you have single wall exhaust pipes? If so, some blueing is inevitable.

 

[bloodthirstysystem]

i'll check after work. it's whatever comes on a 78 standard. i dont mind the blue, just dont wanna do any engine damage...

when setting the timing with points, do you line up the rotor with the "F" or the line to the left of it?? i set them right at F, not sure if this retards it all. it's such a small amount

 

[XS1961]

Cheap chrome.
Cant see a problem myself, I think a blue or yellow tinge looks quite good!

 

[bloodthirstysystem]

gives it some character!

 

[weekendrider]

Cant see a problem myself, I think a blue or yellow tinge looks quite good!

+1

 

[Sundie]

i'll check after work. it's whatever comes on a 78 standard. i dont mind the blue, just dont wanna do any engine damage...

Ah! Then you're double walled. With a crack in the internal pipe (which always happens) letting hot exhaust gasses get to the outside.

You've got holes in your external pipe (which is actually just decorative stock) up near the exhaust outlets, yes? Or holes that *were* there, and someone brazed them up because they were "leaking"?

when setting the timing with points, do you line up the rotor with the "F" or the line to the left of it?? i set them right at F, not sure if this retards it all. it's such a small amount

The T line (1) corresponds with TDC. The F lines (2) are what you set your idle, with a timing light, with the bike running, at idle. The line to the left of that (3) is where you should see your timing light strobe to when you apply full advance (rev to about 3k). The mark on the alternator rotor (4) is what you're setting all this to.

I've always found it easier to set full advance, then tweak carbs to achieve a proper idle, after making sure the ATU comes back to neutral.

 

[bloodthirstysystem]

the right side pipe has a hole up by the motor, the left side does not and it does not look like someone plugged the hole (unless they chromed it after). the left side is the blue one too. hmmmm

i'll set it with a timing light. harbor freight has some cheap ones, are they absolute garbage? http://www.harborfreight.com/catalogsearch/result/?category=&q=timing+light

will i need a light with advance?? my guess is yes

 

[Sundie]

maybe someone replaced a single stock pipe? That would explain it.

A non-advance timing light will work fine. You just line up what line you need. I suggest lining up 3 and 4 at 3000 rpm.