Looks like the neoprene all melted away from the nylon backing.
Mark
Mark
McCulloch Mini and Small CC Chainsaw's
- Thread starter Overtrained
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I thought for sure it must have been "replaced" with whatever someone had lying around. It sounds like this could be the remains of the original check valve?
I have a few options to try making a new one: (unused Walbro diaphragms)
I do have a genuine Walbro check valve kit, but I want to see if I can make one (for science).
I have a few options to try making a new one: (unused Walbro diaphragms)
I do have a genuine Walbro check valve kit, but I want to see if I can make one (for science).
Just curious..., Aren't they more of a 'fabric' type material like a metering diaphragm vs. the rubber/plastic/mylar/teflon pump diaphragm material?
And don't forget about using a .22 casing as a hole punch in a pinch!
And don't forget about using a .22 casing as a hole punch in a pinch!
I have a number of the original kits and most are the neoprene coated fabric. There are a few that look more like the Teflon diaphragm material. I have seen a few come apart that I believe to have been the rubber covered fabric that most of rubber was gone.
Mark
Mark
I think I should be saying "nitrile" rather than "neoprene".
Mark
Mark
I have to examine the new Walbro check valve disc that I have, it's obviously tiny but appears similar to what Mark is describing. Whatever came out of my carb was badly deteriorated, it didn't look like the welch plug had ever been removed.
I don't know how critical the material is, I think Manic84 used teflon and it worked. I'd really like to find a cheap source of material since that Walbro check valve kit is running around $11!! for a tiny piece of material and the brass insert.
I don't know how critical the material is, I think Manic84 used teflon and it worked. I'd really like to find a cheap source of material since that Walbro check valve kit is running around $11!! for a tiny piece of material and the brass insert.
Did some science today fellas.... in my opinion a nitrile pumper diaphragm is the closest material to an OEM walbro check valve.
Walbro metering diaphragm is .15mm thick:
Walbro pumper diaphragm is .2mm thick:
OEM check valve disc is also .2mm:
Making a disc from the pumper diaphragm:
Side by side... I think this is gold:
Walbro metering diaphragm is .15mm thick:
Walbro pumper diaphragm is .2mm thick:
OEM check valve disc is also .2mm:
Making a disc from the pumper diaphragm:
Side by side... I think this is gold:
Have you guys examined the check valves in some of the other kits for compatibility/usefulness? Normally includes the retaining ring as well. Can usually find them for 6 ~ 8 bux on the bay. 'Course making your own is obviously the way to go if that approach is as easy as it would appear.
I have not seen or found any MDC K-1 rebuild kits that include the actual "rubber" check valve disc. At least one K1 kit that I bought did include the tiny round metal screen and retaining clip, but not the disc.
The only kit I know of that comes with the brass insert and rubber disc is the genuine Walbro kit (Check valve Walbro 86-523 kit) which cost me over $11.
Like you suggested, it appears that I can make the rubber disc for pennies on the dollar from pumper diaphragms and the punch comparer to the Walbro kit.
The only thing I have to decide is whether to put this saw back together with the Walbro check valve or my homemade one to see what happens.
Also...what is the best thing to use to install the new welch plug? It looks like the center is naturally indented in the process...
I am very interested to know how you go about replacing the check valve if you do not remove the brass retainer, or if you remove the retainer how do you get it out without damage?
Mark
Mark
Several previous discussions with Manic84 on servicing these check valves, he explained that he frequently was able to very carefully fish a new check valve into place without removing the brass retainer using a probe. (I'm thinking a magnifying glass and a steady hand help as well.)
This is all uncharted territory for me, and this particular Mini Mac 25 which is in otherwise immaculate condition but ran horribly has forced my hand to try replacing a check valve. If I can pull it off without removing the retainer, it will certainly help. It would also make it possible to make my own check valves out of surplus diaphragms and replace them without purchasing any other components.
