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Author Topic: motor is racing on my Dolmar 421.Help!...Fixed  (Read 455 times)

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Offline 47sawdust

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motor is racing on my Dolmar 421.Help!...Fixed
« on: February 23, 2019, 03:41:47 PM »
Yesterday I went to use the Dolmar 421.Started fine,started doing some work and the motor began racing and wouldn't idle down.The fuel mix is the same I always use and run the same fuel in my Jonsered w/o incident.
I gave it a thorough cleaning,tightened the carb,same scenario today.The saw rides in a scabbard that is attached to my tractor.Might be vibration has loosened something.
Any thoughts are appreciated.Thanks,Mick
Mick
1997 WM Lt30 1999 WM twin blade edger Kubota L3750 Tajfun winchGood Health Work is my hobby.

Offline sawguy21

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Re: motor is racing on my Dplmar 421.Help!
« Reply #1 on: February 23, 2019, 04:20:07 PM »
Sounds like it is sucking air between the carb and cylinder.. Check the impulse line, it may be cracked. Also check the boot between the air box and cylinder for holes
old age and treachery will always overcome youth and enthusiasm

Offline Hilltop366

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Re: motor is racing on my Dplmar 421.Help!
« Reply #2 on: February 23, 2019, 05:29:00 PM »
Does it do that all the time or after it has run for a bit?

Air leak, fuel supply (pump), tank vent.

Offline thecfarm

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Re: motor is racing on my Dplmar 421.Help!
« Reply #3 on: February 23, 2019, 06:12:34 PM »
I would not be running it!!!  I had my Husky do that,I think when I turned it sideways?
Model 6020-20hp Manual Thomas bandsaw,TC40A 4wd 40 hp New Holland tractor, 450 Norse Winch, Heatmor 400 OWB,YCC 1978-79

Offline Air Lad

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Re: motor is racing on my Dplmar 421.Help!
« Reply #4 on: February 24, 2019, 04:44:42 AM »
If it's been a good saw and given good service for yonks now may be the time to invest in the basic parts that fail after time. Carb kit . Fuel/impulse lines . Intake boot . Test crank seals . A  refurbish can save the cost of replacing a good saw that needed some love.
Of course the problem could be to do with throttle linkage if it's reving mad.
Have a good visual check with the lid off . May be something simple.
Good luck Mick
Ms 170/260c /039...Husk 142e/240e...Unloved Chinese 51.2cc that hasn't done anything wrong...2 x dead Mculloch's ..Vintage Poulan.. and a vintage Echo that still runs beaut

Offline Hilltop366

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Re: motor is racing on my Dplmar 421.Help!
« Reply #5 on: February 24, 2019, 11:01:34 AM »
I gave it a thorough cleaning,tightened the carb


Was the carb loose? if so the gasket may have been damaged.

Another thing I have seen was the fuel line cracked causing air leakage because it is under suction you will not see any leaks, or if the pickup line in the tank is cracked it will only cause an air suction leak when the fuel level is below the damaged part of the line the lean running condition will temporarily go away when the tank is refilled.

Of coarse it could have picked up some dirt and have an obstruction in a carb circuit or carb gummed up if it has been sitting for a while. Also a good point about the linkage by Air Lad.

Offline 47sawdust

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Re: motor is racing on my Dplmar 421.Help!
« Reply #6 on: February 24, 2019, 11:31:24 AM »
The linkage seems fine,moves as it should.Will replace fuel line tomorrow, former forum sponsor Chainsawr is a Makita/Dolmar dealer who lives an hour away.This is a great saw,I hate being w/o it for long.Starts first or 2nd pull,light,great for limbing and felling pecker poles.I wouldn't say the carb was loose,I tightened the screw less than a quarter turn.
Thanks for your help.
Mick
1997 WM Lt30 1999 WM twin blade edger Kubota L3750 Tajfun winchGood Health Work is my hobby.

Offline 47sawdust

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Re: motor is racing on my Dolmar 421.Help!...Fixed
« Reply #7 on: February 25, 2019, 11:28:58 AM »
Went to see Scott aka Chainsawr today.He installed a carb. kit,fuel filter and new fuel line while I waited.Problem was the fuel line.
Anybody within driving distance of Stannard Vermont,he is the guy to go to.
Mick
1997 WM Lt30 1999 WM twin blade edger Kubota L3750 Tajfun winchGood Health Work is my hobby.

Offline sawguy21

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Re: motor is racing on my Dolmar 421.Help!...Fixed
« Reply #8 on: February 25, 2019, 11:33:16 AM »
 8) Thanks for letting us know
old age and treachery will always overcome youth and enthusiasm

Offline Hilltop366

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Re: motor is racing on my Dolmar 421.Help!...Fixed
« Reply #9 on: February 25, 2019, 12:41:34 PM »
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