Stihl 024 air leak

[ihatesaws]

The gauge is shown here:

https://www.arboristsite.com/threads/proper-metering-height-walbro-wte-carb.346658/

 

If I put a straight edge on the flat part of the carb where the metering gasket contacts and stick in a 0.7mm feeler gauge such that one side touches the straight edge and the other the metering lever will that be okay?  At the moment the lever looks a bit low.

[spudulike]

With these carbs, if the diaphragm has a small nipple, the metering arm lines up with the carb body and if the diaphragm has the more pronounced nipple, it lines up with the cut out in the bottom of the diaphragm bowl. 

If you have done a few, you will know what I mean.

With any saw that is playing up on idle or high revs, a full pressure and vac check is invaluable in proving the engine is airtight. Have you managed to do this yet? After 8 pages, I don't really want to check...sorry!

[Muddy42]

I agree that a full pressure and vac check would be worth it if you are still struggling. Block of the exhaust and behind the carb and send pressure/vacuum through a modified spark plug.  Dunk the saw in water to reveal the most stubborn leaks. You don't even need to take the clutch and flywheel off which can be tricky.

[ihatesaws]

15 hours ago, spudulike said:

With these carbs, if the diaphragm has a small nipple, the metering arm lines up with the carb body and if the diaphragm has the more pronounced nipple, it lines up with the cut out in the bottom of the diaphragm bowl. 

If you have done a few, you will know what I mean.

With any saw that is playing up on idle or high revs, a full pressure and vac check is invaluable in proving the engine is airtight. Have you managed to do this yet? After 8 pages, I don't really want to check...sorry!

I wrote a summary in the last page so you don't have to read eight pages.  The nipple is 2mm in length while a WT diaphragm nipple is 3mm.  Is the carb body B in the picture? Does this mean the lever should line up with B?  The correct tool would seem to put the lever 0.7mm below B.

 

[spudulike]

A ...

 

and the nipple should be the longer one.

 

Edited May 15, 2023 by spudulike

[ihatesaws]

I put the modified tank housing on the 024S and didn't have much luck with the wte1.  When you said the nipple should be the long one do you mean the 3mm WT one?  I put a carb kit on the wt194 and this is the closest I can get to a working saw. The L screw seems very sensitive.  I have to nudge it a tiny bit richer from time to time to keep the  rpm down.  On tuning the L screw when I turn it in from 1 1/4 turns out to find the max revs it starts to take off at around  1 turn out without any sign of a drop in rpm, 4000,5000 etc and then I lose my nerve and back the screw out again.  Should I be braver?

 

I do notice that when I take the fuel hose off the carb on the ms290 fuel spurts out of the hose everywhere.  The tanks on the 024's don't seem to build any pressure.  Is that of any relevance?

Edited June 6, 2023 by ihatesaws

[spudulike]

The MS260 one is 3mm compared to the MS200t being 1.5mm - this is the measurement from both sides of the diaphragm.

The difference in set up is that the 3mm MS260 metering arm is set level with the diaphragm bowl bottom whereas the 1.5mm MS200 is set to be level with the carb body - the part the diaphragm sits on. 

Your description of an L screw tune is completely wrong. With your saw set with the L screw at 1 1/4 turns and idle around 2500rpm, if you turn the screw in, you should get the saw rising possibly 250-500rpm just before the saw dies. If your saw is revving as you say, either the idle screw is far to far in or the saw has a big air leak.

One of my own test with saws is that if you can wind the L screw all the way in and the saw still runs, the saw has an air leak or the idle screw is wildly to far open. 

I would suggest having the carb off and looking at the throttle valve then adjusting the idle screw so the valve is ever so slightly open - easy to see looking at it against a bright light. Set the H & L screws to 1 1/4 turns, refit and initially adjust the idle so the saw idles OK and then do the adjustment.

