Welcome to the DoItYourself Forums!

To post questions, help other DIYers and reduce advertising (like the one on your left), join our DIY community. It's free!

Rough or inconsistant idle in Craftsman chainsaw


tronicsman1's Avatar
Member

Join Date: Sep 2006
Posts: 3

09-29-06, 12:02 PM   #1  
Rough or inconsistant idle in Craftsman chainsaw

I just about rebuilt my Craftsman (2.0 Poulan) chainsaw right down to a new piston ring and upper connecting rod bearing. All new gaskets and new silicon sealer around the bottom half of the crankcase. Walbro carb has been rebuilt with the appropiate kit. Current ignition module is good putting out a sharp blue spark. Now, the 64 thousand dollar question. The saw fires up perfectly! B...U...T I'm having trouble getting a smooth and consistant idle out of it. Sometimes she'll idle perfectly for 15 minutes and then die. But she'll fire right back up! Other times, the idle will increase in RPM'S all by itself, and then back down to normal. (Suspecting an air leak maybe?) I started out adjusting the high and low mixture screws at 1 turn out each, and been playing with the low speed adjustment. Maybe a quarter turn here or there. Even less at times. I know I'm close with this, but I'm not quite there yet. Does anyone have a better idea of what's going on? Am I in the right ballpark here? Do you suspect an air leak maybe? Hard to believe though with all new gaskets! I'd appreciate anyone's help with this....Regards, tronicsman1

 
Sponsored Links
mla2ofus's Avatar
Member

Join Date: Jan 2005
Posts: 478
TX

09-29-06, 08:01 PM   #2  
My first question is: why do you let a 2 cycle engine idle for 15 min? I've never done that w/ any 2 cyc. I'd think that would be hard on the spark plug due to oil buildup on it.
I don't think you have an air leak because it normally wouldn't come and go. You did install new crank seals?
For carb adjustments I adjust the hi speed needle at full throttle and then adjust low speed needle at idle. Some fine tuning w/ small adjustments to either is needed to get idle set right.
JMHO,
Mike

 
cheese's Avatar
Forum Topic Moderator

Join Date: Jul 2001
Posts: 16,571
GA

09-29-06, 10:25 PM   #3  
The increase in RPM indicates a lean condition due to either a fuel delivery problem or an air leak in the engine case or intake. If you didn't replace the crankshaft seals, this would be a good place to check.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
tronicsman1's Avatar
Member

Join Date: Sep 2006
Posts: 3

09-30-06, 09:20 AM   #4  
crankshaft seals

The 15 minute idle time may have been an exageration on my part, but it was the first time I fired the saw up since the tear-down. Basically wanted to see how it reacted. It seems both of you suspect crankcase seals? Sorry to say, I didn't replace them. On the advice of a neighborhood shop, 9 times out of 10, they're in good shape. Was he BS'n me? Tell you one thing, I'm not tearin' this saw down again. I still think it's mostly a carb adjustment but the sometime rise in RPM's then returning to normal has got be bugged!

 
mla2ofus's Avatar
Member

Join Date: Jan 2005
Posts: 478
TX

09-30-06, 08:11 PM   #5  
Well,I'm sorry to say this may be the "10th" time.If you don't want to tear it down again,try some more carb adjustments. If it doesn't go away,either live w/ it or sell it.
Mike

 
tronicsman1's Avatar
Member

Join Date: Sep 2006
Posts: 3

10-01-06, 07:00 AM   #6  
inconsistant idle

Well Mike, I was afraid you were going to say that on the seals. But anyway, how about a starting point on the mixture screws at 3/4 out on the high speed, and 1-1/2 on the low speed? I read this SOMEWHERE! Also, just when DOES the idle screw on the throttle linkage come into play?. I appreciate all your help here even though some of it wasn't exactly what I wanted to hear! I know, I know. The truth hurts sometimes.....Mike

 
puey61's Avatar
Member

Join Date: Apr 2004
Posts: 3,224
NY

10-01-06, 01:48 PM   #7  
Perhaps you can avoid a tear-down and one of the seal lips has curled in and simply lost its seal this way. Pull the clutch off as well as the flywheel and have a look. Maybe you can correct this without any major disassembly if this is, in fact, your trouble. Here's hoping!!! Do you know the trick to help determine if you have a seal leakage issue with two-strokes?

 
mla2ofus's Avatar
Member

Join Date: Jan 2005
Posts: 478
TX

10-01-06, 06:09 PM   #8  
This probably isn't SOP,but I've always set 2 cyc carbs by starting out w/ both screws turned out 1 1/2 turns from lightky seated.This easier to do if you clamp bar in a vise so chain doesn't hit the vise while running.Start it and hold throttle wide open while slowly turning hi speed screw out until engine starts slowing down(ie:running too rich),then turn hi speed in until engine speed is at max. Now if it will idle,turn low speed either way until idle is smooth as possible. If it won't idle turn idle speed screw in until it will keep running w/o a finger on throttle.Turn low speed either way until engine speed starts increasing,when it does turn idle speed screw out(on all these adjustments IN is clockwise,OUT is counter clock)to get it down to where chain will just stop moving. If you can't get chain to stop moving, turn low speed in or out some more to see if you can get so you can turn idle speed screw out some more. Hope this is plain enough.
Puey is right. You can probably see any seal damage by removing flywheel and clutch. If in doubt,take it to a small engine shop for a leakdown test.Perhaps he will enlighten both of us about the trick for seal leakage.
Hope this helps,
Mike

 
puey61's Avatar
Member

Join Date: Apr 2004
Posts: 3,224
NY

10-02-06, 03:16 AM   #9  
The PTO end (clutch) is relatively easy to perform but the mag end (flywheel) is not so simple or safe, for that matter. But it's typically the PTO seal to blame. Use a spray can of flammable fluid - carburetor cleaner works best - and as the engine is running at idle spray a small dose of cleaner onto the seal. A change of RPM's will indicate a leaking seal. On the clutch end, remove the clutch to do this, exposing the bare crankshaft. On the flywheel end, you can merely attempt to spray in the direction of the seal and hope you make contact with the spray mist at the seal. Remember, the flywheel must remain installed in order for the engine to run and therfore it will be spinning with the engine and can be a hazard and you must exercise extreme caution with this in mind. Use the straw that comes with most spray cleaners as well as eye protection and hand protection. Also, be aware of the possibility of the spray mist backfiring at you from the air circulation from the flywheel.

 
mla2ofus's Avatar
Member

Join Date: Jan 2005
Posts: 478
TX

10-02-06, 04:50 AM   #10  
Thanks,Puey, that's a good trick to know.
Mike

 
Azis's Avatar
Visiting Guest

Posts: n/a

10-02-06, 07:05 AM   #11  
Azis
I dont think the spray need be flammable. It is not the spray leaking into and aiding in combustion, rather it temporarily seals the air leak which in turn changes the fuel air mixture and causes the rpm change. I have used WD-40 and even silicone spray with the same result.

 
Search this Thread