New Exhaust Headers - Ruined

I bought a MAC 2 into 1 exhaust system (headers and muffler). I know MAC isn't great stuff, but it's within the amount of money I was willing to spend for an exhaust. The headers are black instead of chrome.

Within 60 seconds (no exaggeration) of starting the bike up, the paint on one of the headers began bubbling. It began right at the exhaust collar and slowly started working its way down the pipe. After it cooled down, the paint has a "cracked" look to it.

The other exhaust pipe didn't seem to be affected. However, there is a slight leak at the collar. I don't know if that has something to do with it.

Also, the carburetor is a fresh rebuild. I guess it's possible it could be running lean/rich. I'm not sure yet since I just put it back on. But I wouldn't think this is a lean/rich issue since it happened so quickly.

Anyway... any thoughts on whether this is my bike? Or just a faulty paint job on the headers by MAC?

paint on painted headers, unless its a ceramic coating, will always burn off within minutes after they start getting hot and takes about 20 minutes to stop smoking. i'm not a bike expert by any means, but i've dealt with enough headers on chevys to know. and the painted 4-1 header on my kz1000m1 did the same thing.

I spent about 25 years dealing with painted headers and I know this: the paint has to be cured before you fire the engine up or it will bubble off. I hang the pipes up in the garage and use a 1500 Watt heat gun I got at Harbor Freight for $10 to gradually heat the whole pipe set up heating both the outside and inside. Do it gradually, cook the hell out of it and let it cure overnight and you should be good. The maker should cure the pipes but I suspect the time and expense of doing it means some get skipped. Sounds like yours did.

PaulyWally wrote: IAlso, the carburetor is a fresh rebuild. I guess it's possible it could be running lean/rich.

If it's a 750 twin it was jetted lean at the factory. I recommend upping the pilot jets to 50 (it will run better and not be so lean).

If the AFR was really lean... it is possible to see the headers glowing cherry red. It happened to me once in a KLR650.

Hmmm... good info. Thanks all.

So now that some of the paint has bubbled/cracked, what are my options at this point? Should I just try and cure the rest of the pipes and "deal with it"?

Rust Oleum has a very good high temp spray can that goes up to 2000°f

I would contact MAC first and see what they say then make a decision. If they won't replace them there is a couple of options. Coat the INSIDE with Eastwood Hi-Temp Internal Exhaust Coating and wrap the headers. Don't wrap the headers without coating them on the inside and out. If you do you will destroy the headers from the inside out.
Or just coat them on the outside with Eastwood Hi-Temp Coating . Hope this helps. If it were me I would coat the inside and the outside.

I don't know what MAC KZ750 twin headers look like, but why not just take them off, sand down and put new high temp paint on them? If properly cured the paint will last. You can cure the paint on the bike by letting the pipes warm up a little bit, wait for them to cool, run the motor a little longer, etc. Do this several times then take it out for a short ride. Tedious but it does the job.

I have several 2-stroke bikes with painted expansion chambers and that's how I paint and cure the pipes.

There are many good paints out there. I like to use KBS Coatings www.kbs-coatings.com/
they're not expensive and the products work well.

The high temp header paint I use on my gun parts (nothing internal) cures at 300°f. So I would have a hand held thermal thermometer and wait till the header reaches that and do the method kapahulu suggested since I don't think a header will fit in your oven

60ratrod wrote: The high temp header paint I use on my gun parts (nothing internal) cures at 300°f. So I would have a hand held thermal thermometer and wait till the header reaches that and do the method kapahulu suggested since I don't think a header will fit in your oven

That's why I always hang them up and shoot them with a heat gun. In my experience, if you try to "use cure" them by running the engine a little and then shutting off over and over they don't cure well because the heat is being applied only on the inside. Better results if you heat the outside and inside and gradually bring the temp of the piece up. In the 25 years I ran painted headers, the coating lasted a few years then had to be redone. If you don't cure them well, they can bubble or flake off but the paint also gets very soft and rubs off.

EDIT TO ADD: considering how many hours I wasted sanding, painting and curing those pipes over the years..... the smart money would have been to get powder coating but it didn't exist 20 years ago.

Kapahulu wrote: I have several 2-stroke bikes with painted expansion chambers and that's how I paint and cure the pipes.

Unfortunately, the four strokes seem to run a whole lot hotter.