Dolmar Chainsaw refuses to start

[eugene89us]

@AxFan20 I got an email with your message, but I do not see it here. I figured when the piston is at BDC, the ports that connect from crankcase to the cylinder are exposed (or so I thought) which would allow any fuel to evaporate from crankcase to the piston and out of the exhaust port (which was open with piston all the way down). If I raise the piston to TDC, the exhaust port will get fully closed by the piston skirt. The only access to crankcase at TDC would be from the intake side in that case.

 

[pioneerguy600]

That means I have compression and spark, because fuel in the cylinder will fire up the saw for a second or two. So I do not have fuel delivery then... But why? Two working carbs, fully functional fuel lines and clean fuel filter. Perfectly healthy intake boot as well as impulse line. All sealed properly onto the cylinder intake and impulse line nipple.

So your problem is it won`t pull fuel after it initially starts, hard to tell what is the problem from reading your thread. Saw won`t crank , mentioned more than once is not a term I work with, not a term I have come across in any workshop manuals, to me it would mean the engine can`t be turned over. However now that it has been determined that the engine will hit and run a bit on prime then that leaves just a fuel delivery problem. In a nutshell if the fuel line is good, fuel filter passes fuel through they are eliminated, comes down to impulse if both carbs are known to be good. Place a dab of hard grease in the impulse line and pull the saw over rapidly, the grease will be spit out or drawn in, that will determine if there is impulse. A vac gauge can be used in place of the grease if you have one but far as I can tell you are waiting for one.

 

[pioneerguy600]

@AxFan20 I got an email with your message, but I do not see it here. I figured when the piston is at BDC, the ports that connect from crankcase to the cylinder are exposed (or so I thought) which would allow any fuel to evaporate from crankcase to the piston and out of the exhaust port (which was open with piston all the way down). If I raise the piston to TDC, the exhaust port will get fully closed by the piston skirt. The only access to crankcase at TDC would be from the intake side in that case.

When your piston is at BDC or all the way down the cylinder is totally blocked off on a bridged port cylinder.

 

[eugene89us]

@pioneerguy600 Yes, I am handy, but by no means an engine specialist. I am a pharmacist by training. Cranking in my mind is engine starting, sorry for confusion. Chainsaw refuses to start basically.

Yes, the engine turns over with a pull cord. The effort on the pull cord is same as when it ran (more compression than my new Stihl, so I always have it on the ground with a shoe inside the handle). Turns over fine, there are no restrictions. Compression shows 175 to 180 psi, basically about same as brand new. Timing is good per flywheel position at TDC and coil fires the spark plug when plug is removed and grounded. New spark plug replaced just in case. Fuel line and filter definitely without restriction, I can easily lose a lot of fuel when I pull carb off the fuel line. Even when I depressurize the tank, it stil somehow had enough pressure to still leak fuel from the line when disconnected from the carb. I need to plug to line to avoid losing fuel into the area where carb sits.

The only part I am not proud about flipping around my story is fuel delivery. Initially, I saw fuel on the spark plug and fuel was present when I removed muffler. Figured fueling was looking to be fine. But yesterday when I pulled it at least 5 or 6 times o choke, I would have expected the plug to be wet, but the plug and the cylinder were all bone dry.

I was hopeful that crank filled with fuel was the issue. After all, it would follow my bad fuel hypothesis. I mentioned that saw turned off as the fuel was getting toward the bottom. There was some, but filter was no longer fully submerged. When I put bad fuel in, it would not restart. I cranked it probably 50 times. Is it possible that with the cranks that I have an ounce of liquid fuel in the crank? Yes! And I hoped so. But I left the saw at BDC for a day, and when it did not work, I figured it was not the cause. It sounds to me that it was not the right way to do it. Tonight, I will disassemble the carb as well as remove the boot and the impulse line. I will then inspect the crank directly from the intake side with a borescope. I should be able to see fuel in there if it is flooded significantly. I should also be able to turn it exhaust up and intake down with cylinder at TDC and any fuel should come out. Do you think that would be reasonable next step?

 

[river of smoak]

I've tried the boot in the handle method of starting and it sucks ! I feel like you just can't get decent cranking speed [which could be your issue] and to me it's awkward . With the bar and chain removed , try holding the saw with your right hand [ access to depress throttle ] and pull starter handle with left . this is essentially "drop starting " push the saw away from you while at the same time pulling the starter handle towards you . this will give you what I think is better cranking speed . Try this with throttle depressed and then not , try using your syringe with mix into the carb if your plug seems dry after repeated attempts . If the saw briefly runs , repeat this method and get ready to keep it going by injecting fuel into carb throat as the saw starts to come to life , just don't over fuel it which may flood it . holding the throttle open will generally clear slight flooding

 

[pioneerguy600]

