Modded 394 lean tuning issue WTF...

[RIDE-RED 350r]

He stated that when first built the saw ran fine and predictably. Then over time it would lean out in long cuts, doing so quicker and quicker. He would retune it and then it would go pig-rich. Then eventually it got to the point that now matter how far open with the H jet it was still too lean

 

[Deets066]

I know

Damn near lay money that the intake is 82 or more though, just sayin

 

[Chainsaw Jim]

Fixed

I hope I wasn't too misleading.

 

[RIDE-RED 350r]

I know

Damn near lay money that the intake is 82 or more though, just sayin

Ok, but can you help me understand why it would run normally at first and then progressively get worse? Legit question, you have been doing this alot longer than I have

I can certainly see where too much intake can make the intake charge lazy and lose atomized fuel mix in the case. What's stumping me is how it progressively got worse

 

[Deets066]

Ok, but can you help me understand why it would run normally at first and then progressively get worse? Legit question, you have been doing this alot longer than I have

Not sure really, I don't think anyone came up with a reason either. Sometimes saws are just weird like that. But with less intake it wouldn't need drilled. He even said the lean issues followed the ported jug to the other good saw. Thus, meaning there was a pin hole in the casting of the jug. Or the porting caused it.

 

[RIDE-RED 350r]

Not sure really, I don't think anyone came up with a reason either. Sometimes saws are just weird like that. But with less intake it wouldn't need drilled. He even said the lean issues followed the ported jug to the other good saw. Thus, meaning there was a pin hole in the casting of the jug. Or the porting caused it.

True, the issue following the cylinder certainly leads in that direction.

Kind of a similar example... I recall reading an article by Olav Aaen (renowned snowmobile racing guy) about sled racing back in the day. This particular article focused on over-carbing an engine and how going with huge carbs on cylinders that can't efficiently support them they were running huge main jets to compensate for the loss of velocity in the carb Venturi due to being run on a smaller displacement engine. Basically they had to make up for that loss in velocity with more fuel.

 

[Deets066]

True, the issue following the cylinder certainly leads in that direction.

Kind of a similar example... I recall reading an article by Olav Aaen (renowned snowmobile racing guy) about sled racing back in the day. This particular article focused on over-carbing an engine and how going with huge carbs on cylinders that can't efficiently support them they were running huge main jets to compensate for the loss of velocity in the carb Venturi due to being run on a smaller displacement engine. Basically they had to make up for that loss in velocity with more fuel.

That's exactly true, with less velocity of the smaller engine it won't pull enough through the Venturi. With a diaphragm carb anyway.
I've got an 024 super with a WJ 69 on it. Seems to work best with the largest jet possible. Without drilling.

 

[wcorey]

I see that all the time.

So why do you think that is, what are the dynamics of it?

 

[Deets066]

So why do you think that is, what are the dynamics of it?

How much intake duration are you running

 

[Chainsaw Jim]

So why do you think that is, what are the dynamics of it?

Nothing has yet been proven that the saw wasn't showing signs from the get go. Were only going from your perspective and a bunch if runs at a gtg while other saws were probably running in the background to make it nearly impossible to hear.

 

[Mastermind]

I had one 3120XP that did exactly the same thing. One....out of dozens that I've built the very same way. Drove me nuts. I finally drilled the seat, and fixed it.

I'm thinking it had the ignition timing a little further advanced on this one cause Cliff Helsel broached the flywheel for me, but I'm not 100% sure. Retarding it some helped, but it would still end up going lean after a few big cuts.

It was this saw that made me start cutting a path from the spring well across to the high speed feed hole. If nothing else, it added volume to the metering area.

I will be trying to install a larger needle and seat in the WG carbs as soon as I get some "extra time".

 

[wcorey]

If you have a lot of intake duration it's very common to have to drill the carb. Where are you at on the intake here @wcorey

Not sure, I'm not home to check notes, if I can find them.
My "usual" on this saw would be something like 98 118 80
but I'm not above going a couple degrees too far on the intake when cutting bases.

 

[wcorey]

Nothing has yet been proven that the saw wasn't showing signs from the get go. Were only going from your perspective and a bunch if runs at a gtg while other saws were probably running in the background to make it nearly impossible to hear.

Point taken...

Though actually it was run at a half dozen gtg's by multiple users plus dozens of dyno runs on a few different occaisions.
Plus the backyard testing.
Not a lot of overall hours but a chit ton of short runs.

Bottom line for me is that regardless of if it was showing "signs" from the get go, it got progressively more pronounced over a substantial period of time, in a very obvious manner. After it became very obvious, nothing I could do changed it's decline into unusability.

 

[Chainsaw Jim]

I will be trying to install a larger needle and seat in the WG carbs as soon as I get some "extra time".

I just did that with a Zama EL50 and it worked great.

 

[Chainsaw Jim]

Point taken...

Though actually it was run at a half dozen gtg's by multiple users plus dozens of dyno runs on a few different occaisions.
Plus the backyard testing.
Not a lot of overall hours but a chit ton of short runs.

Bottom line for me is that regardless of if it was showing "signs" from the get go, it got progressively more pronounced over a substantial period of time, in a very obvious manner. After it became very obvious, nothing I could do changed it's decline into unusability.

Which exact fuel filter were you using? Was it modded?

 

[Deets066]

Which exact fuel filter were you using? Was it modded?

If it was the fuel filter then drilling the jet wouldn't fix it

 

[wcorey]

What was it that caused the carb to need drilling?

If I understand tthe question correctly, this is what I'd like to get a handle on, more or less point of the thread.

I look at that it was "breaking in", "seating the rings"... but really what does that mean in practical terms?

If it's just gaining comp then just bump the comp to begin with...
If I believed that...
Something more related to dynamic comp?
Lessening friction in the cylinder?
What's going on in there...?

 

[wcorey]

Which exact fuel filter were you using? Was it modded?

Tried running it without the filter...

 

[MustangMike]

As the saw breaks in it runs stronger, more RPMs, needs more fuel. Could be a combo of rings, bearings, seals just getting into fighting mode!

So Bill, now I want to run this saw, please also bring it to NY GTG also!!!

 

[wcorey]

But with less intake it wouldn't need drilled. He even said the lean issues followed the ported jug to the other good saw. Thus, meaning there was a pin hole in the casting of the jug. Or the porting caused it.

But the intake duration stayed the same while the condition got worse.

One of the first things I checked was the jbweld patch on one transfer bulge. I often like very flat tranfer roofs and nice deep radius transitions so grind a lot out in those corners, therfore tend to break through on occasion.
Not unexpected...

Plus it passed multiple press/vac tests, wouldn't do that with transfer holes...