This is all uncharted territory for me, and this particular Mini Mac 25 which is in otherwise immaculate condition but ran horribly has forced my hand to try replacing a check valve. If I can pull it off without removing the retainer, it will certainly help. It would also make it possible to make my own check valves out of surplus diaphragms and replace them without purchasing any other components.
The next question is can the brass retainer somehow be fashioned out of common materials...
Well...today was quite eye-opening. I decided to try installing a new check valve without removing the brass retainer.
After about 15 minutes of trying I was about to come back and say that it was impossible and that Manic84 had been jerking our chain...but I kept at it, and I was absolutely able to get a new check valve into place.
It took some patience and careful use of a very small probe, but I was finally able to get the disc into place. I tested the valve with a small piece of tygon fuel line and it worked splendidly. I can blow air into the throttle body but it shuts and doesn't let air into the high speed fuel circuit. I actually used one of my homemade check valves that punched out from a Walbro diaphragm.
Total materials to replace the check valve (not including tools) is a spare diaphragm and one stens welch plug.
New check valve installed and the brass retainer undisturbed:
After about 15 minutes of trying I was about to come back and say that it was impossible and that Manic84 had been jerking our chain...but I kept at it, and I was absolutely able to get a new check valve into place.
It took some patience and careful use of a very small probe, but I was finally able to get the disc into place. I tested the valve with a small piece of tygon fuel line and it worked splendidly. I can blow air into the throttle body but it shuts and doesn't let air into the high speed fuel circuit. I actually used one of my homemade check valves that punched out from a Walbro diaphragm.
Total materials to replace the check valve (not including tools) is a spare diaphragm and one stens welch plug.
New check valve installed and the brass retainer undisturbed:
Well done. Is there not a retaining snap ring somewhere in the mix, or am I thinking of a completely different carb and check valve?
I didn't install the screen and retaining clip yet, I wanted a pic of just the disc in place in the original retainer. You are correct!
Thanks, I will try that soon as I have a MM25 and PM6 laying in wait here now.
Mark
Mark
Here's the welch plug installed after I installed the screen and retaining clip. I'm pretty happy with how this went, previously I was too intimidated with removing welch plugs but now that I've done it, it's not bad at all. I also realize how many tuning issues I've probably fought because of deteriorated check valves. Not to mention how many times I've blasted compressed air through those circuits not realizing there was a tiny rubbery disc in there....
MM25 goes back together today, for the 4th time. If it still runs awful it might get cannibalized for parts....
MM25 goes back together today, for the 4th time. If it still runs awful it might get cannibalized for parts....
Outstanding effort. I just hope that carb is actually cleaner than it looks (inside and out) and its appearance is due to impregnated age stains or discoloration from exposure to any number of popular cleaning agents known to discolor such alloys. I can't imagine it being dirty after all you've put into it. LOL
Frankly, I'm putting my money on the saw firing right up and running great.
Frankly, I'm putting my money on the saw firing right up and running great.
Well...I'm stumped. It started after about 10 pulls, at first I thought it was perfect. Then it's the SAME symptoms as when I first assembled it, will not smooth out on top. At this point I'm doubting it's a carb issue at all. Carb adjustments will not eliminate the stutter, I can go rich until it starts to load up or lean until it starts to lose rpms. Here's a video, this is pretty much exactly how it ran before I adjusted the metering lever and then even before replacing the check valve. It's like my spark is cutting in and out when I rev it???
Honestly my next step is the process of elimination. I have other mini macs to fix, I'm going to swap carbs and see if I have an ignition issue. Argh.
Pogo: you could eat off that carb, its been scrubbed and been through the ultrasonic cleaner, its just discolored.
Honestly my next step is the process of elimination. I have other mini macs to fix, I'm going to swap carbs and see if I have an ignition issue. Argh.
Pogo: you could eat off that carb, its been scrubbed and been through the ultrasonic cleaner, its just discolored.
Sounds like the timing is seriously delayed. I'd start looking at the ignition.
