Dolmar 420 issue.....

[Shari]

My Dolmar chainsaw was acting up against me today - didn't seem to want to run at full power all the time. I stopped cutting to see if I could figure out what was wrong.

So far I've figured out the gas tank was probably vapor locked (hissing sound when I took off the gas cap) so I think I have to get a new gas cap for it.

Took off the bar/chain after releasing the vapor lock and it runs a little less rough w/o the bar/chain - put the bar/chain on, start it, release the clutch and it idles decently but then it kills when given power....... chain rolls free by hand....... so I dunno.......

I used it about 2 weeks ago and it ran fine........ Two weeks ago I did trash three drive teeth, replaced the chain and it cut fine for the rest of that day. Cleaned out the groove in the bar when I replaced the chain, there's no splaying out of the bar groove that I can see.

Drive sprocket looks good. It's oiling the chain good. Clutch seems to lock/unlock correctly.......... Gas is mixed and new....

Anyone have any ideas what's wrong?

I don't have any immediate need to cut anything but would like to figure out what's wrong......

 

[MasterMech]

So far I've figured out the gas tank was probably vapor locked (hissing sound when I took off the gas cap) so I think I have to get a new gas cap for it.

Usually saws are vented via a separate tank vent, not the gas cap itself.

 

[Shari]

Usually saws are vented via a separate tank vent, not the gas cap itself.

Thanks, MM, I'm checking the manual to figure out where that would be located.

 

[NH_Wood]

A bunch of simple things to check. Check air filter - if it is clogged clean (I use gentle compressed air - blowing from inside the filter to outside) - if real bad, just replace. Fuel fliter - ever replaced? Cheap and easy fix - if the filter begins to clog, less fuel getting to engine. Check spark screen on muffler to see if clogged - if so, clean or replace. If clogged, good to remove muffler and check the exhaust port for build-up - clean if needed. Replace spark plug if old - probably not the problem here, but it sounds to me like a basic tune-up is likely needed on your saw - worth doing. Those the easiest and cheapest things to try first and you'd be surprised how often one if these issues solves the problem - especially if you are not really tough on your saws. Cheers!

 

[Shari]

All good suggestions, NH. Sounds like I know what I'm doing tomorrow.

 

[NH_Wood]

Let us know how it turns out - will be fun. Cheers!

 

[bogydave]

A bunch of simple things to check. Check air filter - if it is clogged clean (I use gentle compressed air - blowing from inside the filter to outside) - if real bad, just replace. Fuel fliter - ever replaced? Cheap and easy fix - if the filter begins to clog, less fuel getting to engine. Check spark screen on muffler to see if clogged - if so, clean or replace. If clogged, good to remove muffler and check the exhaust port for build-up - clean if needed. Replace spark plug if old - probably not the problem here, but it sounds to me like a basic tune-up is likely needed on your saw - worth doing. Those the easiest and cheapest things to try first and you'd be surprised how often one if these issues solves the problem - especially if you are not really tough on your saws. Cheers!

+1
Everything I thought to check & then some. !

Can't improve on NH's ideas.

 

[MasterMech]

While you're cleaning things up, check to make sure the muffler screen isn't plugged up.

Does the saw exhibit these symptoms right away or only after having run for a few minutes?

 

[bogydave]

Check spark screen on muffler to see if clogged -

While you're cleaning things up, check to make sure the muffler screen isn't plugged up

Too late MM. NH nailed that one too

 

[Shari]

It runs rough w/o bar/chain. Installing bar/chain it dies almost immediately after brake release/accelerating.

I've been reading the manual and don't find anything specific to my issue(s). I also found the schematics online so I copied that to use as my road map tomorrow which I really need as I've never opened up a saw before.

If anyone is willing, here's where I found the schematic: (broken link removed to http://www.bartonsmallengine.com/pages/OemParts#/Dolmar/PS-420_Chain_Saws_-_Gasoline/Air_filter%2c_muffler/2S01340002/2S01340002B) There's a drop down list to get to various areas of the schematics.

