No fire! Great spark, good fuel flow

[MI Old Saw]

I am looking for some tips on what to try next on an XL12 engine that won’t fire.

I have this gem of an XLS pump. It looks hardly used and it has great compression. I could tell by some of that varnish color around the choke plate that the carburetor needed cleaning first, so I rebuilt that with new gaskets and diaphragm. It immediately drew fuel through the clear fuel line. It’s a bit of an oversized and lengthy fuel line on this thing, so I know it’s pulling hard because it filled the hose after 5 or 6 pulls (wick filter).

I have perfect spark. It’s bright and blue and the kind you can even hear.

I have not had this thing pop… Not once. I bottle-fed through the carburetor at one point and still nothing. Carb has been off three times now and looks ideal, and filled with fuel. I even broke down and gave it a shot of starting fluid. Nothing at all.

I was thinking perhaps timing? But, I would’ve assumed with all of this pulling and pulling and direct feeding, I would have had a wet spark plug by now and I do not. On other saws I have had, they seem to flood pretty easily, and this one should’ve flooded 10 times over. I don’t see anything wrong with the reed.

🤦‍♂️

[MI Old Saw]

[stillsawing]

Try a new spark plug, I have had plugs that would not spark proper under compression. The spark gets leaked off before it can reach the electrode. Is your pump been updated with a conventional style spark plug? Mine still has the T type.

[MI Old Saw]

I am all for the ez things first! I will try a plug and happily admit if that changes things.

I am not sure what you're referencing in the plug differences?

[1001projex]

Spark plug dry? Once you verify spark jumps the gap, I would pull the plug and shoot some fuel (not much) directly into the cylinder. Pop your plug back in and see if she goes. If she does then I hate to tell ya but it sounds like fuel making it to the carburetor but not out of it.

[xl130]

Can you put gas in the spark plug hole and get it to fire?

[MI Old Saw]

So today I really dug in. I tried a couple other plugs known to fire well. I Rebuilt the carb again. I found the diaphram and valve lever were “off” from some of my others. The result was the tab on the diaphram was not catching and remaining in place on the lever. That fixed the fueling issue, and now it will flood.

However, I still have no fire. Even with fuel into the plug hole, not so much as a pop. I have spark that will jump 1/2”.

I pulled the pump assembly and removed the exhaust to get a good look at the piston and cylinder. They look new and compression is great.

I am still at a loss. Even with incorrect timing I should still get it to pop.

[edju1958]

Leon had a saw that was doing the same thing a couple yrs.ago.the spark was jumping 1/4 in.,but no fire.He ended up putting a new condenser in it & it fired up & ran great.I'd suggest a different/new condenser,one you know is good.Condensers when weak are just like plugs & won't fire under compression.

[MI Old Saw]

Jan 30, 2022 12:03:24 GMT -5 edju1958 said:

Leon had a saw that was doing the same thing a couple yrs.ago.the spark was jumping 1/4 in.,but no fire.He ended up putting a new condenser in it & it fired up & ran great.I'd suggest a different/new condenser,one you know is good.Condensers when weak are just like plugs & won't fire under compression.

I’m certainly willing to give that a try. I don’t believe I have any condensers handy, not without tearing apart another saw, which I am getting a little tired of doing.  

I suppose I’ll order one and table My saw Projects for now. We’re finally forecast to have a day above freezing this Tuesday, but only for a very short time. I have some tractor pressure washing that needs to be done, after some prep. 

[edju1958]

Make sure the condenser is a known good one.Just because it's new doesn't mean anything,they can go bad just sitting on a shelf.These saws are 40+ yrs.old & most of the condensers are just as old.I generally don't say this,but it may be worth it to put an electronic chip in,at least for testing purposes.It's always good to have a chip on hand,they can be used in just about any model.And they're not expensive either,generally from $12-$15.

[xl130]

Sounds like a condenser as Ed suggested.

[MI Old Saw]

Today’s update:
Robbed a parts donor XL-12/Wico of its condenser, but decided to try a known good condenser instead. So, I pulled apart a good running XL-AO/Wico. The condenser looked different, but by the IPL should be the same.

I put the “bad” condenser into the XL-AO, and it runs normally.

