[John O]

I guess I'll go first.

I have a Poulan Woodshark chain saw that is very difficult to start. I usually have to keep the thottle open with my foot to get it going. Then once started, it won't hold an idle. I've been pretty religious about emptying the fuel then running it out when I knew I wouldn't be using it for a while.

If I were diagnosing this on a car, I'd say a clogged fuel jet or filter, but since I know zip about small carbs, I'm a little shy about just tearing into it. So, where it start? Are there any on-line guides for basic trouble shooting?

John O.

 

[hankster]

Basic Trouble shooting... right here... :lol: Althought these will be real basic instructions, you'll get the idea. I’ll run through some steps that should be able to help you.

The main cause of poor idle on a chainsaw is a plugged carb screen (fuel filter), a carb that is out of adjustment or an air leak.

The easy fix is if it is the carb adjustment. While adjusting a carb is almost an art and can quickly cause you to pull your hair out, it can be done if you take your time and go one step at a time. If you get flustered, step back for a few minutes, take a break and try again a little later

Here is a quicky on how to try adjusting it.

First, make sure the spark plug is good. Change it anyways; even good looking plugs can be bad. Also check the air filter and clean it. If REALLY bad, you may have to replace it.

Pull the adjustment stops on the carb. You can use needle nose pliers to pull them off... just grab a hold of one edge of them and give a yank.

Now carefully close the needles noting how many turns it took to close them. Don't tighten them too much, when you feel resistance, that's enough. But since you know full size engine carbs you know all about this.

Open each needle 1 1/2 turns

Prime the carb 10+ times. That's right, 10+ times. The primer is not really a primer, but a "purge" bulb. It doesn’t shoot fuel into the cylinder but circulates fuel through the carb. Priming the extra times will help flush the carb screen of any gunk that might be there.

Set full choke and full throttle if you don't have a throttle lock.

Try starting. If it "pops", set choke to 1/2 and keep trying. It should start if everything else is OK (compression, timing, etc.)

Once it starts, if it won't idle, turn up the idle speed till it will idle.

If the engine is in good shape, the idle mixture screw should be set 1 1/4 turns to 2 turns. In rare cases it may take up 2 1/2 turns. Just try opening the idle mixture 1/8 turn and slowing the idle speed. You just have to play with each setting until you can get it so it idles and accelerates properly. This isn't the final setting, but we want to first get the idle mixture close before we move to the high speed.

If you have gotten this far, it's time to run it at high speed. Rev it up. If it sounds like it is starved for fuel or sounds like it runs good, open up the high speed needle 1/4 turn and try again.

Keep opening the high end until it starts to run rough. You will be able to hear the difference when it starts to "4 cycle"... almost like it is missing or hitting on every other stroke. Once you hear this, close the high end screw 1/8 turn at a time until this just barely stops or only seldom does this.

Note: Setting the high end too lean will surely burn up the motor. It's better to err on the rich (fat) side then the lean side.

If it smokes a lot and runs rough (we call this 4 cycling), then close the needle 1/4 turn and try again. Use the above procedure to set the high end needle.

Now it's time to see if it still idles properly. If it doesn't reset the low needle and idle speed so it does. This is a balancing act where you adjust the needle a little and cut the idle speed down until the chain stops. Now quickly pull the trigger, if the engine hesitates or sounds like it is starved for fuel before it accelerates, the low end needle is too lean, open it 1/8 turn and try again. If the engine loads up at idle, the low end needle is too rich.

The biggest mistake here is opening the low speed idle too much and opening the idle speed to compensate for the rich mixture. A sign of this is a saw that won’t idle for very long as it dies from flooding.

Once you get the low speed/idle set, go back and recheck the high speed setting.

A couple things to remember.
For the most part, adjusting the high speed needle will not affect the low speed. Adjusting the low speed mixture WILL affect the high speed setting.
Do not compensate for a rich low speed setting by cracking the idle up. The saw should idle for at least one minute without dying… that is the bare minimum.
Do not run the high speed too lean or you’ll end up needing a rebuild.
If your high and low end adjustments get too far out of wack when adjusting, you can go back to the 1 1/2 turns out for each and start again.

I’ll get to checking for air leaks in my next message.

 

[hankster]

We use a couple tricks to check for air leaks.

First thing to do is make sure the crankcase bolts are tight. Turn the saw over. Most Poulan models will have 4 screws on the bottom of the case. Tighten these real tight. These screws hold the crankcase together and can work loose causing air leaks.

