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View Full Version : Pontification please. Pulan petrol priming/purging problems.


Loose rivets
25th Nov 2013, 19:47
It's a chainsaw. It has the ubiquitous rubber bulb that primes - or is it purges - the starting process.

I'd always assumed it pushed some fuel into the carb, but it does not draw its supply via the main filter in the tank, so would introduce dirt if this was the case. Also, the larger pipe simply goes back to the tank.

The later one was so rotten that it broke into many fragments, so I'm not sure how far it went in. Anyone clued up on this world-wide primer process?

Lon More
25th Nov 2013, 19:57
remove the pipe. You should then be able to see, with the aid of a lit match, exactly what the problem is.

Loose rivets
25th Nov 2013, 22:00
Darn forums are totally contradictory. Can't believe it would pull unfiltered fuel, but that's what some are saying.


A lit match? Sigh. Should it not be, a lighted match?

RINKER
26th Nov 2013, 07:36
Hi Loose Rivets
Is the saw not a Poulan as opposed to Pulan ?.
Anyway the primer should draw fuel through the fuel filter otherwise the carburettor screen will get clogged.Chainsaws have diaphragm carbs which have an integral fuel pump operated by crankcase pressure so they can operate at any angle without fuel starvation, unlike gravity feed systems like found on lawnmowers etc.They all have a choke for cold starting regardless of whether they have a primer or not.The reason for the primer on later models from approx mid 90's onwards is to get the fuel to the carb quicker so you don't have to pull the starter cord for too long which, because it is turning the engine over it is also pumping fuel to the carb.Normally the primer draws fuel through the carb through the fuel filter and returns fuel in a loop back to the fuel tank through an open ended line.Often in the workshop I see where people have been messing about with the saw and they get the connection of the lines mixed up. So try to operate primer and see (it will only pump one way)if it is pumping in the correct direction as described above.
Hope this helps
R ( Main agent for most brands, sales repairs etc for 30 years)

SOPS
26th Nov 2013, 08:33
I must say, it never ceases to amaze me the depth of knowledge we have here on JB. Ask a questions about priming chainsaws to fixing guidance systems on the Shuttle, and someone usually can help.:ok::ok:,

MagnusP
26th Nov 2013, 08:41
Agreed, SOPS, and yet in the eight years I've been active here, no-one but no-one has been able to explain to me the workings of a woman's mind. It shouldn't be rocket science (Hell, I've been involved in rocket science and even it isn't rocket science), but it's incomprehensible to me.

RINKER
26th Nov 2013, 10:50
Hear hear ! Chainsaws no problem. But women Much as I love them ;different kettle of fish. Having said that my other half is a qualified car mechanic and then worked in our workshop on chainsaws etc so she redeems herself no problem.
R

G-CPTN
26th Nov 2013, 10:55
Are we talking about a pulchritude primer? Is that some sort of pump?

M.Mouse
26th Nov 2013, 20:47
Agreed, SOPS, and yet in the eight years I've been active here, no-one but no-one has been able to explain to me the workings of a woman's mind.

That one is simple, see the diagram below.

http://bertc.com/subfour/truth/images/womansBrain.gif

Loose rivets
28th Nov 2013, 05:22
Sorry! For some reason my computer isn't showing the un-reads in highlighted black.

RINKER - Thanks for the detailed reply, although it wasn't as gripping as the quest for a female brain circuit diagram. ;)


Well, put the part on, and it seemed to be working, but today it failed to start without pouring fuel into the air inlet. :ugh: Tried it both ways just in case, but your comment about the method of pumping answers old questions.

I'm concerned the main bearing seals may be damaged. It's been standing most of its life and must be at least 15 years old. However, I set about this 18" thick Mesquite stump until it stopped again. I'll look in detail just how this thing gets its fuel pumped. There may be grot in the line from the crank. I'm assuming it's not a mechanical link.


G-C. I perceive precious perceivable pulchritudinous parts pertaining to this particular primer, though it would have been a wonderful word to scheme into the heading.

