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#109312 11/11/20 07:05 PM
Joined: Jul 2018
Posts: 2,085
Likes: 80
Tyler Offline OP
SENIOR TECHNICIAN
This came over my bench a couple months ago. Stalled during idle after 2 cuts and wouldn't restart

No compression - I asked the guy if he put oil in it. He said he put the fuel in there (fuel cap) and the oil in there (pointing to oil cap).

So straight fueled. Was his brothers, who recently moved into a unit and gave him the saw. First day and he stuffed it.

He left it for parts. I pulled it down that afternoon - classic 4 corner seizure, but not severe. Plus a stuck piston ring. Took 180 then 360 grit sand paper to the scores in a criss-cross hone pattern

Washed all out with petrol, cleaned up piston ring and piston, resealed and re-joined the barrel to the case.

Put it all back together, assembled with a new chain I got on Bunnings clearance for $10 (open pack). Fired after 3 pulls but after 2 hours of stuffing around yesterday afternoon, I had all but given up. It has borderline compression and I figured it just wasn’t creating enough vacuum to suck the fuel in properly.

Today (after it sitting overnight with 98ron in the tank), it fired up and I could coax it to keep going. End of a long tuning session saw it idle at min 3500rpm (chain doesn’t engage but max in manual is 3400). Anything below that and it slowly dies. It still does it occasionally if you idle it more than 2 minutes. Have it revving out at 10500 out of cut (12500 spec) as that gave the most power in cut.

Only thing I can fault is it throws out a tonne of bar oil (as you can see by the cardboard). Plus it’s a bit cantankerous to hot start but 2 pulls with the throttle lock engaged seems to get it going. Put a 1/4 of a tank through it doing some pruning, and seems alright

Pretty good considering I gave it a 20% chance a working.

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Tyler #109316 11/11/20 08:04 PM
Joined: Feb 2006
Posts: 4,675
Likes: 164
SENIOR TECHNICIAN
I personally would dice it and look for a better one after that result. He stuffed it alright.


Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!
Tyler #109317 11/11/20 08:30 PM
Joined: Jul 2018
Posts: 2,085
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Tyler Offline OP
SENIOR TECHNICIAN
MF, this was mainly just an experiment to see if it would. I already have too many chainsaws - a Victa 16in which I bought new on clearance, and Ozito 10inch Arborist which I bought new on clearance, 2x Ryobi pole pruners bought new on clearance, plus an older Poulan Arborist saw.

I bemoan doing any inherently dirty work with any of them - this Ryobi's main jobs will be the crappy cutting of palm trees (which grow dirt up in them) stumps, and roots if required.

Keep it on a diet of 40:1, sharp chain, clean filters and run it until it dies

Tyler #109318 11/11/20 09:05 PM
Joined: Feb 2006
Posts: 4,675
Likes: 164
SENIOR TECHNICIAN
Good idea. Your use and abuse bush basher saw!
You'll probably grow so fond of it you'll miss it when it does die!

Good going getting the mule runningTyler.


Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!
Tyler #109321 11/11/20 11:03 PM
Joined: Jul 2018
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Tyler Offline OP
SENIOR TECHNICIAN
Don't know how long it will take to kill it MF. If it had a chromium cylinder, then it would die in short order as the chrome would be flaking off.

The entire work of all the chainsaws combined is around 3 - 4 full skip bins over the year, plus filling up probably another 2 equivalent in the 240l council bin in dribs and drabs.

Probably last for many years to come, getting progressively harder to cold start until it becomes a parts donor

