Mac headers ?

[Duster]

Need advice: I just finished doing alot of work on my 79SF and part of the work included installing one size smaller pilot jets due to fouling plugs at idle. It had not been started for 3 months and new Mac exhaust headers turned gold on 2,3,4 and purple on # one almost instantly. It didn't even have time to warm up enough to turn the choke off. Question?? Should I go ahead and let it run till it is warm enough to test everything or do I have a serious problem and should start over on the carbs. Duster

[xssiveone]

Mac exhaust headers turned gold on 2,3,4 and purple on # one almost instantly.

The gold is normal for Mac, and most aftermarket exhausts due to them being single wall tubing. Most factory ones won't as they are made from double wall tubing.

The purple one however does indicate a problem. That cylinder is running too lean a fuel mixture. When you installed the smaller pilot jets, did you clean the carbs out good? Sounds like you might have some plugged passages in this one.

[TopCatGr58]

Hey Duster,

Like Brian said, you probably need to do a more thorough cleaning of the carbs, the pilot circuits. Running rich at idle could be caused by many factors, NOT just the size of the pilot jets. The floats could be too rich, Pilot SCREWS turned too many turns OUT, air filter clogged.

Also, what type of plug are you using? Is there any corrosion between the plug wire and cap? Did you try swapping the #1 and #4 plug wire to see if the fouling changed? The off color does indicate an imbalance, but of what is the question. And now with newer pipes, your bike will actually breath better, and so you should need at least the OEM pilots if not even larger ones, and mains as well!!! Are you running the OEM airbox, or Indy Filters? Indy's will also further lean you out!! A little purple/blue is better than gold, at least you know you're not going to BURN a hole in your pistons!

[Duster]

Thanks fellows:
I'll reclean carbs and replace pilot screws with the recomended that I removed. It had Mac exhaust on it before(old) and I'm using the factory air box. It was running good before, except #3 plug would foul if I sat at a idle for any lenth of time. Floats were set as low as I could get them to stop fouling on the other plugs.
Duster

[Duster]

T C: Do I understand you right that the purple/blue is better than the gold? Duster

[beechfront]

my two cents

in my experience - headers seem to blue more in extreme temperature changes (cold weather)

[TopCatGr58]

Well, Duster,

I was just saying that if it was a choice between BLUE for richer, and gold for leaner, that running a little richer is better for the engine than too lean, more damage can be done when it's too lean. Too rich will waste gas, possibly foul the plugs sooner, carbonize the combustion chamber. Too lean can burn pistons, cook the oil faster.

Like Beechfront stated, bluing could be caused by more extreme temp changes, hot engine and exhausts vs. cold environment, however you've seen both colors on same set of pipes, so it does seem more diagnostic for rich/lean conditions in your situation.

With only 1 carb acting up, aside from recleaning the pilot circuit, you may want to double check your float in that carb to make sure it doesn't have any leaks!, which would cause it to sink, and make it more rich than the other carbs. Also reinspect the pilot screw, the tip can get messed up easily. Okay, good luck!
T.C.

[xssiveone]

TC, are you sure about that? I was always told that if the exhaust turned blue, it was too lean and the colour change was due to overheating. If it's running rich, won't it actually be cooler?

My buddy has a Mac 4-2 on his '78 and the pipes turned gold about halfway down to the second bend almost immediately.

[TopCatGr58]

Hey Brian, and Duster,

Boy does that shoe leather taste good!! After some more research, and banging my head to clear the cobwebs, my apologies for the aforementioned misinformation.

As previously stated, most of these aftermarket chrome pipes are single walled, so the heat affects the finish, with modest heat they turn gold or straw colored. With MORE HEAT, they turn BLUE. So....your 1 cylinder with BLUE pipe WAS apparently running LEANER than the others, not a favorable condition. Aside from a carb being maladjusted, it could also indicate an exhaust leak, cracked pipe, gasket!

My sincere apologies for misdirecting your approach, and thanks to Brian for keeping me straight. I've said all along, I'm no GURU, and being human, am prone to the occasional mistake! That's why it's a FORUM, watching each others back!!

Don't mind me as I fall from my humble pedestal back down to where I belong! T.C.