Watching AFR - heat soak fluctuations
 

Probably too much data.

Ran the boat yesterday. I made some changes to jetting and power valves. Still trying to get it dialed in but things are in much better shape now. The fuel curve is now pretty flat and I’m now focusing on the transition circuit to get things ironed out - the carburetors were extremely rich after dropping the emulsion and MAB. Current jetting is 86/93 with a 070 pvcr and 8.5 pv. Still adjusting but much much better especially above 3k.

Interesting observation though… I ran the boat a pretty much all day and noticed that after sitting, engine off and hatch closed, that the readings were much leaner. Eventually, they’d come back down but at times I was seeing readings in the upper 13s. Without the gauge you’d never know this was happening - I know that as temperature increases that more fuel is needed to maintain the proper ratio but wasn’t really thinking about until I saw it on the gauge.

In fuel injection systems, the IAT is monitored and with the output of the O2, the ECU compensates to keep the a/f constant. How do you compensate with the carburetor? If someone didn’t have this data, most probably wouldn’t even consider this.

They did an Engine Masters on this.
When the fuel gets warm its less dense, remember the old Moroso "cool cans" that had a coil of tubing in a can? You were supposed to put ice in the can to keep the fuel cool and make more power.
They actually proved that it works, if you used a bypass fuel pressure regulator it would help cool the fuel bowls more rapidly and supply cooler fuel after sitting.

Right. Cool Can, icing the manifold, etc.

I’d think that the fuel coming out of the tank would help this, but with the engine room closed and radiant heat, it would take a lot of fuel running everything to cool it down.

Was an interesting observation.

Lean condition can also be missfires.

I put a fuel cooler on the return side of my fuel system on the cig.
The Supercat engines also had the same thing .. I thought I was special but AETCO has been doing this for years he told me . Now I dont feel so special lol