Jonsered 2051 carb replacement advice

[Johnny356]

Hi folks, I love forums. Having messed about with cars and bikes for over 20 years I don't know what I would have done without my -usually US-based- brothers on forums. Now I am getting older, thoughts of horsepower and handling are changing to thoughts of trailers (I got my first recently ) and chainsaws, and the like.

I had 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.

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, 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 marking 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 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.

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, inlet and outlet) 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.

 

[Bob Hedgecutter]

My first jump to answer would be massive air leak before "needs a new carb".
A wash, rinse, spin cycle in an ultra sonic cleaner and new carb kit will do wonders for the original carb no doubt, but your saw really needs a true to cylinder size compression test with a proper small engine tester and a full leak down pressure and vacuum test to check for air leaks.

The flooding you are seeing could be caused by continual attempts to start feeding enough unburnt fuel into the combustion chamber to near hydro lock the saw and have unburned fuel splutter out the muffler.
The fact it fires on WOT and screams at high revs then dies- screams massive air leak to me.

The 2051 is one of those odd saws like the 340, 345, 350 Husqvarna but most like the 350 in that the flat based cylinder sits on an alloy riser block that clamshell mounts the crank in the plastic cup that forms the base of the crankcase- so it is kind of pro like in the cylinder mount and consumer saw like in the crank holding.
These are areas that can form massive air leaks, the crank seals, gaskets between plastic to riser block, warped riser block, failed joint between riser block and cylinder and loose bolts that hold the entire assembly together.

The 2051 was the very first saw to be a TURBO (Jonsered speak for Air Injection) and was in its day a real wee hotrod of a 50cc saw, bit like the Husqvarna 346XP people love to rave about, or the Husqvarna 353. It is a good saw and worth fixing- but will not last long if you keep trying to start it, get it to run and melt the piston to the cylinder wall because it is massively lean via an air leak.

You probably want to find a new small engine "specialist" as well.