Carb Guru? WJ-69 and Clone comparison

[Mastermind]

Have you tried a different coil?

 

[jmssaws]

Is this the saw I built?

I've seen partially plugged impulse barbs on stihl cases that cause all sorts of wonky issues. Next time you have it that far down poke a drill bit through it and make sure it's clean.

Yes it's the one you built.
It was fine and one day it just started doing it.
It absolutely won't run with a wj69 on it even one I know is good it won't idle for more than a few seconds.
I don't know how it makes a difference but a carb with the snorkel runs worse.

Another thing is that carb on it is a original aluminum flywheel 066 carb that has never been rebuilt and the diaphragm is stiff in it and it's the best one I've had on it,what would make it run better with a stiff diaphragm? Impulse?

 

[jmssaws]

Have you tried a different coil?

I've had every coil but a red light on it,2 flywheels and 8 or 10 carbs and it's definitely worse with certain carbs,even a good one off another saw may barely idle on it or not at all. It's either lean or fat with no in between. Any will run wfo and tune on the high.
It's very strange to have good power and start it again 10 min later and it be a freak,if I didn't know how strong it can be I'd not be fooling with it but something is off.
Any gas and any oil or plug it runs the same,coil harness have been changed,the only thing that hasn't been replaced twice is the bearings and cases.
Absolutely 100% no airleak.

 

[junkman]

I have a fix for these kind of problems .

 

[srcarr52]

Yes it's the one you built.
It was fine and one day it just started doing it.
It absolutely won't run with a wj69 on it even one I know is good it won't idle for more than a few seconds.
I don't know how it makes a difference but a carb with the snorkel runs worse.

Another thing is that carb on it is a original aluminum flywheel 066 carb that has never been rebuilt and the diaphragm is stiff in it and it's the best one I've had on it,what would make it run better with a stiff diaphragm? Impulse?

Stiff diaphragms can change pop off pressure, usually it will make it a few psi less.

 

[jmssaws]

Stiff diaphragms can change pop off pressure, usually it will make it a few psi less.

Then I need less pop off pressure.
Any idea why?

 

[Motorhead]

Here is what it does,idles to fast,almost 3200 then will load up and almost die then gain rpm back and do it over and over. Throttle response is good and it stays tuned on the high side. What in the hell is causing this?

. Walboro carbs have a capillary valve in them,it is a very fine screen that does affect both the high and low side of the carburetor when it's dirty.The carb kits do come with the capillary screen.You might want to google it.Good luck

 

[srcarr52]

Then I need less pop off pressure.
Any idea why?

Because ported saws have less vacuum at the carb than normal saws do because the intake duration is longer. At the same time the pulse to the pump side of the carb has less energy. Less vacuum due to larger intake duration, less pressure do to better flowing and more transfer duration.

Nip the double or triple winds on the metering spring each extra flat wind is usually around 1/2 psi pop off.

 

[jmssaws]

Because ported saws have less vacuum at the carb than normal saws do because the intake duration is longer. At the same time the pulse to the pump side of the carb has less energy. Less vacuum due to larger intake duration, less pressure do to better flowing and more transfer duration.

Nip the double or triple winds on the metering spring each extra flat wind is usually around 1/2 psi pop off.

I put a stock muffler cover on and it stopped doing it.
Goes to show every saw is different because every one I build has way more opening than this one and are fine.
It won't idle lower than 3200 but it's not erratic. Kills power though so erratic idle is gonna have to be what I want.

 

[srcarr52]

I put a stock muffler cover on and it stopped doing it.
Goes to show every saw is different because every one I build has way more opening than this one and are fine.
It won't idle lower than 3200 but it's not erratic. Kills power though so erratic idle is gonna have to be what I want.

It that the muffler that came on it? Did you remove the screens? I saw that you cut back the deflector some.

 

[junkman]

So saws do need some kind of back pressure to keep vacuum up ?

 

[jmssaws]

It that the muffler that came on it? Did you remove the screens? I saw that you cut back the deflector some.

It's the one that was on it.
I removed the side screen and trimmed the deflector back but I did that the day I got it and it ran perfect up till a few weeks ago. Something has changed that made it need less opening,impulse I weaker or maybe the piston is wore on the intake side? There's 15 or more 1122's sitting in the shop right now that will tune just fine with more opening than it and this one did,I put a impulse line on it but didn't check the barb so maybe it's half plugged or something.
It does idle more stable but it hurt it bad loosing the extra port.

 

[jmssaws]

Here it is with a stock muffler cover and no ignition advance,it's way behind its usual self but does idle some better

 

[srcarr52]

It's the one that was on it.
I removed the side screen and trimmed the deflector back but I did that the day I got it and it ran perfect up till a few weeks ago. Something has changed that made it need less opening,impulse I weaker or maybe the piston is wore on the intake side? There's 15 or more 1122's sitting in the shop right now that will tune just fine with more opening than it and this one did,I put a impulse line on it but didn't check the barb so maybe it's half plugged or something.
It does idle more stable but it hurt it bad loosing the extra port.

Didn't you say you took some compression out of it, or was that a different saw?

 

[srcarr52]

So saws do need some kind of back pressure to keep vacuum up ?

Probably not for vacuum but for pressure to the fuel pump. The pumps need both a vacuum and pressure pulse to work. That is why they don't work well if you hook them up to a source from the intake which doesn't have a good pressure pulse. The big alky tilly's have a double diaphragm pump to work when hooked up to an intake pulse.

 

[jmssaws]

Didn't you say you took some compression out of it, or was that a different saw?

Haven't touched the cylinder.

 

[Mastermind]

Here's a thought. I replace these o-rings on a lot of carbs. If they are too loose the screws won't stay set, and they suck air around them. These can cause some weird tuning issues.

 

[Redfin]

Probably not for vacuum but for pressure to the fuel pump. The pumps need both a vacuum and pressure pulse to work. That is why they don't work well if you hook them up to a source from the intake which doesn't have a good pressure pulse. The big alky tilly's have a double diaphragm pump to work when hooked up to an intake pulse.

Can I assume an intake pulse is one that closed off from primary compression?

 

[srcarr52]

Can I assume an intake pulse is one that closed off from primary compression?

Intake pulse, as in tapped into the intake port, not into the crankcase.

 

[Deets066]

Intake pulse, as in tapped into the intake port, not into the crankcase.

You mean like I did on my 394?