Tyler #113710 10/01/22 11:26 PM
Joined: Jul 2017
Posts: 80
Trainee
Hi Hope someone picks this up as the post is a little old. My neighbor has given me a Ryobi PCN 4040, S/N 05/25 000836 it apparently belonged to his uncle. Looks as though it has done nothing at all, all the paint is still on the bar and the chain is dull but never been sharpened. It has a bar tip protector that I have never seen before which is a good idea for a home handy man saw but no idea how long it has been sitting for.
The story so far, initially I thought someone may have accidently put oil in the fuel tank by mistake as the sparkplug was dripping with oil but it is equally as likely that someone pulled and pulled on the rope until they had saturated everything with oil and the fuel has evaporated away. The fuel was also pretty thick and smelled like shellac probably just old.
I flushed the motor and fuel tank out with petrol and then added new 20/1 fuel attached a drill and gave it a run for awhile with the spark plug out. It was evident that it was running pretty rich by the stuff coming out of the plug hole. Put the plug back in and ran it with the drill. After about a minute it fired but quit. Removed the plug and it did not appear to be excessively wet but eye sight is pretty poor these days. Tried a bit of straight fuel (no oil) in the plug hole and the motor fired and ran for a few seconds and quit, several times. After each short run fuel ran out of the exhaust and possibly back out of the carburetor throat (not sure about that but a lot of fuel it could have run from the exhaust under the housing and back underneath the carby),
Decided to bite the bullet and pull it apart enough to get the details off from the carburetor and maybe get a new one. Unfortunately there is not much information on the the carby unless ZAMA CHINA is significant, there is a small 5 on one piece, I will attach a photo. I removed the plate at the top carby and sprayed a little carby cleaner around the needle valve and other parts and put it back together. The saw started and ran but revved very fast and when you depressed the accelerator it died. Seems to have fixed the flooding excessive fuel problem.

Took it apart again and took the bottom off from the carby and sprayed a little carby cleaner around. Reassembled and this time it starts and revs its little heart out but if you pull the accelerator it does not die. I discovered that if you pushed the accelerator arm closed with a screw driver it would drop back to an idle. Thought I had it licked. Pulled the carburetor out again and shortened the sheath around the accelerator cable where it goes into a holding (mounting) block by about 2mm. (sorry I should have taken a photo. Reassembled and now there is a tiny amount of slack in the cable and you cannot manually close the accelerator any further.

The saw started and revved its little heart out and you cannot slow it down by pushing on the accelerator linkage, (the idle adjustment screw is not touching the linkage) I started it and tried a few different things for no success. I mixed up a new batch of 20 to 1 and added a little extra oil for good measure gave the primer a dozen squeezes hoping to flush the fuel through. It started first pull and smoked a little and revved flat out. I gave it a couple of runs but the same result every time. The high and low idle screws are covered with some sort of plastic yin and yang thing, which I have been reluctant to try and remove. You can only turn them about 30 degrees for the low and 20 for the high. I have tried them in a variety of static positions but don't seem to get a different result. They are pretty difficult to adjust when it is revving and I am a little reluctant to let it rev that high for to long but it does not seem to make any difference.

The gasket between the carby and the intake manifold is not the best but I don't think that would be causing this problem.

Probably the only things left that I can think of is to be a little more severe with the mixture screws and get them out somehow and spray a little carby cleaner in there and then try to get a replacement carburetor.

Open to any suggestions

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If I can get a large enough hammer it will run for awhile just trying to get away from me
Tyler #113712 11/01/22 01:54 AM
Joined: Jul 2018
Posts: 2,085
Likes: 80
Tyler Offline OP
SENIOR TECHNICIAN
Hi Byomarimba

I will say it has been a fair few months since I did any work on my pcn4040, so a bit hazy memory.

If your idle screw it that far out (ie throttle shut that much) and it still revs mad, I would say there must be an air leak down stream. Flip the saw over and there are 4 bolts that torque down the cylinder (yes the whole cylinder is torqued down by bolts through a plastic case - asking for trouble).

check none of them are loose.

There is a rubber intake boot that is behind the carby the retaining rings are easy to inadvertently pop partially off when moving and wriggling the carby off.
check this rubber boot is properly popped into the plastic plate behind the carby. check the retaining ring is properly around where the boot meets cylinder (this is fiddly)


What is the state of the metering diaphragm under the plate shown in first photo? It is some derivative of a c1u zama carby, so this sort of diaphragm would fit https://www.ebay.com.au/itm/121652830910?

