Dolmar Chainsaw refuses to start
- Thread starter eugene89us
- Start date
Help Support Arborist Forum:
Did you check the flywheel key?
Sounds like you have good compression and spark, if the spark is occuring at the wrong time it won't fire.
Mark
Sounds like you have good compression and spark, if the spark is occuring at the wrong time it won't fire.
Mark
See post 1 he goes into detail what he checked.
eugene89us
ArboristSite Member
Yeah, I am certain the timing is spot on compared to when it was brand new. No change to timing of magnet to the coil at TDC. Here is a photo of exhaust side piston.
No crank this evening after all day in the house. Cylinder looks good with no evidence of any damage. Positioned piston at bottom dead center to open ports from crankcase, placed saw on the side in case some of that bad fuel got pooled below piston. Will give it 1 more day to dry more. Vacuum and pressure tool in the mail. Tomorrow is garbage day, thinking maybe I should end my suffering?
No crank this evening after all day in the house. Cylinder looks good with no evidence of any damage. Positioned piston at bottom dead center to open ports from crankcase, placed saw on the side in case some of that bad fuel got pooled below piston. Will give it 1 more day to dry more. Vacuum and pressure tool in the mail. Tomorrow is garbage day, thinking maybe I should end my suffering?
Dumb question - how did you check the fuel filter? I would have just replaced it to eliminate the question.
eugene89us
ArboristSite Member
I checked by blowing out and sucking in on the fuel hose once everything dried out. Also, after depressurizing the gas tank, once I took off the carb, the fuel was running out of fuel hose. There is definitely flow.
Is the stock carb on now and have you tampered with it?
eugene89us
ArboristSite Member
I was running DM13B carb that was originally recommended by user 166. It came with easily removable limiters. In the other forum where saw is running, I had low screw about 1 full turn out and high screw about 1.25 turns. That created nicely idling saw and the high speed was around 13900-14100, was four stroking nicely when free revved. Currently, I put the original carb on it (14A, I believe) with limiters. No change. I doubt it is the carb, cannot be. It ran beautifully until stalling from running out of gas and then my fiasco with freshly purchased bad gas that I refilled it. And while Stihl recovered immediately with fresh new gas from another station, Dolmar decided to pass away. Looks so freaking nice, I have not even had a chance to put a scratch on it. Mityvac MV8500 is on its way. I think the only thing left to test is pressure and vacuum. Yes, the saw is new, but it is 15 years old. And seals and gaskets are also 15 years old. And we all have experienced old rubber going bad. If the saw passes the pressure and vacuum test, I will officially be stumped by it..... I pray it is something I can find, because I am running out of options here.
Mike Ray
ArboristSite Operative
may have the fix , had same problem, there is an old post on here that shows the fix. Its obviously flooded, it's the tank vent, anyway easy to ck. white disk left side lower rear has a duckbill valve under it clip one corner off the flat side. have to take a bolt out of antivibe or something can't remember. I haven't had any trouble since.
Vent part number, 957 114 061
eugene89us
ArboristSite Member
It is strange, because the saw had zero flooding issues before. Yesterday, I had it drying all day with piston at bottom dead center with ports open to atmosphere. There was no liquid fuel anywhere in the saw, and I even had tank drained. When I was ready to re-test, I refueled it right then and cranked immediately. Still absolutely nothing. I don't think it is flooding issue, there was no fuel in that saw to flood. I am still suspecting some type of crankcase leak that is affecting fuel delivery and proper fuel/air mixture. I will have the vac/pressure tester by tomorrow via FedEx, will give that a final test. I think by that point, I will have gone through all the testing done at small engine shops.
Is the choke closing 100 percent?
Did you try dropping some fuel into the carb?
Doing so will eliminate all the other support devices, if the engine has spark as stated it will fire off with a bit of fuel supplied to the cylinder. If it does not fire off and the spark arrives at the right time then it is most likely there is not enough compression to allow combustion. I have seen and repaired more than one saw that was basically run only a tank or less of fuel where the rings broke, the saw stopped and would not restart. There was no apparent scoring showing through either port but the rings had broken just out of sight of the exhaust port.
eugene89us
ArboristSite Member
@lone wolf Yes, the choke closes 100%. If I disassemble the top plate of the carb after cranking, the area below diaphragm always has fuel. So I believe it is receiving fuel. Now whether enough or not, that is the question. When I poured a little fuel down the air intake, it burped a couple of times. I didn't think it was fuel delivery problem at first, but now that is my primary suspect. And I do not think it is on the intake side since I tested all the lines and 2 carbs. When diaphragm is removed, if I manually depress the needle level, it will deliver fuel without hesitation. And it worked just a well for 2-3 tanks of gas, so something sudden and major must be going on.
