Question about Poulan Pro Chain Saw 46cc 20"

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Why can a small carburetor cause and engine to overheat?

I understand why lean jetting and things like that can cause overheating, but why can an improperly sized carb on the small side cause overheating issues? I read that the volume of mixture in the cylinder shouldn't change in the cylinder, so that kinda kills my theory that you are simply increasing the amount of mixture for added cooling... although that may be negated by the extra power and heat from burning more mixture. Anyone know for sure?

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A carburettor is chosen by the volume of the venturi on it. A small carburettor will not be able to supply a rich enough mixture. Evaporating gasoline, just like alcohol rubbed on your skin, takes out heat as it turns to vapour (that's evaporative cooling). If there isn't enough gasoline evaporating in the engine, the engine overheats. So, choose a carburettor that is at least big enough for the engine it feeds. As engine displacement is fixed, what changes is the amount of gas the carburettor can feed, hence, a small carburettor supplies a too little volume of a too lean mix.

Posted on Mar 11, 2009

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Settings for mixture screws


Most Chain Saw Engines Have Three Carburetor Adjusting Screws:
1. Idle Speed/Throttle Stop - This is the adjustment that controls how much the throttle valve (butterfly) stays open when the throttle trigger is released. If this adjustment is set too low, the engine will die when the throttle trigger is released. The throttle valve (butterfly) simply cuts off the supply of combustible air/fuel and the engine stops. If this adjustment is set too high, the high idle speed will cause the centrifugal clutch to engage and the chain will run. This is a dangerous condition and should never be allowed.
2. Low Speed Fuel Adjustment (marked L on carb, this is the low speed jet)- This is the adjustment that controls the proportion of fuel in the combustible air/fuel mixture at idle speed. An adjustment that is set too rich will cause the engine to load up and die at idle speed. A mixture that is too lean will starve the engine and cause it to race or surge. An extremely lean adjustment will cause the engine to die, too.
3. High Speed Fuel Adjustment (marked H on carb, this is the high speed jet) - This is the adjustment that controls the proportion of fuel in the combustible air/fuel mixture at cutting speed. It would not be accurate to say that this is the most important setting, because all of these adjustments need to be accurate for a saw to perform its best, but this is the adjustment that determines how the saw runs in the cut. An adjustment that is set too rich will not allow the saw to reach the RPM level necessary to build maximum power. Throttle response may also be sluggish and the engine would smoke and perform poorly. A mixture that is too lean will allow the engine to reach an RPM level where bearing failure and cylinder seizure are likely. It will also lack power in the cut and tend to run very hot.
The preceding information briefly explains rich and lean running conditions. It also identifies the three adjustment screws and their function. It should be noted that some chain saws lack the high speed adjustment needle. These saws have what is called a "fixed jet" which is set from the factory. "Fixed jet" carburetors are used to prohibit the saw operator from setting the adjustment too lean and damaging the saw. Unfortunately, they also often prohibit the saw from achieving maximum performance.

Apr 11, 2016 | Chainsaws

2 Answers

What causes a saw to stop working wen it gets hot


It could have a temperature sensor that shuts it off when it gets overheated.

Oct 02, 2015 | Chainsaws

1 Answer

Chainsaw wont idle properly


Most carburetor problems now days are caused by using gasoline with alcohol in it. It is very caustic and causes the idle (smallest) jets in the carburetor to plug up so the engine will not idle properly. The only fix that I have been successful with was to take the carb apart and run a small wire through the jet to open it up and then used only gasoline without alcohol in it. There are typically a few stations in towns which still sell that type of gasoline.

Feb 11, 2015 | Poulan Chainsaws

2 Answers

My stihl ms 260 chainsaw wont idle down to low idle


High idle is usually a sign of running too lean, or having an air leak around the carburetor mount, or even somewhere else on the machine. if turning the low mixture screw out half a turn or so doesn\'t help, I\'d start looking other places for a leak.
Check things like the plastic plate the carbie mounts to (intake manifold) and all the gaskets associated with that area.
Also, check your fuel lines aren\'t perished, they can cause air to suck up into the carbie and cause issues.
If you still have no luck it\'s possible one of the main crank seals may have gone, causing air to suck in around the crankshaft.
This is best left to a qualified small engine repairer to replace, as they can be dicky to get in there without damage.
Hope that helps!

