Ms460 Running Weird

[SAWFISH]

I have a ms460 that Runs great most of the time, but sometimes (most of the time) when I am running it at a little over a idle to take some branches off it seems like it want's to die like it's out of gas but when I rev it up a few time it is ok again. I mostly notice this when I am done cutting through a large log at full throttle and then make a mark on the log where my next cut is going to be it will just want to die out. It has done this for some time now and it is really starting to get the better of me. The saw starts fine and runs great for the most part, it is just when it comes down from high rpm's it does not like being ran on low rpm's -- if that makes any sense--
Any help on what to look for would be greatly appreciated.

Brian.

 

[Lobo]

As this MS460 can not be an old saw IMHO the first possibility would be with the carb, I suggest you take the carb apart an clean it very thoroughly and carefully, reassemble and let her rip.

 

[TimberPig]

Sounds like the carb needs to be adjusted on the low end circuit.

 

[SAWFISH]

I probably should add when it does act up if I free rev. it at hight rpm's a few times it will stay running like normal.

 

[Billy_Bob]

Also check air and fuel filters.

 

[smcowboy1974]

Turn out the low speed screw 1/4 to 1/2 a turn counterclockwise. That may help you out.

 

[bugfart]

It's a lean symptom beginning to occur.
Pressure test the saw.

Both H and L lean settings can stall the saw at throttle. Not just L. Turn both 1/8 CCW till you pressure test. I bet it goes away.

 

[Lakeside53]

It's a lean symptom beginning to occur.
Pressure test the saw.

Both H and L lean settings can stall the saw at throttle. Not just L. Turn both 1/8 CCW till you pressure test. I bet it goes away.

Totally agree. Don't run it like this. Fix it now or you'll rebuild the saw soon... Your limiter caps may prevent the adjustment some are suggesting, but if you can't adjust it with the current limiter range, find out why.

 

[SAWFISH]

How do you pressure test the saw?? Last night I gave it a good cleaning and I noticed that the plug looked a little black (carbon?) Maybe it's fowled? I took the air cleaner of and then took the black plastic guard piece off that sits in front of the carb. and noticed that there was a slight oil film on it. Could the oil film be from the oil\fuel mix being off? I read that the boot fron the carb to the engine can get cracks in it and cause it to run poorly, but with the naked eye and not taking the boot off I did not see anything that looked wrong with it. I just went out and bought a new plug for it and some new 2 mix oil, what is your thoughts on changing those 2 things first and seeing if it makes a difference? I really don't have time to take it into the shop but yet I don't wan't to dump the money into a new one either.

Thanks, Brian

 

[Lakeside53]

Both the plug and the oil film are quite normal. Your plug can get black by just a rich idle in a few minutes so if you were trying to look at color, you'd have to determine the color at both idle settings and power settings. The oil film is just kick back though the carb and within limits, very normal.

To do a real pressure test, you need to loosen the muffler, insert a rubber dam between the muffler and cylinder, remove the carb and replace it with an adapter and then pump up the engine to .6 bar (say 9-10 psi).

Unless you have the carb adapter, and pressure pump, it's not practical for you to do a pressure test.. I do a quick and dirty pressure test by moving the piston to block the exhaust port, plug in a pressure pump (hand bulb with guage) into the impulse line, push my thumb into the carb boot (carb is off) and pump away. The engine will leak a little, but you can see immediately at .6 bar if the carb boot and impulse line are bad.


I wouldn't start replacing boots and hoses without a test. They are expensive - you could buy an after market pressure pump/gauge for less. These last for years and would be unusual on and MS460 unless you had a bad buffer etc.

 

[SAWFISH]

Well I put in the plug and messed with the H and L settings and it statrs right up idles fine runs great in the cut but once warmed up it still want's to die after medium - high
rpm's after under a load. So I had the better part of me take it into the shop and I called him via phone about it and he doesn't think that it is a problem with it sucking air in because it runs just fine at idle, starts easily, and runs fine at high rpm's with no load. He adjust the H and L settings and installed a new breather vent on the tank because the one one that was on it seemed a little suspicious (for $5.00 installed worth the try) I guess that I will see how it runs this weekend when I cut up some bigger logs.

Thanks for all the input so far, If anyone has any other ideas they are much appreciated, Brian