XL-12 Won't Run Full Speed

[phandad]

New member here.  I have an XL-12 that's been in the family since new.  Based on serial number date coding, it's a 1972 model.  Info about the saw is here:

houseofhomelite.proboards.com/thread/6140/figuring-out-when-homelite-built?page=6

Some background.  The saw had a fair amount of use in the 70's, some in the 80' through the mid 90's and sporadically since.  The saw had been sitting unused for about 5 years.  Never had an issue getting it running again with a little patience and numerous starter pulls.  Same this time, but the saw didn't want to "power up" (run full speed) for cutting.  After a bit of coaxing, it did - I figured the carb had a bit of gunk in it that finally cleared out.  I've used it off and on for a couple weeks.  After some heavy use (20" bar, almost full length cut), I shut it down to do some digging around the trunk of the tree so I could get a nice low final stump cut.  After digging and a beer break, the saw wouldn't restart.  It would pop and run a bit, but not longer than about 10 to 15 seconds at a low speed, not much above idle.  

I figured it was carb problem, since messing with both the low and hi speed jets had no effect.  A spare Tillotson HS-179B carb had been purchased years ago, so I decided to install it.  Took a while to clean up the carb "box" I'm not sure it was ever cleaned.  

So with the new carb, the saw now runs at idle, but won't fully power up.  It was best when first fired up, and I was able to cut some with it, but I could easily stall the chain.  It seems to be missing at higher speed as you get puffs of blue smoke as it tries to rev up.  I thinking it's an ignition issue.  Condenser is failing or points arcing or some other issue.  (The points and condenser may be original; I know they haven't been serviced since 1978)  Opinions of my diagnosis please.

I've been reading past posts to educate myself, especially the Ignition Thread.  I have had success adding ignition modules (Nova II, Megafire) to old single cylinder cast iron Briggs engines.  So I was thinking of doing the same to my XL-12.  However, the success rate doesn't sound promising as a long term fix.  It appears my XL-12 would be a fairly easy conversion to the newer solid state ignition coil system.  All you need is a replacement ignition coil mounting plate (part# 943261) and a solid state module & core (part# A94605S) and get the flywheel off.  Is my thinking correct?  

Thanks in advance for your thoughts. 

PS: As I mentioned in the reference post above, I was expecting the carb to be a Tillotson HS-179-B based on what I could see of it before I removed it and the UT-10080 IPL. But after I removed it, it's stamped "HS96A 2"; a couple of pics:




I haven't been able to find this carb listed in any IPLs, so maybe the saw was serviced while in my Dad's possession (pre 1978) and the original carb was replaced.  Notice the choke lever, it has 2 smaller holes compared to the HS-179B.  I had to bush the choke rod to work with the HS-179B.  I noticed a new choke rod is included in the Homelite HS-179B conversion kit.  

Anyone familiar with this carb? (Tillotson doesn't reference it on their web site)

[nighthawk]

Look at the hole on the bottom of the carburetor. Lightly push on that metal you see. Does it move very easily or is there resistance? It only moves a very small amount.

Your problems are most likely carb related but there are some other things it could possibly be.

I would start with new fuel line and carb rebuild. A small pinhole in the fuel line can cause problems as well as the smallest problem inside the carburetor can cause issues.

If you are getting good strong spark then I would pay more attention to the carb and fuel line.

While you are at it I would check the cylinder and Piston. Just pull the muffler off and take a look inside. Take a picture and post it.

How much compression do you have? If you do not have a tester the easy way is just to hold the saw by the rope. If it falls easily then we will want to explore that more. If it takes a good second or so to get past the compression to drop a little then you should be good. This is not an exact way to test but can be used for a quick idea. Make sure your spark plug is in!

[phandad]

nighthawk, thanks for the reply.



Answers to your questions.



The old carburetor (removed) diaphragm moves very easily, not very much as you said.



As to the fuel line, I tested it with a syringe when I replaced the fuel line there is plenty of fuel flow IMO (the in-tank fuel pickup was replaced with new before the test).



As I'm pretty far "into" the saw (just got the flywheel off today) I can't check the spark or do a compression check.



I did take the muffler off and here are the pics, first with the piston down, second with the piston up:
  



I'm still thinking it's ignition related since the muffler is very wet which indicated to me, un-burned fuel.  

More it a bit about what I found after getting the flywheel off.  

And thanks again for your response.  

