What the f..........is going on here?

[Savage Saws]

I second what Jim is saying. I have found that alot of these aftermarket carbs have poorly machined needle seats and once they "pop off" they continue to bleed fuel into the metering chamber and flood the saw out. Also, you need to seal your welsch plugs with nail polish and not motoseal. The motoseal will peel away/disintegrate when immesed in fuel perminately, where as the nail polish is neural.

 

[traffic903]

The metering lever is getting stuck open during operation.

I thought that too and so I replaced all of the components. No difference. I did however replace with china carb kit, so probably just swapped same for same when you think about it!

 

[traffic903]

The AM carbs really are a cluster fck lately. I just got through diagnosing a carb that would flood the engine within two pulls of the recoil so its not doing like the OP`s saw is but I had the owner mail me the carb, I tried online to diagnose and have him fix it but couldn`t figure it out til in my hands. I did a methodical teardown looking at each part very closely. This is what I found on this particular carb, the little nub on the metering diaphragm that presses on the metering lever was .010 longer than an OEM one, the metering lever offset was way off, couldn`t bend it far enough to make it work, tossed both aside. Opened up the pump side and found the pump diaphragm was totally incorrect for the carb, it left the impulse port and bowl completely open to incoming fuel, the fuel just ran straight down the impulse line into the crankcase. After installing a completely new OEM kit with proper adjustments I first tried a pressure test and the carb failed, there was an air leak in two places between the pump side cover and the gasket. No matter how tight I turned the holdown screw it still leaked. I could have just swapped the cover for a spare OEM one but instead flattened out the leaker using a couple of machinist files, voids could clearly be seen after just a couple strokes of a flat single cut file, several more strokes brought the cover flat/true enough for it to seal easily with just the gasket. Installed the carb on one of my test bed saws and it then ran just fine, will tune and hold a tune, reinstalled it on one of my work saws and it ran 4 tanks of fuel through it without further adjustment or problems. Long story but it just goes to show how bad some of this AM stuff is getting. Couple years back the AM carbs seemed to be way better and far less problematic.

I agree. Consistency is non existant and quality is dropping by the day.

 

[traffic903]

The last post reminds me about the aftermarket kits I've seen. The alignment of some patterns are slightly off and will never work.
If you haven't tried replaced the spring and kit with oem then you should do so. If you've already tried both at once then start inspecting the metering pin and shaft for clearance issues. The metering passage may have a bad seat connection which can cause intermittent flooding.

Very good info Jim, thank you. Gives me a solid direction to head. Might see how I go with the oem carbs when they arrive and then look at this a bit more. I can tell you that the problem started (well it definitely became worse anyway) after I put the Highway popup piston in. Have you got any thoughts on why it is more evident once the motor warms up? (Actually I just thought about this more - that's probably just me not holding it wfo unless it is warm!!!)
Thanks again.

 

[traffic903]

I second what Jim is saying. I have found that alot of these aftermarket carbs have poorly machined needle seats and once they "pop off" they continue to bleed fuel into the metering chamber and flood the saw out. Also, you need to seal your welsch plugs with nail polish and not motoseal. The motoseal will peel away/disintegrate when immesed in fuel perminately, where as the nail polish is neural.

Cheers mate. I've heard so many conflicting opinions on sealing welch plugs. I went with a tiny amount of motoseal around the lip after install to try and seal any leaks. To be honest, the plug probably wasnt/isn't an issue anyway. I did worry whether the motoseal would last at the time, but it is supposed to be fuel proof. Will steal some of my wife's nail polish when I look at this again. Might try and find a magnifying glass or similar to inspect the seat also. Thanks for the reply.

 

[Chainsaw Jim]

Typically the welch plug will seal tight when punched in place and will not need any sealer. Those are generally the ones having a snug fit to start with, along with a perfectly smooth and undamaged rim/seat.
Even though they are tight I still use heavy duty fingernail clear coat to finish them off after I punch them in place. I wet the seal with the clear coat all the way around so it has a chance to seep into any available space, then I wipe the whole thing clean with a q tip before it dries so there's nothing left exposed to break loose and plug jets up.

 

[traffic903]

Typically the welch plug will seal tight when punched in place and will not need any sealer. Those are generally the ones having a snug fit to start with, along with a perfectly smooth and undamaged rim/seat.
Even though they are tight I still use heavy duty fingernail clear coat to finish them off. I wet the seal with the clear coat all the way around so it has a chance to seep into any available space, then I wipe the whole thing clean with a q tip before it dries so there's nothing left exposed to break loose and plug jets up.

Noted. Thank you Jim.