In all my years running and working over chainsaws have I ever needed more than a few minutes to clear even the most flooded cylinder/crankcase. Just remove the sparkplug and tilt the saw upside down, pull the engine over rapidly 8 -10 times, put the plug back in and hold the throttle wide open, pull it over like you mean it and with the throttle wide open the engine will cough a few times until it starts. Saws will sometimes flood while working in the woods, we don`t waste a day restarting them. Most times I can restart a badly flooded saw in just a couple minutes by holding the throttle wide open and several fast pulls over, one does not have to wait for nature to evaporate excess fuel from a saw`s crankcase. Also try the hard grease diagnosis to test impulse, I have used that many times when I did not have a vacuum gauge with me. The vacuum/pressure wave runs the fuel pump in the carb, without it the engine will sometimes start but stumble or run erratic at idle but cannot reach high RPM. I have already mentioned that leaving the piston at bottom dead center actually blocks the crankcase off almost air tight so that would impede drying it out.
I see river of smoak had posted while I was typing up my reply, his post is very valid also. The monkey humping a football method of pulling over a chainsaw is as mentioned a poor method for starting these saws, the engine needs to be pulled over very fast to generate enough spark when the cylinder is under compression it takes much more spark energy to jump the sparkplug gap. I have been working with other owners of this saw model and they were having a bad time trying to get them started, it proved out they were not getting enough revolution speed from the recoil using most any other method than the dropstart.

 

[lwmibc]

Maybe read this thread; a search for 'Dolmar won't start' is a rich one!

https://opeforum.com/threads/dolmar-ps510-wont-start.26788/

 

[AxFan20]

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 deleted my response because I realized my thoughts were wrong. The original stall might have been bad gas or tune with rings seating. Is it possible you reversed fuel line routing ? From the fuel filter to the pump side of the carb. From the carb to the short nipple on purge bulb. Long nipple on purge returns to fuel tank. Note that the purge bulb does NOT push fuel into the carb. You said fuel lines were full of gas but plug was dry.

 

[eugene89us]

No purge bulb on a Dolmar, them and Stihl have decided against it. Before the final cut, the saw would burp on the second choked pull and would start on the second fast idle setting. When hot, it would restart on the first pull in any non choked setting. I was amazed it was as good as my Stihl MS 261. I am thinking I will stick with Stihl in the future... Still hope I can get her going, just have not had much time to work on it.

 

[Ralf1e]

You said from the start you had a nice blue spark. A blue spark is a sign of a failing capacitor. Have you tried a different coil to see if the original is failing under heavy compression?
Just a thought.

 

[lone wolf]

I still ain't convinced both carbs are good! How can you be positive?

 

[lone wolf]

I've tried the boot in the handle method of starting and it sucks ! I feel like you just can't get decent cranking speed [which could be your issue] and to me it's awkward . With the bar and chain removed , try holding the saw with your right hand [ access to depress throttle ] and pull starter handle with left . this is essentially "drop starting " push the saw away from you while at the same time pulling the starter handle towards you . this will give you what I think is better cranking speed . Try this with throttle depressed and then not , try using your syringe with mix into the carb if your plug seems dry after repeated attempts . If the saw briefly runs , repeat this method and get ready to keep it going by injecting fuel into carb throat as the saw starts to come to life , just don't over fuel it which may flood it . holding the throttle open will generally clear slight flooding

Drop start while the air filter is off is my method when flooded to clear them, usually works every time.

 

[eugene89us]

I can't be 100% positive, but I am pretty certain that carbs are good. The carb that I used from the beginning, DM13B, I took it apart, inspected everything including diaphragm, flap gasket, and both seals. I also checked the needle and made sure it sealed properly, which it does. Checked the needle level to ensure it is precisely at the level of the walls of the carburetor, which it was from factory. Used guide by Vintage Engine Repair channel to verify all the passageways are clear, which they were. I guess I can call Zama to see if they would do warranty replacement on 13B carburetor.

The chance that I am not spinning the saw enough to have it started does not make sense, since I have started it with ease when cranking it for the last month that it was working properly. Why all of a sudden the same technique would not work does not make sense. This saw was repeatable and reliable up until the point that I was low on gas and it stalled to never restart again.

I tested 2 OEM coils - the light gray high speed coil as well as my replacement red coil. Both produce the same quality spark. Since my red coil came in gently used, I even splurged $25 on Chinese replacement coil, which also produces the same quality of spark.

I have tried 3 coils and 2 carburetors (one of them brand new), I checked the compression, I verified no damage to piston or cylinder with borescope. So far, there is nothing. I got all my testing equipment over the weekend, I will test the saw for any leaks this week at some point and will post the results. I will also do formal fuel line test with proper pressure to satisfy even the strictest crowd for objective testing (other than my current method of blowing and sucking through fuel line, impulse line, and intake boot with my mouth). I did all the testing with air filter off and did some testing with muffler off, I basically had the saw down to basics. I have not reattempted since last week, been a little busy at work.

