Stihl 461, troubeshooting.

[paddyvero]

Hi all. I have a 461 that I cant get running, so looking for advice/ assistance.

Its a 4yr old saw, that works hard.

It will fire up, runs rough and then cuts out.

I have pulled it apart, sprayed the carb with cleaner, and set it to factory spec, although the H screw doesnt seem to have a limiter?

New plug.

Bore and piston look good to me, seems lots of compression.

Exhaust port is blackened but open, and I have removed the spark arrester.

Has fresh fuel in it. 

 

Any ideas?

[Rough Hewn]

Do you get a spark from the plug?
Are you getting fuel through?

[Stubby]

split impulse line ?

[spudulike]

Be thankful it doesn't have fuel injection and auto tune

As others have said, check the impulse line as without it, there will be little fuel being pumped in to the carb. Check the pump diaphragm is in good condition, especially on the pump flaps that can get pierced by the hole underneath. The most common carb issue is the good ol gauze strainer. It can sometimes look clean but take it out and use a strong light and magnifying glass to look through it and ensure those open areas are OPEN!

Check the tank breather, unlikely to be fully blocked but worth cleaning off. Make sure the fuel line is OK, not likely to fail on a 4 year old machine but you can  be caught out.

Change the plug, they can crack and do all sorts!

When it starts: -

1) Are you able to rev it out to near maximum revs?

2) is the engine smoking and running like it is on choke?

3) is the engine screaming?

4) Will the saw idle but not rev?

5) Does the saw pulse and misfire?

6) Is the idle speed high if the saw can idle?

Sometimes these carbs get some pretty strange issues and I have found that the only way to clear them is 1 hour in a dedicated ultrasonic cleaner on high heat and using a decent carb additive. I am guessing in these cases, the check valve or some of the hard to get to cavities have resin, water or debris in them and only a good boil will shift it as carb cleaner doesn't touch it.

In this I am assuming, from your description, that the saw has decent compression!

[paddyvero]

Thanks chaps, things to do later then.

Spud, it will rev up but not to maximum.

Yes it is smokey. Currently cant get it to idle, wont run long enough to tune it at all. 

I have a feeling its the carb, especially as our fuel here has lots of ethanol in it. 

[spudulike]

OK, sounds like it is running rich, make sure the choke flap valve is opening fully, make sure the air filter is clean, the H screw should be one turn out if the limit cap has been removed and if it is still bad, I would suspect a leaking check valve so a deep Ultrasonic clean may be in order.

[paddyvero]

Ive taken it apart again today.

Impulse line looks fine, didnt remove it though.

Fuel line also looks fine, and tank breather.

Took the carb apart and cleaned it as best I could with carb cleaner.

Air filter is clean.

 

Its running a little better, revs out to near max, but chain runs fast without throttle, if I apply chainbrake it will stall out quite quickly, but if I adjust the LA any lower it wont run at all. 

 

I have another strong running 461, so Ill swap the carb out and see what happens. 

[Stubby]

Might be an air leak from some where . Crank seals maybe ?

[paddyvero]

Stuck another carb in, ran well on tick over, revd up well, abit smokey, but wont work under load at all! 

[Haironyourchest]

My one melted the crankshaft bearing on the clutch side, just for fun, see if there is wiggle in the crankshaft.