Carb High Jet Lean After Rebuild - How to Fix?

[tomalophicon]

Spark plug seated fully?

 

[drf255]

I’d pull the carb back apart. Clean all as instructed with carb cleaner.

Make sure vent hole in metering cover plate is clean (Long shot).

Sometimes carbs just have crap in them one can’t get out. It’s usually in the tiny pinhole L circuitry under the Welch plug and not the H circuit.

If you have the ability, check popoff pressure. It’s possible something got mixed up and it’s too high. I know you used an OEM kit, but I’ve seen it happen. I got a new OEM 036 piston from Stihl once that was packaged with a12mm circlip-for real. It was in the same sealed bag as the 10mm pin.

 

[SteveSr]

Saw was very hard starting cold, then ran great once started. Now it starts in a few pulls cold, idles great, i just can't get enough fuel to it at WOT.

Since you used a "W" gauge we are assuming that this is a Walbro carb. What specific model? Should be some numbers stamped/etched on the side of the carb. Post a good photo.

If this is a WT-426 there are actually 2 "H" circuits. The main is fixed and the screw is the bypass. If the main were plugged it might cause these symptoms.

 

[rking453]

Spark plug seated fully?

Yes it is, saw runs perfect with a different carb.

 

[rking453]

I’d pull the carb back apart. Clean all as instructed with carb cleaner.

Make sure vent hole in metering cover plate is clean (Long shot).

Sometimes carbs just have crap in them one can’t get out. It’s usually in the tiny pinhole L circuitry under the Welch plug and not the H circuit.

If you have the ability, check popoff pressure. It’s possible something got mixed up and it’s too high. I know you used an OEM kit, but I’ve seen it happen. I got a new OEM 036 piston from Stihl once that was packaged with a12mm circlip-for real. It was in the same sealed bag as the 10mm pin.

Yes nothing is perfect, could be something off with the kit, even though it is unlikely. Can you tell me how to check pop-off pressure?

 

[rking453]

Since you used a "W" gauge we are assuming that this is a Walbro carb. What specific model? Should be some numbers stamped/etched on the side of the carb. Post a good photo.

If this is a WT-426 there are actually 2 "H" circuits. The main is fixed and the screw is the bypass. If the main were plugged it might cause these symptoms.

It is a WT series carb, pretty sure it is a WT-194. I can get a picture tomorrow.

 

[rking453]

Didn't have much time to look at it today, switching onto night shift for the week. Last night I took everything apart, used carb cleaner and sprayed every orifice, needle seats, etc. I put the original metering lever arm back in, and it indexes right at the tip of the "W" tool, same as I had the new lever. I was hopeful cleaning may have helped, but today I gave it a try before heading to work and it still cant get enough fuel when the throttle is opened up. I am going to put a whole new kit in it tomorrow and see where that gets me.

 

[huskihl]

Didn't have much time to look at it today, switching onto night shift for the week. Last night I took everything apart, used carb cleaner and sprayed every orifice, needle seats, etc. I put the original metering lever arm back in, and it indexes right at the tip of the "W" tool, same as I had the new lever. I was hopeful cleaning may have helped, but today I gave it a try before heading to work and it still cant get enough fuel when the throttle is opened up. I am going to put a whole new kit in it tomorrow and see where that gets me.

Are you certain the impulse line is hooked up? And good?

 

[rking453]

Are you certain the impulse line is hooked up? And good?

It is brand new OEM on both saws. Both saws run great with the one carb. Both saws have the same issues with the "problem" carb.

 

[SteveSr]

Didn't have much time to look at it today, switching onto night shift for the week. Last night I took everything apart, used carb cleaner and sprayed every orifice, needle seats, etc. I put the original metering lever arm back in, and it indexes right at the tip of the "W" tool, same as I had the new lever. I was hopeful cleaning may have helped, but today I gave it a try before heading to work and it still cant get enough fuel when the throttle is opened up. I am going to put a whole new kit in it tomorrow and see where that gets me.

Really strange... The 194 is a simple full range carb. However, I had had this happen on a Zama when the main nozzle check valve gets stuck closed. It will idle all day but never rev up. This is a non-repairable fault and I believe the generic WT-194 is still available. There is a blow / suck test that you can do on the "H" circuit and you should hear the check valve disc moving up and down. If you dislodge it now it may work for a while but will eventually fail again... at the most inopportune time. Best to just replace the carb.

 

[rking453]

Really strange... The 194 is a simple full range carb. However, I had had this happen on a Zama when the main nozzle check valve gets stuck closed. It will idle all day but never rev up. This is a non-repairable fault and I believe the generic WT-194 is still available. There is a blow / suck test that you can do on the "H" circuit and you should hear the check valve disc moving up and down. If you dislodge it now it may work for a while but will eventually fail again... at the most inopportune time. Best to just replace the carb.

