Throttle Response

[Farmer_Nate]

How does one get the best possible throttle response from a saw? I want my saws to leap into action when I trigger 'em.
What variables affect it?

I have a particular saw is cold blooded. It starts and runs great, but when it's cold throttle response is weaker. After warming up, it is more snappy. I of course warm all my saws before really getting on the throttle or loading them.

Tell me if I am wrong...things that affect it:

1 ) L screw. Should be a little rich?
2) Chain and chain lube and chain size, i.e. weight and chain friction, stuff that takes energy to get things going?
3) Idle speed? Faster idle jumps more on trigger press?
4) Design of engine such as "blowdown" and stuff like that?

Thanks

 

[sean donato]

Too many variables to pinpoint why one saw has better response then another. Carb settings, carb size, fuel atomization, fuel pooling, ignition timing, design of intake tract, ect.

 

[lone wolf]

How does one get the best possible throttle response from a saw? I want my saws to leap into action when I trigger 'em.
What variables affect it?

I have a particular saw is cold blooded. It starts and runs great, but when it's cold throttle response is weaker. After warming up, it is more snappy. I of course warm all my saws before really getting on the throttle or loading them.

Tell me if I am wrong...things that affect it:

1 ) L screw. Should be a little rich?
2) Chain and chain lube and chain size, i.e. weight and chain friction, stuff that takes energy to get things going?
3) Idle speed? Faster idle jumps more on trigger press?
4) Design of engine such as "blowdown" and stuff like that?

Thanks

Buy a 500I

 

[Mad Professor]

If all else is well place to start is ritchen Lo

 

[Farmer_Nate]

If all else is well place to start is ritchen Lo

Yeah, but the saw already smokes a bit on 40:1. May be too rich still?
Will too rich H cause poor throttle response or is it unrelated?
Saw 4-strokes but not in the cut

 

[user 122190]

Buy a 500i. Very fast response.

 

[Farmer_Nate]

Buy a 500i. Very fast response.

That would be nice, but a bit off topic.
I am talking about most other older carbureted saws.
Of course a fuel injected machine is going to have that feature.

 

[user 122190]

That would be nice, but a bit off topic.
I am talking about most other older carbureted saws.
Of course a fuel injected machine is going to have that feature.

My old, now gone, ms290 was getting sluggish. Rebuilt the carb and became like new with quick throttle responce.

 

[bwalker]

If all else is well place to start is ritchen Lo

That will make throttle response doggy.
To get crisp throttle response you need the LS on what most of you would consider the lean side, not overly rich.

 

[quattro.pilot]

this is a deep rabbit hole of a question.

for the variables already mentioned how could one not also consider that rotating mass plays a part......and then for that matter too what about the throttle linkage i.e. push rod (357xp) vs. roller push rod (242xp) vs. cable (372) vs. others?

 

[bwalker]

this is a deep rabbit hole of a question.



for the variables already mentioned how could one not also consider that rotating mass plays a part......and then for that matter too what about the throttle linkage i.e. push rod (357xp) vs. roller push rod (242xp) vs. cable (372) vs. others?

Fly wheel and crank mass plays a part, but mostly how fast it revs out and the engines response to changes in load.
When throttle response is talked about its mostly about how crisp the carb settings are. On a saw your kinda limited as it only has two jets. As a result you ifetn can't get them laser crisp like you can on a bike or sled carb that have 5 or 6 jets.

 

[Farmer_Nate]

Thanks all.

Since the saw in question is an older Husqvarna similar to another I have which performs better, I am still leaning toward carb adjustments being the culprit.

Carb parts such as diaphragms are new.
Seals check out in both vacuum and in pressure.

I can definitely double-check linkages. I guess slop there could cause problems for sure.

 

[quattro.pilot]

On a saw your kinda limited as it only has two jets.

Ya I can see how the 2-jet design is ultimately limiting. A far more even and tuned fuel delivery would be with multiple fuel jets.

 

[Mad Professor]

That will make throttle response doggy.
To get crisp throttle response you need the LS on what most of you would consider the lean side, not overly rich.

You get idle/Lo sorted out. Go to Hi. Back to idle/Lo. Repeat. Maybe twice

If bogging when opening throttle it's too lean on Lo.

 

[Farmer_Nate]

OK

I have done the method before of ...

1) listen to idle speed,
2) turn L screw,
3) listen to idle speed,
4) adjust L to find highest idle speed location,
5) then richen L just a tad from there to lower idle a tick

I always make sure H is rich enough to cause burbling or 4-strokin' at the top end while unloaded.
Maybe it is still too rich overall

 

[Mad Professor]

OK

I have done the method before of ...

1) listen to idle speed,
2) turn L screw,
3) listen to idle speed,
4) adjust L to find highest idle speed location,
5) then richen L just a tad from there to lower idle a tick

I always make sure H is rich enough to cause burbling or 4-strokin' at the top end while unloaded.
Maybe it is still too rich overall

I put Lo halfway between race(lean) and die(rich) and reset idle. Repeat.

 

[bwalker]

You get idle/Lo sorted out. Go to Hi. Back to idle/Lo. Repeat. Maybe twice

If bogging when opening throttle it's too lean on Lo.

You went it set just rich enough it doesn't lean bog when you crack the throttle.
This is another reason MTronic/Autotune is a good thing.

 

[Farmer_Nate]

Sensors are nice.

 

[Mad Professor]

Sensors are nice.

Until they go bad.

I like the old pre-limiter carbs.

I like my old truck with a manual choke that I can work on with simple tools, even if I have to warm it up and be careful cold weather not to flood it. Todays kids are baffled with a car/truck choke, soon they won't know what a clutch does..........

 

[Farmer_Nate]

True