Stihl 024 Won't idle and bogs!

[gillettadam]

Hi all, new here so be gentle! I don't do a massive amount of cutting but do mess about with getting older machines running, mostly for the fun of 'the project!' A friend of mine has a nice clean 024 which has sat for many years full of stale fuel. The fuel tank was a fairly bad mess as the fuel pipe has mostly dissolved and the filter wasn't much better. The saw has had the tank cleaned out and a new fuel filter and fuel hose fitted. The carb has been dismantled and cleaned and has had new diaphragms and gaskets. We've played with the mixture settings but keep going back to the factory settings as whatever we do seems to make it worse not better! The saw struggles to idle and when you open the throttle you have to blip it several times to get over the bog but once it's revving nicely its an absolutely brilliant saw with plenty of power. The saw is being run on fairly fresh aspen fuel which other machines seem quite happy with, but we did put brand new fresh pump fuel with red stihl hp oil in it which made no difference. Having done this work on it and it still having problems we have another friend who works for a local mower shop who has given a second opinion on the carburettor and has come to the same conclusions as us. He also did the carb rebuild with us. As a last resort yesterday we tore down the saw to check the impulse line and the intake boot but both looked in good order. The saw has good compression and starts well from cold with the choke. There is no muffler screen, and the cylinder and piston aren't scored. further there is no play in the crank bearings.

Summary
Stale fuel rotted fuel line and filter
Filter & fuel line replaced, Carb cleaned and rebuilt.
Saw starts, but will not idle and struggles to accelerate without blipping the throttle repeatedly to get rpm up.
Saw has been tried on both Aspen and brand new fresh petrol with red stihl hp oil neither makes a difference.
Carb mixture reset several times with no improvement and a second opinion on mixture taken from a local lawnmower guru, but he couldn't tune it in either.
Impulse line and intake boot checked and both look fine.
Saw has good compression with no play in crank bearings and no scoring to piston and cylinder.

The only things I can think of it being now is either the carburettor is damaged somehow, possibly a worn throttle shaft or damaged check valve. The crank seals leaking... hopefully not. Or possibly the coil doing something weird for some reason. But I'm asking here in case someone has a brilliant idea or has had a similar problem before, because it's got 3 of us fairly stumped! Pun intended!!

Cheers!

 

[Vintage Engine Repairs]

Hi,

Pressure and Vac test the saw, lines and nozzle check valve.
Clean the carb screen and confirm fluid flows through both the 3 idle drilling’s and the high speed circuit. Did you take out and clean under the welch plug?

Warm regards, Tom

 

[gillettadam]

Hi Tom,

Many thanks for your reply. I think a pressure test is a good idea. I will have to have a look how to do that as it's not something I've done before.

The carb screen was nice and clean when we rebuilt the carb. How do I confirm that fuel is flowing through the idle drillings and the high speed circuit? Should I just remove the adjusters and give a quick blast with some carb spray and see where it comes out from? The Carb was cleaned in an ultra sonic. The welch plug was not removed.

I do have a good running 029 which I think shares the same coil so I might swap the coils around just to rule that possibility out, unless you think that's silly?

Cheers for the advice,

Adam

 

[Vintage Engine Repairs]

Hi Tom,

Many thanks for your reply. I think a pressure test is a good idea. I will have to have a look how to do that as it's not something I've done before.

The carb screen was nice and clean when we rebuilt the carb. How do I confirm that fuel is flowing through the idle drillings and the high speed circuit? Should I just remove the adjusters and give a quick blast with some carb spray and see where it comes out from? The Carb was cleaned in an ultra sonic. The welch plug was not removed.

I do have a good running 029 which I think shares the same coil so I might swap the coils around just to rule that possibility out, unless you think that's silly?

Cheers for the advice,

Adam

Hi Adam,

Yes yes and, hmm you can but I wouldn’t just yet

I don’t believe the coil is your issue - I wouldn’t waste your time with that yet.

