Dolmar 100 Starting
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If you are going to pull the carb apart and can get a kit for it, might as well put one in...
Does it fire if you dribble fuel in the neck of the carb?
Does it fire if you dribble fuel in the neck of the carb?
If I give it a sniff of fuel it will fire for a second. I just ordered an OEM kit for it. I had it at a mechanic who returned it to me and its not running. It looks like he cleaned the carb body and intake, cut out a new intake gasket, and replaced the fuel line. It was holding fuel pressure in the fuel line at the carb just now, but once I loosened the carburator and started working it off it started hissing and the fuel level in the line dropped. Is this an indication of anything? The mechanic never mentioned putting in a carb kit but he may have. If he did its not doing much or maybe he didn't do it right?
Giles
Burning Hunk
Sounds like your mechanic just cleaned the OUTSIDE of the carburetor. I would be looking for a qualified mechanic or at least, clean fuel tank just in case!
So got the carb fully rebuilt. New everything including removing and cleaning under the welsh plugs. She fires right up. Only problem now is carb tuning. It runs at full throttle but seems like it is missing a little power. When it drops to idle she shuts off. I can raise the idle but it sounds like the idle is good. Compression is great - saw is very little used. Thinking its a mixture issue. I put the screws back to original settings but they were most likely played with by the previous owner to get it started. Finally, if you point it down it shuts right off. Any other direction its OK but straight down will shut it off. The shut off switch is loose and keeps shutting it off - will disconnect the switch tomorrow and I think that may alleviate the problem where it shuts off when pointed down. But now, how do I adjust the carb properly so it has a little more top end and comfortably idles.
Giles
Burning Hunk
If there were any, Did you remove the restrictors from the carb adjustment screws?
I would start with the both screws out 1 1/4 turn. After saw is warm, if L screw is lean, it will hesitate , bog or go dead when you quickly advance throttle. If this is the case, adjust the L screw out 1/8 turn at a time--checking. H screw should be adjusted to "fourstroke" burbling sound at maximum throttle--This is IMPORTANT! However this burbling sound should not be heard while heavy cutting.
Just remember counterclockwise---richer.
Giles
Burning Hunk
L screw is more difficult and more critical. Just try to adjust for maximum rpm and then turn screw out 1/8 turn at a time until rpm drops and engine sounds like it is slightly flooding (which it will be)
A lot of mechanics just hold the throttle wide open and adjust--I don't do an engine like that!
So just an update with some questions:
I adjusted the High and Low screws as specified here.
Now it fires up on choke, runs at full throttle and part throttle positions. Once it drops to idle it wants to shut off. I ended up screwing in the idle adjustment screw all the way and now it will idle. What did I do wrong?
I adjusted the High and Low screws as specified here.
Now it fires up on choke, runs at full throttle and part throttle positions. Once it drops to idle it wants to shut off. I ended up screwing in the idle adjustment screw all the way and now it will idle. What did I do wrong?
Jon1270
Minister of Fire
Jon1270
Minister of Fire
Can you describe exactly how you adjusted the carb? There's a place upthread where you asked, "Could you say I should adjust the H screw to make max RPM?" and you didn't get a clear answer to that so I'm wondering what you ended up doing. In any case, you absolutely should not adjust the H screw for max RPM; it's the L screw that gets that treatment.
Sorry I should have specified.
I turned both Low and High screws out 2 turns. And thats where I am at now. Doing that has left me with the idle issue which I didn't think could happen given that I thought I was putting the carburetor at its baseline? Not sure where to go from here with adjustments - whether it is still the High and Low screws or if I have a problem elsewhere that I have to resolve first. Oh and it wants to die if I point the bar downward.
I turned both Low and High screws out 2 turns. And thats where I am at now. Doing that has left me with the idle issue which I didn't think could happen given that I thought I was putting the carburetor at its baseline? Not sure where to go from here with adjustments - whether it is still the High and Low screws or if I have a problem elsewhere that I have to resolve first. Oh and it wants to die if I point the bar downward.
Jon1270
Minister of Fire
Okay, that's probably too far out (too rich) for both screws. There's no fixed number of turns out that you should use; it varies with temperature, elevation, the particular fuel mixture you use, etc. Generally after a carb rebuild you'd start with both mixture screws one turn out, though the recommended initial setting varies +/- a quarter turn depending on the saw model. Those won't be the final positions, but it should be close enough to get it started.
What you want to do is to set the idle mixture first, then the high speed mixture. Adjust the idle SPEED screw so that the chain is just barely moving. Then adjust the idle MIXTURE screw until the saw idles smoothly, doesn't hesitate when you grab the throttle (which would be too lean) or gradually flood and stall when you let it idle for a longer period of time or tip the saw nose-down. Adjust the idle speed screw to the point where the chain doesn't move at idle.
High-speed adjustment comes next, and I don't have time at the moment to describe that. Will follow up later.
What you want to do is to set the idle mixture first, then the high speed mixture. Adjust the idle SPEED screw so that the chain is just barely moving. Then adjust the idle MIXTURE screw until the saw idles smoothly, doesn't hesitate when you grab the throttle (which would be too lean) or gradually flood and stall when you let it idle for a longer period of time or tip the saw nose-down. Adjust the idle speed screw to the point where the chain doesn't move at idle.