RINKER
29th Nov 2013, 18:32
Hi Loose Rivets

Unfortunatley Chainsaws can be tempermantal sometimes, if I had it in my workshop I could probably get to the bottom of your problems.First thing I would sugggest you do before you waste time or money on it is check the condition of the piston and cylinder. This is ALWAYS how I start on any small two stroke engine. Just take the Exhaust off and with the spark plug removed using a torch look into the exhaust port and whilst turning the engine over slowly with the starter (with the kill switch off ) make sure there is no scoring on piston.This is the hot side of the cylinder and the first to fail if it's had a bad fuel oil mix or is running lean due to poor carburettor setting or as you suggest is drawing air through bad crankcase seals or any other gaskets (inlet etc).If it's scored on the inlet side (which is very unusual in a chainsaw) this is caused by poor air filtration.
Getting it started is one thing but when it cut out did it slowly peter out and die
(ie too much air, not enough fuel) or did it stop instantly which is more likely an electrical fault.
Another thing Chainsaws no matter how powerfull, MUST be 100% sharp, no exceptions. If not it causes all sorts of problems and they can only cut clean wood , not roots or wood contaminated by mud, grit etc.
Overall, initially it sounds to me like the saw is running lean and that can be caused by a variety of problems, but that can cause uneconomical to repair damage to the piston and cylinder.Fingers crossed.
Hope this helps, keep it coming I will help if I can.

R

Loose rivets
29th Nov 2013, 19:19
Many thanks.

It petered out much in the same way a carb emptying would. Though without a conventional float chamber it happened in a couple of seconds.

The compression is good. Indeed, it seems to almost be kicking back sometimes, with quite a vicious tug on the cord. But then it runs well for a while.

Ignition timing varying? Mmmm . . . food for more thought. I've never known it kick back before.

I've had to go back to house wiring mode today, but tomorrow I will somehow ascertain accurately if it is drawing fuel. The fact the bulb never purges itself is perplexing. At best, it seems half full and repeated pumping keeps discharging air back into the tank. It seems air is getting in somewhere, I'll see if the carb is introducing air. So, pipes, bulb or carb. Air's coming from somewhere.

http://img.photobucket.com/albums/v703/walnaze/PpruNe/Chainsawing3_zpsec33b5d3.jpg (http://smg.photobucket.com/user/walnaze/media/PpruNe/Chainsawing3_zpsec33b5d3.jpg.html)

tartare
29th Nov 2013, 19:59
Woman's mind = quantum process.
All normal laws of Newtonian male explanation break down.
Also prone to spooky action at a distance - if she's pissed off with you then mother in law automatically will be too in the absence of any phonecalls or other apparent contact whatsoever.
Best approach - expect the uncertainty principle.

Lon More
29th Nov 2013, 21:20
Should it not be, a lighted match?

general usage (http://forum.wordreference.com/showthread.php?t=39177&langid=13) would suggest not.

Dushan
30th Nov 2013, 01:39
Agreed, SOPS, and yet in the eight years I've been active here, no-one but no-one has been able to explain to me the workings of a woman's mind. It shouldn't be rocket science (Hell, I've been involved in rocket science and even it isn't rocket science), but it's incomprehensible to me.

It was explained to me that it very similar to a browser with 2,750 tabs all open at the same time.

Loose rivets
30th Nov 2013, 02:10
Dopeee bugghars

It's a bloody lighted match. A lit match??!! Kah! This match wot I lit.:ugh:


https://www.google.com/search?q=a+lighted+match+v+a+lit+match&tbm=isch&tbo=u&source=univ&sa=X&ei=Q1aZUuusC5bYoATV64GADg&ved=0CFEQsAQ&biw=1760&bih=827#q=a+lighted+match&tbm=isch

cattletruck
30th Nov 2013, 13:16
Is it a cheapie Chinese model with a plastic carburetor? I had one that would be a PITA to start then after 15 minutes it would stop and never start again until it cooled down. The fix was easy, throw away the paper gaskets and use gasket glue to join them up again.

Loose rivets
30th Nov 2013, 17:17
No, it's a chunk of aluminium/aluminum. I'm in me doin'-things togs and off to the garage.

However, my neighbor is a fireman. He is hardly ever home cos houses here are made of kindling. When he is home I feel obliged to chainsaw quietly, since the stump is nearest to his property. Chainsawing quietly is a challenge. :p

B Fraser
30th Nov 2013, 22:01
I would throw it away and buy a Stihl...... and a decent set of protective gear. A chainsaw can remove flesh at the rate of 1lb a second.

G-CPTN
30th Nov 2013, 22:47
I would never ever use my chainsaw without wearing my protective gear.

I have had cause to be thankful when a kickback caused the chain to approach my face and cut through my face-guard.

Mechta
30th Nov 2013, 23:00
Regarding the kickback, its not unknown for Woodruff keys to shear, allowing the flywheel to move round a bit, resulting in incorrect ignition timing. In a similar vein, if a rotary lawnmower kicks back, check the blade is tight. The loss of flywheel action from a loose blade will make it into a vicious brute.

