Vintage Jonsered 2051 non start/carb replacement question

[Johnny356]

Hi, I have signed into a couple of forums to try and figure this out. Thanks for having me here.

 

So, I have struggled with a reluctant, bad, cheap chainsaw for a few years and so decided to invest in a reluctant, cheap, good chainsaw. So I bought the Jonsered off ebay for £100... we have a family connection to Sweden, so it felt correct, and I hoped it would be a nice, well made old thing that I could keep running as a weekend firewood tool and occasional help clearing our local roads that get blocked every winter it seems.

Advertised as running and 'lively', it arrived with a worn bar and chain of course, but nice enough and had decent compression (on the starter cord at least), as well as having the heated handles option. It started and was indeed lively - for around 25 minutes. It then stopped suddenly and would not restart for love nor money.

I have: Checked air filter and fuel filters - both clean already. Replaced fuel with fresh UK 95RON fuel, and semi synthetic 2 stroke oil that is about 2 months old at 50:1. Replaced plug. Checked for spark against the case- present, and absent when cut off switch is on. I have removed the muffler and it is not blocked. The piston has light markings but doesn't look too bad. And I have stripped the carb and sprayed it through with carb cleaner and compressed air, and rebuilt with a rebuild kit.

It will still not start. It appears to be flooding when I am trying to start it. I don't have easy-start spray but it won't start on carb cleaner. I had a brief start happen a couple of times with full throttle applied, it just revved like crazy and then died.

I spoke to a local small engine specialist who immediately said - 'carb - but you might struggle to find one'. He also offered to clean the carb in his ultrasonic cleaner but said it may not help, so I am undecided whether to do that next.

There are a couple of rebuilt 2051 carbs for sale on US eBay but they are an unknown quantity and not cheap, so will be almost the price I paid for the saw after shipping and taxes. There are no immediately obvious applicable chinese carbs for this saw.

So, my questions are - can anyone suggest anything else I can do to troubleshoot this saw?

If not, if I find a chinese carb for a 50cc saw that has the same dimensions (mounting bolts spacing, inlet and outlet diameter) is it worth trying this? I would need to modify throttle linkage I guess.

The carb is Walbro and has 21-263 3-4 and HDA 68a on the casing.

Thanks for any help,
Johnny.

[Stubby]

13 minutes ago, Johnny356 said:

Hi, I have signed into a couple of forums to try and figure this out. Thanks for having me here.

 

So, I have struggled with a reluctant, bad, cheap chainsaw for a few years and so decided to invest in a reluctant, cheap, good chainsaw. So I bought the Jonsered off ebay for £100... we have a family connection to Sweden, so it felt correct, and I hoped it would be a nice, well made old thing that I could keep running as a weekend firewood tool and occasional help clearing our local roads that get blocked every winter it seems.

Advertised as running and 'lively', it arrived with a worn bar and chain of course, but nice enough and had decent compression (on the starter cord at least), as well as having the heated handles option. It started and was indeed lively - for around 25 minutes. It then stopped suddenly and would not restart for love nor money.

I have: Checked air filter and fuel filters - both clean already. Replaced fuel with fresh UK 95RON fuel, and semi synthetic 2 stroke oil that is about 2 months old at 50:1. Replaced plug. Checked for spark against the case- present, and absent when cut off switch is on. I have removed the muffler and it is not blocked. The piston has light markings but doesn't look too bad. And I have stripped the carb and sprayed it through with carb cleaner and compressed air, and rebuilt with a rebuild kit.

It will still not start. It appears to be flooding when I am trying to start it. I don't have easy-start spray but it won't start on carb cleaner. I had a brief start happen a couple of times with full throttle applied, it just revved like crazy and then died.

I spoke to a local small engine specialist who immediately said - 'carb - but you might struggle to find one'. He also offered to clean the carb in his ultrasonic cleaner but said it may not help, so I am undecided whether to do that next.

There are a couple of rebuilt 2051 carbs for sale on US eBay but they are an unknown quantity and not cheap, so will be almost the price I paid for the saw after shipping and taxes. There are no immediately obvious applicable chinese carbs for this saw.

So, my questions are - can anyone suggest anything else I can do to troubleshoot this saw?