High-speed adjustment comes next, and I don't have time at the moment to describe that. Will follow up later.
WOW! Thank you! That is precise and what I needed! When you say idle mixture screw you mean the "L" screw?
Jon1270
Minister of Fire
Yep L indicates the low speed / idle mixture screw.
After you've got the idle set, it's time to adjust the high-speed mixture (H screw). Up to a certain point, the engine burns cleaner and makes more power as you lean it out, but if you lean it out too much then the engine will rev too fast and combustion temperatures will get too high, very possibly destroying the motor in short order. Adjusting the high speed without a tachometer depends on your ability to hear a particular sort of rhythm in the sound the engine makes. The rhythm you're listening for, commonly called "four stroking," should occur when running the saw at full throttle with no load, i.e. spinning the chain in the air, not cutting any wood. The rhythm exists in this situation because the engine is getting a little more fuel than it can use and is not actually firing on some revolutions, resulting in a sound that's something like the sound of a single cylinder four-cycle engine (i.e. most lawnmowers). You want to gradually adjust the H screw until you find a setting where it "four-strokes" at full throttle with no load, but just barely "cleans up" or stops "four stroking" under load, i.e when making a normal cut. If it four strokes under load, then it's set too rich. If it doesn't even four-stroke when not under load then it's too lean. This is a fine adjustment; don't expect to find the sweet spot by turning the screw 180 degrees at a time.
The big challenge with tuning by ear is learning to recognize that sound. Videos and recordings don't always have the greatest audio quality, and don't always make it clear what you're listening for, so this is how I've tried to describe it. I'm just copying this from an answer I gave to a similar question elsewhere:
First, try making a sustained "Z" sound, as if you're imitating a bee's buzzing: Zzzzzzzzzzzzzzzz. Got that far? Okay, now while you're doing that, try pulling the tip of your tongue back away from your front teeth, along the roof of your mouth until the tip of your tongue starts to flutter and make a sound more like a rapid D D D D D D D D D, very similar to a rolled R, made up a series of distinct beats as your tongue repeatedly hits the roof of your mouth.
Four-stroking is like the latter sound, the D D D D D D D, and that's what you want to hear when the engine is running but not cutting anything. The ZZZZZZZZZZZ sound, smooth with no staccato beat to it, is the absence of four-stroking, and that's what you want to hear when you begin a heavy cut. It should switch back and forth between the two, from ZZZZZZZZ in the cut, and then back to D D D D D D D D when you ease up the pressure and the engine doesn't have to work so hard; this is what people are referring to when they say a saw should "clean up in the cut." If it sounds like ZZZZZZZZZZ even when it's not working hard then you're running lean and courting a scored piston. If it sounds like D D D D D D D D even when working hard then you're wasting fuel and performance isn't what it should be.
After you've got the idle set, it's time to adjust the high-speed mixture (H screw). Up to a certain point, the engine burns cleaner and makes more power as you lean it out, but if you lean it out too much then the engine will rev too fast and combustion temperatures will get too high, very possibly destroying the motor in short order. Adjusting the high speed without a tachometer depends on your ability to hear a particular sort of rhythm in the sound the engine makes. The rhythm you're listening for, commonly called "four stroking," should occur when running the saw at full throttle with no load, i.e. spinning the chain in the air, not cutting any wood. The rhythm exists in this situation because the engine is getting a little more fuel than it can use and is not actually firing on some revolutions, resulting in a sound that's something like the sound of a single cylinder four-cycle engine (i.e. most lawnmowers). You want to gradually adjust the H screw until you find a setting where it "four-strokes" at full throttle with no load, but just barely "cleans up" or stops "four stroking" under load, i.e when making a normal cut. If it four strokes under load, then it's set too rich. If it doesn't even four-stroke when not under load then it's too lean. This is a fine adjustment; don't expect to find the sweet spot by turning the screw 180 degrees at a time.
The big challenge with tuning by ear is learning to recognize that sound. Videos and recordings don't always have the greatest audio quality, and don't always make it clear what you're listening for, so this is how I've tried to describe it. I'm just copying this from an answer I gave to a similar question elsewhere:
First, try making a sustained "Z" sound, as if you're imitating a bee's buzzing: Zzzzzzzzzzzzzzzz. Got that far? Okay, now while you're doing that, try pulling the tip of your tongue back away from your front teeth, along the roof of your mouth until the tip of your tongue starts to flutter and make a sound more like a rapid D D D D D D D D D, very similar to a rolled R, made up a series of distinct beats as your tongue repeatedly hits the roof of your mouth.
Four-stroking is like the latter sound, the D D D D D D D, and that's what you want to hear when the engine is running but not cutting anything. The ZZZZZZZZZZZ sound, smooth with no staccato beat to it, is the absence of four-stroking, and that's what you want to hear when you begin a heavy cut. It should switch back and forth between the two, from ZZZZZZZZ in the cut, and then back to D D D D D D D D when you ease up the pressure and the engine doesn't have to work so hard; this is what people are referring to when they say a saw should "clean up in the cut." If it sounds like ZZZZZZZZZZ even when it's not working hard then you're running lean and courting a scored piston. If it sounds like D D D D D D D D even when working hard then you're wasting fuel and performance isn't what it should be.
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