Nov 17, 2013 | Stihl Chainsaws

1 Answer

Need initial carbuetor settings for jonsered 2041 chaisaw


Hi Ian
Before you remove or try to adjust your low and high speed jets you should always count the number of turns it takes to lightly seat the idle mixture screw and high speed needle adjusting screws.
Be sure to write the number of turns down on a piece of paper so you will know how many turns from the seated position to open the jets when you go to reinstall them, or if you remove them for cleaning or replacement.
If you have aready tried to adjust them then the adjustments below should get it running for you for final adjustment when warm.
Normally you will adjust your idle jet to 1/2-3/4 turn open from the bottom seated position.
Then you will re-adjust the low speed of the engine when the engine is warm by turning the idle screw in or out till the engine runs smoothly at idle speed, around 1200 RPM.
The high speed jet is adjusted to 1 1/2- 1 3/4 open from the bottom seated position, after the engine is warm.
Then re-adjusted by turning the High Speed jet adjustment screw in or out till the motor runs smoothly at high speed.
Alway use the "lightly seated" method if you have not changed the screw settings.
And a little help on rebuilding the carb below.
***************************************************************************
Sounds like you have dirt/debris in your caburetor jets,fuel passages or a diaphgram that is becoming non-flexible.
Check/Clean/Replace your Air Filter, a dirty air filter can make your engine run to rich with fuel.
Also be sure to check and clean your spark arrestor in the exaust,if you have one installed on your engine.
Note: ALWAYS USE COMPRESSED AIR TO CLEAN YOUR JETS AND PASSAGES, VERY IMPORTANT.
Note:Before you disassemble the carburetor:
Write down on a piece of paper or take a picture of how the linkage attaches to your carburetor for later reference when you go to reinstall your carburetor.
Mark each piece with a awl, or some kind of instrument that will make an alignment scratch before you disassemble the carburetor into separate pieces.
That way you will know which way it goes back together when you reassemble it.
Sometimes you can get by with priming the carburetor or by using a very small shot of starting fluid and letting it run a few times like that, and it will flush the gunk out of the jets,but most of the time you will need to rebuild the carburetor.
Be sure to check your fuel tank for water and dirt/debris, if there is water/debris then you need to clean your tank.
Check you fuel line condition after a while they will degrade and need replacment.
Check/Clean/Replace your fuel filter if you have one, normally they are located in the fuel tank of chainsaws and weedeaters.
When you remove your fuel lines from the carburetor be sure to make a drawing to how the lines are connected to the carburetor or take a pictue for later reference.
Normally the big line will be the line the fuel filter is connected to inside of the tank.The smaller of the two lines is the return to the fuel tank from the carburetor after it is pumped thru the carburetor by the primer bulb.
Make sure you are using fresh fuel...and oil if your using a two cycle chainsaw or weedeater with the oil to the right mixture...too much oil as it can cause hard starting and excessive smoking.
If the chainsaw/trimmer is over a couple of years old, then I recommend that you buy and install a new carburetor repair kit,because the diaphragm will get hard and that will cause it to be hard to crank.
The diaphgram may look good and flexible, but it can be deceiving and not act as a fuel pump as it should because it has become too hard and will cause hard starting,start and run and shut off, etc.
When you clean your carburetor, I recommend that you use a laquer thinner type cleaner to clean and dissolve the laquer build-up in the float and needle jet passages.
Be sure to remove all plastic and rubber parts before using the laquer thinner because it can dissolve the plastic parts and render them unuseable.
Be sure to use COMPRESSED AIR to blow out all the fuel and air passages.The higher air pressure is needed to blow some of the trash/debris from the fuel or air passages.
Be careful when blowing out the passages, because there are sometimes small rubber type seats in the bottom of some of the passages.
Keep in mind that the float (if you have one) for the carburetor must be level when you go to reassemble the carburetor or follow the instructions you get with the carburetor kit, or you could also ask the parts man that you get your kit from.
When you clean your carburetor and remove the jet screws, you will first need to lightly seat the jet screws.
But before you lightly seat the jet screws count the number of turns it takes to seat the jet screws from their original position.
Be sure to mark the turns down on a piece of paper.
That way when you put the jets back in, you know to lightly seat them first and then turn them back out to their original position before you started.
Note:
The little spring inside of the carburetor goes under the float arm.
That is where your fuel inlet needle/float valve is located...on the arm at the end.
Normally there is a small indention in the carburetor base and a small protrusion on the underneath of the float arm where the spring will be in the right postion for installation.
The spring will set in the indention and you will install the float arm with the needle/float valve and float rod into position over top of the spring,you will push down until it is in position and then you can tighten the screw that holds the float arm assembly in position.
Once you have your carburetor cleaned/rebuilt that should solve your problem.
Please take time to rate me
Bud

Apr 19, 2013 | Chainsaws

1 Answer

I have a TROY-BILT model 020242 , the engine keep shutting off after running for about 1min or 2 and start every time with no problem after stalls. Any idea of what can be causing this?


Hi coyoterick...
Your float valve is sticking in your carburetor causing this problem..
Follow the directions below and you will be running in no time
---------------------------------------------------------------------------------------------------------------------------------------------