 

[lone wolf]

I can't be 100% positive, but I am pretty certain that carbs are good. The carb that I used from the beginning, DM13B, I took it apart, inspected everything including diaphragm, flap gasket, and both seals. I also checked the needle and made sure it sealed properly, which it does. Checked the needle level to ensure it is precisely at the level of the walls of the carburetor, which it was from factory. Used guide by Vintage Engine Repair channel to verify all the passageways are clear, which they were. I guess I can call Zama to see if they would do warranty replacement on 13B carburetor.

The chance that I am not spinning the saw enough to have it started does not make sense, since I have started it with ease when cranking it for the last month that it was working properly. Why all of a sudden the same technique would not work does not make sense. This saw was repeatable and reliable up until the point that I was low on gas and it stalled to never restart again.

I tested 2 OEM coils - the light gray high speed coil as well as my replacement red coil. Both produce the same quality spark. Since my red coil came in gently used, I even splurged $25 on Chinese replacement coil, which also produces the same quality of spark.

I have tried 3 coils and 2 carburetors (one of them brand new), I checked the compression, I verified no damage to piston or cylinder with borescope. So far, there is nothing. I got all my testing equipment over the weekend, I will test the saw for any leaks this week at some point and will post the results. I will also do formal fuel line test with proper pressure to satisfy even the strictest crowd for objective testing (other than my current method of blowing and sucking through fuel line, impulse line, and intake boot with my mouth). I did all the testing with air filter off and did some testing with muffler off, I basically had the saw down to basics. I have not reattempted since last week, been a little busy at work.

Has the flywheel key been looked at? I know you said something about magnets lining up but?
You can't even get it to fire for a second with gas put into it?
Did you choke it with the air filter off with your thumb?
Test the impulse port and see if the needle wiggles back and forth on the Mitivac.

 

[eugene89us]

No, I had it successfully fire that one time when I replaced DM13B with original DM14A carburetor. That nice waterfall of fuel got the fuel delivered into the piston, which even my wife noticed from the house hearing the saw start to idle for 2 seconds, then it died and did not restart with replacement carb either after that. I was fairly convinced I had it fixed when it showed signs of life but alas. I did not try to choke with my thumb, will try it next. I did not take flywheel off, however, but magnets line up perfectly as they were brand new before my first cranking.

They call these saws screamers. Absolute bull on that! These Dolmar saws are quiet - they sound line Honda engines on those Accords. I was running my MS 261 saw this weekend finishing bucking my firewood. The son of a gun is a real screamer. I check on the tune monthly on it. It runs at 2800 idle and I maxed it out around 14,200 at WOT. If anything gave me ear pain, it is MS 261. That is a real screamer. Dolmar ran around same at WOT, but the thing is really quiet in comparison. That is the reason I want to get her back working.

 

[eugene89us]

I need to drill out the stopped pins from the MS 261, the high jet is wound out completely. The manual says max RPM is 14000, and I clocked 14200 on it. Two other quick attempts got me clocking 13800-14000, but I would like to keep that thing well below 14000 if I can. Darn EPA, but I still have 6 months of warranty, which keeps me from messing with carb on my Stihl

 

[blades]

I 've only had two fail to start issues over the y past 25 years with my dollies, Kill switch went flaky on one and impulse line developed a crack/leak on the other. That was a 116SI oldest one of the bunch.

 

[eugene89us]

I tried to drop start the Dolly, the compression is too good, it does not have enough weight for me to drop start her. LOL. When I do monkey starting, it is no issue - pulls beautifully. I hold the handle with right hand and pull cord with the left, throw the saw down and it won't go. If I let it hang on the starter cord, it will go down, slowly, as compression releases. Otherwise, no go. Too much compression, folks... Have not tested vacuum and pressure in the crank, will plan to do next couple days when rain pauses my outdoor plans. We will get this question answered once and for all. If I fail, who wants to buy a project saw?

 

[lone wolf]

I tried to drop start the Dolly, the compression is too good, it does not have enough weight for me to drop start her. LOL. When I do monkey starting, it is no issue - pulls beautifully. I hold the handle with right hand and pull cord with the left, throw the saw down and it won't go. If I let it hang on the starter cord, it will go down, slowly, as compression releases. Otherwise, no go. Too much compression, folks... Have not tested vacuum and pressure in the crank, will plan to do next couple days when rain pauses my outdoor plans. We will get this question answered once and for all. If I fail, who wants to buy a project saw?

Too much compression, is it flooded?
You should pull the flywheel and look at the key while you are at it.

 

[eugene89us]

Definitely not flooded, I dried it at TDC with choke open and throttle tied open to dry the crankcase and spark plug pulled to dry the cylinder. All were bone dry when I tried to drop start it yesterday, but I did not give it much effort as my goal was to finish mowing lawn before next wave of rain comes...