Peculiar Carburetor Issue(s)

[heimannm]

I work on a lot of different saws, most are just inexpensive homeowner type saws but none the less, I do have some practical experience. I am quite familiar with setting the metering lever to the proper height, and how to "tweak" it a little if need be depending on the conditions; for example on a fixed jet carburetor you can set them just a bit lower than book value to reduce the typical over rich high speed setting.

I have run into this peculiar situation from time to time and wanted to know if anyone else has had this experience. The latest project was a Mini Mac with the Zama carburetor. I set the metering lever correctly, put the saw together and it would not pull fuel, it would run on a prime. Pulled it all apart (the only way to access the carburetor on the MM) and reset the lever, put it all back together and the saw ran as well as a Mini Mac can. Set it down to work on something else for a bit and tried to run it again...now it was badly flooded. Pulled the spark plug and left it set overnight.

Next day it was clear that fuel was leaking into the crankcase so I took it all apart again and this time the metering lever was bent way up causing the flooding. Reset the lever again, and the saw worked just as it should.

Can anyone help me understand how that metering lever is getting bent and out of adjustment when the carburetor is fully assembled. I don't recall this ever happening with an SDC that has a fork on both ends (diaphragm and needle) but I can't say for a fact it never happens.

Thanks for your input.

Mark

 

[Woodslasher]

Something something Mini Mac something something

Well that's the issue right there! All joking aside, I seem to recall someone (@Manic84 or @MacAttack ?) having a similar issue with a MM but I can't remember what the fix was.

 

[grizz55chev]

Well that's the issue right there! All joking aside, I seem to recall someone (@Manic84 or @MacAttack ?) having a similar issue with a MM but I can't remember what the fix was.

You need the patience of a Saint to work on them, in my humble opinion.

 

[a. palmer jr.]

I've had similar experiences with the little Homelite XL saws, got two right now that I've taken apart, rebuilt carbs, fuel lines, etc. and still they don't run as they should. One, an XL2 only has the one adjustment screw, runs good high speed for a while but can't get it to idle right! After a while it dies and is hard to start. I've given up on them for now, it's about 100 degrees in the shop..

 

[heimannm]

Nobody else has had this happen?

 

[Woodslasher]

Nobody else has had this happen?

I've had poorly set metering levers, factory mis-set metering levers, metering levers that magically came unhooked from the diaphragm (or so I'll claim), but I've never seen a self adjusting metering lever. Just for curiosity's sake, you do know to "cycle" the metering lever a bunch after you set it to make sure it's actually set correctly, right? If you don't do that it'll look like it's set right but it moves up and down a few times it'll wind up being a little higher than it should be.

 

[fossil]

Nobody else has had this happen?

Very odd. Looking forward to a possible cause.

 

[a. palmer jr.]

Very odd. Looking forward to a possible cause.

You're saying that the inlet lever bent itself while it was running?

 

[heimannm]

Dan - yes, I am very careful to work the lever multiple times and recheck it, I know that they do sometimes settle a little after you cycle them a few times.

apj - that is exactly what happened, first it flattened out to the point there was no fuel movement, then it went way in the other direction causing it to flood badly.

I do know how critical it is to get the metering lever set correctly and I am particularly careful when working on the Mini Mac series since it is a lot of effort if you have to pull one back apart to service the carburetor again.

I know it is very strange to have them move but since this is not the first time I've had the experience I wanted to know if others have run into the same thing.

Mark

 

[Old2stroke]

Maybe it's not the lever that is changing it's amount of "bend", just the rubber tip on the end of the inlet valve settling deeper into it's seat?

 

[Woodslasher]

Maybe it's not the lever that is changing it's amount of "bend", just the rubber tip on the end of the inlet valve settling deeper into it's seat?

That could be, I know that fuel can make the needles swell if they're going bad. I had a Husky 390 that was pig-rich, wouldn't clean up in the cut, and didn't need the choke to start when cold. Based off of that list a local saw guy recommended that I swap out the needle and sure enough, once the needle was swapped it was a bit leaner, it cleans up in the cut, and it needs the choke when it's cold.

 

[heimannm]

The tip "swelling" could explain the one that flattened out and would not pull fuel, but what could cause the metering lever to bend the other way resulting in an over-rich condition?

Mark

 

[fossil]

The tip "swelling" could explain the one that flattened out and would not pull fuel, but what could cause the metering lever to bend the other way resulting in an over-rich condition?

Mark

I wonder if the needle is hanging up or binding.

Grabbing at straws maybe but I can't imagine how the lever would bend.

