Rich coming off of WOT

[millerlite]

So first ill explain the problem, then the backstory.

Nomatter the state of tune, the saw dies coming out of a cut. The high is tuned perfect. Low perfect. The only way to have it not die, is to tune the idle lean of highest idle, and give it more air to keep the chain almost turning. Throttle response is non existant like this. I have checked the main check valve, lever height, changed that higher and lower, etc. Always same issue.

The saw is a chainsaw chainsaw g2500 fine china. It has a tube in the muffler and baffle gutted. No porting yet. Worked pretty good with stock carb just slow. I put a chinese cs400 carb on it and opened up the boot to match. Im trying to get it working, because now this set up absolutely rips. The saw is a play toy but I do climb with it also so i wqnt to have it well mannered.

It is definitely flooding itself out. Is this a case of too big of a carb? Any thoughts on modifying the throttle plate notch, or the transition holes in the low? Metering lever spring and height? Im not sure where to go with this.

Edit: Oops, I meant to post this in the general saw section

 

[Mastermind]

Moved it for you. I'm a little biased (ok, a lot biased) towards China saws. So I'm gonna blame that for the issues.

 

[David Young]

the metering lever is hanging up some how. It is also possible that the check valve in the main jet is not sealing well.

 

[EFSM]

Try raising the pop-off pressure, maybe a stronger metering spring or setting the lever lower than it should be.

 

[millerlite]

Thanks guys, the china saw is not the problem, it ran great besides expected power, till i put a wt9×× (whatever cs400) carb on it. Now it has the issue. Other carb back on, fine. Ive checked the impulse, i set the lever lower, then higher. Seemed about the same after tuned. Ive checked for air leaks, swapped diaphrams. I swapped metering levers and spring from another carb. Springs might be the same though. I just tried widening the notch in the throttle plate. No change, might tig weld that back up. Looking at the carb the step after the venturi was pretty sharp and thought maybe puddling fuel. Set it up in the lathe and bored that back at a shallow angle to the main. Picked up more power, no change in tune issue. It seems strange that revving up its lean, and back down it floods.

Since this is an experiment, has anyone put a big carb for the saw size on a saw and had this issue? I am stumped here and wonder if the carb is too big for the saw. Idle wants to tune in at only 0.5 turns out. High needle is 2.5t. Edit: i believe the venturi is 0.53 inches or so. Stock was 0.375 and the main blocked half the venturi.

 

[millerlite]

If the check valve wasnt sealing wouldnt this cause a lean condition and not a rich one? I punched it out of the carb, checked it, and put it back in. Seems fine, but maybe i should get another.

 

[David Young]

it sounds like the main jet with those jet settings.

What is the pop off pressure? does it reseal after pop off?

the carb venturi itself is not too large for that size saw but the idle circuits could be. like any engine a smaller carb/venturi will behave better.
the Husky 335xp was 35cc and came with a 13.49mm walbro WT stock.

 

[millerlite]

Makes sense. Pop pressure i am not sure. I can test it later. For reference, on my mildly ported cs400 my settings are 3t out on high and 1.25t on low. So maybe you are right and the idle circuit is too big? Also, a 35cc saw is still 30+ percent larger than the little 25cc fine china and im sure it doesnt have the best port work. Wonder if there is a better carb option out there.

 

[millerlite]

Pop off at 13 to 14 psi

 

[millerlite]

it sounds like the main jet with those jet settings.

What is the pop off pressure? does it reseal after pop off?

the carb venturi itself is not too large for that size saw but the idle circuits could be. like any engine a smaller carb/venturi will behave better.
the Husky 335xp was 35cc and came with a 13.49mm walbro WT stock.

What should the pressure be? What is the effect of pressure vs lever height?

 

[David Young]

What should the pressure be? What is the effect of pressure vs lever height?

You are in the right range for pressure. The pressure can tune the ramp in from low to high, the lever height needs to be close to what the manufacturer spec is, normally level with the bosses or the out side of the carb. another thing to look at is make sure the gasket and diaphragm are in the right sequence, Make sure you have the right Diaphragm. some have small nubs, some are larger and some are designed to connect into the meter lever.

In any case too high and the inlet needle may not close and would cause the needle to stay open. and it will be too rich. too low and you would likely see a lean condition on the topside.

as simple as this area of the carb is look at everything close and clean it very well

Do the needle drop in and out of the hole with nothing but gravity?

put a qtip with some of the cotton removed in the inlet needle hole, soak with a drop of gas. spin the qtip in there does it come out clean or have some black gunk?

If you put the meter lever on the pin while holding the pin in your fingers will the lever swing completely free?

 

[huskihl]

More often than not, I see people running them overly rich on the H jet when they do this. It will wet the case and transfers so that once it comes down to an idle, there’s too much residual fuel for it to burn

 

[millerlite]

You are in the right range for pressure. The pressure can tune the ramp in from low to high, the lever height needs to be close to what the manufacturer spec is, normally level with the bosses or the out side of the carb. another thing to look at is make sure the gasket and diaphragm are in the right sequence, Make sure you have the right Diaphragm. some have small nubs, some are larger and some are designed to connect into the meter lever.

In any case too high and the inlet needle may not close and would cause the needle to stay open. and it will be too rich. too low and you would likely see a lean condition on the topside.

as simple as this area of the carb is look at everything close and clean it very well

Do the needle drop in and out of the hole with nothing but gravity?

put a qtip with some of the cotton removed in the inlet needle hole, soak with a drop of gas. spin the qtip in there does it come out clean or have some black gunk?

If you put the meter lever on the pin while holding the pin in your fingers will the lever swing completely free?

Thats what I thought. And these are all good points. I have already checked all these things. Ive ran into carb issues before but not like this. Im pretty stumped.

