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Stihl MS360 PRO will not draw fuel and run

Started by joneebgood, March 31, 2021, 03:00:39 PM

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joneebgood


 
I have had this saw for at least 15 years and it has been a wonderful workhorse.  It never gave me a problem until last fall when it just died in the middle of a log.  It did restart but only ran another two minutes and then died permanently.  It seemed to be getting fuel but would not run even with a shot of ether.  The local small engine repair shop immediately checked the compression and said that it only had 70# and therefore it would "never" run.  "It might run on ether but will not have enough compression to ignite the fuel mixture".  I tried to explain that it had all the power in the world and had stopped abruptly rather than just becoming harder to start over time.  He insisted it needed a complete rebuild and proceeded to quote me a shocking number.
 
I couldn't find any other cause for the problem so I ordered a piston, rings and new cylinder head and proceeded to disassemble the saw.  As I pulled the spark plug wire from the recess where it passed through the block I realized the insulation was broken and it had probably been shorting out at times.  As I already had the parts I replaced the piston and cylinder and also replaced the coil.  The saw started right up and ran better than ever.
 
So, with that for history I have since cut several cords of wood and ran the saw for many hours over several weeks without an issue until yesterday.  I had been sawing for an hour or so and the saw all of a sudden sounded strange.  It had a different sound and would just not make the usual rpms and didn't seem to have the usual power.  It cut out after only a minute so I checked for fuel but it didn't need any.  It did restart once but in less than a minute it died permanently.  It will run with a shot of ether but is just not drawing fuel into the cylinder.  I don't think I have ever had the carb apart so I tore it down and did find a couple of pockets of dirt that needed cleaning.  I reinstalled it but the saw would still not fire.  All I could think of was dirt in the main jet as there was plenty of fuel in the line as well as in both reservoirs in the carb.  I tried running my welding tip cleaner through the jet but it just wouldn't go all the way through so I ordered a replacement aftermarket carb.
 
After installed the new carb the saw started right up but ran at such a high rpm that I shut it down in less than a minute.  Both mixtures screws were about 4 turns open so I closed them some and tried to restart the saw.  It would not fire.  Again, it will run on a shot of ether and there is plenty of fuel in the carb but it just doesn't seem to have any suction to draw it into the cylinder?  Thinking the fuel vent may be plugged I tried to start it with the gas cap off but it made no difference.  It acts just like it did with the original carb.  I did have a replacement rubber manifold sleeve that fits between the carb and the cylinder head but it didn't seem to be the correct diameter to fit my saw.  I removed the original rubber sleeve and checked for cuts and breaks and reinstalled it to make sure that I wasn't loosing suction there but it did not make any difference.
 
I apologize for the length of this post but I wanted to give all the background in the event one of my recent repairs has caused this issue.  I can pick the saw up by the pull cord so I know it has significant compression but it just doesn't seem to be drawing the fuel into the cylinder.  I appreciate any comments or suggestions.  Thanks for reading. JIM
 
 

Mad Professor

Never use ether on a 2-stroke, use a shot of mix.

What did original P/C look like?  Do you still have them?  I might be interested in buying the cylinder.  PM me.

Chi-Com aftermarket carbs are junk, like most Chi-Com stuff......is the new coil and/or P/C Chi-Com?

Have you checked/replaced the fuel line and/or filter (with OEM)?

Start off by pulling the muffler just to check the P/C.  Will it fire with a shot of mix? If so you have a fuel problem or vac leak.  Did you replace/check impulse hose when you did the P/C?




DHansen

If you turn the mixture screws back out to where they were with your replacement carburetor and try to restart it.  See if starts and runs at the high RPM again.  Then see why it is running high RPM's.  The speed of the engine is determined by air intake.  Where is it getting the air.  Is the throttle closed, throttle blade not sticking or damaged?  Unmetered air entering crankcase or intake after the carburetor?  How high of RPM's are we talking?  If you are getting WOT type RPM's it would eliminate restricted exhaust issue.  Would also eliminate a spark issue. You could check compression and eliminate that as an issue.  What do you mean by both chambers were filled with fuel?

joneebgood


Thank you both for the suggestions.  I did not replace the impulse hose originally, as it looked perfect.  I also did not see any cracks or breaks in the rubber manifold from the head to the carb.  I will order both of these items and replace them just to rule them out.
 
I have replaced the fuel filter.
 
After trying to start it several times I pulled the fuel line off the carb and there was lots of fuel in the line.  It even was under a little pressure and bubbled out as if the sun was expanding what was in the tank.  I removed the carb and took off both the top and bottom covers and both areas were also full of fuel.  This was the replacement carb that I had just mounted so it was dry when I started.
 
I removed the muffler.  The rings and piston that I can see are perfect, shiny and still looking brand new.  The original piston that I had replaced was scored so badly near the exhaust port that one ring was crushed in the groove.  There are no scratches on this piston yet.  I asked the local repair guy to confirm compression and he gave it a couple of pulls and said "it pulls real hard, there is lots – that's not your problem".
 
