Vintage Jonsered 2051 non start/carb replacement question

[Lee roy]

On 09/11/2022 at 20:03, spudulike said:

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.

 

On 05/11/2022 at 17:29, 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.

Hi Johnny from how you have described your issue you need to vac test the casing then take it from there also would advise 40:1 mix for the older Jonsereds if you can with E5 / vpower I hate E10 makes known good stong machines run like crap, 50:1 only came about because of epa regs in US, many recommend the same ratio for 50+cc Stihls 🤷‍♂️. 

You won't get the saw to kick on carb cleaner but will with a mist of gt in the intake if it's going to.

For it to rev away it doesn't sound to be carb but crank seals passing if the saw has stood for any length they will have been dry unless greased when built.

👨‍🔧🧑‍🏭