Small but terrible

[Escape08]

I have currently 2 mowers one with a bag, one without (side discharge)

My question is why is it the smaller 148cc (oiled-foam filter) consume more gas than the 190cc (paper air filter)? I de-carbonized both with same result. Both are B&S flatheads. Annually I cleaned both air filters, if necessary, replaced for a new one.

The small 148cc B&S on the left and 190cc B&S on the right.

 

[supton]

Same style of carb? I wonder if the bigger engine has a better carb and simply runs leaner.

 

[Escape08]

Same style of carb? I wonder if the bigger engine has a better carb and simply runs leaner.

Yes, same style carb and gas tank

 

[Brian123]

Flat Head Engine Old Style

OHV Engine New Style

 

[fantastic]

Same style of carb? I wonder if the bigger engine has a better carb and simply runs leaner.

That's right... Emissions compliance. Otherwise I would question if the older one's carb was tampered with.

 

[wag123]

Yes, same style carb and gas tank

Negative.
The two engines use completely different carburetion systems.
The smaller 148cc engine has a Pulsa Prime carburetor which only has one fuel circuit that covers the entire RPM/load range. It is cheap and crude but it works. The larger 190cc Quantum engine uses a more sophisticated float bowl type carburetor that has two fuel circuits, one for high RPM/load operation and one for low RPM/load operation, each of which is optimized for the engine's respective fuel needs at any given RPM/load and as lean as possible across the range. Additionally, the Quantum engines were designed from the start for lower emissions and fuel use.

 

[Escape08]

Negative.
The two engines use completely different carburetion systems.
The smaller 148cc engine has a Pulsa Prime carburetor which only has one fuel circuit that covers the entire RPM/load range. It is cheap and crude but it works. The larger 190cc Quantum engine uses a more sophisticated float bowl type carburetor that has two fuel circuits, one for high RPM/load operation and one for low RPM/load operation, each of which being optimized for the engine's respective fuel needs. Additionally, the Quantum engines were designed from the start for lower emissions and fuel use.

Wow, so I think this maybe the answer. Out of curiosity I took off the air filter box of the 190cc and sure enough compared to the other one is so much different. I was wrong, all along. I had never had taken out both carbs for a clean-up. I thought the only advantage of the 190cc is that it has an advanced no prime mechanism at start-up and more plastic cover for aesthetic look.

 

[mk378]

Also the gas tank on the Quantum is larger. If you're comparing how much you can mow with one tank it's not going to be close.

 

[350Rocket]

I have to half fill my quantum as the gas tank cracked at the seam. It also seems to run at a slightly lower speed than my previous 3hp 1981 Briggs. Pretty sure the old one used a full tank in around the same time as the newer (1999) does a half tank.
My quantum carb has a primer though while the old one was automatic choke.