Pull those limiters straight off with flat nose pliers

Regards

Last edited by Tyler; 11/01/22 01:54 AM.
Tyler #113742 12/01/22 12:10 PM
Joined: Jul 2017
Posts: 80
Trainee
Thanks Tyler
I will try and get a second look at it this afternoon and get back to you tomorrow
Regards


If I can get a large enough hammer it will run for awhile just trying to get away from me
Tyler #113747 12/01/22 05:54 PM
Joined: Jul 2017
Posts: 80
Trainee
Hi Tyler,
I checked the items you mentioned no problems there, so I thought taking the carburetor apart again would be the way to go, got it out and started pulling it apart before the brain kicked in. Obviously for the motor to run fast the butterfly valve must be open. I think air getting in from anywhere else would make the mixture to lean and it would not run at all. . There is a system on the other side of the carby that when the choke is engaged it opens the accelerator and is meant to release when you pull the trigger. That was the problem. Just didn't think to pull the trigger while it was revving off from the bench.
Put it back together but I think I have created another problem
Pull the rope once with full choke, turn the choke off and it starts and revs on the next pull then dies. You can keep it running by pulling the choke in and out but timing has to be good. I could not get it to run by having the choke partially on, it was all or nothing.
I am guessing that I have damaged the diaphragm or one of the other gaskets as it only gets enough fuel to run with the choke out.

Decided that the easiest thing to do would be get a new carburetor. The genuine one is available on Amazon from the US for $26.00 or an aftermarket one on Ebay Australia but shipped from China for $29 but it comes with fuel line spark plug filter and gaskets. went for the Chinese one as they are sending it express so I should have it in 2 weeks
and I could not find any details on shipping from the US one.

For future reference the Chinese carburetor says it replaces ZAMA CIM-H58 ( A through to D)

I will let you know how it comes out.

Attached Images
20220112_114107.jpg (142 KB, 54 downloads)

If I can get a large enough hammer it will run for awhile just trying to get away from me
Tyler #113968 31/01/22 05:25 PM
Joined: Jul 2017
Posts: 80
Trainee
Once again I have managed to make a simple job (dirty carburetor, I checked what I had dumped out of the fuel tank and it was just oil) into several days of entertainment. The after market carby arrived ahead of time, installed it and the saw would not start, removed it and replaced the fuel lines and purge bulb. Managed to get the saw started but same problem as before, it would not idle. I suspected it was sucking air at the intake manifold as the new gasket supplied was the wrong one and the old gasket was in very poor condition. Removed it and rechecked everything that Tyler mentioned earlier where I may have an air leak. No idea what the hole is for in the bottom of the intake manifold below the throat but removed the plastic ring and pondered it for awhile. See pic. Reassembled same problem. In desperation I removed the low idle jet sprayed a little cleaner around and reassembled to approximately the same position. Saw would not start at all. Turned the low speed jet in quarter of a turn and it started. Did a static tune (may not be the correct term but by ear with the motor running) and jet was nearly 1/2 turn from where it was when it arrived. Foolishly put the bar and chain back on and tested it. Not enough power to cut a toe nail. Did a tune on the high speed jet finding it was more than half a turn away from original as well. Saw runs and cuts but a little hard to start. A common problem when ever I attempt a static tune.
I guess the purpose of this forum is to learn something, and I figure if I remove that carby one more time there is a 50 50 chance that I will connect the accelerator cable before screwing it down.
I have used generic carburettors 3 times in the past with perfect results, but for the benefit of future users it may not be wise to assume they are not just plug and play.
Tyler, thanks for your help on this, there would not be anything wrong with the old carby that a competent clean and reassembly wouldn't fix, maybe a diaphragm, I see that you are local, if you want it for a spare just send me a personal message with your address and I will stick it in the car and drop it in sometime when I am in your area.

Attached Images
20220131_152201.jpg (195.6 KB, 46 downloads)

If I can get a large enough hammer it will run for awhile just trying to get away from me
Tyler #113970 31/01/22 11:45 PM
Joined: Jul 2018
Posts: 2,085
Likes: 80
Tyler Offline OP
SENIOR TECHNICIAN
Hi Byomarimba

Thanks, but I need another chainsaw like a hole in the head haha

Already have the ryobi, 2 ozito arborist saws, mac/talon, victa and rover saw, not to mention vintage solo, poulan and mac saws.

I think you can probably get this one running yourself.

It is doubtful it would have run even if you knew to blip the throttle to get it off fast idle. It would have stumbled and stalled most likely

I had a terrible time getting mine running, literally hours. I thought it was the engine damage but maybe they are all problematic.

