Newbie refurbishing a Poulan 4218

[dmitrym]

Hello folks!

First post here. I picked up a Poulan 4218 off craigslist to refurbish. I can't get it started, though occasionally it does catch for a couple of cycles.

I bought a carb rebuild kit off Ebay and replaced the carb and the spark plug.

1. Confirmed that there's spark.
2. New fuel; confirm that it's getting to the cylinder (it sprays out when the spark plug is out and pull the starter).
   1. Confirm that the primer bulb is working (I see the fuel being pushed around).
3. Air filter shouldn't be an issue; tried running it without one.
4. Compression feels ok ("thumb gauge") and the piston isn't scored much from I can see.

I've got fuel lines/fuel filter with the carb rebuild kit so I might try that even though I see fuel being delivered when I prime the saw.

Anyway at this point I'm kinda stumped. I'm a software guy by day so this is a new area for me. I'd appreciate any advice!

 

[RED-85-Z51]

These had just barely enough compression to run when under ideal circumstances...if the piston isnt pristine, compression is probably too low

Sent from my SM-G996U using Tapatalk

 

[SteveSr]

Compression feels ok ("thumb gauge") and the piston isn't scored much from I can see.

Scored much? Shouldn't be scored AT ALL! Remove the muffler and post some good photos of the piston through the exhaust port. You may be polishing a turd.

 

[dmitrym]

There was quite a bit of fuel in the muffler and around. What's that about?







Here a couple of shots of the piston:

 

[SteveSr]

There was quite a bit of fuel in the muffler and around. What's that about?

Time for an OEM carb kit. Stiff metering diaphragm is likely holding the needle open and dumping fuel into the saw so much that it runs out the muffler. BEFORE you tear apart the carb for cleaning remove the limiter caps and using the correct tool count how many turns it takes on each screw clockwise until lightly seated. This way you have a starting point when you put everything back together.

While you are in there just plan on replacing the fuel lines and filter. If the saw has two different diameter lines drill out the tank to make everything the larger line. Use only Tygon branded and labeled "4040" line. The AM stuff will turn to goo in 6 months. Same with carb parts.

BEFORE you remove the carb and fuel lines take good photos of the fuel line routing to make sure that it goes back correctly!

You can also find an owners manual and more importantly IPL at www.poulanpro.com.

Here a couple of shots of the piston:

Piston looks good

 

[heimannm]

If you are planning on getting into this hobby you should acquire a compression gauge and some way to pressure/vacuum test the crankcase.

If compression is too low (less than 100 PSI on a piston ported saw) it is unlikely to run. If the crankcase seals are leaking it won't run or will be very inconsistent due to air getting into the crankcase and diluting the mix.

The fact that yours is spewing fuel through the muffler could indicate insufficient compression to fire and the mix is just passing through. It could also be that the carburetor is badly out of adjustment and the ratio is so rich that it is simply flooding out.

Mark

 

[Old2stroke]

As has been pointed out, if you get fuel spitting out the plug hole when you pull it over, the saw is badly flooded. Do a search on "flooded engine" to find out how to properly clean it out. If you have good spark, there is probably nothing wrong except for the flooding which could just be a simple carb problem or due to faulty starting procedure. The primer does not squirt fuel into the engine, if it is plumbed correctly (often wrong), it just sucks fuel up through the carb and circulates it back into the tank, it's there to purge air out of the fuel supply line and fill the carb.

 

[dmitrym]

Hey folks, just wanted to provide a quick update. It ended up being badly flooded. Couple of ounces came out of the muffler and then quite a bit from the cylinder. I can now start it, just need to tune the Low screw so it idles well. Thanks for your help!

 

[heimannm]

It is always good to find out when things works as they should.

Mark

 

[dmitrym]

Hey folks,

I may have been a tad optimistic. The saw fires up right away but has trouble idling. I've re-seated the L adjustment and backed it out a tad but that seems to set the idle way too high. If I turn in it, it bogs down pretty and dies. I'm gonna get an RPM gauge to see what's actually going on, meanwhile any tips on adjusting the idle?

Dmitry

 

[Vintage Engine Repairs]

Clean air filter,
Tension and sharpen chain
Fill fuel and oil tanks full
Clear spark screen

1. Seat L and H and open both up 1 turn
2. Unscrew LA until it doesn’t touch cam
3. Turn LA in until it contacts cam and 3/4 turn more

Start saw and let warm up.

4. bring idle up to just before chain creaps (or 500 Rpm above idle if you have a tachometer)
5. Turn L in and out until it runs fastest

If chain is moving (or rpm is above 500rpm + idle spec) here, bring LA back out to stop chain moving (or 500rpm+ spec) and the repeat point 5

6. Turn L out slowly until rpm smooths out - normally 1/8 - 1/4 is enough and then tweak LA for good idle speed - no chain creep (or set to spec)
7. Pull trigger,should accelerate with little to no hesitation
8. Pull trigger and hold at WOT, very quickly turn H in until it runs smooth and screams, then turn H back out until you hear it start to 4 stroke. (This process should be done in less than 5 seconds) (or 500rpm below max WOT specified in the manual)

9. Make a cut with the saw - saw should only clear up from 4 stroking under good load - 1/3 of the diameter of the log is a good indication. If it clears up as soon as the chain touches the wood it’s too lean.

If you aren’t careful with point 8, you can damage your saw so proceed with caution.

