Advice on valve adjustment on MK2

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lbmalleo

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May 9, 2020
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Montana, United States
Hi Guys,
I tried digging up info on this but couldn’t find the answer I was looking for so I apologize if the subject has been talked about already.
I upgraded an MK2 with M3 internals, got the power block, plenum and other internals. I installed everything myself, I’m from Argentina so tend to DIY everything since we don’t have any certified technicians close by, plus you learn a ton by fiddling!
Anyway, the gun is a .25 caliber, I am shooting 34 grain slugs. I currently have the gun tuned at 140Bar, shooting at 940fps. I have found the peak speed to be 960 and tuned back to 940. The problem I am having is that the valve adjustment knob is turned all the way out, any tiny little turn down on it brings down the speed considerably, from 960 down to 915-920 with a tiny little turn. I decided to back down the speed with the internal (small) hammer spring adjustor. I‘ve been getting nice groups but I still think the reg pressure is too high and I still think that the gun is not in “harmony”. I am getting peaks in speeds and very irregular shooting, plus, on some shots the sound varies.
I have a feeling I need to get the Valve adjustor to work better for me, the question is, how can I get the valve adjustment knob to work better for me? Should I increase hammer weight so the valve stays open for a longer period of time? Should I change the length of the little valve rod stem to get a different pre-load?
Luckily I have a few replacement springs and hammer weights. Any suggestions would be greatly appreciated!!
Saludos,

Lucas
 
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You forgot to mention your barrel length. Here are a few things to consider. The higher the reg setting, the faster your valve is going shut. So that makes the valve adjustment more sensitive. Where you have your C1 set influences your valve knob. But a gun is still tunable with the C1 set at 5.7mm or 6.5mm. I’ve owned 2 MKll’s with M3 internals and now three M3’s. I don’t have to move my valve knobs much to reduce velocity once I turn the knob in to where it starts to work. As far as barrel length goes, if you have a 600mm barrel your reg setting is not too high shooting those 34gr slugs. If you have a 700mm and your valve knob starts working the second you turn it when it’s backed all the way out, then you might want to add a little hammer weight.
 
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Vetmx said:
You forgot to mention your barrel length. Here are a few things to consider. The higher the reg setting, the faster your valve is going shut. So that makes the valve adjustment more sensitive. Where you have your C1 set influences your valve knob. But a gun is still tunable with the C1 set at 5.7mm or 6.5mm. I’ve owned 2 MKll’s with M3 internals and now three M3’s. I don’t have to move my valve knobs much to reduce velocity once I turn the knob in to where it starts to work. As far as barrel length goes, if you have a 600mm barrel your reg setting is not too high shooting those 34gr slugs. If you have a 700mm and your valve knob starts working the second you turn it when it’s backed all the way out, then you might want to add a little hammer weight.
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Thanks for your reply, I have a 700mm barrel. I was thinking about starting over and re-tuning everything from 0.
I bought the gun used and it’s been very difficult since I bought it, all the internals are new and I installed them but the gun is still a pain to tune properly. I have a Wildcat that I bought new and its properly tuned, very accurate and powerful.
 
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Well buying a FX used adds something to this. What you started with and were used to might not have been right from the day you received the gun. You are on the right track. You rebuilt the gun. Hopefully didn’t use any aftermarket gizmos. Now you can start your own baseline. If you just went back to your old hammer settings after installing all the new stuff, that’s not a good idea. Start over with the valve wide open and work your way up with the reg and hammer to slightly above where you want to start testing. With a single reg MKll once you find your max speed for a reg setting, clicking the wheel down 20fps is a good place to start before touching the knob. I usually went down 30fps from the regs max speed because it gave me wiggle room up and down with slugs. The gun also started sounding better before I even touched the knob.
 
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Vetmx said:
Well buying a FX used adds something to this. What you started with and were used to might not have been right from the day you received the gun. You are on the right track. You rebuilt the gun. Hopefully didn’t use any aftermarket gizmos. Now you can start your own baseline. If you just went back to your old hammer settings after installing all the new stuff, that’s not a good idea. Start over with the valve wide open and work your way up with the reg and hammer to slightly above where you want to start testing. With a single reg MKll once you find your max speed for a reg setting, clicking the wheel down 20fps is a good place to start before touching the knob. I usually went down 30fps from the regs max speed because it gave me wiggle room up and down with slugs. The gun also started sounding better before I even touched the knob.
Click to expand...
Thanks so much, this is just what I needed, a step to step procedure! I‘m often hesitant and don’t know where to start and when to finish!
 
