eugene89us
ArboristSite Member
Good morning. I am a bit at loss currently. As I posted previously, I started using NOS Dolmar 5105 S chainsaw within the last month. So far, it went through about 2 tanks of fuel. She was ripping through wood like there is no tomorrow. In fact, I posted a video here of her starting, idling, and cutting.
I was bucking one of the younger oak trees that was recently dead. The saw was going strong, very hot MS afternoon. As I was bucking its last cut, the saw turned off in the cut. I opened the gas cap - the tank was not completely empty, but it was almost there. Figured the fuel filter was not fully submerged anymore, must have been low tank. I also recently got fresh 93 octane ethanol free gas that I use with all my saws. Mixed 50:1 with Red Armor as I usually do. The saw refused to restart.
I got my Stihl chainsaw - my primary saw. Finished bucking with it. Once it ran out of fuel, I refueled it as well and it ran kinda slow on that gas. It would die at idle, though would restart at fast idle. Of course, here I have confidence to say that I must have gotten old gas from the station. It is $4.6/gal (vs. ethanol 93 octane runs around $1/gal cheaper). I dumped gas from both. To be on the safe side, I went ahead and splurged on Moto Mix. Stihl chainsaw perked up immediately, would idle beautifully again without issue. But even with bad gas, it would still start at fast idle, but it would not idle well on its own.
Trying to rejuvenate Dolmar has not been as straightforward. I dumped all the fuel, replaced with Moto Mix. No start. I took the carburetor out, cleaned it out. Later on, I even put my spare new carb on it - so I know carburetor is NOT the issue. Checked the fuel line and filter - perfectly new, no restrictions. The tank holds some pressure when closed, no vacuum is formed there. Compression at spark plug is right at 180 psi. Took the boot off and inspected the intake boot as well as impulse line - both perfectly healthy. Both hold pressure and vacuum when tested with my mouth on one side and finger on the other. Checked the coil. The plug sparks nice blue spark when out of the cylinder. Well, I have a spare new backup coil. It also sparks when grounded, no avail - saw does not restart with spare coil. So that eliminates coil issue. Used a business card to gap the coil. Found a perfect one that shows 0.0100 inch on my caliper. If I push the caliper tighter, I can get 0.0098. I think that is as perfect gap as you can make it. Oh yeah, replaced spark plug with new NGK BPMR7A, gapped at 0.02. Inspected piston when the saw was disassembled. Brand new looking. Does not even have any carbon on it, all factory markings there without a scratch on both intake and exhaust sides. I took a photo of brand new out of the box flywheel. Currently, when piston reaches TDC, the magnet position is spot on where it was when it was brand new, so getting flywheel out of time is also not the case.
At this point, I am completely at loss. The saw that was cutting through wood like it is nothing is now a paperweight. I know it has compression, I know it has spark, I know the carb is good. I even took the muffler off to test it to eliminate muffler or spark screen issues. After so many deperate pulls, the muffler opening gets wet, so I know the saw is getting fuel. Once in a while, it will sputter a bit. Yesterday, in fact, it almost started. Ran for about 2 seconds and died again. My only last option is to check the seals. I will need to order vacuum and pressure tester to do so and then test in case there is a leak at the seals or gaskets. But that makes it unlikely after only 2 tanks of gas.
Searched forums. A couple folks were in same predicament. Some had coil issues that did not spark at all - mine sparks well, and tested 2 coils anyways. One ended up trading it back to dealer after not finding solution with same symptoms as mine. It is a simple engine, I am just not sure where else to look. Any ideas would be appreciated greatly.
I was bucking one of the younger oak trees that was recently dead. The saw was going strong, very hot MS afternoon. As I was bucking its last cut, the saw turned off in the cut. I opened the gas cap - the tank was not completely empty, but it was almost there. Figured the fuel filter was not fully submerged anymore, must have been low tank. I also recently got fresh 93 octane ethanol free gas that I use with all my saws. Mixed 50:1 with Red Armor as I usually do. The saw refused to restart.
I got my Stihl chainsaw - my primary saw. Finished bucking with it. Once it ran out of fuel, I refueled it as well and it ran kinda slow on that gas. It would die at idle, though would restart at fast idle. Of course, here I have confidence to say that I must have gotten old gas from the station. It is $4.6/gal (vs. ethanol 93 octane runs around $1/gal cheaper). I dumped gas from both. To be on the safe side, I went ahead and splurged on Moto Mix. Stihl chainsaw perked up immediately, would idle beautifully again without issue. But even with bad gas, it would still start at fast idle, but it would not idle well on its own.
Trying to rejuvenate Dolmar has not been as straightforward. I dumped all the fuel, replaced with Moto Mix. No start. I took the carburetor out, cleaned it out. Later on, I even put my spare new carb on it - so I know carburetor is NOT the issue. Checked the fuel line and filter - perfectly new, no restrictions. The tank holds some pressure when closed, no vacuum is formed there. Compression at spark plug is right at 180 psi. Took the boot off and inspected the intake boot as well as impulse line - both perfectly healthy. Both hold pressure and vacuum when tested with my mouth on one side and finger on the other. Checked the coil. The plug sparks nice blue spark when out of the cylinder. Well, I have a spare new backup coil. It also sparks when grounded, no avail - saw does not restart with spare coil. So that eliminates coil issue. Used a business card to gap the coil. Found a perfect one that shows 0.0100 inch on my caliper. If I push the caliper tighter, I can get 0.0098. I think that is as perfect gap as you can make it. Oh yeah, replaced spark plug with new NGK BPMR7A, gapped at 0.02. Inspected piston when the saw was disassembled. Brand new looking. Does not even have any carbon on it, all factory markings there without a scratch on both intake and exhaust sides. I took a photo of brand new out of the box flywheel. Currently, when piston reaches TDC, the magnet position is spot on where it was when it was brand new, so getting flywheel out of time is also not the case.
At this point, I am completely at loss. The saw that was cutting through wood like it is nothing is now a paperweight. I know it has compression, I know it has spark, I know the carb is good. I even took the muffler off to test it to eliminate muffler or spark screen issues. After so many deperate pulls, the muffler opening gets wet, so I know the saw is getting fuel. Once in a while, it will sputter a bit. Yesterday, in fact, it almost started. Ran for about 2 seconds and died again. My only last option is to check the seals. I will need to order vacuum and pressure tester to do so and then test in case there is a leak at the seals or gaskets. But that makes it unlikely after only 2 tanks of gas.
Searched forums. A couple folks were in same predicament. Some had coil issues that did not spark at all - mine sparks well, and tested 2 coils anyways. One ended up trading it back to dealer after not finding solution with same symptoms as mine. It is a simple engine, I am just not sure where else to look. Any ideas would be appreciated greatly.
