tuning carbs by measuring exhaust temp

is this possible? i thought i would give this a try, i have a real good digital thermometer and i stuck it down the exhaust on my '77 750twin, i'm reading 175 on one pipe and 152 on the other, so i think i should make the air/fuel mixture richer on the hotter pipe, since both plugs are looking clean. anybody ever tried this?

measuring at the exhaust tips is hit or miss..I would use a infrared thermometer and check the temps on each exhaust runner as they exit the head. The tempuratures will vary. As far as tuning an engine by going off of exhaust temps, I personally would not use that method. However, a really high tempurature would note a lean condition, cooler would note a rich or non-firing cylinder. I personally use the tempuratures of the exhaust to find out if individual cylinders are firing.

Tuning by EGT (Exhaust Gas Temp) has been done for years, although it's normally done with a thermocouple mounted near the exhaust port.

Being a well known cheapskate, I tune using the spark plugs

For starters,u really dont have a good starting point as to what is the ideal temp., in a cylinder. once u have the bike tuned,by other means (jetting,seat of pants,crisp thottle response,no burbbling on the top of the rpm range.)Then take a reading. keep the readings handy,(wright air temperture down,baro.)then any performance change in the future would be a good starting point. jetting can be alot of work, but its worth it when its all said and done!

Moved thread to carburetor area...

My take? I think the carburetors need to be synchronized and the idle mixtures tuned correctly. This will probably equalize the temperatures in both cylinders as the mixtures are different now. By changing mixtures in each carburetor to try and equalize the temps, you will just be creating a tuning nightmare.

It works for boilers residential or commercial and I am sure it will work for the bike engine,but you have to have a combustion analizer Testo or any other company that makes them.This way is a lot better than your vaccum gauges.

I use vacuum gauges to equalize the vacuum allowed through the carburetors. If the carburetors don't have the same amount of vacuum actuation, then performance will be extremely rough... the carburetors can not compensate for different levels of vacuum caused by the slides being out of synchronization by using different jetting set ups in each carburetor which would be the only way you could use the heat method directly. I suspect there is a reason why tuners use vacuum gauges and not thermometers for this task.

If you tried rejetting to equalize performance based on cylinder temps rather than synchronize and tune using conventional methods, I suspect it would be nightmare but heck, this is an interesting discussion and perhaps you don't understand what a vacuum gauge does.

The important tuning characteristic is essentially to have the same air/fuel mixture (through every range of operation the carburetor supports) in each carburetor and the easiest way to be precise is to equalize vacuum first. I know of no professional tuner that would have different jetting in each cylinder. I know of cases where the two inner cylinders on a four cylinder bike will have slightly richer main jets because the center cylinders run hotter and to compensate for the greater temps but this only causes the air/fuel mixture to be the same across all four cylinders. Similarly, Kaw uses slight richer jetting on two carb V-twins (Vulcan VN1500A/B/C models) on the rear cylinder to equalize air/fuel as the heat on the rear cylinder (out of air flow) tends to make it hotter and thus leaner. But, the normal way of jetting is to use the same jets on each multicylinder carb assembly.

This is a quote from the Morgan Carbtune instruction:

A Guide to Carburettor Synchronizing

"Carb balance will affect the response, smoothness, mileage, performance and running temperature of your engine.

Carb synchronisation consists of adjusting each throttle valve for carburettors or fuel injection throats so that they pass as much fuel-air mixture as all the others. This balances the load carried by each piston.

If one carb is opened further than the others that cylinder will run hotter than the others. The other carbs will also supply a richer mixture and mileage will suffer."

www.carbtune.com/inst.html