The tank and fuel spurting....., the fuel in the tank gets pressurised when the fuel gets warm, if the tank is fitted with a ONE WAY breather that only lets air in, the fuel will spurt on disconnecting the fuel line. Some tanks have TWO WAY breathers such as the fibre pills and coarse screw in tube types and these will be less likely to spurt when the fuel line is disconnected. It is however, worth checking your fuel line for blockage and checking the fuel filter is not blocked. I have seen the part alloy ones have metal oxide blocking and issues in manufacturing or just old age.

Goodluck

[ihatesaws]

13 minutes ago, spudulike said:

The MS260 one is 3mm compared to the MS200t being 1.5mm - this is the measurement from both sides of the diaphragm.

The difference in set up is that the 3mm MS260 metering arm is set level with the diaphragm bowl bottom whereas the 1.5mm MS200 is set to be level with the carb body - the part the diaphragm sits on. 

 

Thanks.  I'll have to digest all of that and think about it.  On the nipple I'm just measuring the length of the nipple with calliper jaws touching both ends.  The WT bowl is deeper with a corresponding longer protrusion on the WT gauge compared to the WTE bowl and gauge so I thought that would explain why the WT nipple is 3mm and the WTE one that I got is only 2mm.  It has a shorter distance to go down into the bowl to reach the lever.  The 2mm diaphragm must be the right one as it was well used and stuck to the gasket which was stuck to the carb body so it must have worked.

[ihatesaws]

On the carb tuning my idle was high as I started with a high idle to be sure it would start.  I found the stihl tuning guide which says to adjust idle screw to 3300 and then adjust L to find the maximum revs.  If you go over 3700 adjust idle back to 3300 and continue search.  Then at the end reduce idle to 3300 and richen L to the recommendation, in this case 2500.  I read in forums that 024 and 026 have trouble with fuel puddling and it's better not to set the idle too rich and they all fluctuate quite a bit so it's better to keep a higher idle to compensate for that.  So I just set it to around 3000 at the end and that worked pretty well, at least initially.

 

I put a new metering diaphragm and gasket from a k10-wat kit into the WTE1.  This has a 3mm nipple and the carb worked better than before.  I removed the limiter cap on the H screw to get the revs down low enough.  I ran maybe a tank or a tank and a half through the super with the wte1 over the past few weeks.  My overall impression was that when cold the idle was 2500-3000 and pretty stable.  WOT was around 11000rpm.  When the saw got hot WOT was going over 13000rpm and when the saw went back to idle it tended to idle more at around 3500 but pretty stable still.  A clear sign of an air leak I thought so I pressure tested the saw again while hot but couldn't detect anything.  Took off clutch and oil pump and sprayed fuel on clutch seal but no change in rpm.  I had the flywheel off earlier in the year and that seal looked good as well.  I tried releasing gas from a map torch around the saw but couldn't change rpm except at air filter.  I let saw cool down but it wouldn't behave itself while cold then either.  Tried it another day then and it was alright for a while again.  Today after heating up a bit the wot rpm was over 13000 but when it came back to idle the idle began to sink till it died so that doesn't indicate an air leak.  Anyway I'm going to park the super for a while.

 

I've ordered the meteor piston for the 024.  I cleaned up the original cylinder.  I don't think there was any aluminium transfer as there were no white patches and when i put in sodium hydroxide there was no fizzing.  I then sanded it a bit with my finger and there is a bit of blackness here and there but I can't feel anything.  I just took off the cylinder and I see that the paint is half gone inside the crankcase.  That will continue to flake off.  The oil tank was a real mess with paint when I split it the first time. Should I split it again and remove all the paint?  Also when I put in a new crankcase gasket I didn't use any sealant as I had enough bits to juggle putting the case back together again but should I use some?

[spudulike]

The oil tank state won't change anything and a tank full of nuts and white spirit will loosen up any loose paint rather than stripping it down. 

On the crankcases, they shouldn't need sealant and if the pressure and vacuum tests are good, the issue is elsewhere.

Sometimes old saws can drive you mad like this. Generally, swapping out the carb resolves the issues like I probably stated earlier. 

These saws do wear their piston skirts so worth fitting a new piston if you haven't already. If that doesn't do it then their isn't much left to suggest.