HELP! Ported 026 Problems

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Woody33

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Hi Everyone,

Its my first post on AS but I've been following the site for about a month now. I know a little about small engines and have spent lots of time with chainsaws (captain of the lumberjack team in college so I got to play with Stihl 026,044,066 etc.) and I've recently started my own collection of chainsaws with an 026 and an 044. Picked them both up on kijiji for a great price and to my surprise they were both in top condition putting out slightly over 150psi on the compression tester - the 026 was bought to drop 3 maples in a backyard and then never used again! Anyhow, through my continued readings on AS, I decided to port them both. I started with a MM but more and more reading led to the decision to moderately port the 044 and (attempt) a more aggressively port the 026. The 044 turned out awesome! I ported the intake and exhaust (without raising, lowering or widening the ports) trimmed the fat off the piston windows, and removed the excess material on the bottom of the transfer ports (again without raising, lowering or widening etc.). I also raised the squish by removing the stock gasket and replaced it with a beer can gasket. I slapped on a dual port muffler and am quite pleased with the results.

For the 026 I ported the intake and widened it to within 2mm of the piston skirts, did the same for the exhaust but never raised or lowered them. I removed the excess material on the bottom of the transfer ports and slightly widened them towards the uppers and angled them. I trimmed the fat from the piston windows and of course, I drilled out the stock muffler to add a MM as well to accept the extra flow. I never screwed around with the squish and left the stock base gasket in place. I also replaced the rings as well while I was in there.

I bought a can of the STIHL pre-mix 93 octane $10 a liter fuel and was hoping the saw would scream right out of the gate but it didn't. It would idle when the saw was cold but when I gave it throttle it would bog out and stall (I say "bog" and "stall" because I am inexperienced and don't know if this is in fact because it is running too rich). I tried to tune the carb (it has both H/L adjustment screws) and I could at one point really get the saw to scream (but I know its running real lean and that's not good) and it had no power in the cut. I spent a good hour just trying to set the idle, and then the H adjustment but it seems I can't find the optimal spot. I can set it to idle good, but I either need to slowly "pulse" or "blip" the throttle to get it revving high (in which it will eventually stall) or if I just go WOT it stalls flat out. I've tried turning down the L adjustment screw etc, and think I have tried damn near every combination of both the H and L adjustment screws and nothing will let the saw at WOT. This is where my inexperience kicks in and I'm at a loss. I have read more and see most people have 044 carbs in ported 026's which leads to one of my questions: do you think this port job is "aggressive" enough to require a larger carb like that from an 044? Could there be an air leak somewhere as the idle is quite inconsistent (sometimes it idles nicely but if I blip the throttle the idle starts increasing) and now the best way to describe the running condition of the saw is "messy". The best tune job I can do is to have the saw at WOT and not stalling but rev up to peak rpm and then die down and then rev back up to peak rpm and die down again over and over with an obvious lack of power in the cut. I'm just going form memory from last weekend when I had a chance to play with the saw again but before I start throwing money at a new carb etc. I thought some AS members could shed some light on my problem.

Thanks in advance guys!


P.S. - I mostly used the ported 026/stock 026 comparison post from Mastermind to do the work...thanks Mastermind!
 
I cleaned the carb and replaced it (fear of old gas being left behind since it had been sitting for who knows how long) before I ported it and it was running good and strong. I never removed the carb while I was porting the cylinder so I never thought it would be the problem. That's why I'm thinking after the port job, the old carb is inadequate to move the amount of fuel required. Anymore thoughts?
 
You'd have to do some pretty radical porting for the stock carb to be unable to provide sufficient fuel or air to the carb. Typically a carb that is on the small size will provide better throttle response and just hurt you on the top end. Honestly I can't ever think of a gas carb that backing out the needle screws has refused to deliver enough fuel on a hopped up two stroke. If you switch to running methanol then yes you'll need to drill the fuel passages larger.

Since you didn't remove the carb when porting perhaps you got a small piece of metal clogging one of the fuel ports. The fuel passages are pretty small and it won't take much to block them.
 
tolman_paul, I wasn't sure if it was possible to "out-gun" a stock carb or not. You just answered my question, much appreciated. As far as a dirty carb I doubt that is the issue, I made sure the jug was spotless when I put it back together and made sure the saw was far, far away when I was doing any grinding but it never hurts to double check. I will have to check on that air leak issue, I could have cracked a line when putting things back together.

I appreciate the responses fella's, keep them coming. Won't get a chance to look at the saw for a few days until I get back home but I'll post any updates if I figure out the problem!
 
I would rebuild the carb. Just because it ran ok before does not mean something has not changed and messed up. I have been out cutting with saws and one minute they are running great and the next minute the saw will cut out at full throttle because something got in the carb. It is an 026 and it is an older saw, I would put a kit in the carb. All it takes is a weak diaphragm.
 
Ya, for the cost of the rebuild kit its definitely on the "to do" list to start ruling some of these issues out.
 
Carb diaphrams can die at inopertune times and make you think something else is going on with the saw.

When I rebuilt my husky 181 it fired right up after being in peices for over a year. I hadn't rebuilt the carb. Then the next week the saw refused to run. It would fire up, run for a second or two then die. I tore the carb apart several times to no avail. Turned out the fuel tank vent decided to stop venting all of a sudden. Go figure, 30 y/o saw after a rebuild and the vent decides to stop working to agrivate the heck out of me.
 