I've been looking for a gas line vent on the schematics but haven't found it yet........

The saw is new-to-me but was a used model so filters are suspect right now.

PS The last thing I used it for was noodling...... maybe I plugged up something with noodle debris???

 

[jeff_t]

If it idles decently and dies when you give it gas, it sounds lean, like sucking air somewhere. Check the intake boot and fuel and impulse lines.

 

[MasterMech]

(broken link removed)

Page 1 of the IPL (same diagram you posted) item 7.

Also pictures here.

(broken link removed)

Please note, the tank vent is only a likely culprit if the saw runs a few minutes before it dies. Vent the tank by removing the fuel cap, and then run the saw again. If the symptoms repeat, (saw runs good for a few minutes and then starts to act up) then I'd look into the vent. If the saw seems to have trouble from the get-go, then check for a plugged fuel line/filter or muffler screen.

 

[MasterMech]

If it idles decently and dies when you give it gas, it sounds lean, like sucking air somewhere. Check the intake boot and fuel and impulse lines.

Air leaks on a two-stroke generally result in poor idle performance. That's the only thing this saw is doing well by the OP's description.

Poor performance at high speed or under load could also be a plugged jet or passage in the H circuit of the carburetor. But I'd rather confirm the fuel lines, filter, muffler screen, and tank vent are ok before having the OP tear into his carburetor.

 

[jeff_t]

Air leaks on a two-stroke generally result in poor idle performance. That's the only thing this saw is doing well by the OP's description.

Poor performance at high speed or under load could also be a plugged jet or passage in the H circuit of the carburetor. But I'd rather confirm the fuel lines, filter, muffler screen, and tank vent are ok before having the OP tear into his carburetor.

I'm not going to argue, 'cause you are da man, but I've had similar symptoms with all three issues. All worth checking at any rate.

 

[MasterMech]

I'm not going to argue, 'cause you are da man,

I have been known to be wrong before. Astonishing perhaps, but it does happen.

 

[Shari]

Well, I located the problem - the bar wasn't seating properly with the chain adjustment knob.

I took that chain/bar off and on at least 6 times and thought I had it all seated properly with the tensioner but apparently not. Go figure!

There is a different bar I can get that has the tensioner located on the bar - I might look into that for the future.

 

[NH_Wood]

Glad it seems to have fixed the problem - still seems strange though - your description of the problem doesn't seem to match the fix in my mind, but, if it worked, good on you! Cheers!

 

[lukem]

Well, I located the problem - the bar wasn't seating properly with the chain adjustment knob.

.

That was going to be my 364th guess.

 

[PapaDave]

having the OP tear into his carburetor

"I have been known to be wrong before."

Yep, Shari's a she/her.
Sorry, couldn't help myself.

 

[Danno77]

For the record, when a saw runs FINE without the chain and poor with it, the problem is clutch related. Sounds like your unseated bar was basically holding the clutch so it couldn't run right.

The thing that gets me (and others, maybe) is that it was running rough without the bar, that should not have been something that would make a difference.

P.S. outboard clutch and brake on the cover are just asking to have a whole host of these problems. the solution is Stihl. (and you know I'm not super picky on brands)

 

[Shari]

The thing that gets me (and others, maybe) is that it was running rough without the bar,

I'm with you on scratching my head on why it bogged w/o the bar also. I did brush off the air filter - it wasn't too bad but cleaning it never hurts.

I used my saw today to cut up some pretty big stuff (for me, it was big - 24" rounds) and she ran fine.

I am SO glad I was able to figure out the issue - last time we took a chainsaw in for repair the shop returned it to us in a box with every stinking nut/bolt/spring removed and said "Can't fix it. That will be $80." After an argument with the manager (which included me asking where my bar & chain had walked off to) I told them no way was I going to pay $80 for a box of parts when I'd brought in a fully assembled chainsaw. I walked out the door with my 'boxed chainsaw' and have never gone back there for repair of anything.

 

[PapaDave]

Shoulda' told 'em they'll be getting a bill for the work to reassemble the saw.
Hard to get a saw running that's not put together.