Hey folks. I bought a PSI gauge to see if my unloader needed to be adjusted because I wasn’t getting the power I expected, especially when doing concrete. Used my green tip since I have a 4 gpm unit and was only registering 1200psi. Messed with the unloader and it would bog and kill the motor at the 3500 mark. I settled at 2000psi because my motor would actually run without bogging. How much psi can I expect in comparison to manufacturer specs? I have a Honda gx390 and a comet 4000psi pump. Thanks in advance, I’m still trying to get everything dialed in. I didn’t know if it worked like horsepower on a car and X% was lost through the drivetrain 
G’day Al
What size is your “green” tip?
Does the engine have a rev counter?
At 4 gpm a #4 tip will create 4000 psi of pressure
while a #5 is 2500 psi and #6.5 is 1500 psi. These are from a “nozzle capacity chart” and are “theoretical”, reality will depend on the friction/power loss from the hose - longer & smaller diameter will restrict flow and therefore pressure.
The motor shouldn’t bog & die. Is it running well - clean air filter, fresh fuel etc?
Is the unloader ok? they often need cleaning and greasing (with water based silicone grease)
Thanks for the reply. Unfortunately no rev counter, but the motor runs great. It only bogs when my psi gauge reaches 2500+ and the trigger is squeezed. It’ll run wide open with the psi gauge at 3500 but as soon as I pull the trigger is bogs and dies. Could it be a water supply issue? Getting choked out with no water at the higher psi? I mostly do soft washing, which its perfect for but in need to be able to clean driveways for add on services. I tried it with several different tips. Red, green, yellow. They all seemed to make the engine bog at 2400. The motor has fresh gas and the air filter looks good. My next step in trouble shooting is increasing the diameter of the hose that goes into my inlet and setting up my unloader bypass. Then changing the spark plug. I honestly had no idea the unloader had to be greased so I’ll try to look up how to do that. Honestly, I bet my problem is in the unloader somehow. I bought the unit used. It had a wacky set up for mobile car detailing. I redid it all. It also came with a “messed up” AR pump that I’m going to have rebuilt. It is currently running a comet pump.
If it will run on bypass (the internal spring sets the pressure that is held & triggers the bypass) but not on external flow it could only be the unloader - does it bypass back to the header tank or return to the water inlet? Check the hoses & connectors are all flowing freely.
Unloaders can be dis-assembled (get a parts diagram from the manufacturers website) - there are o-rings that need to be in good condition and lubed, plus small passages that can be blocked with debris. If that fails to get it running, unloaders are cheap.
Thanks, I Will definitely look into that. It’ll flow just not what I expected or need. It puts out 2400 psi on the dot. What should I be trying to get out of this 4 gpm/4000 psi pump is my main question? Like the weekend for instance. I’m washing a pretty good house and the owner asked about doing the driveway as well. It would be great to add another $100 to the job, but my output would make it take way longer than I’d like to do the driveway. I don’t have a surface cleaner yet either. I will end up doing the driveway and losing time because I don’t want him to call someone else.