What kinda compression does it have now? And what's the squish? What rings did you use? Factory jug/slug right? I'm thinking your squish is gonna be fat and compression not great due to a bad set of rings.
 
Z71Mike - Compression is about the same, about 155ish warm. I never played with the squish so I'm assuming it hasn't changed since the same gasket is still in use. Put in a new set of rings while I had the saw apart, do you think I should lower the squish some?

Discount hunter - The carb was never attached to the cylinder while I was grinding, I meant I never removed the stud nuts and pulled the carb off (to clean) when I removed the cylinder for grinding, I removed the carb prior to the port job and once I bolted it back up, it never came off. When I removed that rubber boot from the carb to the intake I plugged it with cloth so nothing would accidentally make its way back into the carb.

I really appreciate the help guys, I was at a loss a couple days ago and now I can't wait to tackle this project again! I feel I did a good job on the porting and there is just something small (like a carb rebuild) that needs to get done in order for the saw to run properly.
 
Factory rings? Or something else? I've seen a huge difference in 4 different brands of 026 rings.
 
I'm not very familiar with the 026, so this is just a general reply.

As the others have eluded to, it sounds very much like the saw is running lean.

Since you hadn't changed anything with the carburetor, even with the porting and muffler mod, the saw should have at least run somewhat close to normal when reassembled.

The first couple of things I would suspect:

- Fuel Line - Is it kinked, pinched, split or was it otherwise damaged during the work?

- Pulse passage - Check to see if the pulse passage is plugged. Again, I'm not real familiar with the 026 so I don't know if it has a flexible hose or what.

Since there is still a stock base gasket, and the carb wasn't removed from the boot/manifold, I doubt there's an air leak at those points.
 
You need to do a vacuum / pressure test starting with the engine assembly especially if you are reusing the gasket that was originally on the saw. You have an air leak some where. I suspect it will be around the cylinder base. You can use the search function if its working and find some threads on how to do the tests. If you can't pm me and ill help you out. You can roast apiston in no time running your saw with the symptoms you mentioned.

sent by any means necessary!
 
I mentioned this in another 026 thread. I had a saw come into the shop that was exhibiting an air leak/lean symptom and the owner hadn't put the nuts on the back of the carb to hold it on. He was holding it on with just the air filter. This allowed a big leak.
 
I mentioned this in another 026 thread. I had a saw come into the shop that was exhibiting an air leak/lean symptom and the owner hadn't put the nuts on the back of the carb to hold it on. He was holding it on with just the air filter. This allowed a big leak.

The stud nuts are definitely on there. Based on what everyone is saying there is an air leak somewhere, I just gotta find it. I've done some research and watched videos on YouTube about doing a leak down test etc. I just don't have the equipment to do one. I'll look into finding a cheap way to do one and hopefully figure out where the problem is coming from. If I had to guess I would say I probably pinched/poked a line while putting them back together or it could be the cylinder gasket but I looked pretty closely at it before using it again and it was in great shape.

Not sure if this is related at all (don't think so) but it leaks heaps of bar oil while running. Would this be the pump or another seal? I've never ripped into the oil pump before...that will be next on the list.
 
Your wanting to perform a Vac/Pressure test, NOT a leakdown test. That is for engines with valves. I.E, Stihl's 4Mix engines. In this case all you need is a good tester from an auto supply store. Mitey Vac makes a good one that will do both vacum and pressure. It is a good investment if your working on saws. Then all you need from your Stihl dealer is a sealer plate(0000 855 8106), about $1.50, to seal off the exhaust. You can also use a piece of cut inner tube, but the dealer one is cheap enough. You'll also need a flange(1118 850 4200), about $20. This bolts on where your carb is now, and allows you to introduce the pressure or the vacum.
Block the muffler off with the sealing plate, bolt on the flange, make sure the decomp is not pushed in if you have one and apply pressure to the saw to a max of about 7psi. It should hold it for a minimum of 30seconds. If the needle drops, get out a spray bottle of soapy water and start looking for the leak.
 
Your wanting to perform a Vac/Pressure test, NOT a leakdown test. That is for engines with valves. I.E, Stihl's 4Mix engines. In this case all you need is a good tester from an auto supply store. Mitey Vac makes a good one that will do both vacum and pressure. It is a good investment if your working on saws. Then all you need from your Stihl dealer is a sealer plate(0000 855 8106), about $1.50, to seal off the exhaust. You can also use a piece of cut inner tube, but the dealer one is cheap enough. You'll also need a flange(1118 850 4200), about $20. This bolts on where your carb is now, and allows you to introduce the pressure or the vacum.
Block the muffler off with the sealing plate, bolt on the flange, make sure the decomp is not pushed in if you have one and apply pressure to the saw to a max of about 7psi. It should hold it for a minimum of 30seconds. If the needle drops, get out a spray bottle of soapy water and start looking for the leak.

Thanks for clarifying... I see Can Tire sells a cheap vac/pressure tester for $30, I'll pick one up and see what I can do. I really appreciate all the help, I have lots of theories to run with now! Hopefully I can get it up and running sooner than later:chainsaw:
 
I would take a good look at your intake boot since thats something that I could see getting in the way or getting torn or not sealing properly for you. On my last rebuild I put the boot on the jug first, then had to pull it through the hole in the handle. If its been sitting, it could have been brittle and now has a tear in it somewhere that you didnt notice before.

Also, did you replace the impulse line when you had things apart to do the porting?
 
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