Walbro carb help

[Patrick62]

when they work well, it is nothing short of amazing.

When they don't it is.... amazing....

Okay gentlemen. I need to figure out what to do here. I have this mint 2171 Jred that I ran 3/4 of a tank outta today. The engine runs really well, compression is excellent. When the carb is wiling to provide the correct mixture it is amazing! Started out pretty good. adjust the L a touch leaner for the lofty elevation I am at, and dial the H in to something around 12,500. Tossing chips... really well. 20 minutes later and something ain't right. Adjust it a bit? Didn't help. It goes into a "bog mode" RPM refuses to climb above about 7000 and power is way way down. The sound of the engine is like it is 4 stroking... missing quite frequently. On the next cut, it might wind up normal, or run in the bog mode. roll of the dice.

I was just thinking here, while typing this out. Could this be a ignition problem? And not a carb problem??

How would I check it out?

Come to think about it... when it went into "bog mode" it was not dumping a ton of smoke... that might imply a igniton problem. Now the next question, would be.... spark plug? Coil? Muffler bearings??

Thanks in advance. The saw is a real joy to run, smooth and responsive when it is willing to cooperate.

 

[7hpjim]

when they work well, it is nothing short of amazing.

When they don't it is.... amazing....

Okay gentlemen. I need to figure out what to do here. I have this mint 2171 Jred that I ran 3/4 of a tank outta today. The engine runs really well, compression is excellent. When the carb is wiling to provide the correct mixture it is amazing! Started out pretty good. adjust the L a touch leaner for the lofty elevation I am at, and dial the H in to something around 12,500. Tossing chips... really well. 20 minutes later and something ain't right. Adjust it a bit? Didn't help. It goes into a "bog mode" RPM refuses to climb above about 7000 and power is way way down. The sound of the engine is like it is 4 stroking... missing quite frequently. On the next cut, it might wind up normal, or run in the bog mode. roll of the dice.

I was just thinking here, while typing this out. Could this be a ignition problem? And not a carb problem??

How would I check it out?

Come to think about it... when it went into "bog mode" it was not dumping a ton of smoke... that might imply a igniton problem. Now the next question, would be.... spark plug? Coil? Muffler bearings??

Thanks in advance. The saw is a real joy to run, smooth and responsive when it is willing to cooperate.

Simple stuff first, fuel line, filter, impulse line, intake boot, carby bolts tight, sounds like intermittent lean and your spark plug will show white, almost sounds like a cracked fuel line or fuel filter fell off line inside tank, but I would check the simple stuff first and not run it until you get it sorted out and keep us posted.

 

[50blues]

When it start to mess up, loosen the gas cap and see if it helps. Could be the vent is plugged. Or all the stuff listed above.

 

[Patrick62]

Okay.... here we go.
I gonna swap spark plugs just cause it is easy to do. I don't think I would burn a hole in a piston with a STIHL plug in there...
I could try the pop the cap thing, but if it were going lean from not enough fuel the first thing it would do is rev to the moon before it died... that ain't happening. I know a saw that is going lean. Me thinks that if the carby were going stinking rich to the point of dropping RPM by a factor of half then it would generate a large plume of visible smoke. Kind of like the old 16 to 1 saws and then mixed a little on the rich side..!! (cough). But it ain't doing that either.

IF it was a honkin intermittent air leak, then it would go lean and die. It ain't doing that either.

It does sound like my log splitter. pop.... pop ...... pop...... Hmmmm 4 stroking while pulling chips outta a log. How can that be....

Mis fire.... I will test that theory with a point of ignition. Like a blow torch and point that exhaust at it. Better yet, I will trot it right on over to Air Care Colorado and have a emission test done on a Jonsered chain saw. Then for a comparison, we can test one of the Stihls. This could be interesting.

It is missing. Sometimes. Now, let's see here. It is some sort of a electronic assembly in there that is getting it's signal from a magnet that is flying by at warp speed. Seems to be workable, most of the time. If the scr or other mystery circuits in there were questionable I would think that it would just up and die (releasing the magic smoke). Spark plug.

I am gonna charge out here and trot (cold feet and all) over to the shop and swap a spark plug for a known good one. Removed from a orange saw.

Nothing to lose.

If that don't fix it I really think the previous owner would be miffed if I sail forth and start over reacting and assuming that simply every thing that could possibly be checked is gonna need to be checked out!

----> interesting story from awhile ago, and related to this thought process....
I have a diesel pickup out here. it's injection pump was messed up so that it would not run above a certain throttle position. I was directed to talk to "bob" who knows about diesels.... he said that it was blown head gasket! Would need to take apart the engine to fix it up. Loses compression when revved up. What? It idled pretty good but could not go anywhere with it.... clouds of smoke from over fueling, and then it just would quit running. Take foot off pedal and it would run again... blown head gaskets?? Come on bob..... Paid a diesel mechanic to fix the pump and once we got the lines to quit leaking it is just fine. hundreds of cords of wood to show for it.... never had the gaskets replaced.... 5.9's are pretty tough to kill.

Ol' Bob would have had parts of my engine scattered all over the place

 

[Patrick62]

inconclusive on the plug. Might be a smirch better. Still think it is ignition rather than the carb. Went out and blasted some blocks by headlight.

Okay I can visualize this next test. I will strap a motorcycle battery to my belt and put a timing light on the plug. if it quits sparking then it will quit flashing.

Feet are soaked in the 6 inches of global warming. Tired of messing with it, and tomorrow is a work day.