Carb advice please... I think!

[Seanturpin]

Hi guys, I hope this is the right place to ask...

 

I got an old stihl 020av as a project to get it running. So far I've got it to run, but it was pretty much full throttle! Idle screw was set right out, and L/H screws all the way in bar half a turn. The throttle was unresponsive and the choke was the only thing that slowed it down.

 

I took the carb off and cleaned it all out, the seals and diaphragms look fine. So I put it back together hoping for joy but now the fuel isn't going through at all. It's getting into the carb, but not out the other side.

 

Would anyone be able to point me in the right direction as to what to look at next to get it going?

 

Any help would be really appreciated!!

 

Sean

[hawthornheavyhorses]

Spud or GardenKit will be able to advise

 

However from my newly aquired knowledge of carbs it doesn't take very much at all for them not run. Also it is very easy to put the gasket and membranes back on the wrong way round, thankfully I noticed before I put it back in. .

 

For the sake of a tenner I would take the carb back out and out a full new (genuine) rebuild kit it. Also make sure you have the correct kit !!! (see my MS260 thread)

 

Also have you taken off the Exhaust and checked the piston for scoring?

[Seanturpin]

Yeah the exhaust is off and it all looks to be in great shape. I'll have a look at your thread now.

 

As said, any advice is much appreciated!

[spudulike]

Firstly the racing idle will be down to the L screw being in too far, take it out one turn from fully in and do the same with the H screw, I have tuned one of these saws recently and adjusting the L screw effects the H setting so you need to find the correct balance.

 

The saw will need to have the idle reset with the H&L screws set like this and once this is done the saw should have some sort of pick up if revved with the right setting coming from ensuring an even idle, followed by a clean midrange then the H screw adjusted for decent high revs and possibly a re-tweak of the L screw.

 

These saws are not the easiest to adjust! If one turn on both screws or thereabouts doesn't sort it, there are a number of things that could be wrong - crap in the gauze filter in the pumping section is one of them and worth checking out.

 

I found the needle valve on mine was leaking due to the plating on it breaking down - details on the "Whats on my bench" thread.

[pgkevet]

The only 2-stroke carbs i play with are on my petrol helicopter models..and repeat experience has shown that carb cleaners are as likely to soften oily sludge and move it as they are to clean it right out.

We usually keep a spare new carb handy: if swapping for the new carb solves the problem then, yes, rebuild or (better) chuck the old one: those walbro carbs are about £36 and a rebuild kit costs £12.50 and doesn't always solve the issue. If the new carb makes no difference then carry on hunting for the real cause..commonly an air leak under it's manifold or header or in the crank case...

I muts admit i was suprised at the price quoted for new 200 carbs for this saw.

 

..just saw the crap in the gauze filter comment. The screen in my carbs is a known blockage too.. we pick out that tiny round gauze disc, cook it glowing with a lighter and pop it back..works better than just trying to blow through to burn any filtered clunk rubbish off

Edited January 10, 2012 by pgkevet

[spudulike]

The fast running can be an air leak but the carb set to 1/2 turn isn't right and will cause the idle to run fast, it may also be the throttle sticking open slightly due to a sticky mechanism or butterfly valve.

 

A can of carb cleaner costs £1.50 and does a good job of cleaning carbs, I do use an ultrasonic cleaner on persistant offenders and the only carb that has given me terminal problems had a worn L screw seat and I had to admit defeat on that one!

 

Worn pumping gaskets and diaphragms can cause issues - one thing worth checking is the state of the fuel filter and fuel pipe - both can cause these types of problem!

 

Good luck

[GardenKit]

walbro carbs are about £36 and a rebuild kit costs £12.50 and doesn't always solve the issue. I muts admit i was suprised at the price quoted for new 200 carbs for this saw.

 

 

maybe a little numeric dyslexia with the price. The S16a carb is quite common on an 020T (whats an 020av?) and retails at about £63, as opposed to one in a Stihl box at £91. (Prices inc vat)

Of course the carb on this saw maybe a different one.

In any case, as Spud says, this carb should overhaul OK unlike the one on the newer MS200T which can be a bit tempramental.

[GardenKit]

whats an 020av?

 

should read 'whats on an 020av?' i.e carb make and model.

[spudulike]

Just to clarify, I think we are talking about the 020AV - the predecessor to the 020T and followed by the MS200T.

 

My parts list state a WT15A Walbro on this saw!

 

I generally try to fix carbs - new ones can be pricey and may not be needed!

[Seanturpin]

Wow I'm amazed at the responses especially since I'm new to the forum, I've not had this many quality replies on any other forum, if any when I've been new.

 

I got it running last night. Had the carb off, a friend of mine stared at it until he understood the path of the fuel and he then explained where it went, how it pumps etc. We put tiny drops of fuel in the H/L screw holes until the carb was full and it came out the other end, that meant it wasnt blocked... Well the theory did anyway!

 

I then put it all back together knowing that the carb was full and stood a better chance of getting fuel through, but other than that we hadn't really done or changed anything.

 

It fired up 2nd or 3rd pull. Revved it's nuts off!

 

The thin bar from the trigger to the carb was bent passed 90 and wouldn't let it sit at idle, so we bent that back to shape, then adjusted the idle screw once running and then the H/L screws accordingly.

 

Fuel pipes are all in great shape as is the filter.

 

I'd love to know why fuel wasn't going through as right now it feels like I got lucky rather than actually sussed the problem!

 

Thank you all for your advice