mtngun
Addicted to ArboristSite
Remember a few years back someone posted a thread about a 660 that kept going through top ends, even though the dealer couldn't find anything wrong with it ? And it finally turned out to be the wrong fuel filter, one that was just a little too restrictive ? The problem was hard to isolate because it only reared its head intermittently. I want to say the OP was Tommy Hall, but I could be wrong.
Anyway, I'm having a similar problem. My 066 has gone through several top ends, and it's getting mighty old.
The symptom is that the WOT RPM's creep up after sustained high speed running, like milling. The idle speed does NOT increase, only WOT.
It starts up fine, idles fine, at first makes good power, but after you've run it WOT for a while, it loses power and the WOT RPM creeps up. I can set the "H" to a very conservative speed, like 11,000 - 12,000, but at the end of a long (12 foot) cut, it's turning 13,000 - 14,000 ! After you do this a few times, the top end is toast.
Naturally, the saw has been leak tested, under both vacuum and pressure, over and over and over again. I eventually did find a tiny leak at the base gasket, and fixed it, but the WOT creep did not go away.
Sometimes the decomp valve leaks a little, but almost every decomp valve I've ever tested leaks a little, so I don't *think* that's anything to worry about.
The fuel line has been leak tested. Ditto the plastic elbow on the carb.
The tank vent seems to work -- you can blow into it easily.
The carb is always tuned conservatively by tach.
Mix is fresh WP synthetic 40:1.
The carb has been gone over time and time again with new parts. However, one thing I notice is that every time I have the carb apart -- and it has been apart frequently -- the inlet screen always needs to be cleaned. The inlet screen is dirty enough that it could be causing the WOT creep. Sorry, I forgot to take a pic of the inlet screen before I cleaned it, but it had a thin layer of fine dust across the entire screen, even though it had only seen a tank or two since the last cleaning ! ! !
The fuel filter was changed recently. I've been using the aftermarket filters from Bailey's, QA 00003 503504. They look just like the correct OEM filter #0000 350 3504. However, when I opened up the filter to see what was inside, there was only a tube of open cell foam. The pores of the foam are pretty large so it's basically useless, IMHO. Only the steel mesh is doing any good, and apparently the steel mesh is passing fine dust to the carb and letting the inlet screen plug up quickly. I don't know how that compares to an OEM filter, because I don't have one on hand to look at.
Does anyone know what's inside an OEM 0000 350 3504 filter ? Is it open cell foam like the Bailey's filter, or is it something more substantial ?
Any suggestions for things I might be overlooking ?
In addition to fixing the previously mentioned tiny leak at the base gasket, there have been other issues that may have compounded the problem:
-- last summer the fuel line tore where it connects to the fuel filter, letting dirt get sucked into the carb, clogging the inlet screen, and scuffing a piston. Replaced fuel line, filter, rings, and cleaned up piston. Ran fine for a while The fuel line incident was posted in a separate thread last summer.
-- at some point not long ago, the tip of the oiler spring broke off. The broken spring was rubbing on the clutch drum enough to still put out a little oil, so I didn't catch the problem right away. To make things worse, I was using a hard nose bar at the time. The dry hard nose bar combined with the creeping WOT to fry a piston.
-- Cleaned up jug, new piston, fixed oiler, ran fine for about a tank of gas. Then WOT started creeping up again and the piston has light scuffing (still usable). Only thing I can find wrong is a somewhat dirty carb inlet screen.
I'll work on getting an OEM filter. In the meantime, I may try running without the inlet screen. That may let fines gum up the needle and cause flooding, but that's better than frying a top end. :msp_ohmy:
Any suggestions ? This is driving me nuts.
Anyway, I'm having a similar problem. My 066 has gone through several top ends, and it's getting mighty old.
The symptom is that the WOT RPM's creep up after sustained high speed running, like milling. The idle speed does NOT increase, only WOT.It starts up fine, idles fine, at first makes good power, but after you've run it WOT for a while, it loses power and the WOT RPM creeps up. I can set the "H" to a very conservative speed, like 11,000 - 12,000, but at the end of a long (12 foot) cut, it's turning 13,000 - 14,000 ! After you do this a few times, the top end is toast.
Naturally, the saw has been leak tested, under both vacuum and pressure, over and over and over again. I eventually did find a tiny leak at the base gasket, and fixed it, but the WOT creep did not go away.
Sometimes the decomp valve leaks a little, but almost every decomp valve I've ever tested leaks a little, so I don't *think* that's anything to worry about.
The fuel line has been leak tested. Ditto the plastic elbow on the carb.
The tank vent seems to work -- you can blow into it easily.
The carb is always tuned conservatively by tach.
Mix is fresh WP synthetic 40:1.
The carb has been gone over time and time again with new parts. However, one thing I notice is that every time I have the carb apart -- and it has been apart frequently -- the inlet screen always needs to be cleaned. The inlet screen is dirty enough that it could be causing the WOT creep. Sorry, I forgot to take a pic of the inlet screen before I cleaned it, but it had a thin layer of fine dust across the entire screen, even though it had only seen a tank or two since the last cleaning ! ! !
The fuel filter was changed recently. I've been using the aftermarket filters from Bailey's, QA 00003 503504. They look just like the correct OEM filter #0000 350 3504. However, when I opened up the filter to see what was inside, there was only a tube of open cell foam. The pores of the foam are pretty large so it's basically useless, IMHO. Only the steel mesh is doing any good, and apparently the steel mesh is passing fine dust to the carb and letting the inlet screen plug up quickly. I don't know how that compares to an OEM filter, because I don't have one on hand to look at.
Does anyone know what's inside an OEM 0000 350 3504 filter ? Is it open cell foam like the Bailey's filter, or is it something more substantial ?
Any suggestions for things I might be overlooking ?
In addition to fixing the previously mentioned tiny leak at the base gasket, there have been other issues that may have compounded the problem:
-- last summer the fuel line tore where it connects to the fuel filter, letting dirt get sucked into the carb, clogging the inlet screen, and scuffing a piston. Replaced fuel line, filter, rings, and cleaned up piston. Ran fine for a while The fuel line incident was posted in a separate thread last summer.
-- at some point not long ago, the tip of the oiler spring broke off. The broken spring was rubbing on the clutch drum enough to still put out a little oil, so I didn't catch the problem right away. To make things worse, I was using a hard nose bar at the time. The dry hard nose bar combined with the creeping WOT to fry a piston.
-- Cleaned up jug, new piston, fixed oiler, ran fine for about a tank of gas. Then WOT started creeping up again and the piston has light scuffing (still usable). Only thing I can find wrong is a somewhat dirty carb inlet screen.
I'll work on getting an OEM filter. In the meantime, I may try running without the inlet screen. That may let fines gum up the needle and cause flooding, but that's better than frying a top end. :msp_ohmy:
Any suggestions ? This is driving me nuts.