Yes it has been driving me crazy trying to track down the issue. Easily had the carb off and on both saws 30+ times now. I see I can get an OEM replacement carb for $65 on ebay. May end up going that route here soon.

 

[Old2stroke]

When the high speed circuit won't deliver enough fuel, could be because dirt stuck in circuit (remove H screw and spray cleaner, might have to remove a welch plug), nozzle check valve is not opening properly (most can be easily replaced but are NEVER part of a kit), fuel pump diaphragm is too stiff to supply adequate fuel (the plastic acetate one is the worst). Forget pop-off pressure, has nothing to do with the problem. Pressure will often build up in the fuel tank and most vents will only allow air in, not out, and if the pressure gets high enough it can force fuel past the inlet valve and cause flooding, the pop-off pressure is the point where this can happen and it just has to be above the maximum tank pressure, usually about 10psi is enough.

 

[J D]

If you still have the old gaskets/diaphragms match them up against the new ones to check for any minor discrepancies

 

[rking453]

Well I put a whole new kit in the carb. Blasted every possible orifice, and needle seats again with carb cleaner. Still not running right. If I give it full throttle now it will stay running for a few seconds. Real doggy, only a little more speed than idle. Until it finally starves itself. I'm not sure what else to do at this point, besides buy a new carb.

 

[tomalophicon]

might be something worthwhile here

 

[J D]

Starting to look like it's the main nozzle check valve... If you remove the H screw & spray cleaner in the hole it should freely shoot out the main nozzle.

Using compressed air or an aggressive cleaner like brake cleaner can damage the little disk inside of it

 

[rking453]

Starting to look like it's the main nozzle check valve... If you remove the H screw & spray cleaner in the hole it should freely shoot out the main nozzle.
View attachment 927610
Using compressed air or an aggressive cleaner like brake cleaner can damage the little disk inside of it

Okay I will give this a try, if it is the check valve were would I find one to replace it?

 

[sean donato]

Okay I will give this a try, if it is the check valve were would I find one to replace it?

Just get a new carb at this point. Haven't seen check valves readily available in some time, and your specific carb is still made. Between time and money spent your in over the cost of a replacement carb. Some guys have had success replacing them with home made ones or somehow found one. Nit worth the effort imo.

 

[SteveSr]

Well I put a whole new kit in the carb. Blasted every possible orifice, and needle seats again with carb cleaner. Still not running right. If I give it full throttle now it will stay running for a few seconds. Real doggy, only a little more speed than idle. Until it finally starves itself. I'm not sure what else to do at this point, besides buy a new carb.

Now this sounds like the metering chamber is being emptied faster than the pump will refill it.

There may still be something wrong with the fuel pump. Check the impulse passage to make sure that it gets to the pump diaphragm. I once had a similar carb where the fuel inlet wasn't drilled to sufficient depth. Held pressure nicely, but no fuel!

Make sure that the pump diaphragm is right next to the carb body with the gasket on top. Make sure that the flappers on the diaphragm are not bent. Remove the input screen and make sure that it is not gummed up.

Lastly, these older Walbros with the plastic fuel elbow are known to crack and leak. In this case it will allow the carb to suck air instead of fuel. This fault can also be found with a pressure test on the fuel inlet. These elbows are available as a replacement part.

 

[rking453]

Now this sounds like the metering chamber is being emptied faster than the pump will refill it.

There may still be something wrong with the fuel pump. Check the impulse passage to make sure that it gets to the pump diaphragm. I once had a similar carb where the fuel inlet wasn't drilled to sufficient depth. Held pressure nicely, but no fuel!

Make sure that the pump diaphragm is right next to the carb body with the gasket on top. Make sure that the flappers on the diaphragm are not bent. Remove the input screen and make sure that it is not gummed up.

Lastly, these older Walbros with the plastic fuel elbow are known to crack and leak. In this case it will allow the carb to suck air instead of fuel. This fault can also be found with a pressure test on the fuel inlet. These elbows are available as a replacement part.

Yes I think you are right about the metering chamber. It acts like it has enough fuel for a moment when you pull the throttle, as if it was emptying out the metering chamber. If you blip the throttle twice the second time it will have nothing, but if I let it idle for a few seconds, it will have fuel for a moment again.

I put a second brand new screen in today.

The kit came with a variety of pump diaphragms. I obviously replaced the old with the new that looked the same. But it has no flaps. Some of the other diaphragms in the kit do. Maybe I should try one of the different diaphragms?