Header color- running lean

Hey guys, I have an 83 xj750rk seca. All original my dad was the original owner. We even still have the pre-purchase checklist from the dealer and the little yellow yamaha owner card. Anyways..

I've cleaned the carbs 2 times, and synced them multiple times. I don't have an actual yics shutoff tool, I use a peice of all-thread that I have put electrical tape around in certain spots to block of the ports and it works really really well. I haven't color tuned it yet due to the fact I can't afford to buy one, but it seems to be running lean on cylinder 1. The header is far bluer in color from heat than the other 3 cylinders. A thermal scan reveals no problems, the temps on all 4 header within 8* of each other. Now what do you think could cause this? Valve adjustment (done 1,000mi ago)? The carb "out-of-sync"? Or is that a sign of the carb being clogged, or is it normal. I will post a few pics when I get home, I'm at school rn. My apologies for the long post, I'm just super passionate about my bike and I know how it supposed to work so when it's not I freak out. Thanks for any info you guys can give me.

 

The stock headers are double walled and should not blue. Are you positive that it has the full factory exhaust?
When was the last time that the carbs were serviced?
Have you used propane or carb cleaner to check for vacuum leaks around the intake boots and throttle shaft seals?

 

Yes. The bike is completely stock. The last time they were service was about a month and a half ago, and that's when I used a small propane torch to Check for vacuum leaks, there were no leaks that I could find. The bike has 21,500mi on it

 

Hmm.... I will make a WAG based on wht you have told us about how the bike runs, and the temperatures you are seeing.

The inner header pipe on #1 has a hole in it, allowing exhaust gasses to blue the outer pipe.

BUT>>>> Here is what I want you to do. Pull the plugs and look to see if #1 is running lean.

 

I pulled the plugs on all 4 cylinders just incase, and they're all white with a little ashy tone to it. I replaced the plugs at 19,873 miles according to my service book. I'm getting about 33-36mpg average, and mostly highway riding at about 55-60mph for about 15mi one way. I get about 150-163mi on a single tank. My father said it never got above 35mpg. If it's advertised 50mpg, what could I do to get this 50mpg?

 

It runs extremely well. The power and acceleration is very linear. If you guys have a color tune that you would be willing to part with for cheap let me knows ASAP

 

50 MPG requires conservative riding, and never going above 55MPH. I've gotten that, but only when touring and without a headwind.

You can tune without a color tune. Do one cylinder at a time. Turn the idle air screw out until the idle speed drops, turn back in until the idle speed drops again then set the screw midway between the two. Be sure to count your turns carefully. Repeat the process on the remaining three cylinders.

Ash white is lean, but still on the safe side of lean. Given what you've said about the other headers and cylinder temps, and the plug colors being even across all four, I think you may just have a hole in the inner header tube on #1 or have had a temporary lean condition on #1.

 

That's for your help k-moe. I'll try to adjust the screws this weekend if I have time. Will each carb be different on the initial turns out, or different? Also what is your average mph?

 

Baseline for the idle air screws on the later fine-thread screws (which you have) is 2.5 turns out. Most of us end up around 2.75 turns out from a soft seat.
My MPG varies a lot since I live on the great plains (wind can be a friend, or an enemy). I average around 40 MPG during my summer trips, and 33 around town. I can see 50 MPG all day long if I ride like grandpa and have a wind free day.

 

Thanks k-moe. So I neglected to say before that the bike seems to be running rich without the choke on. At least that what it smells like in the exhaust. So with the plugs the color they are and the exhaust smelling rich, could it be running rich and that's causing the header to blue because of the little unburned fuel in it? And could that cause my gas Milage to be what it is?

 

If you were running rich there would be carbon deposits on the plugs. Being rich would not cause the headers to blue. Rich engines run cooler; bluing happens because of a lean condition. Your gas mileage is what it is because the 55 MPG that was advertised is based on the old EPA test loop. That test loop has nothing to do with real world conditions, and they never went over the (then) 55MPH national speed limt. Your fuel economy is in the ballpark for normal riding in at modern speeds, and with modern fuels.

 

Gotcha. I'm just about to start with the pilot screws, so we'll see how it turns out. Is there a way to find and fill the whole in the inner pipe, I have my welding certs in mig and tig?

 

Keep in mind that I am ASSUMING that there is a hole. To find out if there is one you would need to pull the header off, or find a flexable borescope that is small enough to fit into the emissions inspection port.

Unless you have a trained squirrel that is TIG certified you won't be fixing a hole in the inner tube without having to cut the outer tube for access, in which case buying a good used head pipe is a much better choice.
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If it were me I would make sure that she's not running lean, and keep riding. The blueing will polish out.

 

Okay thanks k-moe. I ended up turning all the screws out to about 2 3/4 and WOW did that make a difference. After resyncing it, the whole bike feels waaaaayyy better. Also most of the rich smelling exhaust went away

 

Awesome

 

If only...

 

what was the temp of the pipes? just wondering

 

Around 190-195*. After about an hour of highway riding 55-60mph they got up to 212*