Exhaust pipe temperature

[jan.bauwmans]

When I point at the exhaust pipes of each cylinder with a heat gun, the pipe of cylinder 2 is abt. 100 degrees Celsius colder than the others. Other 3 show more or less same temp.

Already checked :
- valve clearance
- spark plug fires, gap set
- idle mixture screws checked
- synchronized carbs and all nozzles in the top spray fuel
- ignition timed
- checked cylinder top and sides with mini camera and all looks ok

The pinz drives very good, just did a check of the temp during routine maintenance.

Anyone an idea what could be the cause ?

Tnx !

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[Hugues]

100 C difference?!?
How much do you measure on each?

[jan.bauwmans]

Cylinder 1 3 4 abt. 310 degrees Celsius and nr. 2 abt. 200.

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[ChickenPinz]

Can you show us a pic of where you're doing the measurement? Presuming you're using a non-contact IR-type meter, it's important to make your measurements all at a similar distance so size of the sensed area will be similar.

I would swap spark plugs between two cylinders and see if the symptoms move.

Do you have good compression in all cylinders? Bad compression would result in poor power out of that cylinder.

[jan.bauwmans]

I measured at the same distance, cylinders 1 3 4 show abt. the same temperature. Switching the spark plugs doesn't solve it.

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[ChickenPinz]

I'd do a compression check now

[ChickenPinz]

There's another old-school test sometimes called a power-balance test.

You one-at-a-time disconnect each plug wire and see if the RPM drop is the same. That'll give you an idea if all cylinders are contributing equally. If the RPM drop is the same, then I'd say the temperature difference is a red herring.

[rmel]

What your are describing is possibly a case of exhaust valve seat recession.
During the compression cycle the gases are escaping out the exhaust with no
igniting. Most prevalent at low RPM, at higher RPM and HOT some ignition
will occur.

The best test for this is a Leakdown test, with the cylinder under pressure
you can then literally hear the cause of the leak, either out the tail pipe if
Exhaust valve or into the sump if rings. A compression test will tell you just
that but won't tell you the cause.

If you have a seat recession issue, the root-cause is typically running too lean.
This could be for all cylinders, in which case #2 was the worst, but all will be
showing signs, or could be just one cylinder due to a Carb metering issue.