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flame coming from exhaust

Started by levi, November 07, 2010, 10:04:45 AM

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levi

Hi, I thought someone here might be able to help me.  I recently bought a makita dpc7321 14" power cutter, or "cut-off saw"  It was factory refurbished.  I have probably run 4-5 tanks of super unleaded, mixed with synthetic 2 cycle oil, just like the manual tells me to.  After it is used for more than 5-10 minutes, it will release a 3-4 inch yellowish flame out of the muffler when I let off the gas.  It only seems to happen when decelerating, and only after it is warmed up.  After I realized what was happening, I could look in the spark arrestor, and it is glowing red the whole time it id running if you look inside of it.  I can't believe this is normal?  The funny thing is that the engine, and saw seem to be running perfectly, and the thing idles just fine.  I was just wondering if anyone here has any ideas what is going on?  Thanks.

levi

After doing more research, it seems that this may be a problem with the catalytic converter, or something. is it possible to just take it out?

Rocky_J

The catalytic converter is doing exactly what it's supposed to do, cook your motor in order to 'save the environment' by reducing emissions.  ::) The problem is that the catalytic converter is an afterthought and the motor (and plastic cover parts) aren't designed to work under such extreme temperatures. So it works perfectly but your saw will only last half as long before it cooks itself to death.  :'(

If you're not afraid of toxic dust, gut the muffler. Otherwise replace it with a non-catalytic muffler and then retune the carb.

Cut4fun

Cool get us some video in the dark.  smiley_sidelightbulb smiley_idea

sawguy21

The problem is the length of time the engine spools down with the throttle closed courtesy of the large wheel. It is now drawing an overly rich mixture which sounds off when it reaches the hot muffler. What Rocky said.
old age and treachery will always overcome youth and enthusiasm

levi

So this is one of those units that is made to be legal in California?  If I take the muffler off, I should be able to remove the cat converter?  If I do that, and that only, will I still need to tune the carb?  Thank you for the help.  I am not extremely savvy when it comes to small engine mechanics.

Rocky_J

Think of a motor as an air pump. If you plug up the outlet then you can't draw as much in the inlet. If you unplug the outlet then that will increase the amount of air being drawn in. To prevent the motor from running lean and burning up you need to increase the amount of fuel to match the increased airflow. This will result in more power. The increased fuel flow will also mean better lubrication (the oil is mixed in the fuel) and lower temperatures (no glowing hot catalytic converter melting your saw).

A word of caution on the catalytic muffler. That is some nasty stuff, worse than asbestos. I would recommend wearing protective gear while handling it (gloves, long sleeves and respiratory protection).

levi

So what does removing the cat converter entail.  Do i just take the muffler off, and it will be self explanatory?  Then is it a must to re-tune the carb?

kenskip1

What you want to do is remove the muffler and if can be separated simply remove the inside. Should be a screen of some sort.What this does is it retains heat and this does not let the engine breath.If you are able to remove the inside portion then you will more than likely have to make  some small carburetor adjustments. Your saw will thank you with improved throttle response, easier starting, and more power, Ken
Stihl The One
Stihl Going Strong
Stihl Looking For The Fountain of Middle Age

Al_Smith

I doubt seriously of a cat converter even works well on a chainsaw .First of all you have oil in the gas for one thing .Secondly a chainsaw doesn't have an auxillery air pump like an automobile .The danged converter has to have residual heat to even work ,which is basically like an afterburner .

Early on when they first stuck the danged things on cars they had to retard   the valve timing on a 460 Ford by 1/2 tooth to get enough raw fuel to even get the stupid thing to work .After fuel injection was available they advanced the valve train once again and finally got back to the power that large engine was designed to produce .

levi

Thanks, I am going to try to do it tomorrow. It is really amazing that they would put one of these things in this saw.  It glows red hot once it's warmed up, and every time you let off the throttle, after it's hot, a flame literally shoots out right next to your hand. The first time it happened, I just about threw the saw on the ground.  I thought it was going to blow up, or burst into flames. Remember, this is a demo saw I have so the handle is right by the muffler.  One thing I can say is that they make it clear to only use synthetic 2 cycle oil.  I think it has something to do with the cat converter.  I really appreciate all the replies.  I'll let you know how it goes.

Al_Smith

The very idea of attempting to provide a more clean exhaust discharge from a tiny little engine like on a chainsaw is an exercise in futility .In the over all scheme of things they don't burn enough fuel to even get concerned about .

Then you hang a converter on it that poses the possibilty of causing fires ,burning the operater and basically shortening the life of the engine .What on earth are they thinking . ??? If they are so concerned about environmental type things it would appear to me that more times should be spent on more important matters such as large industry that just pays a certain fine for their pollutants rather than waste time on a itty bitty small tool .

Bill Gaiche

Al I agree. Is there really that many saws running at any given time that really makes that much effect, I doubt it. I dont hear a saw but just every once in a while but I hear cars, trucks and industry everyday an they are effecting things. bg

levi

Well, Tonight I took apart the saw, and took out the muffler.  The problem is I dont know if I can take it apart without destroying it.  It has a single torx screw right in the middle of it that is holding the metal sheet that holds everything together.  They actually welded the screw in place in 2 spots.  That shouldnt be a problem.  I will bring my metal grinding blade home tomorrow, and cut the welds.  The main problem I see is the metal sheet that I should be able to unscrew, is locked in by 1/8 inch of metal from the other half of the muffler.  The main body of the muffler wraps around the metal sheet on all sides just a little.  I could hardly get a screw driver under it, and even then, it didn't seem like I could bend it.  Maybe once I loosen the welded screw, the thin flat sheet will be flexible enough to pop out, but I don't know if I'd be able to get it back in.  Do I even need to? The thin metal sheet is inside of two other main metal casings. What if I just cut the sheet out with a metal grinding plate, and removed everything, then put the main casings back together??  I should post a picture so you guys can understand what im talking about better.  I'm just hoping somebody with some experience with these things might have some tips for me.  I will check, and see if I can just order a new muffler without the cat converter tomorrow.  I'm just afraid they don't offer one.  Thanks again.

sharkey

Hi Levi,
Maybe just use a small cut off wheel (dremel) and cut the muffler in half, then gut it and weld the outside halves back together.  Might be easier overall? 

Otherwise, Baileys Logging a site sponsor, should offer a 'jungle' muffler for that unit.  Jungle mufflers have baffles in them for noise but no spark arresters or catalytic converters. 

Whichever option you choose, dont forget to open the high side carb jet a little to compensate for the better breathing ability of the less restrictive exhaust.           

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