Hi
Sounds like you have dirt/debris in your caburetor jets,fuel passages or a diaphgram that is becoming non-flexible.
Check/Clean/Replace your Air Filter, a dirty air filter can make your engine run to rich with fuel.
Note: ALWAYS USE COMPRESSED AIR TO CLEAN YOUR JETS AND PASSAGES, VERY IMPORTANT.
Note:Before you disassemble the carburetor:
Mark each piece with a awl, or some kind of instrument that will make an alignment scratch before you disassemble the carburetor into separate pieces.
That way you will know which way it goes back together when you reassemble it.
Sometimes you can get by with priming the carburetor or by using starting fluid and letting it run a few times like that, and it will flush the gunk out of the jets,but most of the time you will need to rebuild the carburetor.
Be sure to check your fuel tank for water and dirt/debris, if there is water/debris then you need to clean your tank.
Check you fuel line condition after a while they will degrade and need replacment.
Check/Clean/Replace your fuel filter if you have one, it may be located inside of the fuel tank.
Make sure you are using fresh fuel...and oil mix if your using a two cycle chainsaw with the oil to the right mixture and not too much oil as it can cause hard starting.
If the chainsaw is over a couple of years old, then I recommend that you buy and install a new carburetor repair kit,because the diaphragm will get hard and that will cause it to be hard to crank.
The diaphgram may look good and flexible, but it can be deceiving and not act as a fuel pump as it should because it has become too hard and will cause hard starting,start and run and shut off, etc.
When you clean your carburetor, I recommend that you use a laquer thinner type cleaner to clean and dissolve the laquer build-up in the float and needle jet passages.
Be sure to remove all plastic and rubber parts before using the laquer thinner because it can dissolve the plastic parts and render them unuseable.
Be sure to use COMPRESSED AIR to blow out all the fuel and air passages.The higher air pressure is needed to blow some of the trash/debris from the fuel or air passages.
Be careful when blowing out the passages, because there are sometimes small rubber type seats in the bottom of some of the passages.
Keep in mind that the float (if you have one) for the carburetor must be level when you go to reassemble the carburetor or follow the instructions you get with the carburetor kit, or you could also ask the parts man that you get your kit from.
When you clean your carburetor and remove the jet screws, you will first need to lightly seat the jet screws.
But before you lightly seat the jet screws count the number of turns it takes to seat the jet screws from their original position.
Be sure to mark the turns down on a piece of paper.
That way when you put the jets back in, you know to lightly seat them first and then turn them back out to their original position before you started.
Note:
The little spring inside of the carburetor goes under the float arm.
That is where your fuel inlet needle/float valve is located...on the arm at the end.
Normally there is a small indetion in the carburetor base and a small protrusion on the underneath of the float arm where the spring will be in the right postion for installation.
The spring will set in the indention and you will install the float arm with the needle/float valve and float rod into position over top of the spring,you will push down until it is in position and then you can tighten the screw that holds the float arm assembly in position.
Once you have your carburetor cleaned/rebuilt that should solve your problem.
Please take time to rate me 4 thumbs up

Sep 05, 2011 | Chainsaws

2 Answers

My Homelite ZR10926 16-Inch 33cc Ranger it is starting, idling, it dies when I accelerate it. I assume is the carburetor, maybe ? thank you.


It probably is not getting enough fuel. Check the filter in the tank. If it has been sitting with stale gass this filter plugs up.
Try running the engine with some choke. If this helps, try adjusting the carburetor high speed screw.

Jun 04, 2011 | Homelite ZR10926 16 Chain Saw

1 Answer

I run two gx160 engines on a prokart. when i hit the throttle on the one engine it hesitates and goes to stall. ive stripped the carb and cleaned all the jets but it still happens! any ideas? cheers Pete


If these engines are two-stroke, check the lower diaphragm in the stalling engine carburetor to make sure the material is flexible with no cracks as this diaphragm directly affects fuel mixture settings. If they are 4-stroke engines, take the carburetor off and remove the main jet. Just behind the main jet is a device called an emulsion tube that mixes air with the fuel just before it is dumped into the carburetor throat. Look into the carburetor throat and look for a short brass tube sticking into the venturi area. Use the flat of a screwdriver to push down on the tube which should cause it to fall out of the main jet hole--clean it in carburetor cleaner and check the small holes in the side and the main hole through the center of the tube. Hope this gets you running again!

Dec 09, 2010 | Chainsaws

1 Answer

Setting the carb twe jets


These people explain better than anyone else I have found. The sound files are very helpful too.
Carburetor Adjustment by Madsens.com
http://www.madsens1.com/saw%20carb%20tune.htm
CW is leaner; to lean will destroy the saw. If over tightened closed (CW) the adjustment screw faces are easily marred; marred adjustments are difficult to impossible to set properly.
Clean the air filter; adjusting with a dirty filter can cause a run lean condition once cleaned and the saw run.

There are 2 wav (sound - idle & full – not highlighted) files that I find most helpful, I think you will too. HTH
Lou

Dec 26, 2009 | Poulan Wild Thing 2375 18" Gas Chain Saw...

1 Answer

Cuts out on high revs 240 chain saw


Many saws made today are using electronics for engine control. If the engine rpm's starts to rev to high, the electronics in the coil will start to 'cut out' some of the spark. This is normal in this senerio.

But, now the real problem causing the senerio;

Fuel starvation - 'lean fuel' condition
Basic things to check:
1) spark plug
2) spark arrestor in muffler
3) fuel lines and tank filter
4) turn adjustment needles out (counterclockwise) 1/4 to 1/2 turn
*if all of the above are OK and/or do not improve performance then:
Remove Carburetor
5) replace gaskets/diaphragms
b) use a spray carb cleaner to clean jets, holes, and body of carb

Nov 10, 2009 | Husqvarna Chain Saw 20" Bar

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