 

[XP_Slinger]

Lots of good advice, especially on the Welch plugs.

Not a great carb guy either just thinking outside the box here...is there a chance the the high and low speed jet screws are installed in the wrong spots? Usually the diameter or pitch of the threads are different but you never know with the Chinese stuff. Might be worth a look if nothing else pans out.

I had a terrible experience with a Chinese carb on an atv and hence have never bothered to try one on a saw.

 

[traffic903]

Lots of good advice, especially on the Welch plugs.

Not a great carb guy either just thinking outside the box here...is there a chance the the high and low speed jet screws are installed in the wrong spots? Usually the diameter or pitch of the threads are different but you never know with the Chinese stuff. Might be worth a look if nothing else pans out.

I had a terrible experience with a Chinese carb on an atv and hence have never bothered to try one on a saw.

The H and L screws are different for sure. I had them out to clean the carb and they are definitely different sizes. I was careful to install them in their respective place. I think Jim is onto something with the metering lever sticking, or it could just be a number of things together. Weird problem though hey?!

P.S. When you doing another 2 series build?? I have the opportunity to buy a well used 281 here for about $250Aus. It's hard not to pull the trigger. I've been thinning the heard. Down to 18, but don't know if I can hold out!

 

[PogoInTheWoods]

Pull the components out of your good 660 carb and put em in one of the problem carbs to see where that leads. Wrong pump diaphragm and bad metering components would be quickly determined if they are the problem.

 

[XP_Slinger]

The H and L screws are different for sure. I had them out to clean the carb and they are definitely different sizes. I was careful to install them in their respective place. I think Jim is onto something with the metering lever sticking, or it could just be a number of things together. Weird problem though hey?!

P.S. When you doing another 2 series build?? I have the opportunity to buy a well used 281 here for about $250Aus. It's hard not to pull the trigger. I've been thinning the heard. Down to 18, but don't know if I can hold out!

Well at least they made them to the standard we’d expect, worth a try I guess lol

Almost done building my 262, there’s a thread going for it. http://opeforum.com/threads/262xp-rebuild-junk-pile-save.12289/

I’d snag that 281 if I were you

 

[traffic903]

Pull the components out of your good 660 carb and put em in one of the problem carbs to see where that leads. Wrong pump diaphragm and bad metering components would be quickly determined if they are the problem.

Wasn't too keen to do that as I don't want to mess with the oem carb and ruin something. BUT, I may do that when the used carbs get here. Cheers.

 

[Moparmyway]

The metering lever is getting stuck open during operation.

Or popoff is way low

 

[traffic903]

I’d snag that 281 if I were you

I know you would!! You are crazier about 2 series saws than probably anyone!! LOL.

 

[Larry B]

Sounds like the fuel tank is pressurizing and then forcing the metering valve open causing it to flood. Might want to compare the oem carb spring to the AM one.

 

[traffic903]

Or popoff is way low

Yes thought about that too along the way. That's why I changed out the spring, because I had originally trimmed it to get pop lower (it was OFF the scale high when I tested it during the build). This is why it has been so frustrating, because I have tried so many different things to pinpoint the exact cause.

 

[traffic903]

Sounds like the fuel tank is pressurizing and then forcing the metering valve open causing it to flood. Might want to compare the oem carb spring to the AM one.

Will try the oem spring in it for sure. I have also released the pressure from the tank and problem still remains. Even ran it briefly with the cap open (saw slightly on its side) and there was no change.

 

[Basher]

If it were me with this problem first thing would be replace the full kit with OEM components, less chasing ones tail that way, then check for sealing and pop off pressure. The inner parts that come on these carbs now are often way off specs for OEM carbs and don`t work correctly in AM carbs either. A new OEM kit only costs me $8.50, just too cheap and easy to cover all the bases so I am not fiddling around wasting time. If the carb will not work after a proper rebuild then dig deeper.

 

[Basher]

Are you able to say why you think that could be it? Can I do anything about that? I thought I read somewhere that the check valves aren't serviceable. But I'm probably wrong there. Carbs aren't my thing. Give me fuel injection any day!

The check nozzle very well could be the problem here, they dump fuel into the carb throat when the engine passes a set velocity and vibration level to slow the engine, prevent over revving. They just punch out and install a new one, preferably OEM. Punch the old one into the carb throat, install a new one from the fuel bowl side, try to get it approximately set where the existing one was, not really necessary to get it precisely the same depth but close.

 

[traffic903]

they dump fuel into the carb throat when the engine passes a set velocity and vibration level to slow the engine

That is exactly what is happening! Hmmmm................