Ok I have both the Zama and Walbro gauges for setting these things. I have read alot of info on Walbro and Zama procedures on their respective websites. My question is when it says flush and you put gauge or straight edge on it per correct setting most of the time the other end of the lever is actually quite a ways from lifting needle off the seat due to slop in the pivot or fulcrum , or whatever it is called where the pin goes through the arm. Just out of curiosity I have taken an old diaphragm and removed the fabric leaving just the round metal deal with the tit thang in the middle that presses on arm and found that it just BARELY lifts needle off seat when fully depressed . Is it an all or nothing proposition when engine is running as to how much needle is open or does it vary with demand? Should one bend lever so that any thing below flush is raising the needle off the seat or just set it flush or whatever per the gauge and don't worry about the other end?
Needle and seat question
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AND I've noticed what you are asking and also on some careful close inspections of some of the walbro kits the replacement needles are not exactly the same, therefore I keep a heads up and compare the setting of the lever of the old needle before removing, especially if the carb was know to run ok at some time and then carefully compare the new and old needle before proceeding to replace the needle.
I've seen some of the Walbro's kits that I had to set (slightly adjust both) the lever height and the forked fulcrum at the needle. The little fork at the needle has to push down on the needle groove enough to seal off (hold back) 3 to 5 psi of air pressure at the gas line input. If it don't the carb will flood.
In answer to your question, and referring to Walbro HDC type carbs
you have to pay attention to the forked end also. Fork too high and carb will flood because the needle does not have any spring loaded down tension to hold back the gas inflow, and too high the carb will starve for fuel because too much downward pressure on the needle. and I've seen no mention of this in the carb kit procedures. Walbro just seem to assume all replacement parts are exactly the same, etc.
I check such with a mityvac by gently pushing down with finger on the lever to open the needle then let the lever at rest at it's correct height and then apply mityvac pressure going towards 3 lbs. If not holding back 3 lbs the fork is not at the bottom of the needle groove, the needle is only seating by it's own weight instead of using the spring fulcrum.
When you get this setting correct and the gasket/diaphragm then installed in proper orientation the carb normally operates correct for receiving fuel from the tank.
I've also seen some of the Walbro carb kits labeled as to the correct kit but were just wrong even the metal on the pump diaphragm was not correct. (no metal button)
I've seen some of the Walbro's kits that I had to set (slightly adjust both) the lever height and the forked fulcrum at the needle. The little fork at the needle has to push down on the needle groove enough to seal off (hold back) 3 to 5 psi of air pressure at the gas line input. If it don't the carb will flood.
In answer to your question, and referring to Walbro HDC type carbs
you have to pay attention to the forked end also. Fork too high and carb will flood because the needle does not have any spring loaded down tension to hold back the gas inflow, and too high the carb will starve for fuel because too much downward pressure on the needle. and I've seen no mention of this in the carb kit procedures. Walbro just seem to assume all replacement parts are exactly the same, etc.
I check such with a mityvac by gently pushing down with finger on the lever to open the needle then let the lever at rest at it's correct height and then apply mityvac pressure going towards 3 lbs. If not holding back 3 lbs the fork is not at the bottom of the needle groove, the needle is only seating by it's own weight instead of using the spring fulcrum.
When you get this setting correct and the gasket/diaphragm then installed in proper orientation the carb normally operates correct for receiving fuel from the tank.
I've also seen some of the Walbro carb kits labeled as to the correct kit but were just wrong even the metal on the pump diaphragm was not correct. (no metal button)
Thank you for your response. I see your point in having to have enough pressure to hold needle down. Something I had discounted before. In the future I will try your methods , including pressure of 3 psi. I just never understood why in all the youtube vids and fsm's I have used as guidelines when working on these things never elaborated on the subject. It is always just casually referred to as a simple matter of adjustment . I have seen several that when adjusted per instruction the fork at full travel was barely-if at all - raising needle off seat. But after thinking of what you are saying here I now see that it doesn't really have to pull up on needle. Fuel should push it open and fork should hold needle down as to regulate flow? Unlike a float carb where the weight of the float lifts the needle or pulls it down off of seat?
