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Makita concrete saw dpc7321 won't start has fuel and spark compression seems low 60 psi what should it be?

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Anonymous

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I'm a retired engineer and work PT as a tool tech for an HD rental ctr.

Compression on a new cylinder/piston is 160 psi. When it drops into the 130~140 psi range the saw becomes hard to start. Below 130 the saw will not run properly and at 90 they are toast. This is mainly due to improper fuel/oil mix (must be one bottle of 50:1 synthetic oil per gallon of regular gas. I use 6 bottles to 5 gallons for addition protection). Because this type of tool works in extremely harsh conditions (concrete dust) it is also imperative to keep the air filters clean. Wash the foam pre-filter after each use with plain water from a garden hose and discard after operating 6 times. Toss away (change with new) the paper filter if dust is present or when changing the pre-filter. Also check the carb hose to the cylinder inlet for cracks. My cost to get a cylinder/piston from Makita runs app. $130. When looking into the cylinder, streaks on the exhaust side indicate improper fuel/oil mix. Streaks on the intake indicate dirty air intrusion.

Good Luck.

Posted on Nov 30, 2010

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  • TIMOTHY Aug 01, 2012

    HI MY NAME IS TIM I INSTALLED NEW PISTON AND HEAD ON MY MAKITA IT WORKED FINE FOR A DAY NOW IT WONT START THE PLUG IS GETTING WET AND IT HAS SPARK CAN YOU HELP PLEASE

  • TIMOTHY Aug 01, 2012

    SORRY ITS ME TIM IT IS A MAKITA DPC7321

  • Mike Thorne Smallwood
    Mike Thorne Smallwood Dec 16, 2018

    The head PSI is relative to the cubic measure of the cyliner displacment, there is no set pressure measure for all engines. A legitimate engineer would know that.
    These saws run at about 50-60 head psi under pull start, period.
    The biggest issue for these saws is crankshaft seal leaks and crankcase leaks. These saws use a split crankcase and the gaskets, cylinder gasket and or crankcase gasket can leak over time.
    Unless you're running the saw without intake filters, the piston head and piston are likely fine. Check for 50+ psi at head. The crankcase has no vacuum test point short of carb intake.
    If the saw has spark and fuel and good head pressure of 50PSI plus... the crankcase is like conpromised and needs new seals and gasket.
    Be certain the intake suction tube from carb is in good condition.
    Then focus on crankcase gasket and crankshaft seals.

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Anonymous

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I got same problem ,i used my saw only ones.never again makita !!!

Posted on Jun 03, 2010

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Anonymous

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Im stumped, i have a makita dps7311 cut saw it has awsome blue fire 1/2" on spark tester only 75lbs comp. its got fuel getting in the cylinder. even with a shot starting fluid, not even a fart. Can anyone help?


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Posted on Feb 22, 2010

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  • Anonymous Feb 22, 2010

    it is a question not a answer that i am asking

  • ORYHULKEN Oct 04, 2010

    COMPRESSION SHOULD BE 120-150LBS FOR DPC7321 CUT OFF SAWS, REMOVE THE PLUG AND SHINE A LIGHT INSIDE THE CYLINDER AND LOOK FOR VERTICAL SCRATCHES IN THE CYLINDER WALLS, LOW COMPRESSION IS USUALLY A LEAN FUEL PROBLEM. MEANING THAT STRAIT FUEL WITH NO MIX OIL WAS USED IN THE SAW AND CAUSED IT TO RUN TO HOT. A BAD BASE GASKET OR PISTON RING COULD ALSO RESULT FROM WRONG FUEL USAGE AND THE MUFFLER WILL ALSO BURN UP OR BECOME CLOGGED, CAUSING THE STARTING PROBLEM.

  • roccolocanto Mar 05, 2011

    to oryhulken , well if it does have vertical lines on the cylinder walls then does it need a rebuild.

  • TIMOTHY Aug 01, 2012

    YES IT DOES YOU CAN TRY TO PUT A NEW PISTON RING FIRST THAT MIGHT WORK

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Pieter Vleeshouwers

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To know the Filters are clean the compression is tight the fuel and the GASKETS but also the seals of crankshaft are smooth they have high priority by this kind of saws for long lasting jobs (Dolmar) Makita models even the L+H ADJUSTMENT is so high important because much brands will have a default adjustment made and then the adjustments for fuel difference and after service and run-in period are forgotten and thats gives the worsed problem you can find the adjusters by most engines on differend brands are fixed in a [ Limited range of motion ] on base of exaust pollution emission of harmful gasses ask your dealer if the carburetor is have this special adjusters behind capped screws that liked on screws but are still for the real screw nozzles sometimes to buy a special adjustment screwdriver for it to adjust .
If you have informed by the dealer what he thinks is the best listen to the advise but if you have doubt between a rised problem after an expensive defect of a very young machine is to adjust the L nozzle clockwise so that it is made the highest rpm on half trottle turn clockwise asfar that the motor almost will stops that is the point from of to give back of that point a quarter turn back on yourscrew driver counterclockwise and now begin adjust the L nozzle a little bit in the both directions so you can hear its gonna react as fast as possible on the trottle then give a little fraction counter-clockwise only when pulling thetrottle react fast repeated and go then only to full trottle when the engine is a little bit warmed up a 4 minutes then make it full ttrottle and then turn the H adjustment easy much more counterclockwise then the H adjuster was adjusted from factory that will begive the most damaged saws if they have a yelling sound its became to hot and are to dry running it made the piston worn much more then you think but turn the H nozzle much enough (more fuel) so you can hear slowly release the rpm sound of the motor back and screw until the engine is beginning to give a little bit constantly a 4 stroke sound and play around that point test the saw on a good object and feelthat is having much more power then than you were expect then you know that its gonna get enough - fuel to lubricate the whole saw for shure a little bit ridge adjusted is better by alkylat fuel because that will give not hard peaces on the exhaust (grooved pistons) and used with a good fuel that its lasting longer then only a few years , alkylat fuel has a higher lubrication quality by different octane number by special engines with a special used decompressor thats why 1:40 1:50 mix in high quality alkylat is the same as even with normal Ultimate with a castrol 2 stroke 1:30 or 1: 33 oil mixture but the adjustments must be done on every service after a while when gaskets filters are replaced after a ew years and even sometimes by some sparkplugs . sparkplugs must having a whiteblue hearing spark if the spark is red colored then ask your dealer allways on motornumber and year of build for a new ignition coil if a replacement sparkplug is not give a smooth spark.

Posted on Dec 14, 2016

Anonymous

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Your compression should be between 90-120 lbs on 2 cycle. Not enough compression

Posted on Mar 11, 2010

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Makita concrete saw dpc7321 won't start has fuel and spark compression seems low 60 psi what should it be?

That does seem low, but it's a 2cycle.
It hasn't been run hot or w/o proper gas/oil mix has it ?
Will it fire with a squirt of starter fluid ?
If you squirt some oil into the spark plug hole, does the compression go up very much ?
If it has spark and won't fire w/starter fluid sprayed in thru the carb, it's most likely a ring/piston/cylinder problem.
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