Could a Clogged Fuel Nozzle=Lean Mixture?

hish747

hish747

Pre-takeoff checklist
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Hish747
Could clogged or partially clogged fuel nozzles on a carburated O-320 cause a cylinder to run lean/hot?
 
hish747 said:
Could clogged or partially clogged fuel nozzles on a carburated O-320 cause a cylinder to run lean/hot?
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Just one cylinder on a carburated engine? I'm inclined to look elsewhere.
 
No, carburetors don’t work like that. Maybe an induction leak
 
If OP would provide more details would help.

I’ve seen folks with bypassing Primers lean the mixture in flight.

Non primer equipped cylinders appear to run hot/lean.

Yes; attorneys were involved.
 
Clip4 said:
No, carburetors don’t work like that. Maybe an induction leak
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Thank you. We are looking at the intake valves to see whether they are seating properly. But wanted to check on other potential causes.
 
hish747 said:
Thank you. We are looking at the intake valves to see whether they are seating properly. But wanted to check on other potential causes.
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Check the intake gaskets and hose clamps too.
 
Magman said:
If OP would provide more details would help.
I’ve seen folks with bypassing Primers lean the mixture in flight.
Non primer equipped cylinders appear to run hot/lean.
Yes; attorneys were involved.
Click to expand...

Thanks for your response. This is the left engine on a Grumman Cougar. Things seem fine except that #2 and 4 CHTs are too high as shown on an EDM 760. On departure CHTs will shoot upwards of 450 degrees and higher if no action is taken. Baffling is good. Mag checks are great. Making full RPM. All else seem normal. What other details would be helpful?
 
hish747 said:
fuel nozzles on a carburated O-320
Click to expand...
FYI: a carburetor provides fuel mixture for all cylinders at the same rate. A fuel injection system provides fuel at each individual cylinder.
RyanB said:
Check the intake gaskets and hose clamps too.
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^^^ This plus the entire intake system.
 
hish747 said:
Thank you. We are looking at the intake valves to see whether they are seating properly. But wanted to check on other potential causes.
Click to expand...
A "leak-down test" (differential pressure test) will quickly let you know if you have any air going where it shouldn't. Though leaky intakes are known to vent hot gasses into the manifold, thus making their presence obvious.
 
Weird and unlikely, but I had the same thought as Magman. Leaking primer-equipped cylinders run well, non-primer equipped run hot. I am not familiar with the Grumman Cougar fuel system.
Which cylinders are primed and which are not?
 
All cylinders are primed. I know that this engine tends to have weak a primer system. I recall hearing that the primer nozzle holes are smaller than the ones found on other O-320s. Could clogged or weak primer valves cause high CHTs?
 
Have you actually laid eyes on the primer fittings?

The primer nozzles should be doing absolutely nothing once

the engine is started.

If the Primer Pump does not shut off you can have fuel going

to “ primered cylinders”.

Leaning the mixture in that condition could cause “ non-primered cylinders” to

be excessively lean.

If are not leaning the mixture the the primer system will not cause any

cylinder to run hot.

You said “ if no action is taken”.

What action do you take for a fix?


You could pressurize the Induction System for leaks.

Pull carb Heat ON , disconnect Carb Heat duct and pressurize with a leaf blower

or pressure side of a CLEAN vacuum cleaner.

Squirt soapy water to check for leaks.

Lots of folks here to help get this addressed.
 
"Have you actually laid eyes on the primer fittings?"
No but it is having it's annual inspection and I've asked that those be looked at.

You said “ if no action is taken”.
What action do you take for a fix?

Reducing power below a normal climb setting. Using a richer mixture than what I would normally use and what is used on the right engine. Of course, I understand that with carbs, mixture are quite imprecise.

Lots of folks here to help get this addressed.

Yes, I really appreciate this community! Thank you Magman and others!
 
The real issue here is high CHTs on the #2 and #4 cylinders. We checked the baffling and it looks good. No intake or exhaust leaks found anywhere. Mags are great. Primer nozzles were cleaned. No change in CHT, still high.

Would an issue with rings cause high CHTs? The other thing I notice is that the oil gets darker much more quickly on the engine with high CHTs than the other one.
Are we just left with pulling the cylinders for replacement or overhaul?
 
Yup, a partially clogged jet can cause a lean condition, but the engine would really run like crap too, most likely.
 
Did you pressure check the induction system?

There is also a Service Bulletin on carb split line gaskets.
 
hish747 said:
The real issue here is high CHTs on the #2 and #4 cylinders. We checked the baffling and it looks good. No intake or exhaust leaks found anywhere. Mags are great. Primer nozzles were cleaned. No change in CHT, still high.

Would an issue with rings cause high CHTs? The other thing I notice is that the oil gets darker much more quickly on the engine with high CHTs than the other one.
Are we just left with pulling the cylinders for replacement or overhaul?
Click to expand...

Start simple. Could it be an indication issue? Swap probes with opposite and see if problem continues.
 
I should've mentioned that the first thing I did was to replaced the probes with new ones. No difference.
 
hish747 said:
I should've mentioned that the first thing I did was to replaced the probes with new ones. No difference.
Click to expand...

Now look to the induction system as was mentioned. Couplings, gaskets, air box, etc.
 
Checked at annual and they reported that the induction system was fine. I wonder if worn piston rings could cause this?
 
Did the mechanics do a leak test on the induction system or just a visual?

One issue with not being involved in your maintenance is all your information is hearsay.

Who gave you the worn rings suggestion?

Time for a second shop opinion?
 
Domenick said:
Did the mechanics do a leak test on the induction system or just a visual?
One issue with not being involved in your maintenance is all your information is hearsay.
Who gave you the worn rings suggestion?
Time for a second shop opinion?
Click to expand...

First induction system check was a visual inspection. I was involved with that one as it was done when I changed out the CHT probes. I'm very hands on but the annual inspection was scheduled several states away as it was a condition of sale when I bought the aircraft. The worn rings was just me spitballin' as it seems a possible source of increased friction on the cylinders. The annual was the 'second opinion'.
 
Sounds like the time for an induction system pressure test.
 
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