On the subject of thread drift. I did wonder if Loose Rivets had wandered off topic earlier:

Tried it both ways just in case, but your comment about the method of pumping answers old questions.

:eek::E:}

RINKER
1st Dec 2013, 11:26
Hi again loose rivets
Advice on protective clothing is valid I'm also a qualified tree surgeon and never use my saws without all the gear.However if your saw is not running it's not as dangerous as it could be !.
As far as Poulan as a manufacturer goes they are not too bad I did sell them here in the UK about 20 years ago and they are way better than chinese stuff.
I wont get into the best models or brands just now but happy to advise if required.For instance Stihl are fine but entry level models are best avoided.
As you and Mechta mentioned, ignition timing could be an issue but I doubt it.A lot of machines nowadays annoyingly have the woodruff key moulded into the aluminium flywheel from you guessed it; aluminium and they are prone to failure.If it's the traditional steel type in a slot they are less likley to fail on a chainsaw.
( unlike lawnmowers which is a different matter.)Sometimes if you remove the flywheel nut ( RH thread on the flywheel side) you can see if it's sheared.TOP TIP to stop engine turning over when removing flywheel nut , remove spark plug and take some nylon cord about 6mm or 1/4 inch diameter about 20cm , 8 inches long, bend in half and with the piston rotated to the bottom of it's stroke push the closed end of the cord into the cylinder through the spark plug hole leaving enough outside to retrieve it later, then slowly turn flywheel anticlockwise allowing the piston to jam the cord inside the top of the cylinder jamming the engine allowing you to GENTLY unscrew flywheel nut. Refitting just reverse procedure.Removing the flywheel can be tricky and may require special tools.Normally the only thing to set on the ignition is the air gap (about .3mm)
between the magnets and the ignition module.
I still think you most likely have fuel starvation problems.First make sure the in tank fuel filter is spotlessly clean, if in doubt replace it. Get an original or if not a local saw dealer who may deal in Oregon products will probably stock Tillotson ones which are fine or my favourite filter is Husqvarna part no 503443201.Then be absoloutley sure you do not have even a pin hole in the fuel pick up line, which is common. I check them by removing and sealing one end and pressure check to about 0.4 bar.
Also check the carburettor retaining screws are tight as if loose apart from drawing air at the inlet manifold you will get a bad impulse from the crankcase to the carburettor and hence will get poor internal fuel pump operation.
Also make sure the fuel tank is venting ok. Normally if it's not , the saw will stop after a few minutes and then loosening the fuel cap will allow it to start again.
Last thing for the moment, depending on the marketplace your saw was destined for , the carburettor may or may not have an adjustable H (high) and L (low) fuel jets. If it does try turning the H jet anticlockwise about an 1/8 of a turn and see what happens.
If this all fails I will explain how to check out the carb.
A couple of other things,is the saw is kicking when starting, believe it or not it can be caused by the starter pulley starting to splay apart due to wear which then allows to cord to catch on itself as the splayed pulley is wider than designed.Also we haven't mentioned spark plugs. Whether likely or not it's always worth fitting a NEW one (not something that has been lying about) and be certain it's EXACTLY the correct specification.
Also make sure you are using Fresh fuel with the correct ratio of two stroke oil, intended for air cooled horticultural machinery. (not outboard 2t oil for example )
I'm back offshore today to fix much bigger things for a few weeks but have internet on board so will keep an eye on this thread.

Good luck

R

Loose rivets
3rd Dec 2013, 18:30
Lots of good stuff there, thanks. Aluminum Woodruff key? :yuk:

Top tip indeed. Have to see if my motorcycle shop-owner-friend does that.


Having cut the end off the fuel pipe and reconnected it, I got a much more realistic pressure in the primer bulb. The saw ran, and I felled the huge stump outside the back patio. Then I went to cut of a small stump that stopped me rolling the log, and the darn thing wouldn't go again. Air being pushed up the tubes. I'm just about to investigate this scenario:



Then be absoloutley sure you do not have even a pin hole in the fuel pick up line, which is common.

However, when it did go, it was good. An 18" Mesquite stump did take the edge off a fairly new chain. But I expected that. Back to garage for more fun.

RINKER
3rd Dec 2013, 19:03
Well see how it goes.Sounds like some progress
Working on a 65 Ltr V16 Diesel today and I can assure you a lot less temperamental than a small two stroke. !

Good luck

R