Mine has no gasket between the carby and that plastic. the browny rubber seal is the gasket.

That hole is for the pulse line which controls the metering diaphragm vibrations. If its blocked by the wrong gasket then it won't run well at all.

My other money would be on the fuel lines being backward, could you take a photo of the line routing ?

Its easy on this one to get the lines backward - ask me how I know. How many turns are the screws out?

Another thing, pull the muffler and check for both spark arrester clogging and scored piston.

Tyler #113971 01/02/22 03:41 AM
Joined: Jan 2015
Posts: 1,487
Likes: 23
AVB Offline
SENIOR TECHNICIAN
Well even though 2 cycles are fairly simple they can be a royal pain to those that don't have the experience. It took me several years to get good at the basic non invasive tests. The ryobi in question here is basically a Homelite (TTI) chainsaw...If saw starts at all is a good sign that it should be repairable.

But as Tyler suggest it may only be that the fuel lines connected wrong.

Tyler #113993 04/02/22 04:45 PM
Joined: Jul 2017
Posts: 80
Trainee
Thanks Tyler and AVB, possibly a small misunderstanding, I was only offering you the old carburetor, the saw is running very well just a little nervous about the high speed mixture when tuning the carb by ear I could have it a little lean and cook the motor with a bit too much work. Time will tell, I have cut up everything I had on hand. At one stage I did have the fuel lines on the wrong way around, and I did take the muffler of and check for any obstructions just a bit embarrassed about how many hours I put into it to mention it earlier. I also neglected to mention that when I first got it running after adjusting the after market carb that it was blowing lots of fuel back out of the carburettor. That much that it was condencening on the handle and dripping onto the bench. I can only guess that the spline driver that I first set it up with was to big around on the outside and jammed on the housing when I was first setting it up making me think it was screwed all the way in. as it turned out the low speed jet was out about 4 turns. I have never come across that before and could not find any references to it being caused by poorly adjusted jets.
The low speed jet is out about 1 turn now. I never reset the high speed but it is probably about the same, it was running so I went from there and with the saw revving at about 3 quarters I turned it in about 3/4 turn until the saw slowed then back the other way until it slowed than set it in the middle which would be about half a turn from where it was on arrival so assuming it was set the same as the low originally it is out about 1 turn
What do you mean you have enough chain saws, I would not have thought that was possible. I have 5, this one, the wife bought me one on special from Aldi for $60, an electric Ryobi, a very old Homelite that AVB and others in this forum helped me get going, and if I actually want to cut anything a Husqvarna 460. The Husky is that powerful that it scares me but you will slice through 16" hardwood without breaking a sweat, next would be the old Homelite which would have originally came out with a 20" bar it has power to spare with the 16" bar on it and isn't bothered by 12" logs, but it is noisy, vibrates and the bar is in poor condition. The Ryobi is a little more powerful than the Aldi and a little more robust. Neither has the power to cut much more than 8". I have found in the past that the saws which have a plastic housing (Aldi) to hold the bar on tend to jam and push the chain off when you get into very light stuff like a hedge. The electric one is for the more patient arborist, but the safer option if you are up a tree and the battery goes flat on the reciprocating saw.
Again thank you both for your help


If I can get a large enough hammer it will run for awhile just trying to get away from me
Tyler #113999 04/02/22 08:34 PM
Joined: Jul 2018
Posts: 2,085
Likes: 80
Tyler Offline OP
SENIOR TECHNICIAN
Hi Byomarimba

My mistake, I was in a rush when I sent the reply and always get confused when I rush responses.

I have found the spitting back through the carby is caused by the speed screws being grossly out and the metering lever is set too high.

I would try richening up the low speed jet slightly to improve starting. Mine was sensitive until I got it in just the right position.

My favourite chainsaw isn't actually a tranditional chainsaw at all - its a ryobi expand it pole pruner attachment. Got it from bunnings on a stock clearance model for $40 from memory (store closing). With a few extension poles, I can get most things cut with it.