 

[huskihl]

Is it possible that tank pressure pushed the needle up further than the diaphragm would allow? (Assuming that there’s a tit on the diaphragm that fits into the fork, as opposed to one that only pushes)

 

[Smitty Smithsonite]

I've worked on hundreds of these types of carbs in all kinds of equipment, and have yet to see this happen. That's an odd one, no doubt!

The symptoms you were describing (Minus the flooding) were all just like a broken or damaged check valve present in some newer carb bodies. Not replaceable once damaged - carb replacement is the only option, at least that I'm aware of at the moment.

I've been slowly transitioning away from OPE, and getting into more automotive jobs since installing a 2-post lift a few years ago. Pay is better, although the frustration level is through the roof!! I may transition back, lol.

WHY does 0....P.....E.... always get censored here???

 

[Woodslasher]

I've worked on hundreds of these types of carbs in all kinds of equipment, and have yet to see this happen. That's an odd one, no doubt!

The symptoms you were describing (Minus the flooding) were all just like a broken or damaged check valve present in some newer carb bodies. Not replaceable once damaged - carb replacement is the only option, at least that I'm aware of at the moment.

I've been slowly transitioning away from ***, and getting into more automotive jobs since installing a 2-post lift a few years ago. Pay is better, although the frustration level is through the roof!! I may transition back, lol.

WHY does 0....P.....E.... always get censored here???

Because, many moons ago, there was a large disagreement between the owners of this site and a group of members. Those members left this site and created/joined a site called 0pe forum .com and at least one of the owners on this site had the name of that offensive forum and any variation thereof censored.

 

[atpchas]

Because, many moons ago, there was a large disagreement between the owners of this site and a group of members. Those members left this site and created/joined a site called 0pe forum .com and at least one of the owners on this site had the name of that offensive forum and any variation thereof censored.

The childishness of such a policy notwithstanding, it also highlights ignorance of the well known (Barbra) Streisand effect. Talk about shooting yourself in the foot...

 

[Old2stroke]

The tip "swelling" could explain the one that flattened out and would not pull fuel, but what could cause the metering lever to bend the other way resulting in an over-rich condition?

Mark

Not swelling but, but settling into a lower position in it's seat. As the needle goes down, the other end of the control lever goes up. Looking at the ratio of the length of the short end of the control lever to the length of the long end, if the short end goes down by say 0.002", the long end goes up by at least 0.008". Maybe not a significant amount to cause flooding but those levers aren't that easy to bend and I don't believe there are large enough forces inside the carb to do it.

 

[Okie]

What is the exact Zama model reference model number on the carb?

Also you are probably aware of this, but I really keep a heads up when first replacing a needle and the pump diaphragm on a small engine carb. I look at the lever setting of the old needle and I closely examine both the new needle and the new diaphragm and quite often in last few years they just do not quite match the ones coming out of the carb and I sometimes even take a dial caliper to the diaphragm button, the diameter and length of the new needle this gives me a heads up about possibly installing wrong parts even though the kit number is correct and I pay attention to how much the lever setting changes when the new needle is installed and also clean the old seat good. If the diaphragm lever button is wrong one it will upset the lever setting. Also pay attention to the lever spring that it is not distorted and the correct one and also assume that a Bubba has been in the carb before.
On my own chainsaws I keep the old carb parts where i know where they are until I get a good proof of performance test of the carb.


AND
I would probably think about replacing the needle, the lever and the diaphragm then check the needle and seat with pressure to see it holds ok and if this test fails (the lever bends again or the lever setting changes after running for awhile) the issue is not within the carb itself. When pressure testing the needle/seat you can sometimes with a blunt toothpick through the diaphragm vent hole operate the needle off it seat gently and release so as to see the re-seat pressure hold is ok.
Then if it started flooding again after running for awhile I would make a check of the gas tank venting and something I've seen every once in awhile is a sticky type substance that comes out of gas tanks going toward the carb. It gets past the in tank filter and will cause the needle/seat to become erratic operating. NEW gas mix will start breaking it down/dissolving it enough that it will get to the carb like a liquid sticky glue.

Good to see that someone else gets into them little head scratcher carb issues.
Just got through doing battle with a China clone Walbro that was no good and kitting the OEM Walbro at first was also a failure. (suspected internal non-serviceable check valve issues)
At least I knew the carb was the issue and finally had to get one from Amazon knowing I could send it back for free if no go. It was a genuine Walbro carb and it worked great.

Patience is your friend when flogging that stuff.

 

[Rooshooter]

I wonder if the needle is hanging up or binding.

I recently worked on a Zama carby and had similar happen, it ended up being corrosion where the needle goes causing it to stick sometimes.
Remedy, new carby, problem fixed.