Input the “good” XL-AO condenser into the XLS…no spark at all. So I fiddled with the points and reset the gap, checked all the connections. My spark is back, but it still wont fire.

I inspected everything well. The key and flywheel look great. I am still at a loss. Plug is wet after half a dozen pulls.

[xl130]

If you are getting spark and you have good compression and you still can’t get it to fire with a shot of gas down into the spark plug hole after holding the throttle wide open while pulling repeatedly with a good condenser then you got me stumped too!!!

I really would know what to try next. Sorry!

Edit: the only other thing I could think to check would be the Reed intake. If it was stuck open then maybe it would have a very hard time firing……?

[MI Old Saw]

Jan 31, 2022 19:57:10 GMT -5 xl130 said:

If you are getting spark and you have good compression and you still can’t get it to fire with a shot of gas down into the spark plug hole after holding the throttle wide open while pulling repeatedly with a good condenser then you got me stumped too!!!

I really would know what to try next. Sorry!

On a positive note, the SXL-67 pops off with 2 or 3 pulls, every time! 😜

[MI Old Saw]

I can tell you that the carb situation on these vane governed machines is a bit more tedious to work with. The carb comes out of an XL12 easy, but as soon as you enter that dang vane linkage and the itsy bitsy governor spring into the mix, things will go one of two ways...quick n ez, or cuss-filled and iritating as heck. I have had too many opportunities at practicing on this one! When I poked around at the reed, it looked to be in great shape, and moved as it should. I do not know what to try next. There is fuel, air and fire down there, so it should at least give me a little snort.

[edju1958]

You say it has great compression.Have you done a compression test to confirm it?I've had saws that I thought had great compression,but upon doing a compression test I found out quite the contrary.

[lesorubcheek]

Really a mystery here. Pretty much everything sounds like has been covered. About the only thing that I can think even remotely that hasn't been mentioned is maybe check to see if the muffler is plugged up, possibly from dirt daubers. Never had one plugged up myself, but have heard it can do strange things.

Dan

[rarefish383]

Don't use ether to test your saws. I heard they make a starting fluid for 2 strokes but never seen it. I've heard that starting fluid will wash all the oil off the cylinder. I bought a beautiful XL700 off ebay. Had short video of the saw running. Got it home all excited, no run. Contacted seller and asked how he got it started. Was running it on ehter. Pulled muffler and the rings were melted into the piston.

[MI Old Saw]

Feb 1, 2022 20:31:32 GMT -5 lesorubcheek said:

Really a mystery here. Pretty much everything sounds like has been covered. About the only thing that I can think even remotely that hasn't been mentioned is maybe check to see if the muffler is plugged up, possibly from dirt daubers. Never had one plugged up myself, but have heard it can do strange things.

Dan

Thanks Dan! This has the big ol Nelson can muffler, and when I pulled that to inspect the piston, the saw still wouldn't fire with it removed.

[okie]

Jan 30, 2022 13:05:26 GMT -5 edju1958 said:

Make sure the condenser is a known good one.Just because it's new doesn't mean anything,they can go bad just sitting on a shelf.These saws are 40+ yrs.old & most of the condensers are just as old.I generally don't say this,but it may be worth it to put an electronic chip in,at least for testing purposes.It's always good to have a chip on hand,they can be used in just about any model.And they're not expensive either,generally from $12-$15.

.It's always good to have a chip on hand,they can be used in just about any model.And they're not expensive either,generally from $12-$15.

I keep a chip around just for this test he mentioned. I do not trust them chips for long term use though.
And
I see your have already pulled the flywheel and changed the condenser, but just wanted to add that I've subbed condensers on saws and other eq and got a good run test by just using a automotive condenser hung onto the kill wire coming from under the flywheel. (do not have to pull the flywheel to test)

One I will never forget, I was into a old 3.5 Tecumseh engine with issues such as you mention. 
Finally broke down and replaced the magneto coil after I had been all over all else twice. It fired up on the 2nd pull. Ignition will sometimes get upset/change when under compression.

Stick another mag on it and set the air gap as a last chance shot.
 I would also do a compression test with a gauge and if it's weak make sure the rings are not stuck. (was weak sucking fuel into cylinder then floods easily, no pop or promise is a hint of possible low compression)
What is the compression?