I have a Walbro on a trimmer that just won’t set properly no matter what gauge I use. I hadn’t thought to use the MightyVac. Thank you!
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Thanks again! After using this method of checking under pressure while in the assembly phase I was able to bring a 026 PRO back to life. I think I have probably been overthinking this for a long while. Hence the reason I have more problems with tuning on 2 strokes than about anything else I mess with. Got to the point if I can buy a new locally for 30-40 bucks I don't even try. I do not do this for for a living but have always had the mentality that if I own it I better know how to work on it. As my wife and I are considering updating her pickup from the 2002 7.3 F350 we ordered new I can see I am probably going to have to get over that. Thanks again and again.
Thanks also. I've been slowly cleaning up my old stihl 015av and have been having issues with the carb flooding after installing a carb gasket kit. I tried setting the metering lever as per the walbro instructions but it kept flooding. It was only after I read the description above regarding the closing rather than the opening with the spring that I understood the problem I was having. Once I'd adjusted the lever to be closed via the spring and checked it for sealing that the problem was resolved.
My 1975 saw is a runner again.
My 1975 saw is a runner again.
Poleman
Addicted to ArboristSite
You’ll also need to note that on different carb kits the tit you speak of is of different lengths and will cause flooding.
I ALWAYS pressure check a carb, when needle is installed Ana after diaphram is placed to make sure of its seal. As Okie mentioned the needle arm needs to be able to close the needle or it will flood and even siphon fuel. The impulse supply’s the pressure needed to move the pump diaphram and the needle diaphram opens when it needs too.
Don’t be afraid if a carb is flooding to adjust the needle arm below spec or raise it if you run lean in a long cut..... I’ve found this very helpful in straightens out carbs and getting the correct and top performance from one. Some carbs will be naturally rich while others are lean....quality of production I think, machines not being I spec allowing larger clearances or a newly set machine giving tight specs.
When you pressure check you can make sure needle is seating and if there is still a leak put the carb in water under pressure and you’ll find your leak to address....may be a gasket seal, a shaft or a bad nozzle. Pressure checking can tell you a lot of things.
I ALWAYS pressure check a carb, when needle is installed Ana after diaphram is placed to make sure of its seal. As Okie mentioned the needle arm needs to be able to close the needle or it will flood and even siphon fuel. The impulse supply’s the pressure needed to move the pump diaphram and the needle diaphram opens when it needs too.
Don’t be afraid if a carb is flooding to adjust the needle arm below spec or raise it if you run lean in a long cut..... I’ve found this very helpful in straightens out carbs and getting the correct and top performance from one. Some carbs will be naturally rich while others are lean....quality of production I think, machines not being I spec allowing larger clearances or a newly set machine giving tight specs.
When you pressure check you can make sure needle is seating and if there is still a leak put the carb in water under pressure and you’ll find your leak to address....may be a gasket seal, a shaft or a bad nozzle. Pressure checking can tell you a lot of things.
Please clarify that last short paragraph. If I pressure check and it passes the 3psi or more test then how would I know I had something else leaking? I like the idea of dunking it and watching for bubbles to identify a component failure but I guess I am not understanding how that would point to a shaft leaking unless you had both ends of the venturi capped off? Not trying to be a smartie pants here, just trying to learn and understand. Thanks
Poleman
Addicted to ArboristSite
I pressurize to 7-10 lbs and watch my gauge or let it set while I do something else that’s quick. The gauge will drop if there’s a leak....now it’s time to find the leak. I generally double check the needle. I have had to polish a seat or two in old carbs that were rough. I then pressurize and dunk in water and watch.... maybe even turn it over. Most leaks are from gaskets but occasionally from other places. If there are accelerated pumps or any Chanel’s that run through the throttle shaft it will show. If bubbles are coming from the nozzle it’s bad and if it’s coming from any bleed holes into the Ventura it generally a Welch plug leaking.
I don’t worry about choke shafts since they are so small but you and block the ends of the carb with the rubber seals used for pressure testing a saw and a clamp and test shafts.
I don’t worry about choke shafts since they are so small but you and block the ends of the carb with the rubber seals used for pressure testing a saw and a clamp and test shafts.
