Stihl 461, troubeshooting.

[spudulike]

Not sure where that leaves us. The fault gets sort of better with swapping the carb but the saw has no power???

It is possible it has two faults, that one makes life interesting when diagnosing. Inspecting lines visually is pretty hopeless, you must plug one end and put a bit of pressure on them with a pop off gauge or pressure tester. if the impulse has come loose then that can cause this issue as can a blocked fuel tank breather and a split fuel line.

If you move a good carb from a healthy machine and the revs race then it sounds like an air leak but am not 100% you have done this. You should have 95% of the carb set if set up on another machine.

A bit random this fault! Those impulse lines can come off the union on the crankcase cylinder base.

[paddyvero]

I think it does have 2 faults yes. First a bad carb, second unknown. 

Yes I swapped a carb in from a healthy saw, it ran, idled, and rev up but was gutless, so assuming the original carb is bad, what would make the saw have no power yet run ok with no load?

[spudulike]

Quite a bit: -

Fuel starvation - carb issue, split fuel or impulse line, blocked fuel filter, blocked breather.

Lack of compression through wear or partial seize

Spark/coil/plug/HT issues, kill wire partially shorting

Blocked muffler, carboned exhaust port

Flywheel key failing causing ignition timing to be retarded slightly

Blocked air filter

Split inlet manifold

Choke partially sticking on

There may be more but there you go! If the saw has good compression, the carb is the next most likely failure but if it is a known good carb then it is a toss up between failed rubber parts and HT issues.

 

[paddyvero]

Thanks Spud. 

It seems to me that it has good compression, but I dont have any tools to test that. 

Im getting a good spark and the plug is brand new.

Choke is functioning fine.

Air filter is clean.

The muffler isnt blocked, but the exhaust port is very blackened, how bad would it need to be to cause issues?

The electrical stuff is abit to advanced for me atm.

 

I think its time for it to go to the shop, its 1.5hrs away so was hoping to avoid.

 

Thanks

[htb]

Or send to spud if his is bench is relatively free

[spudulike]

The port size would need to be made smaller with carbon - 1/4 of its size would make a difference - mostly an issue on hedge trimmers and strimmers.

 

My bench is rammed and rammed full again!!!

[paddyvero]

Yeh its not that bad. 

Ah, this saw is in the PNW. Whistler BC, so wont be making the trip to Spud unfortunatly.