If not, if I find a chinese carb for a 50cc saw that has the same dimensions (mounting bolts spacing, inlet and outlet diameter) is it worth trying this? I would need to modify throttle linkage I guess.

The carb is Walbro and has 21-263 3-4 and HDA 68a on the casing.

Thanks for any help,
Johnny.

If its flooding as you say maybe when you rebuilt the carb you did not set the metering arm  height correctly and its letting in too much fuel ?

[Johnny356]

Hi, thanks - I set the lever to line up with the top of the carb block like the guy on youtube showed me! I had a reply on another forum suggesting an air leak and so I am going to look into that.

[adw]

I think before you do too much more you need to find out if it is mechanically sound, it Is somewhat worrying it ran fine for 25 minutes and then will not now re start, it is not going to suddenly have a carb issue after running fine for 25 minutes, my best advise is to lift the cylinder and assess the condition of the piston and ring, I fear the problem lies here.

[spudulike]

As ADW says, don't get too hung up on just item but do diagnose the issue you have.

If the saw is flooding, it may be through excessive trying to start with the choke but as Stubby says, it may be that the needle valve is leaking. A tech would check the needle valve with a pop off gauge or Mityvac gauge. You wont have those but if you stick a piece of fuel line on the carb fuel connection and suck it then stick your tongue on it, it should hold vacuum and stick to your tongue.

As ADW says, you may have had the piston seize or nip up and may have lost compression. A tech would use a compression tester and look for 150psi+ but without that, the experienced would "feel" the compression by pulling over the engine slowly and feeling the engine at TDC...it should give good resistance on the handle.

The other failure may be the coil, you can test for this by taking the plug out, putting it in the HT cap, earthing it on the cylinder and pulling over the saw hard BUT, keep the spark AWAY from the plug hole as the vapour coming out of the hole can ignite...you do this once in your life before becoming aware that it is a very silly and dangerous thing to do, that and it takes all the hairs off your hands, arms, face and head if anywhere near the flame!

It is unlikely the carb would immediately fail...the liveliness may have been from the saw running lean and it may have seized but a pic of the piston thorough the exhaust port would give an indication. Pulling the top end off would give another more detailed view.

There are many people out there that "Swap parts", other people diagnose issues quickly and accurately spending customers £££ only on the parts that are actually needed! 

[Mrblue5000]

Johnny does it have a blue decompression button? Does that make any difference?

[adw]

yes they did?

[Johnny356]

Hi, thanks for the replies, I will investigate these things.

There is some light marking on the piston but I don't know if that is acceptable - I know it isn't in auto engines and so maybe that is pointing to the problem.

It doesn't feel like the saw seized - it would not pull on the starter cord if that was the case?  

I have already checked spark and that is good.

There is no decompression button on the saw.

I posted on another forum and concerns were raised about an air leak.

 

So, I have a project on my hands..perhaps not the best purchase I have made..!

[Trailoftears]

I feel your pain,its no fun diagnosing these mysterious issues unless you are a tech wizz,worse still when you dont know a machines past history/lifestyle.Given the money it cost,I'm sure it grates throwing parts/money at it.I usually go cheap+methodical on something like this.New plug,new fuel lines, new fuel filter,check coil for gap rusty surface,air filter spotless etc.Whilst not all of these suggestions are pertinent,you are at least excluding obvious stuff.You've dealt with the exhaust,carb refurb kit,if you have another fuel cap that fits,its worth a punt.If poss can you start it with the fuel cap off?

On another note, I'd be inclined to have a word in the sellers shell-like!

Good luck with it.

[spudulike]

When we say the engine has "Seized", technically...we mean that the engine has got that hot that the piston skirt has melted causing the engine to momentarily lock up and then as it cools, the engine is able to turn over but the issue is that the piston ring is now locked in its groove rather than being free to move and able to seal the cylinder bore so most of the compression is lost even though the engine can turn over.

Get some pics up of the piston so we can see whats what.

An air leak is unlikely to stop an engine starting unless it is bad enough to stop the lower crankcase making enough vacuum to pull in fuel vapour from the carb.

Edited November 9, 2022 by spudulike