The motor fires right up with a shot of ether but does not seem to draw fuel on it's own.  If the new impulse tube and carb manifold don't help I guess the only thing left might be the crankcase gasket leaking and causing poor suction? Is that a common occurrence?  Is there any way to check or confirm that without a complete teardown?
 
BTW – I would prefer not to use ether as starting spray but – how do you "give it a shot of mix"?   Do you use some baster type bulb to atomize and spray the fuel?

Thanks again for your responses.

joneebgood

Also, I did pull the impulse tube and put some white grease in the opening.  I cranked the engine over both with and without the sparkplug and there was some movement in the grease but you really had to look close to see it.  There may have been some pulsing but definitely nothing very strong.

Tacotodd

Pull the plug and put a little down the hole, replace, start. See what happens next.
Trying harder everyday.

Hilltop366

Should always prime with mixed gas so it gets oil too, it does not need to be sprayed but some in a squirt or spray bottle makes it easier.

Did you check to see if it has a plugged spark arrester on the muffler or if the muffler is plugged?

donbj

I haven't been stumped with the method I use yet unless there has been no spark or insufficient compression. I have a dishwashing soap squirt bottle for giving a shot right into the carburetor. Tip the saw so the fuel will run into the crankcase as you have the throttle squeezed and give a slow pull on the rope to open the cylinder to let the fuel into the crankcase. Put the saw on high idle setting if it has that with no choke. Set the saw down and pull til it fires. Works every time for me. This is how I test fire a lot of the saws I aquire that have fuel line problems.
I may be skinny but I'm a Husky guy

Woodmizer LT40HDG24. John Deere 5300 4WD with Loader/Forks. Husky 262xp. Jonsered 2065, Husky 65, Husky 44, Husky 181XP, Husky 2100CD, Husky 185CD

Old saw fixer

     We always had a squirt oilcan on the bench loaded with fuel mix if needed.  I still keep one on my bench.  Works for 2 and 4 stroke engines.
Stihl FG 2, 036 Pro, 017, HT 132, MS 261 C-M, MSA 140 C-B, MS 462 C-M, MS 201 T C-M
Echo CS-2511T, CS-3510
Logrite Cant Hook (with log stand), and Hookaroon

joneebgood


Part of the reason I always try to list the whole history of what I have done to an item before it stopped working is that, from experience, I often cause one problem when I am fixing another.  That turned out to be the case here.
 
I guess I never really understood how a 2 cycle operates.  I knew the impulse tube delivered a pulse to draw in the fuel but, I guess, I never realized the simple fact that that can only happen in a closed system.  After working through all the suggestions from users on this forum I now understand this saw better than I ever did.  Plus I can probably take it apart and reassemble it with my eyes closed now.  BTW, compared to my ancient Homelite this saw is an engineering marvel.  Extremely well made and well thought out.
 
Anyway, I finally determined it must not be pulsing hard enough to provide fuel and decided to replace the carb to cylinder rubber manifold along with the impulse tube.  There was no obvious issue with either item but I figured I had to keep throwing parts at it until I found the one that worked.  The only other thing I could think of was a leak in the gasket between the crankcase halves.  Silly, I know, but I would really rather find the problem myself that send something out for repair.
 
Now that I am beginning to understand the wonderful way a 2 cycle works I realized the other night (while sleeping!) that there was little chance the crankcase gasket had failed .  But, I also now realize the cylinder to sump gasket could also cause this problem.  Lo and behold, after only a few weeks of hard work the four cylinder bolts had each backed out a turn or two and the gasket blew out.  The screws were so tight when I initially removed them that I was afraid of breaking them off so I only used permatex on the threads when I reinstalled them.  I now know that was NOT sufficient to hold themtight.

I will put the saw back together as soon as my parts order comes and let you know if it starts but I am sure this was the issue.  I caused my own problem!  (As I seem to do more often as I get older)  It was the comments and advice on this forum that were the incentive that I needed to see this problem through.  Thank you all!





 


Mad Professor

Glad you found problem.  Always good to check screws/bolts/nuts after a build and a run-in.

Rather than throwing parts blindly at a problem, diagnose the problem.

Instead of buying an intake boot and impulse line, money better spent on a pressure/vac tester( mityvac 8500).  You can test crankcase/seals and intake hoses for leaks, also test the fuel line and metering needle in carb.

Maybe put the OEM carb back on.............

joneebgood

I had my grandchildren here for ten days so I just got back to working on the saw.  I replaced the cylinder gasket and this time I put locktite on the screws.  I put the original Stihl carburetor back on and it started right up.  I worked it hard the last two days and it runs absolutely awesome!    The screws are still tight and it has all the power it ever had.  Thanks again for all the advice.

Tom King


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