Pressure and Vac test is very simple. Pressure from a very low source, like a bike pump with gauge will even work. Vac not so simple but you may find the fault with pressure alone. Do a quick search for the process. You can even use that for your nozzel check valve. If you plan on rebuilding more saws just invest in the correct tool. Mityvac is a good option, but cheaper models are just as capable.

Yes, you can spray some carb cleaner through the screw drilling’s while blocking the drilling’s within the carb floor with your thumb or fingers. Hold the butterfly open and look down the venturi. Wear safety glasses and make sure every single drilling is spraying fluid - a quick glimps is not sufficient. If in doubt replace the welch plugs, I do it on every carb rebuild regardless.

You can substitute carb spray with wd40 if you are concerned about the nozzel check valve.

warm regards

 

[drf255]

Sounds like a leaky seal, and it’s usually the one under the flywheel. If you lack the tools to check it, just try a new seal on that side and see if problem goes away.

Run saw one time without the airfilter just to see if it runs normally.

Your L screw should be out around 1 turn, if it’s more it’s even more suspect for a leak. Also, make sure boot is in proper postion on the jug. if it’s rorated there will be a lip and puddling will occur.

 

[Wood Doctor]

This brings back lots of memories for me. I rebuilt an 024 AV about eight years ago that had been run over by a pickup truck. Believe it or not, it still runs today. For some reason, the case was still intact and the drive shaft and seals were still intact. About everything else had to be replaced. The owner had nostalgia for it. At least 20 hours of work was required.

 

[mojo jojo]

Spark plug knows the answer

 

[gillettadam]

Hi all, a quick update.

We have had another look this weekend. The saw passed both pressure and vac testing. We do have the saw relatively dismantled so we could get the impulse line and intake boot off for inspecting last week. I have not yet dismantled the carburettor to see if there's a blockage but on inspection the throttle shaft has worn and there is about 0.25 to 0.5mm of play. At this point it doesn't seem worth doing much more with this carb so I think the plan is to buy a chinese clone carb and rebuild the saw with that. I will let you know the outcome!

 

[Wood Doctor]

If this fails, the problem almost has to be electrical. Ignition modules do not last forever. I replaced one in a vintage Husqvarna 50 last Thursday. Symptoms were similar to yours. Suddenly the saw said, "Hello!" I cut two truckloads of firewood with it two days later.

 

[MartDalb]

Yep, checking with a known working carb, would be my next step.

Off the top of me head I recall....

A Stihl ms250, never got it to run right, did all the tricks, swapped carb, ran perfect.

Husky40, spend hours and hours, finally bought a non OEM carb from Amazon.de and it ran perfectly.

Stihl 026, was a solid saw, but would not stop acting up, tested carb, found leak, could not fix it, ran perfect with replacement carb.

Several, Stihl, Husky and Honda trimmers and similar with bad carbs.

on a side note, I don't have a ultrasonic cleaner, just my carb/brake cleaner and carb kits.

Never had a coil go bad on me, unless you count my stupid Mtronic (under investigation atm) and an old Jonsered with a loose (I didn't check before testing it) coil, ran for 30seconds and something didn't sound right .

Keep updating

 

[gillettadam]

Hi all, sorry it's taken a while. The saw is now working well. The clone carb fitted on, it was fairly tight to install as a few of the dimensions were not exactly correct. Not a problem once it's installed but made fitting even more difficult than it was with the original carb, and that wasn't easy. I do wonder if there is a problem with the Walbro carbs wearing out? I had a Stihl Br380 I repaired which had different symptoms (it would run perfect for 30 minutes then would lose power) but again had a worn out throttle shaft on a Walbro carb. I will definitely be checking for wobbly throttle shafts in future when I get a problematic engine! Thanks for the encouragement and advice.

P.S. Very impressed with the 024, seems a really nice little saw. Seems to have much more power than I expected from its size, a bit of a different animal compared to the 029!

 

[rupedoggy]

Throttle bippers wear out shafts.