Though I suggest wearing a hard hat - I managed to spear myself in the head with a wayward branch

The little 12 or 10in 25cc arborist saws are good too

Tyler #118914 02/11/23 05:20 PM
Joined: Jul 2017
Posts: 80
Trainee
Thanks for your help with this one.
Wonder if I could get my status changed from trainee to idiot.
Turned out the saw was a little ripper and I used it quite a bit, for small jobs where you were likely to be cutting sand. Or if somebody wanted to borrow it. Unfortunately, I initially re-attached the governor incorrectly (put the washer in last instead of first) and it damaged the housing. Didn't seem to be a problem, then the brake started seizing, again not a problem I just cut the brake band. But somewhere along the line it damaged the chain oiler. As I mentioned I was pretty happy with the saw and got a new oiler for it. Turns out you need to remove the saw from the housing to replace the oiler, I thought it would be a half hour job. Should have remembered what Tyler said earlier about those screws holding the motor in, they also hold the motor together. Finished up splitting the motor in two.
Installed the oiler and reassembled which was very difficult getting the piston in from the bottom, but would not start, wouldn't even fire. I wish I had done a compression test at this time.
I assumed that the problem was the sump gasket seal. Bought some expensive permatex gasket cement and reassembled. Had a dry run first as there was not enough room to put the gasket cement on and it went together quite well but I did not learn what I did. Put the gasket cement on and could not get the piston back in, finished up breaking the piston ring. Ryobi no longer stock a piston ring for it, so I measured the size of the pieces and determined that was the size I needed. Got 10 from China for $11.00. As you probably know they are too big. Filed one down and using the piston pressed it into the cylinder to make sure it was square and just the right size for the cylinder. Reassembled same result and compression was disappointing. As your aware there are some steps at the end of the piston ring, so I filed the next one down at 45 degrees, about this time I became aware of a pin in the piston ring groove, seems like a good starting place. Reassembled virtually no compression. Lucky I got 10 of these. Very carefully ground one side of the next one down using my imitation Dremel and replicating the other side as close as possible.
I think I may have found the secret to getting the piston back in. Have the piston ring gap on the pin in the piston ring grove and have the gap facing the exhaust port and turn it. I have enough compression to register something on my tester but below where calibrations start (50psi) plenty of spark but no fire. I am turning it over with a drill. Not even firing if you pour fuel in the spark plug hole.
One last roll of the dice, before I go to any more great lengths to get the correct piston ring, I will need to take it apart again and carefully measure the piston is there anything else that could be robbing me of compression or preventing it from firing?
Common sense would be to drop it in the bin but I don't like quitting


If I can get a large enough hammer it will run for awhile just trying to get away from me
Tyler #118921 06/11/23 01:23 AM
Joined: Jul 2018
Posts: 2,085
Likes: 80
Tyler Offline OP
SENIOR TECHNICIAN
I agree it sounds like its bin time but also empathise that at this point its more of a case of finding out why it isn't working more than anything else.

My guess (provided you have tried another plug) would be that cylinder base gasket not being perfect and its just not scavenging fuel right. But it must be pretty bad to not even kick

Mine is still going well. It sat for a full year until june. Fired up 3rd pull despite stuff all compression and did dirty work cutting crap Strellitzia palm down to underground.

Ended up dialling in the carby properly cutting biscuits of 12in bottlebrush branches.

As would be guessed by its internal condition, at optimum setting it was still faster than a very healthy 25cc Zenoah g2500 clone (ozito/gmc/909 arborist saw) but not by a massive amount given its got 60% more cc and has a 325 chain

Last edited by Tyler; 06/11/23 01:32 AM.
Tyler #118935 07/11/23 09:23 PM
Joined: Jul 2017
Posts: 80
Trainee
Thanks Tyler,
I have not actually thrown it out but put it in a box while I think about it. I have a new project just picked up a Victor 2 Stoke reel mower, with a Victor 125 power unit. Never even knew such a thing existed. It will be more rewarding if I can get it going and it comes from a time when they built things to work rather than engineering them to be cheaper. I will let you know if I get back to the chainsaw.


If I can get a large enough hammer it will run for awhile just trying to get away from me
Tyler #118936 07/11/23 09:24 PM
Joined: Jul 2017
Posts: 80
Trainee
Earlier message should have been Victa not Victor


If I can get a large enough hammer it will run for awhile just trying to get away from me

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