The suction on the Kirby Ultimate g is very weak

make sure it has a clean bag and not clogged up

Generation 5, 1996-99
Generation 6, 1999-01
Ultimate G , 2002-05
Ultimate G Diamond , 2005-06
Sentria, 2006 to present

1935 KIRBY Model R*
19?? KIRBY Model 2R
19?? KIRBY Model 3R
19?? KIRBY Model 4R
19?? KIRBY Model C
1939 KIRBY Model 2C
19?? KIRBY Model 3C
19?? KIRBY Model 4C
Model 505 - 1945
Model 508 - 1948
Model 509 - 1949
Model 510 - 1950
Model 511 - 1951
Model 512 - 1952
Model 513 - 1953
Model 514 - 1954
Model 515 - 1955
Model 516 - 1956
Model 517 - 1957
Model 518 - 1958
Model 519 – 1959
Model 560 - 1960
Model 561 - 1961
Model 562 - 1962
1963/64 Sanitronic VII (Sirocco)
1965-67 Dual Sanitronic 50 (Sirocco)
1967-70 Dual Sanitronic 80 (Avocado green)
1967-70 Dual Sanitronic 80 (Avocado green)
1970-73 Classic 1CR (Medium brown, gold bag)
1973-76 Classic Omega 1CB (Dark brown, dark brown pinstriped bag)
1976-79 Classic III 2CB (Candy-apple red, plaid bag)
1979-81 Tradition (Dark blue; intro of paper bag)
1981-84 Heritage (Gray/orange)
1984-89 Heritage II Legend (Charcoal/gray/red)
1989-90 Legend II (Dark rose-pink)
1990-93 Generation 3 (Alabaster)
1993-96 Generation 4 (Medium gray)
1996-99 Generation 5 (Maroon)
1999-01 Generation 6 (Black/Yellow)
2002-05 Kirby Ultimate G
2005-06 Kirby Ultimate G Diamond

http://www.vacuumwizard.com/history-of-kirby-vacuum-cleaners.html

The years each were made/sold are as follows:
Generation 3, 1990-93
Generation 4, 1993-96
Generation 5, 1996-99
Generation 6, 1999-01
Ultimate G , 2002-05
Ultimate G Diamond , 2005-06
Sentria, 2006 to present

An Ultimate G has lots of suction. If you turn on your vacuum and the bag immediately inflates - that is how you can tell if your Kirby is moving air (suction). There is a more modern brush that came out with the Ultimate G Diamond and the Sentria that has stiffer bristles that dig up pet hair better.

Another way to test the suction is to spread some baking soda onto a hard floor and vacuum it up - you can see how much suction your Ultimate G has, or take off the vacuum head and put on a hose and test the suction at the end of the tube.

Ways to increase your Ultimate G cleaning efficiency. Take off the vacuum head and remove the brush roller. Attach your hose attachment and **** vacuum out the head. Put on a new belt, and remove any hair and or string or threads that may be wrapped around the brush roller. Put the roller back on and on the ends of your roller you will see that the ends spin and have numbers on them. If your vacuum brushroll is original - you could have your bristles rather worn and so you can align the #3 on BOTH sides of the brushroller. This would be a good time to consider upgrading to the Sentria Brush.
Remove the bag, and replace with the CLOTH Kirby bag. It has the best filtration and it has the best airflow (which increases what you are referring to as suction). If you want to go the cheap route - at least get the paper Micron Magic with HEPA filtration (but it has slightly less air flow)
Remove the side mini emptor from the vacuum and check to see if there is anything clogged up on either the vacuum or the mini-emptor.
If your engine is running and inflating the bag and you replace the belt, the brush roller and to the cloth dust bag - your vacuum should pretty much run like a brand new Sentria Vacuum. Your vacuum system is outstanding, but may benefit from a little TLC if you have been neglecting it.

check the belt. this is a strong vaccume and even without the belt it will still have a decent amount of suction. If the belt is not tight or intact it can let the motor turn faster which will sound louder. other than that check all the hoses for holes and blockage, be very picky.( look deep and everyware!
good luck
~John

Take a look at the help article here. If bristles are worn you may need to install the brush roll in a different position (details HERE) or purchase a new brush roll.

Good Luck
Rocky
:-)

change your belt, if there is suction from the hose, and you cant see any blockages in the area where the brush roll is then you need to change the belt, even if it isnt broken. putting your hand over the nozzle to feel the suction is not the way to tell if it has suction.

you have to make sure the green light is on.. in the corner .. and if it is that means its working properly. If you have no suction then it is usually the belt and or the bag. so make sure your bag is not full , make sure everything is attatched properly and the green light is on.... The Kirby is the best vac out there and little suction should never be a issue for us.. I am a proud owner of the sentria..Love it..

when you install the hose connector it trips a switch that switches the vac motor into high speed because the vac path is longer using the hose. check the belt after you remove the front. make sure the direction of rotation is in the direction of belt travel stamped in the impeller. try adjusting the head height