Exhaust pipe temperature check

Ever since I had the carbs off this past March (2nd time since I bought the bike) I have been curious to check the exhaust pipe temperatures with an IR thermometer to find out if the cylinders were operating in about the same temperature range. Well, my IR thermometer had taken a dump and I just now got around to replacing it. I started the engine from cold this morning with enough choke for the engine to run at about 2000 RPM and started checking the temps of the pipes at the head connection just down from the retaining clamp about 2", choke completely off at this time, idle speed 1500. The temps came up quickly and stabilized fairly well at around 320F after a few minutes. There was 10-15 deg. differeence between the pipes except for #1 cylinder, it lagged behind by about 30-35F at 285-290. This indicates to me that #1 butterfly should be opened up slightly, is this correct? Turning the mixture screw both ways a half turn had no discernable effect on the temp or engine speed, all the screws are set at 2 1/2-2 3/4 out from seated. The engine runs great, idles very smoothly, revs out quickly with no hesitations or flat spots. I am going to turn the synch screw for #1 in slightly and see what happens. Has anyone else done this test? If so, what were the results?

 

Haven't tried this. Interesting idea. On a side note, were all spark plugs replaced at the same time?

 

Yes, I installed new plugs when I got the engine up and running last fall, haven't checked them since. A word of explanation for the test. In a past life, I owned and operated Mack diesel trucks. One of the tests for determining if the proper amount of fuel was being delivered to each cylinder was to check the exhaust temps at the ports. I think it is a valid test for gas engines as well.

 

Interesting idea, but......

Probably not the same as the truck, and imo, if you're trying to synch carbs by exhaust temp, don't. The best way is with vaccum gagues or manometer, as you know. If you get even temps across the headers but loose your best idle, you haven't improved much.

Seems like your bike is running fine, but if you want to tweak, i'd suggest it might be best to get carb synch set with manometer first, then play with the one mixture screw until you see changes, and allow lots of time for temps to adjust themselves. Cooler temp would most likely mean a richer mixture there, i believe.

Set mixtures with gas sniffer to 3% CO, and synch carbs using manometers.

 

??????? I would not go messing around w/ the carbs based on exhaust pipe heat.
and if you sync carbs, correct me if I'm wrong - #1 is your base that you adjust 2-3&4 to.

 

NUTS, SM beat me to it.

 

FSM says that #4 is the base carb, that is the one with the idle speed adjust screw.

 

You're right, the bike is running IMO extremely well and doesn't really need any major, or for that matter, minor tweaking. I am going to open up #1 carb butterfly just a bit with the synchro screw strictly out of curiousity and see what happens, I can always return it to its' present position if I am not satisfied with the result.

 

:doh: :doh: :doh:

 

How much do you find that the temperature change with moving closer or further from the exhaust port?

Exhaust gas temp is useful in tuning an engine, Too bad you can't check it on the road. When we were roadracing one team had 4 egt gauges on their Kawasaki 550.

 

When I worked with blown alcohol FC engines. We had exhaust temp probes in each exhaust pipe when on the dyno. Which reads the gas temp. Normal good tune temps were 900-970F. Exhaust temps are one way to tune and trouble shoot engines. Though it is just part of the equation and not the main input. Fuel and gas engines will have higher temps.

Most combustion chambers get to 1000-1300 degress when combustion happens with gasoline. Different fuels have different combustion temps typically. I would think using and IR gun may show a lower temp than an exhaust probe reading the gas temp.

 

I realize that my test is not going to be terribly precise, but I was careful to hold the IR thermomter at the same position and same distance from each pipe to get as good a reading as possible. I haven't had the time to adjust and recheck, I'll post the results when I can find my "rountuit".

 

I was careful to aim the IRT at the same spot on each pipe at the same distance, didn't try different distances from the port, I'll try it next time.

 

Update for those who are interested. I finally found my "rountuit" and did some further experimenting. I turned the #1 synchro screw in 1/4 turn and repeated the temp test, this time aiming the IR thermometer at the pipes about 1" from the port connection and 1" from the pipes. The temps came up evenly and stabilized at 280 - 290 degrees for all four pipes. There was no discernable change in idle speed (1000 RPM) or throttle response. I am going to ride this morning and will do another temp check immediately after a stop and see what the temps are.

 

I stopped after about an hour of riding on some curvy county roads, 35-60 MPH and checked the pipe temps. All four were reading 400-420 and cooled to 335-350 after 2-3 minutes of idling. I'm satisfied that all 4 cylinders are burning pretty evenly.

 

You are forgetting something.
The cooler cylinder could have a vacuum diaphram problem or a small pin hole
in the vacuum diaphram cover (corrosion) making the piston act differently.
ALSO what about the needle in the slide? Spring?
Try switching slides from #1 and #3 and see what you get.

Remember.. at idle the mixture enrichment screw for the first 1/4 throttle.

 

air screw, thermos? primitive.



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