@pioneerguy600 But then I would not be getting 180 psi of compression with a broken ring. There would be a reduction in compression. And this is one of the first things I checked with Mityvac compression tester kit. It delivered good 180 psi after around 4 to 5 pulls. Compression is there, spark is there, flywheel position is spot on at TDC (so timing is right), spark is being produced. Two carburetors tested (one brand new purchased for a future spare), both needles keep good pressure and both levels are flush with height of if the carb. I am curious, when the saw is being cranked, if you were to place your finger over the intake port, how much suction would you expect? Because Dolmar has thumb shaped plastic intake, I can place my thumb over the intake to seal it completely and I frankly do not feel much suction. I am currently in what we call "confirmation bias" because I am actively seeking explanations to my hunch with crankcase leak being the issue. Of course, tomorrow or Saturday I will have all my tools to confirm or dispel this hypothesis. But I am thinking if I have checked compression spark, and timing, I haver to investigate air and fuel. If air is not being sucked in well enough through venturi, it will not produce enough pressure drop (Bernoulli's principle) to suck in fuel. Yesterday, when I tried to crank it, I cranked on choke for around 2-3 times, then took to fast idle and cranked 5 times, then back to choke another 3 times, then back on idle another few times. Spark plug is dry. By that point, I would be reasonable to expect liquid fuel in the cylinder, am I right? No suction on my thumb, no fuel after pulling on choke closed - I fear I have a seal or gasket leak where air finds the path of least resistance and prevents air and fuel from being pulled from the carb. That is my current hunch....
@pioneerguy600 But then I would not be getting 180 psi of compression with a broken ring. There would be a reduction in compression. And this is one of the first things I checked with Mityvac compression tester kit. It delivered good 180 psi after around 4 to 5 pulls. Compression is there, spark is there, flywheel position is spot on at TDC (so timing is right), spark is being produced. Two carburetors tested (one brand new purchased for a future spare), both needles keep good pressure and both levels are flush with height of if the carb. I am curious, when the saw is being cranked, if you were to place your finger over the intake port, how much suction would you expect? Because Dolmar has thumb shaped plastic intake, I can place my thumb over the intake to seal it completely and I frankly do not feel much suction. I am currently in what we call "confirmation bias" because I am actively seeking explanations to my hunch with crankcase leak being the issue. Of course, tomorrow or Saturday I will have all my tools to confirm or dispel this hypothesis. But I am thinking if I have checked compression spark, and timing, I haver to investigate air and fuel. If air is not being sucked in well enough through venturi, it will not produce enough pressure drop (Bernoulli's principle) to suck in fuel. Yesterday, when I tried to crank it, I cranked on choke for around 2-3 times, then took to fast idle and cranked 5 times, then back to choke another 3 times, then back on idle another few times. Spark plug is dry. By that point, I would be reasonable to expect liquid fuel in the cylinder, am I right? No suction on my thumb, no fuel after pulling on choke closed - I fear I have a seal or gasket leak where air finds the path of least resistance and prevents air and fuel from being pulled from the carb. That is my current hunch....
When will the Miti Vac arrive?
eugene89us
ArboristSite Member
I had the MOST sign of life when I replaced one carb and brand new unused carb. At that point, I had tank pressurized so when old carb came off, it created a strong spray of fuel from the black fuel line - I had a fountain while pressure was being released. Some fuel I am certain made its way into intake boot. Then I struggled to place new carb in place due to darn metal ring falling out of the green boot, so plenty of time to have that fuel pass into the boot and cylinder. Cranked it, it almost started. I would say it idled for 2 seconds, then died. I think that is conclusive, I have fuel delivery issue. But again, not sure why.
Mytyvac pressure and vacuum tester will arrive today or tomorrow I believe. I got it off Zoro with 20% coupon. That was the least expensive source. Amazon is running promo for $54, but after my fake sprocket fiasco with them, I am done trusting Amazon at this time....
Mytyvac pressure and vacuum tester will arrive today or tomorrow I believe. I got it off Zoro with 20% coupon. That was the least expensive source. Amazon is running promo for $54, but after my fake sprocket fiasco with them, I am done trusting Amazon at this time....
river of smoak
ArboristSite Member
sounds like something may not have been assembled correctly during the carb swaps ? you mentioned having difficulty with that metal ring . the seal between the carb and cylinder needs to be perfect
A saw will start and run with bad seals and even a torn intake manifold. Fuel induced straight into the cylinder only requires compression and spark at the right time. Which one do you not have?
eugene89us
ArboristSite Member
When I was putting in the second carb in, the ring fell out and was in the way. I was trying to figure out why it did not go into place, it was due to ring falling down. No, I am 100% sure that carb is placed correctly. I had my own carb placed when I first received the saw, the carb I replaced back to test whether car was an issue was the one I originally took off the saw. The original carb is also brand new, it never had gas through it until I out it back in to test and make sure that my replacement carb was not the issue. My replacement carb (DM13B) which was recomended as the best carb by user 166 was also brand new from an authorized Zama dealer. It is a pretty easy, straightforward swap, need to have choke closed to slide in in and out easily, and make sure that ring stays in place on the boot. I made sure it did the second time when I did the replacement.
eugene89us
ArboristSite Member
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.
