Bonneville America Forums Forums Technical Forums General Tech AFR Numbers Too Far Apart

Did a compression test on my 2007 America.
Each cylinder reads 125 psi after 3 compression strokes(85 degrees).
Does this number sound correct,,,high,,,,,low?

In addition, I did a leak down test.
I can hear a small amount of air going pass the rings.
Web info says a small amount can be normal. I was just listening for sound, not any number gathering.

Hope you're wondering why I did the above tests,,,,,,,,,,,,,,,,,,,,,,,

I have AFR Sensors on each header to monitor each cylinder(da).
My results are:
13.2 Left
11.2 Right.
Numbers are the same at 2500 and 6000 rpm or any throttle position.

Why are these numbers so far off? A couple of tenths, maybe. Not two whole numbers.

All adjustments on the carburetors(FCR 39), left and right are matching.
Needles, clip position, air and fuel jet settings are the same.
Air Box gone. Foam Filters. Air Inject gone.
D & D Megaphone Silencers(loudest pipes I've ever owned).

Anyone run into this?
Any ideas?

Test on a warm or cold motor?
Throttle open or closed?
Did you try swapping the O2 sensors?

cold motor 85 degrees F
closed throttle
swapped sensors-yes

Have you swapped the sensors?

Open the throttles when performing a compression test. You can't get a good compression reading with them closed.

Try testing them dry then inject a bit of oil in each cylinder to see how much the compression goes up. Big difference can mean ring wear but these engines are usually bulletproof. How many miles on the engine?

Just because all the settings are the same between carbs doesn't mean they really are. If the difference is at idle, adjust your idle mixture to make them the same. Not sure how that is done on the FCRs but it should be adjustable.

Compression Test Update:

Now with Throttle wide open- Both cylinders read 200 psi dry and 200 psi wet.

Bike has 6200 Miles on'r.

Flip-flopped O2 Sensors. No change.

AFR Gap of 2(13.2 and 11.2)is still present at any throttle position or rpm. It's not the sensors.

On a Leak Down Test with oil: Zero pressure drop, zero leaks.


Thanks everybody for your input. Past present and future.


Les

I suggest doing compression tests on a warm motor, if possible.

No explanation for the lateral AFR difference.

Try swapping your pod filters to see if your figures change.

Can you swap the leads since the sensors appear to be giving constant results? Just to eliminate anything else so you can concentrate on the intakes.

Then I think you just have to examine the carbs from float levels to air screw adjustment and see what's slightly different.

How long since the last valve adjustment?

Could be a vacuum leak too.

Hey thanks,,,,,,,,,,,,,,,,,,,,,,i WILL check out those ideas.

I remember seeing something about a gasket or seal installed incorrect(with pic's) on the FCR's from the factory,,,,,,

anyone remember that?