Next, take off the top cover to expose the spark plug and carb. When the saw is running spray some carb cleaner around the base of the carb. If the engine speed changes you have an air leak. This can be caused by loose carb bolts or a cracked carb adaptor.

Those are the main areas for air leaks. If you find an air leak and fix it (or just tighten the crankcase bolts), try running the saw again and adjust the carb.

It is also possible that there is a fuel line crack. This is more or less a visual inspection for fuel leaks and/or brittle fuel lines. Also, look in the fuel tank and make sure the fuel filter is still on the end of the fuel line. Pull the filter out of the tank and make sure it isn’t dirty. Also clean the air filter.

Lastly it is possible the carb screen is plugged. This requires you remove the carb then remove the fuel inlet cover from the carb. In most cases the inlet cover is held on by one screw but, depending on the model of the carb, you may have to remove the purge bulb to get to the inlet (carb) screen.

Once you remove the cover you’ll see the screen. Spray it out well with carb cleaner, put it back together and reinstall the carb. Putting the carb back on can be a real pain. There are a couple of linkages (throttle & choke) that need to be hooked up all the while aligning the carb gaskets and avoiding pinching the fuel line. All this in the space that isn’t designed for your figures to hold everything where they are suppose to be. Again, take you time and take a break if you notice clumps of hair in your mitts.

Anyways, I think I covered most of the high points for the main reasons and how to find and fix them. Other less likely causes are low compression, bad timing from a sheared flywheel key, bad/weak/misadjusted ignition module, badly plugged carb and plugged muffler/exhaust port.

One last thing that is easy to check is for a plugged muffler and/or exhaust port. All you need to do is take off the muffler (two bolts) and look at the muffler for plugging. Also look in the exhaust port for carbon buildup. While looking in the exhaust port, turn the engine over slowly and look for scoring on the piston. The main cause of low compression is scoring of the piston/cylinder on the exhaust side... it'll be pretty obvious if it is.

 

[owl]

Cool! When I read the announcement, I decided to stop by and ask about my chainsaw, and the likely answers are already here. Hopefully I can put it to the test when I get it outta the shedbox it's in.

I might be back....

 

[John O]

Well shoot, that's truly awesome!! Thanks Hank!!! I'm going to print out your post and take it to the garage with me. I'll let ya know how it goes.

John O.

 

[rwmaniac]

i understand the card adjusting Hanskter but i have an old craftsman, it has idle, high, and low, a throttle lock and choke. no primer.

the needles are all out of whack and it will start with a splash of carb cleaner but cant get it to start and run with the mixture.

fuel supply is ok.

should i close all 3 needles and then open 11/2 turns, full choke and lock throttle to start my initial testing to start thanks!!!

i'm confused as most newer carbs just have the idle and mixture screw. thanks a bunch to anyone who replies.

ps. when you say turn the idle or hi lo up? do you mean open or close the needle. thanks.

 

[hankster]

If your saw doesn't have a primer, it is sensitive to dirt in the system... be it the filter in the tank or dirt in the carb.

The idle screw just adjusts the throttle opening when the trigger is released. If you are having problems staerting, just set it so the throttle is cracked a bit... you want a high idle at least at first. The high/low needles should be gently turned closed then opened about 1 1/2 turns.

If it fires on carb cleaner, then we know it's a fueling problem. The problem could be anywhere from the tank to the carb. Plugged tank filter, cracked fuel lines and a dirty carb are the most common problems. Until any of those problems are fixed, you won't be able to get it started.

Your starting proceedure seems correct except the idle screw which normally is not set that tight, but it won't hurt other then when it does start the idle will be REAL high.

 

[rwmaniac]

thanks for the help! let ya know how it goes.

 

[rwmaniac]

ok what next?

well i got the 30yr old buzzard running after a carb teardown and cleaning. it was dirtier than a pit full of mud wrestlers. it runs great BUT i cant get it to idle at all after releasing the trigger lock! just shuts right down. have messed with the 3 screws to no avail, yet it runs great at full throttle and under load. gave up for now. any suggestions appreciated. thanks. BTW its a Tillotson carb! thanks again. later!

 

[duke4949]

the fuel line is leaking or the pump is weak.
www.dukesmanuals.com

 

[rwmaniac]

fuel line aok. pump? do you mean the diaphragm?