Husqvarna t540 bog blues.

[Chris-PA]

And if they would have provided a L screw 99% of the complaints wouldn't exist. My only conclusion is that autotune is still such a crappy setup that with the addition of a L screw it wouldn't meet emissions.

I say crappy just in the context of emissions just to be clear

My point was the opposite - it would be impossible to be less accurate than a conventional carb. They're one step from pouring gas down the intake. The darn things go so rich they misfire just from lifting and increasing the rpm/air velocity a few percent.

I think the feedback system works just fine. Rather the non-feedback modes are still just plain old carb stuff, but they took all the adjustments off. So then you have trouble when the system cannot adjust - like during acceleration.

And really, I don't get why - I applaud trying to make a saw run cleaner while improving performance too, but they've already got strato engines to improve scavenging losses and as I said just about any feedback control at WOT would drastically improve the carbs. Meanwhile other companies just use quad transfers and traditional carbs, plus some cat mufflers on portions of their lineup. The emissions limits clearly must not be hard to meet. You'd think a L adjustment would be OK.

 

[fordf150]

You would think but I assume the L or accelerator pump put them over the limit so they do away with it and set the L circuit just rich enough to not cause problems on most saws. Just speculating though. Maybe the addition of the H solenoid made it impossible to include L screw.

 

[Chris-PA]

You would think but I assume the L or accelerator pump put them over the limit so they do away with it and set the L circuit just rich enough to not cause problems on most saws. Just speculating though. Maybe the addition of the H solenoid made it impossible to include L screw.

The L is pretty much irrelevant with regard to the present limits, and the pump is only active when you are opening the throttle Besides, the extra fuel for acceleration normally comes from an L set too rich anyway - it has to come from somewhere.

I believe the newer AT can control idle mixture and H mixture. It cannot control acceleration mixture (making it vulnerable to bogging issues?).

 

[Rx7man]

It sounds like saws are at the point now that cars were in the 80's.. getting excessively complex because they won't spring for the technology that would make it work right.. 80's cars had carbs with 10 freaking solenoids on them, and miles of vacuum hoses... Now, (at least that part) has been simplified with fly-by-wire and a bunch of other things, and there's hardly a vacuum hose left anymore.

Until saws have full EFI I don't think you'll ever get it just right without getting excessively complex in the process... Of course I don't look forward to computers on chainsaws either!

 

[smokey7]

Why cant compensating carbs/strato saws tollerate partial throttle. I know 3 sifferent guys tbat use them of many models all same lean seize scoring, usually from say less then 1 tank of fuel. All broke in so they were not too tight. All running 40:1 e free with a high quality oil. I use all of there fuels. As a test i gave them a 3400 to see if they could kill it running partial throttle its still running no damage at all. So why cant at/mt strato handle it aithout blowing up

 

[Chris-PA]

It sounds like saws are at the point now that cars were in the 80's.. getting excessively complex because they won't spring for the technology that would make it work right.. 80's cars had carbs with 10 freaking solenoids on them, and miles of vacuum hoses... Now, (at least that part) has been simplified with fly-by-wire and a bunch of other things, and there's hardly a vacuum hose left anymore.

Until saws have full EFI I don't think you'll ever get it just right without getting excessively complex in the process... Of course I don't look forward to computers on chainsaws either!

It's not the same system as the carbs from the 80's (yes I had data sheets for most of those vacuum devices). For one thing here they are only trying to keep the thing from pissing raw fuel out the exhaust, which is what a traditional saw fuel system does under every situation except (maybe) max load WOT.

For any feedback system to be stable you want to have the basic function be pretty close to begin with, and then the feedback loop only needs to pull it in the last bit. So here you want a fuel system that is pretty close when it's not under control (open loop). A carb is a passive device for doing that, and works by virtue of the shape of the parts. An EFI system is an active system - it doesn't do anything without a control system, a high pressure fuel pump, at least a few sensors (rpm, throttle position, MAP or airflow, etc) and an injector.

When you inject fuel into the case of a single cylinder 2-stroke you lose most any advantage an EFI system would have had (fuel distribution and maybe vaporization), and amplify it's disadvantages (cost, complexity, weight size).

And that's without feedback.

You want feedback control, you'll need some way to measure fuel mixture whether you have a carb or EFI. Unless you want a heated O2 sensor on the exhaust you need to do something like the lean-out test used with AT, which is quite clever as it measures the mixture using only rpm changes in response to a momentary lean out of the mixture. It's got to be hard to do if something else is changing the rpm, like during acceleration.

 

[bigbluram]

Give me a carb any day, I can tune w a screwdriver ! My three huskys have been in the shop at least every 3 months for hard starting, hesitation, and so on. Everytime I'm told it's a computer reflash needed. T540 is an amazing saw when running but that's only 2 weeks out of a month on average. Throttle response blows stihl away but my 201 always runs !