Im thinking the idle is going to be have to be modified to work. It could also be a bad china carb. I had to modify all the nipples and linkages to work so id hate to order another carb. I might try plugging the second transition hole, and restrict the main idle jet hole. My thinking is ill be able to run the idle leaner and still get more fuel in on the transition jet for throttle response. I notice most carbs out there have different hole sizes and spacings, surely theres a reason for this.

I do remember playing with lever heights and pop pressure on my ported 026 wt194 to get the throttle response awesome. I recall it being really finicky till i got the pop pressure up to 20 psi.

More often than not, I see people running them overly rich on the H jet when they do this. It will wet the case and transfers so that once it comes down to an idle, there’s too much residual fuel for it to burn

I thought this at first also. But i really think it is not rich on the high at all. If i lean it out anymore it totally cleans up and screams like a nitro rc motor, makes me uncomfortable lol. Right now there is no preceivable 4 stroking at all and if you pull it out of a cut it doesnt pop or 4 stroke. but its richened up so the rpm dropped a bit. This carb has made it want to cut at a higher rpm than it used to be willing to rev to when tuned borderline lean and piss revved. The problem definitely gets worse when its ran richer. Ill have to take a video of the symptoms.

 

[huskihl]

Thats what I thought. And these are all good points. I have already checked all these things. Ive ran into carb issues before but not like this. Im pretty stumped.

Im thinking the idle is going to be have to be modified to work. It could also be a bad china carb. I had to modify all the nipples and linkages to work so id hate to order another carb. I might try plugging the second transition hole, and restrict the main idle jet hole. My thinking is ill be able to run the idle leaner and still get more fuel in on the transition jet for throttle response. I notice most carbs out there have different hole sizes and spacings, surely theres a reason for this.

I do remember playing with lever heights and pop pressure on my ported 026 wt194 to get the throttle response awesome. I recall it being really finicky till i got the pop pressure up to 20 psi.


I thought this at first also. But i really think it is not rich on the high at all. If i lean it out anymore it totally cleans up and screams like a nitro rc motor, makes me uncomfortable lol. Right now there is no preceivable 4 stroking at all and if you pull it out of a cut it doesnt pop or 4 stroke. but its richened up so the rpm dropped a bit. This carb has made it want to cut at a higher rpm than it used to be willing to rev to when tuned borderline lean and piss revved. The problem definitely gets worse when its ran richer. Ill have to take a video of the symptoms.

A video might help diagnose it as well

 

[David Young]

Thats what I thought. And these are all good points. I have already checked all these things. Ive ran into carb issues before but not like this. Im pretty stumped.

Im thinking the idle is going to be have to be modified to work. It could also be a bad china carb. I had to modify all the nipples and linkages to work so id hate to order another carb. I might try plugging the second transition hole, and restrict the main idle jet hole. My thinking is ill be able to run the idle leaner and still get more fuel in on the transition jet for throttle response. I notice most carbs out there have different hole sizes and spacings, surely theres a reason for this.

I do remember playing with lever heights and pop pressure on my ported 026 wt194 to get the throttle response awesome. I recall it being really finicky till i got the pop pressure up to 20 psi.


I thought this at first also. But i really think it is not rich on the high at all. If i lean it out anymore it totally cleans up and screams like a nitro rc motor, makes me uncomfortable lol. Right now there is no preceivable 4 stroking at all and if you pull it out of a cut it doesnt pop or 4 stroke. but its richened up so the rpm dropped a bit. This carb has made it want to cut at a higher rpm than it used to be willing to rev to when tuned borderline lean and piss revved. The problem definitely gets worse when its ran richer. I’ll have to take a video of the symptoms.

Honestly I’d try another carb before I went too crazy. You know it is in the carb bc the old one works.

 

[el33t]

Honestly I’d try another carb before I went too crazy. You know it is in the carb bc the old one works.

It seems to me somewhere, in the case of the bigger carburetor, excess fuel (in comparison to a stock carb) must remain after the throttle is closed when transitioning from WOT. Maybe the idle fuel pocket is just bigger...

I guess that trying a carburetor with a dependent idle system or/and an acceleration pump would have a better chance of success.

EDIT: Of course, if it turns out that the volume under Welch plug is significantly larger, then if the OP still has patience with this carburetor, he can try to reduce the volume of the chamber by using J-B Weld or something similar.

 

[millerlite]

Im liking this discussion. My biggest problem in life is i always need to know why. Another carb might solve the issue, but why? What is the issue with this one? I like the volume theory. I was having that thought last night looking through walboro wt diagrams. Is the needle before or after the plug? This could explain a lot. I was also thinking if the needle restriction was considerably more than the restriction of the jet itself, it could gulp down that volume of fuel in the bowl under the plug. I dont know. Its all a learning opportunity i guess

 

[el33t]

Im liking this discussion. My biggest problem in life is i always need to know why. Another carb might solve the issue, but why? What is the issue with this one? I like the volume theory. I was having that thought last night looking through walboro wt diagrams. Is the needle before or after the plug?

The needle should be before the plug. And, of course, the entire volume of fuel remaining after WOT behind the L needle will count if it really has something to do with your problem.

 

[millerlite]

I took a punch and folded the idle hole half shut and the same with the first transition hole. Beat a new plug in there and set the lever back to 65 thou. Seems much better/fixed. 1 turn on the idle now, throttle response is better, let off and it dips but doesnt stall. Ill put it in a wood pile and do some proper re tuning, hopefully that does it. Sometimes beating on things with a hammer really is the answer

 

[hacskaroly]

Ill put it in a wood pile and do some proper re tuning, hopefully that does it.

Looking forward to hearing how it goes!!