Dolmar 7910 hard to start and bogging issue

[YoungVin]

I recently picked up a Dolmar 7910 new open box off Ebay. First off, it is a bear to start even with the decompression valve engaged. I have to about throw it to get it to fire. Is that normal for it to be so difficult to crank? Secondly, it sporadically has what some think is a misfire or electrical problem where it bogs when you hit the trigger. One mechanic thought it was an electrical problem and when he put in a new spark plug it went away. But then it did it again after I took it home and when I made a small adjustment to the L screw it cleared up (I think I leaned it out, but don't remember for sure). Now it still does it randomly, usually when it's warming up. I will add that when I lean out the L screw (clockwise) the saw will rev a bit and then die out. But when I give it fuel (counterclockwise), I can keep turning and it won't ever die. I didn't see how far I could go, but I might have been out a full turn and a half counterclockwise (from the opposite point when it was dying out lean) and it never died out. Is that normal? Right now it's idling at around 2900 rpms (readings jump between 2800 and 3100). I can't find a service manual online that gives specs for normal idling rpm and other data (which is another question I had for the forum). I found a service manual and of course the owner's manual, but neither give specs or even advice on how to adjust the carb for example. Otherwise, the saw seems to run great, smooth, and I think a bit quieter (not so screamin loud) as some other saws I've heard. I'm not close to a service dealer so any help would be appreciated. Thank you!!

 

[Piotr Pakula]

Do not look for the specification hard, because in used chainsaws it rarely works if it can be started, it does not go out and cuts, nothing more than that you do not need

 

[cuinrearview]

If you randomly start messing with factory carb settings you can quickly find yourself with a hard starting lazy off idle and or over revving saw. Go back to base needle settings and tune it from there. Tuen the idle screw in some to speed up the idle. Start with the low, turn it slowly clockwise until you get the maximum idle speed, then turn counterclockwise until it starts to drop. Take it back to max speed then back it out ~1/8 of a turn. Drop your idle speed until the chain stops turning. Then tune your high speed needle. You want some four stroking at WOT(not on the rev limiter) then a smooth two stroke sound loaded in the cut.

 

[lone wolf]

I recently picked up a Dolmar 7910 new open box off Ebay. First off, it is a bear to start even with the decompression valve engaged. I have to about throw it to get it to fire. Is that normal for it to be so difficult to crank? Secondly, it sporadically has what some think is a misfire or electrical problem where it bogs when you hit the trigger. One mechanic thought it was an electrical problem and when he put in a new spark plug it went away. But then it did it again after I took it home and when I made a small adjustment to the L screw it cleared up (I think I leaned it out, but don't remember for sure). Now it still does it randomly, usually when it's warming up. I will add that when I lean out the L screw (clockwise) the saw will rev a bit and then die out. But when I give it fuel (counterclockwise), I can keep turning and it won't ever die. I didn't see how far I could go, but I might have been out a full turn and a half counterclockwise (from the opposite point when it was dying out lean) and it never died out. Is that normal? Right now it's idling at around 2900 rpms (readings jump between 2800 and 3100). I can't find a service manual online that gives specs for normal idling rpm and other data (which is another question I had for the forum). I found a service manual and of course the owner's manual, but neither give specs or even advice on how to adjust the carb for example. Otherwise, the saw seems to run great, smooth, and I think a bit quieter (not so screamin loud) as some other saws I've heard. I'm not close to a service dealer so any help would be appreciated. Thank you!!

No it aint normal to start that hard. You need to get the proper settings for that carb. Off the cuff try 1 turn out ea. No specs near the adjuster holes? The idle is set about right if it don't stall and the chain isn't moving with the brake off. Also start tuning the L screw first till the saw holds idle ,don't stall and runs good.

 

[Andyshine77]

Do what's recommend above. This video should help you get the low side dialed in.



On top of that the 7910 is a high compression engine the will give you a lot more resistance when you pull her over, even with the decomp. If you're used to smaller saws this seems abnormal to a lot of guys, you have to pull like you mean in.[emoji111]

 

[Ikeholt]

Sounds kind of like a plugged spark arrestor screen.

 

[YoungVin]

Do what's recommend above. This video should help you get the low side dialed in.



On top of that the 7910 is a high compression engine the will give you a lot more resistance when you pull her over, even with the decomp. If you're used to smaller saws this seems abnormal to a lot of guys, you have to pull like you mean in.[emoji111]

Is that you in the video? Thanks for that. I need to distinguish between "hesitation" and a potential electrical/timing problem. His sounded similar to what I have going on. I don't know how far out from bottom the L screw is recommended to be set to begin with, but if it revs then dies when leaned out, I take it I'm in the right spot? It's two turns out right now. As for the setting the H screw, I had never heard about setting it based on how it sounds in the wood. Was the idea that you want to lean it out to where it eliminates the 4 cycle sound with it in the wood? Thanks for everyone's input.

 

[Andyshine77]

Yes my video. You want to turn the L in to where it sounds lime it's running out of fuel than back it out a 1/4 turn and check for acceleration. With the saw warm, back out the H 3 turns, place the saw in a good size chunk of wood slowly turn the H in until it stops four stroking.

 

[YoungVin]

Yes my video. You want to turn the L in to where it sounds lime it's running out of fuel than back it out a 1/4 turn and check for acceleration. With the saw warm, back out the H 3 turns, place the saw in a good size chunk of wood slowly turn the H in until it stops four stroking.

A quarter turn counerclockwise from the lean dying point and acceleration is good, but the idle would then be over 3000. So I have it set at more like a half turn counterclockwise from that point. I have yet to find the specs for recommended idle and max rpms. Is idle rpm about the same for most saws? As for the H setting, did you mention in your video how long the "break in" period lasts and what to change at what point? Another eye raiser with my saw has been a few times when it suddenly increased rpms at wot before I buried it in wood. Is that is a normal kink in the break in process? Thank you!

 

[smokey7]

If its idling too fast with the low set right back the la screw out. Its the 3rd screw not the low or the high. That will lower idle rpm to stop the chain

 

[Andyshine77]

If its idling too fast with the low set right back the la screw out. Its the 3rd screw not the low or the high. That will lower idle rpm to stop the chain

Correct. Idle speed is set using the LA only, the L is a fuel mixture jet.