What is a symptom of a bad or failing check valve? I have never replaced one, I don't like to remove welch plugs because I always think i will ruin something...
I have so many of these MDC carbs now I'm paranoid about these check valves
McCulloch Mini and Small CC Chainsaw's
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What is a symptom of a bad or failing check valve? I have never replaced one, I don't like to remove welch plugs because I always think i will ruin something...
I have so many of these MDC carbs now I'm paranoid about these check valves
A common sign of a faulty valve, is the carb’s severe inability to hold an adjustment. No matter what you do, you’ll always have to go back and adjust it again. Other signs are that it’ll idle erratically, accelerate poorly or just outright stall.
Of course you’ll have to do some diagnostics to rule out other issues first- like an air leak or some other carb issue.
But if it still has trouble even after all things have been run through and the needles are (re)adjusted, the valve will more than likely
be the issue.
The Power Mac 6 service manual has a pretty good rundown on the MDC. But most checklists tend to skimp on the details on when a check valve is failing. (zama comes to mind)
Here is a different and a bit more detailed amalgamation checklist. You can see the valve come up as a cause for several problems.
This is awesome, thank you for sharing
Great info, thanks!
So it sounds like if the saw is running reasonably ok, the check valve is probably working?
More than likely. Although, it really depends on what your definition of "reasonably ok" is.
Just take note on how it runs: Does it idle steady? Does it have good throttle response? Does it load up or lean out? Basic stuff like that. For most of the things I work on, I usually let it sit and idle for 5 minutes. If it can idle for that long and no problems surface; it's probably ready to go.
I like to think the telltale sign of a good running mini mac, is the circular "happy dance" it does on the bench.
Alright, I've finally got around to posting about how I replaced the rubberized check valve with a homemade teflon one. I used a slightly modified leather punch to cut out the valve to size, and then cleaned up the edges with a razor blade.
I reassembled it and it passed the high tech sucky straw test... so far, so good. After start up it ran a bit rich at first (set it that way for peace of mind), but after some fine tuning, it idles perfectly, doesn’t act odd and has great throttle response.
After a few test cuts and running it kinda hard at times, it runs like a Mac should. But the SOUND! Dear God The Sound!!!
The neighbors are still giving me looks. After some more testing over a period of time, I'm very happy with how it performs.
I’ll seldom use the saw, so I expect the valve to last for quite some time. If I do run into any trouble, or it fails in any way (which I doubt) I will give an update.
To all those who gave me tips and ideas along the way - Thank you.
M
I reassembled it and it passed the high tech sucky straw test... so far, so good. After start up it ran a bit rich at first (set it that way for peace of mind), but after some fine tuning, it idles perfectly, doesn’t act odd and has great throttle response.
After a few test cuts and running it kinda hard at times, it runs like a Mac should. But the SOUND! Dear God The Sound!!!
The neighbors are still giving me looks. After some more testing over a period of time, I'm very happy with how it performs.
I’ll seldom use the saw, so I expect the valve to last for quite some time. If I do run into any trouble, or it fails in any way (which I doubt) I will give an update.
To all those who gave me tips and ideas along the way - Thank you.
M
Anybody have a lead on a Zama M1-M7 carb? Got a good running Eager Beaverfor my son to learn on but carb is trashed. Long story, but I know saw runs good so I'm willing to put a carb on it but cant find anything. Hoping someone in this thread may have a lead on one.
Thanks.
Thanks.
So I unmangled the carb on the mini and it runs pretty good for what it is. However I've run in to a rather nasty little problem. When the saw is running and I look down by the carb thru the cutout for the mixing screws there's a lot of sparking going on in there. It's bad enough that when I went to adjust the idle and my hand brushed up against the wrap around bar I get lifted.
I didnt see anything that stood out so I'm hoping somebody here has some suggestions before I tear the saw down again?
Thanks.
I didnt see anything that stood out so I'm hoping somebody here has some suggestions before I tear the saw down again?
Thanks.
There is something deeply wrong here. Sparking? Does it sound/feel like there is anything grinding or contacting something in there? You "get lifted"... like shocked? Does it fire kinda hit and miss or stalls and is hard to restart? There is no other option but to take it back apart and check it again.
If you rule out the grinding theory, the only thing I can think of that would even come close to what you're describing is a bald spot(s) on a wire like the coil lead, and it's arcing off something close by. Check the coil lead for any wear and your wires too.
Did you set the air gap correctly for the coil when you put it back together? I wonder if the flywheel is contacting the coil laminations.
If you're getting shocked, the plug wire is arcing to ground. The insulation doesn't necessarily need to be gone for this to happen. A thin spot that has been rubbing for a long time or a crack will likely be found in the vicinity of your sparks. Once corrected, you'll also likely find that it runs a lot better "for what it is"!
Those mini Macs are packed so tightly, lots of rubbing on the plug wire, fuel line, and that primary coil wire coming from the points. I've had at least 1 where the coil wire was rubbing on the flywheel and was bare metal strands on the flywheel! I use strategically placed electrical tape to help with the rubbing.
The stop switch is right there, could be something amiss...
Mark
Mark
Nothing grinding. Not a bad shock, but enough to get your attention. Starts easy, never misses a beat even when I get zapped. I thought coil lead, but I dont think lead is in that area.
Air gar is .018" give or take a .001"
Pull it over in the dark and you may be able to isolate the arcing.
Could be plug wire, but it never misses a beat. I only got shocked when I tried adjusting idle and back of hand brushed against wrap. Also noticed one time when I adjusted the high needle and my screwdriver got close to the case when on the high needle I saw a few sparks.
At least it would seem like you don't have any fuel leaks!
I have had all kinds of issues with Mini Macs but never been zapped! It's such a basic ignition system, I bet when he tears it down he'll find a spot on the primary coil wire that rubbed through and is touching the chassis.
The bizarre thing is that it doesn't misfire, any time I've been dumb enough to introduce my body into the ignition system of a simple engine, I instantly start to do the jitterbug, and the engine stops firing!
The bizarre thing is that it doesn't misfire, any time I've been dumb enough to introduce my body into the ignition system of a simple engine, I instantly start to do the jitterbug, and the engine stops firing!