 

[RedneckChainsawRepair]

Just some saved info I have on this saw. http://chainsawrepair.createaforum.com/poulan/engine-speed-issue/

Poulan 4218 that is like new pulled 165psi.

The one with scuffed piston pulled 150psi that is a non runner.

Poulan 4218 carb settings were L 2 and H 1.75
Green strato was L 1.75 and H 1.6ish on new carb.

Pic of scored one and other like new one.

 

[dmitrym]

@Gaudaost thanks for that! Really comprehensive.


So, I followed the procedure outlined above. It was idling pretty well at about 2800 if I'm to believe the tach. As soon as I squeeze the throttle it bogs down, at about 3000 rpm.

Upon further inspection, it looks like one of the fuel lines at the carb is slightly cracked. Gonna drain the fuel, replace the lines and try one more time.

Thanks again for all your help!

 

[GoBigRed]

So I know this was mentioned before but I’m not sure if you mentioned checking it.
I honestly think the needle in your carb is set too high. If you purchased a carb and hoped it would be plug and play....that’s isn’t always the case. If the tab that holds the needle is set to high, it will cause everything you have described involving too much fuel. Flooding and not able to tune the low side.

Just a thought

 

[SteveSr]

Upon further inspection, it looks like one of the fuel lines at the carb is slightly cracked. Gonna drain the fuel, replace the lines and try one more time.

This is likely not your problem but does need to be fixed. First, verify that the current fuel plumbing is correct. You should be able to continuously pump fuel (purge air) from the tank through the carb and back to the tank. You should be able to see fuel enter and leave the primer bulb. If this is correct take some good photos of the current plumbing so that you can put it back correctly.

Use only genuine Tygon 4040 fuel line. It will be marked as such on the line. If this saw uses two different diameters of fuel line just drill out the tank for the larger line and switch to a single size line.

For those offering tuning advice keep in mind that this is a strato-saw and may not tune the same as a conventional non-strato saw.

 

[dmitrym]

So I know this was mentioned before but I’m not sure if you mentioned checking it.
I honestly think the needle in your carb is set too high. If you purchased a carb and hoped it would be plug and play....that’s isn’t always the case. If the tab that holds the needle is set to high, it will cause everything you have described involving too much fuel. Flooding and not able to tune the low side.

Just a thought

@GoBigRed the original post I made, when the engine was flooded was with the old carb. I haven't been flooding much (at all?) since the new carb was installed. The carb is not OEM, but it's designed for the same class of saws so I assumed that it would be set to dispense fuel correctly. Do you have any advice on how to reset the needle?

This is likely not your problem but does need to be fixed. First, verify that the current fuel plumbing is correct. You should be able to continuously pump fuel (purge air) from the tank through the carb and back to the tank. You should be able to see fuel enter and leave the primer bulb. If this is correct take some good photos of the current plumbing so that you can put it back correctly.

Use only genuine Tygon 4040 fuel line. It will be marked as such on the line. If this saw uses two different diameters of fuel line just drill out the tank for the larger line and switch to a single size line.

For those offering tuning advice keep in mind that this is a strato-saw and may not tune the same as a conventional non-strato saw.

@SteveSr I see the primer bulb doing it's magic, in fact that's where I first discovered the cracks. Do I understand correctly -- if I continue priming the fuel should drain out of the carb through the input hose?

I'll take a further look today.

Thanks,

Dmitry

 

[GoBigRed]

Most carbs are either set with a gauge or they have tabs on either side of the lever so you can set a straight edge on it and check the height. Kinda hard to explain and sometimes that might not even be correct for the carb depending on tolerances of the manufacturer.
I know the carb you have and it’s used on all the brands that husky owns.
Now that I go back and reread your post I think you need to simply adjust the carb. It’s wither bogging because of too much or too little fuel. If you squeeze the throttle and it dies, then your hi jet is to lean. If it bogs and then starts to pick up speed then you are usually too fat on the hi jet.
Try a half turn in either direction and see if it helps.
If that doesn’t work go back to where you had the hi jet and try half turn both ways on the low jet.

It’s a tuning issue somewhere and that is just trial and error if you don’t have a lot of experience with a two stroke carb. But you will get it

you know once this one gets going you’ll start trolling for another one. Then another one. And then it become an addition. Wait until you dabble in some of the older saws. It was all down hill for me after I bought my first 10 series Mac

 

[Old2stroke]

Bogging just off idle is usually due to transfer ports just behind the throttle plate (part of the low speed circuit) not flowing enough fuel to get the engine speed up the point where the high speed circuit kicks in, backing out the L screw will let more fuel into the low speed circuit but has to be balanced with steady idle speed and clean acceleration. If the ports aren't blocked by crud, then backing out the L screw 1/4 turn at a time from fastest steady idle should cure the bogging. The high speed (H) screw should only be set to get the engine running properly under full load at WOT and should not be changed from this setting to try and cure a problem with the low speed circuit.

 

[dmitrym]

Alright, I’ve taken the fuel out of the tank.

Does this look right? Obviously the filter needs to be reattached. The long line is from the primer, but I’m surprised how high the “main” line is. I guess it works but partially pressurizing the tank?

The two reds are two lines and the green is the filter.

Sent from my iPhone using Tapatalk

 

[MacAttack]

The plastic barb on the left circled in red is the "return" from the carb. The fuel supply line should be connected to the filter (as you said) and should be able to move around to have the fliter lay in the "bottom" of the tank, however the saw is oriented. That's the purpose of the flexible supply line and the weighted fuel filter.