Modded 394 lean tuning issue WTF...

[wcorey]

Is this the one?

Yeah Jer, that be it.
With the welded up handlebar and patched together flag from a conflict with a skidsteer, lol.

That and the stubby bar/square ground chain that I cant seem to find at the moment.


You must have quite the photo archive of all those NY events.
Like J. Edger, a file on everyone...

 

[wcorey]

Agreed

We will leave CT Yank out of the convo (do you remember that Bill?).

What??? He's my best buddy....!

 

[wcorey]

I've been trying to remember this saw, and I cant ........... now I know why

Last time it was at Dan's you wandered over and we were discussing the issues while I had it apart on the ground...

And please don't don't put me in the same sentence with Scott like that, he's on a level with saws I'll never even come close to.
I'm well into the point where it seems like the more I know, the more clueless I feel about it.

 

[wcorey]

Happens a lot to me with 036’s Bill. Run fine, but port them and they do the scream thing. Any restriction in the fuel circuit, from the filter to the nozzle, will do it. Tank vent as well.

Just had the same issue with a 361 I did with an HD50 carb. Screamed until I drilled the carb jet. Where you are with your H needle can be a clue.

I believe it just has to start occurring, then it becomes a vicious cycle as,the rpms climb. As Kev said, it could be thicker mix or more ethanol in the fuel that changed it (if u use E fuel).

This isn't the first time I've had to mess with the fuel system capacity after porting a saw.
Just the first time it occurred over such an extended time after the fact and in such incremental fashion.

My question really isn't about why it would need more fuel capacity after porting.
It's why the need seems to keep increasing as the saw gets more time on it...

If it had much to do with differences in fuel/mix, it seems like it would have been more up/down/all around, instead of a steady decline.

 

[wcorey]

Not to derail much, but what was the dyno numbers on this saw?

I'll have to pull some files to see, there's like a gazillion of them. There are links to a lot of it on here somewhere. I think the upper numbers were around 10 hp...
It did pull the highest numbers of any saw we put on it but we didn't do many bigger saws and no other 394's so...
That said, the dyno numbers were all over the place, I don't give much credence to individual runs, was more of an averaging thing over a bunch of them.

 

[Redfin]

My question really isn't about why it would need more fuel capacity after porting.
It's why the need seems to keep increasing as the saw gets more time on it...

One thing I havent seen mentioned is the filter? Did you run the same filter? Was it a new filter when built? Clean it well during the trouble shooting process?

I could see where along with the ring finding its spot in the jug, the filter continually gets dirtier pulling more fuel. I would think it would take several different issues to empty that side of the carb in a progressive fashion.

 

[usmcbuckwild]

Not to sound stupid, but have you replaced the fuel line? I had a stroked 408 small block Mopar that would do the exact same thing. Tore the engine down 3 times, 4 different carb/intake combos, 3 different fuel pumps, 3 different fuel pressure regulators; was literally pulling my hair out. Turned out to be a weak fuel line that would collapse under draw at WOT. Replaced with braided stainless and engine was a screaming animal.

Is it possible that there is a weak spot in the fuel line that is collapsing and pinching off flow? When the engine gets warm, so do the lines and they get soft as they heat up making it more susceptible to kinking/pinching.

Just an idea.

 

[huskyboy]

This isn't the first time I've had to mess with the fuel system capacity after porting a saw.
Just the first time it occurred over such an extended time after the fact and in such incremental fashion.

My question really isn't about why it would need more fuel capacity after porting.
It's why the need seems to keep increasing as the saw gets more time on it...

If it had much to do with differences in fuel/mix, it seems like it would have been more up/down/all around, instead of a steady decline.

Probably the rings seating and everything breaking in would be my guess. Took about 10-15 tanks for the cabers to seat on a 394 I rebuilt.

 

[Mastermind]

Not to sound stupid, but have you replaced the fuel line? I had a stroked 408 small block Mopar that would do the exact same thing. Tore the engine down 3 times, 4 different carb/intake combos, 3 different fuel pumps, 3 different fuel pressure regulators; was literally pulling my hair out. Turned out to be a weak fuel line that would collapse under draw at WOT. Replaced with braided stainless and engine was a screaming animal.

Is it possible that there is a weak spot in the fuel line that is collapsing and pinching off flow? When the engine gets warm, so do the lines and they get soft as they heat up making it more susceptible to kinking/pinching.

Just an idea.

Very good post sir. This is one of those things that should never be overlooked.

On the 3120XP I posted about, I ran a new piece of line from a water bottle of fuel tied to the handlebar to eliminate the vent, filter, and possibility of a soft or kinked line.

 

[Termitebuffet]

Very good post sir. This is one of those things that should never be overlooked.

On the 3120XP I posted about, I ran a new piece of line from a water bottle of fuel tied to the handlebar to eliminate the vent, filter, and possibility of a soft or kinked line.

You had me til water bottle.....

Sawhawgz, ruining the internet since 2012...

 

[wcorey]

One thing I havent seen mentioned is the filter? Did you run the same filter? Was it a new filter when built? Clean it well during the trouble shooting process?

I could see where along with the ring finding its spot in the jug, the filter continually gets dirtier pulling more fuel. I would think it would take several different issues to empty that side of the carb in a progressive fashion.

Not to sound stupid, but have you replaced the fuel line?

