I HAVE to be doing something wrong....please help!
Aren't you still having some cool weather up there? Ambient temps do hinder higher smoker temps. One thing you can do, if you have a water pan, is to use Playbox Sand (Lowes, Wal-Mart) in the water pan instead. Cover it with a piece of foil to catch the spatters. It will give you a higher and more constant temperature. Make sure you have good air flow also. You may be choking off your fire.
Brother, I've never used one of those units, and i dont know what the weather is where you are, but to bang that temp up it's hard to beat opening her up a little, and throwin' on some more coal.....
Are you starting with a full ring of unlit charcoal, then dump 1 FULLY lit chimney in the middle of that? All vents 100% open? HOT water in the pan? If the weather is under 40° either leave the pan dry or only fill it half way. Is it sitting in a windy area? Wind is a killer for almost all smokers.
Tell us your step-by-step set up and we will see what suggestions we can offer.
We need more info. Are the vents open fully? Do you have a good therm at grate level? What is the outside temp & wind conditions? Is the ash pan clean?
There are quite a few of us with WSM's on here & I don't know of anyone who can't get theirs up over 300 degrees.
My first thought was why do you want it over 225°? But that is your business and not mine. ;)
Remember that water in the pan will start to boil at 212° F and will tend to moderate temperature. I leave water out when I'm doing something like turkey or chicken that does not benefit from a long slow smoke.
Ordinarily I leave the top vent wide open all the time and use the bottom vents to control temperature. Closing them a bit will reduce air to the fire and take temps down. For that reason I found temp hard to keep down on windy days. The wind caused extra air infiltration and resulted in higher temps.
Did you say lighter fluid? I never ever use fluid for lighting charcoal for fear a residue will taint the meat. I use a charcoal chimney with some paper. My son uses a propane flame thrower they sell at Harbor Freight. Either works well.
I use a Maverick thermometer to monitor temps with the cooker temp measured about top grill level. When the meat first goes on, the factory thermometer in the dome reads a lot lower - sometimes by as much as 50° F.
It took me a while to get the hang of good temperature control. Don't be discouraged if you don't get perfect results the first time. It's a skill and the effort you take to learn will be very well rewarded in the results you will achieve!
Edit: You can check the thermometer by putting it in some boiling water. Just don't heat the water in a microwave. It can superheat and boil explosively when the thermometer touches the water. Rather a rude surprise!