Modded 394 lean tuning issue WTF...

[Mastermind]

Very true. Drilling the seat will expose more surface area of the needle exposed to pressure, generating a larger force acting on the lever and lower the pop off pressure.

So, it all comes back to pop off pressure?

You might very well be onto something Shaun. I hesitate to lower pop off on most of the saws I do though. I worry that they will end up sitting out in the sun, and rising tank pressure with overcome POP. I suppose I could alter the tank venting......but then where does the modding end? LOL

 

[srcarr52]

You might very well be onto something Shaun. I hesitate to lower pop off on most of the saws I do though. I worry that they will end up sitting out in the sun, and rising tank pressure with overcome POP. I suppose I could alter the tank venting......but then where does the modding end? LOL

You can't mod the tank vent, the EPA will be all over you.

 

[Mastermind]

You can't mod the tank vent, the EPA will be all over you.

Dammit !!!!!!!

Bastards !!!!!!

 

[p61 western]

Dammit !!!!!!!

Bastards !!!!!!

Yes they are lol. What they don't know don't hurt lol.

 

[RIDE-RED 350r]

EPA are a bunch of fart-knockers

 

[wcorey]

EPA are a bunch of fart-knockers

Actually they’d be the anti-fart-knockers...

 

[RIDE-RED 350r]

Actually they’d be the anti-fart-knockers...

I stand corrected

 

[Chainsaw Jim]

I am trying to convince myself that the EPA is not the "one world order" concept we've all been hearing tales about.

 

[usmcbuckwild]

You can't mod the tank vent, the EPA will be all over you.

So what if, in theory, you added a vapor chamber/expansion chamber with a one way pressure relief valve that could not be externally accessed and routed it to vent into the carb inlet? Similiar to the charcoal chamber and intake vent on an automobile? (But much simpler, obviously)

Yes, I know it was sarcasm

 

[RIDE-RED 350r]

I am trying to convince myself that the EPA is not the "one world order" concept we've all been hearing tales about.

How's that working out for ya Jim??

 

[Chainsaw Jim]

How's that working out for ya Jim??

How's what? Do you ever hear that conspiracy crap and not wonder who they might be talking about? I'm not on that tinfoil hat wagon dude, I'm just entertaining the thought. Lol

 

[p61 western]

How's what? Do you ever hear that conspiracy crap and not wonder who they might be talking about? I'm not on that tinfoil hat wagon dude, I'm just entertaining the thought. Lol

Pics of tinfoil hat lmao.

 

[RIDE-RED 350r]

How's what? Do you ever hear that conspiracy crap and not wonder who they might be talking about? I'm not on that tinfoil hat wagon dude, I'm just entertaining the thought. Lol

Just playing along man.

 

[Brewz]

Ahhh this is a great thread and very well timed.

I too have a hot ported and piped 394 which has a similar issue.
When below full running temp it comes up to full rpm and then suddenly changes tune to this weird flat warble that sounds like it’s very rich, but it’s not.
Then if you lean it out a bit more it will do this and then go lean like it’s sucked the carb dry.

Once it’s at full temp and running a bit fatter it seems to hold steady rpm at WOT but it’s a race saw and needs to rev more.

From memory it’s at about 96/120/80 ish.

I also built a piped 084 for a mate and he said it’s started to go lean after it’s held at full throttle for a few seconds.

I’m thinking I might drill the carb a bit and try the double gasket trick

 

[Brewz]

Well measured the diameter of the fuel feed hole under the metering valve on the WJ-39 and it was about 0.8mm
I dug out a chinese WJ 660 carb and measured the same feed hole. 1.2mm

I drilled the fuel feed out to 1.2mm on the WJ-39 and then decided to open the fixed H jet from 0.56mm to 0.72 but in doing so went through and buggered the main nozzle.

So, wanting to see if more fuel fixes the tuning issues, I modified the chinese 660 carb to accept the husky throttle. Choke didn't matter as it doesn't have one being a race saw.
I had already converted the 394 to external impulse so this made the 660 external impulse perfect.
I have drilled the chinese carbs main jet to .72 and it already has a 1.2mm fuel passage to the meetering valve.
Also gave it a nice fuel feed channel to the H side fuel inlet hole.

Fits and works perfect but being 8:30pm its a bit late to fire up a pipe saw with next door having young kids that will be in bed.

Tomorrow

 

[Deets066]

Well measured the diameter of the fuel feed hole under the metering valve on the WJ-39 and it was about 0.8mm
I dug out a chinese WJ 660 carb and measured the same feed hole. 1.2mm

I drilled the fuel feed out to 1.2mm on the WJ-39 and then decided to open the fixed H jet from 0.56mm to 0.72 but in doing so went through and buggered the main nozzle.

So, wanting to see if more fuel fixes the tuning issues, I modified the chinese 660 carb to accept the husky throttle. Choke didn't matter as it doesn't have one being a race saw.
I had already converted the 394 to external impulse so this made the 660 external impulse perfect.
I have drilled the chinese carbs main jet to .72 and it already has a 1.2mm fuel passage to the meetering valve.
Also gave it a nice fuel feed channel to the H side fuel inlet hole.

Fits and works perfect but being 8:30pm its a bit late to fire up a pipe saw with next door having young kids that will be in bed.

Tomorrow

View attachment 118245

View attachment 118246

View attachment 118247

Hope it works out for ya. I never had much luck with the aftermarket 69's

 

[Brewz]

The old ones were rubbish but this new generation seem to be great.
I have used several lately with no issues.
They are jetted rich, tune fine etc etc.

Tomorrow will tell

 

[wcorey]

Very true. Drilling the seat will expose more surface area of the needle exposed to pressure, generating a larger force acting on the lever and lower the pop off pressure.

So, it all comes back to pop off pressure?

Thinking more about this, raising the lever also puts more free length on the spring, also decreasing pop off.
A lot of different forces at work there...

 

[Chainsaw Jim]

I drilled the fuel feed out to 1.2mm on the WJ-39 and then decided to open the fixed H jet from 0.56mm to 0.72 but in doing so went through and buggered the main nozzle.

No, you actually did something you were supposed to do to begin with. Those things usually need a few more passages.
Always punch out the main nozzle before drilling out the high side or you'll end up with shavings plugging the nozzle all up. Don't forget to back out the high screw before punching out the nozzle on some carbs because the tip of the screw can extend into it and rip a deep gouge on its way out.

Drilling out the high side is rarely necessary with gasoline builds.

 

[wcorey]

Good point about backing the H needle out, that has never occurred to me to do.

I popped the nozzle out on the wj to check the feed holes, they're huge.

I didn't drill the main bypass jet because the useable tuning range on the H was less than a couple turns.
Is this a correct assumption or am I missing something...?