[nighthawk]

Well since you are tearing it down you might as well learn how to pressure test. You would be checking for an air leak. An air leak can cause all sorts of erratic behavior. My background is mostly motorcycle and air leaks are a very common problem for them and saws. From there test the electrical system and compression test it. Then if neither of those are the problem it’s a fuel delivery issue.

I’m still betting on carb issues. We shall see. Mostly because your first post said you could turn the high and low jet with no changes. Then when you changed to a different carb you noticed a difference. Everything about that description tells me carb issues regardless of what else you find. Carb issues are so common that I just start with that before doing anything else. It’s a $20 kit and then you are certain.

[rowdy235]

It’s tough to tell what you’re dealing with without being able to see and hear the saw run. Could be easily an ignition or carburetor problem, or an air leak as nighthawk mentioned.

Before I did anything I’d pull the flywheel and file/gap the points. Over years the points can corrode and what happens is then there is less of the “point” making contact so the area that does gets burned and before long you’re not getting good contact. If they haven’t been serviced since the 70s I am sure they need attention. It shouldn’t take you very long, the hardest part will be getting the flywheel off. You may want to buy or borrow a puller for that. Also helps to have a point file which is about $2 at any auto parts store.

Once you’ve done that let us know if any improvement. I’d also replace the spark plug if you haven’t in a while. Both these things shouldn’t cost much and will make sure you are working with a “clean slate” so to speak.

[rarefish383]

You can still check for spark. I had a Super EZ all apart. Used brake cleaner to spray it down. I had the plug out and got the bright idea to just slide the flywheel on enough to turn it. Stuck the plug back on the plug wire, took my hand and turned the flywheel about half a turn and POOF. It had spark! Brake clean saturated towels take very little to ignite.

[phandad]

Thanks for the additional comments.  I appreciate it.

Finally got to take a look at the points.  Best i can tell, the gap is down to about 0.010".  Some pics:





As rowdy235 suggested, the points definitely need attention.  Now that I see exactly how these points work (never been inside a 2 cycle before - there's no points plunger like I'm familiar with on the single cylinder horizontal Briggs), I would imagine with time the plastic riding the shaft will wear down with time closing the gap.  Between that and contact wear I would think that could cause worse ignition problems at higher rpms. 

I'm tempted to service the points and give it a go, but since the saw has a lot of sentimental value and I don't want to have to pull the flywheel off again, I'm going to convert it to solid state ignition.  The parts are on order. 

However, since both nitehawk and rowdy235 that "air leak" might be a problem, please explain.  I'm familiar with gasket leaks on carburetor to intake port "piping" causing problems, but in my limited experience that is a starting or idle issue, not high speed running issue.  Please explain.  I'd like to learn.  

[sweepleader]

Point gap affects the timing as well as the spark intensity so it needs to be right. The felt oiler there needs a couple drops of oil to reduce the wear on the points rubbing block.

The two bumps on right near the points in your second picture are for use in adjusting the points. Loosen the screw in the picture but leave some pretty good drag on the points, then insert a screw driver between the bumps and twist to move the fixed point to adjust the gap. You will have a lot of leverage so you do need to be careful not to bend the fixed point bracket and misalign the two contacts. Adjustments can be made easily and quickly with only two hands, one for the screwdriver and one for the feeler or wire gage.

A wire gage is easier for me in that it does not have to be quite so carefully aligned to get a good feeling for the correct gap.

[rarefish383]

I think I have 3 saws now with Nova II modules on them. They start and run fine. The Super 1050 has had them for about 10 years, probably more, time fly's. I don't know if it's just getting older, and cranking a 100 CC saw is harder, or if the module advances the timing a tad, making it harder to pull. One saw mechanic that put Nova II modules on all old saws that came to his shop said they do advance the timing a little, Joe.

[phandad]

An update.

As I posted in June, I decided to convert the ignition to solid state.  Ordered the required parts, including a NOS Stens solid state coil.  While waiting for the parts to arrive, I removed the points box/coil mounting plate and cleaned up the area:


Then I installed the solid state ignition coil mounting plate:


And then I waited.  Unfortunately the coil was being shipped from Canada.  It took about 5 weeks to arrive.  By then it was late July and hot, so the repair was put on the back burner.  

About a month ago, I mounted the coil (forgot to take a pic) and flywheel, then checked for spark. 

I'm happy to report a nice bright spark (used a drill to rotate the flywheel).  Installed a new sprocket/drum and reassembled the saw.  It now runs great at all rpms.  

Thanks again to those who replied to this thread.