I know it's a long TL;DR first post and bunch more to read after that but...
Yeah the filter and fuel line was mentioned as checked off the list early on and still more after that.
Most everything typical to this sort of issue was done with a great deal of redundancy over 3 years of... AaahrrrrR....!

One of the first things I do in this type situation, is disconnect the line from the carb and slip another larger/smaller long piece of clear line over/in it and blow through to get an idea of how well it flows. If the filter isn't particularly restricted the line shouldn't be collapsing but if I'm suspicious at all I try running it without the filter.
Then draw fuel up through the line while wiggling the tank around and look for bubbles, most important part here is not to drink any gas, lol.
Ultimately in this case I changed the line anyway, maybe more than once considering how frustrated with it I was getting over the years.

I sometimes try a version of the trick Randy just posted but with just long piece of filled up fuel line off the carb.

I guess you could say it did more or less "take several different issues to empty that side of the carb in a progressive fashion",
even though the fix was one simple thing.
The needle seat was restricting an ever increasing need for fuel as the saw broke in.

What really surprised me was that I first doubled the area of the hole in the seat (.037" to .046) and it still wasn't enough.
I'd have to guess that even though the hole/area was doubled, the way the needle taper sits down in the seat wasn't.

Out of curiosity I'm tempted to drill another carb but only part way down to see if the seat area itself is the real restriction...

Not enough time in the day dammit...

 

[wcorey]

Probably the rings seating and everything breaking in would be my guess. Took about 10-15 tanks for the cabers to seat on a 394 I rebuilt.

Yes but you'd think rings seating would be mostly about compression and maybe a bit about friction.
Is 5-10 psi on an already 200+ psi saw really the overwhelming deciding factor here...?

Only thing I can come up with is that the psi we see cranking it over has a much different dynamic than whats happening at speed.

 

[p61 western]

I know it's a long TL;DR first post and bunch more to read after that but...
Yeah the filter and fuel line was mentioned as checked off the list early on and still more after that.
Most everything typical to this sort of issue was done with a great deal of redundancy over 3 years of... AaahrrrrR....!

One of the first things I do in this type situation, is disconnect the line from the carb and slip another larger/smaller long piece of clear line over/in it and blow through to get an idea of how well it flows. If the filter isn't particularly restricted the line shouldn't be collapsing but if I'm suspicious at all I try running it without the filter.
Then draw fuel up through the line while wiggling the tank around and look for bubbles, most important part here is not to drink any gas, lol.
Ultimately in this case I changed the line anyway, maybe more than once considering how frustrated with it I was getting over the years.

I sometimes try a version of the trick Randy just posted but with just long piece of filled up fuel line off the carb.

I guess you could say it did more or less "take several different issues to empty that side of the carb in a progressive fashion",
even though the fix was one simple thing.
The needle seat was restricting an ever increasing need for fuel as the saw broke in.

What really surprised me was that I first doubled the area of the hole in the seat (.037" to .046) and it still wasn't enough.
I'd have to guess that even though the hole/area was doubled, the way the needle taper sits down in the seat wasn't.

Out of curiosity I'm tempted to drill another carb but only part way down to see if the seat area itself is the real restriction...

Not enough time in the day dammit...

A old trick I was taught was to double the gasket, and raise the lever accordingly. Could save you the hassle of drilling anything.

 

[wcorey]

A old trick I was taught was to double the gasket, and raise the lever accordingly. Could save you the hassle of drilling anything.

That is an interesting idea, though on the face of it seems like it would just increase the storage volume as opposed to throughput capacity and only work in a transient situation.
Something I'd try if I had more time.

 

[srcarr52]

That is an interesting idea, though on the face of it seems like it would just increase the storage volume as opposed to throughput capacity and only work in a transient situation.
Something I'd try if I had more time.

The lever can open the needle valve more since it now has more travel.

 

[wcorey]

The lever can open the needle valve more since it now has more travel.

Ah, lightbulb...

 

[Mastermind]

A old trick I was taught was to double the gasket, and raise the lever accordingly. Could save you the hassle of drilling anything.

The lever can open the needle valve more since it now has more travel.

Sadly, it took me years to realize this trick. We need to be willing to share this stuff more often. I should have mentioned it in my WG mod thread too.

 

[srcarr52]

Sadly, it took me years to realize this trick. We need to be willing to share this stuff more often. I should have mentioned it in my WG mod thread too.

Personally I would have lowered the pop off pressure. You often need to do this on extremely ported saws with a lot of intake timing. The crankcase pulse is no longer strong enough to open the needle for very long.

Also lowered pop off pressure is a side effect of the extra gasket and raising the lever accordingly. It's usually around 2-3 psi of pop off pressure drop to raise the lever that much.

 

[Mastermind]

Personally I would have lowered the pop off pressure. You often need to do this on extremely ported saws with a lot of intake timing. The crankcase pulse is no longer strong enough to open the needle for very long.

Also lowered pop off pressure is a side effect of the extra gasket and raising the lever accordingly. It's usually around 2-3 psi of pop off pressure drop to raise the lever that much.

Something to note is that once the seat is drilled, pop off pressure drops off. On the WGs that I do after drilling they pop at 15psi or so. I suppose it is because the needle is very small in relation to the increased diameter of the hole.

 

[srcarr52]

Something to note is that once the seat is drilled, pop off pressure drops off. On the WGs that I do after drilling they pop at 15psi or so. I suppose it is because the needle is very small in relation to the increased diameter of the hole.

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?