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I re-tuned yesterday afternoon, tried the things that you guys suggested. I ended up with a regular gun but around 10 fps slower than my target speed and the valve adjustment is still way too sensitive, with the tiniest of adjustment is goes down 25 fps. What I find most frustrating is that I can never go back to finding the spot or setting that I had previously. Yesterday for example I found a setting that gave me good results at 930fps but my target speed was 940-945 so I decided to touch the valve adjustment knob to try to get it up to speed and it screwed everything up, tried to go back to the 930 setting and never got it back as consistent. I then realized that I should have played with the hammer spring setting first, well, lesson learned.
I’ll try again today and keep you guys posted. I feel like I’m closer now but still find the valve adjustment knob to be way too sensitive.
Thanks to everyone once again,

Lucas
 
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I had also upgraded the MK2 to M3 Power Block Kit (new power block + larger plenum + larger valve housing), I did some misstakes also with heavier hammer weight but ones back to stock weight the picture got cleaner. the kit valve spring is way too stiff, get back to the original MK2 valve spring - or lighter is better ... but watch for no over travel depend where the C1 is set.
 
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Like others have said, there is nothing wrong with using your original MKll valve spring. It’s a good spring. Unlike the spring that comes in the slug kit, it belongs in a ballpoint pen. As far as target speeds go, here are my thoughts. If you are trying to get back to the 940’s because your gun was super accurate there, that’s fine. That’s a good place to start. But with new components, that might change. That’s the problem with Impact guys and why most owners spend their whole ownership chasing instead of enjoying a dialed in gun. They just keep changing components that wind up changing everything. You probably should just do what’s necessary with slugs since you made such big changes. Start from scratch. Guys hate it, they want short cuts but when you start from scratch and take notes, you learn.
 
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Even with my M3’s, I start at the bottom of the speed and reg spectrum and work my way up in speed and reg setting as I test. Here’s why. These are just random numbers for conversation sake. I back the little hammer screw way out then set the wheel on Max. I set the reg to 130b. Using pellets, I turn the little screw, or micro on a M3 as I shoot across the chronograph until I hit my peak speed for 130b. I’m using pellets and not wasting slugs at this point because all I want to establish is a true baseline. With a 700mm barrel you might want to establish that baseline at 120b. Once you hit the peak speed for a low reg setting, you measure your hammer setting with calipers, I hope you know how to do that, on a M3 I just look at the number and now you have the numbers you need if you ever have to start over without having to go way back to the beginning. Now you shoot a slug or two. If your gun isn’t fast enough at 120 or 130b, your baseline, all you do is bump the reg up and start turning the little screw again until you hit the peak speed for your new reg setting. Fire a slug or two. Now you see a speed that’s a slug speed range you want to try. Remember, your wheel has been set on max this whole time so you can now click it down to shave some FPS. Now I start shooting targets over a chronograph and shave speed with the valve knob. If I don’t find accuracy by the time I’ve shaved off another 20fps with the knob I stop. And here’s the important part of my process and why I establish my max reg speed always at max on my hammer/power wheel. I open the valve all the way open again then reset my wheel to max. I bump up the reg and find my new max speed with the little screw or micro on a M3. Method to my madness? If you work your way up tuning and always have max on your wheel as the max speed for your previous reg setting, you won’t ever get lost. And if you do get lost you have the measurements from your baseline when you started from scratch and know they are truly accurate settings for the max speed at that reg setting. You don’t have to waste slugs every time you bump your reg up. You can find your peak speed with a heavy pellet. Another thing you can’t forget throughout this whole BS slug testing thing is barrel cleaning. Then you have to season it with a couple shots and continue testing. It’s a PITA and that’s why a lot of guys fail.
 
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Vetmx said:
Like others have said, there is nothing wrong with using your original MKll valve spring. It’s a good spring. Unlike the spring that comes in the slug kit, it belongs in a ballpoint pen. As far as target speeds go, here are my thoughts. If you are trying to get back to the 940’s because your gun was super accurate there, that’s fine. That’s a good place to start. But with new components, that might change. That’s the problem with Impact guys and why most owners spend their whole ownership chasing instead of enjoying a dialed in gun. They just keep changing components that wind up changing everything. You probably should just do what’s necessary with slugs since you made such big changes. Start from scratch. Guys hate it, they want short cuts but when you start from scratch and take notes, you learn.
Click to expand...
Thanks for you reply. I am chasing 940 fps because that was the speed at which the slugs I’m using were the most accurate!
I bought the gun used from one of the members here and the gun was messed with on the inside and I was in a way forced to upgrade. In a way, the challenge of taking apart the whole gun and feeling terrified doing so is great, haha!! As I mentioned before, I live in Patagonia, Argentina and have no tech anywhere near me so I was forced to do everything on my own! Learned a lot!
I also love tinkering, I know I’m close to leaving the gun in “harmony” and I’m very thankful for those who have helped me out with advice!!
Mil gracias,
Lucas
 
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