4-mix Pole Saw Technical Help

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FXST

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I need some education on the Stihl 4 mix engines. I have an HT101? that I have to look at tomorrow. power head runs poor. this thing is all over the place as far as issues. sometimes wont idle. stalls on initial acceleration. sometimes will rev to high rpm and maintain rpm or just flatten out and die. you name A symptom it will do it. thanks to this site I have become what I consider decent at 2-stroke repair and diagnosis, but this is the first 4-MIX I have ran across other than a few for routine maintainence and carb/ fuel issues. It is approx. 2 or 3 years old. I can find out tomorrow for sure. Initial inspection of Engine internals, muffler, piston cylinder looks good, minimal carbon, valves open close etc. seems ok. what should the compression be on these? does crankcase vacuum and pressure still need to be checked- I would assume so but? are there a lot of tech issues or bulletins on these engines? what kind of problems are you guys seeing with these? The fuel system is new. everything from tank to carburetor. I convinced myself it was a internal carb issue and replaced the carburetor and fuel tank (the tank leaked) all new lines filter etc. what next? coil timing issue? weird engine failure. any help greatly appreciated!
 
Have see the coil on some of those 4 mix motos do weird things,,, run sort of ok when cold but when heats up becomes intermittent,,,,,,,,I'm thinking the coil is shot,,,, probably warranty?????

Also exessive carbon build up but you stated it was pretty clean,,,
if ya get it going suggest switching to Ultra synthetic and a minimum of 89 octane mix,,,keeps carbon at a minimum:clap: :clap:
 
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Yes.. and if so it wil be under warranty so take the entire unit to your dealer.

Compression? Don't bother - it has a decomp valve in the engine that will lowball any measurements you make.

If it's three years old, and has some hours (150+).. you should check the valve-rocker gap.
 
Yes.. and if so it wil be under warranty so take the entire unit to your dealer.

Compression? Don't bother - it has a decomp valve in the engine that will lowball any measurements you make.

If it's three years old, and has some hours (150+).. you should check the valve-rocker gap.

Yup ... this would be correct, and ... even though this operates under 4-stroke principles, it still needs to have the crankcase properly sealed, so when you check the valve lash, be sure to reassemble with a new rocker cover gasket so that there are no leaks.

DAMHIKT .... :)

cheers eh?
 
This usually ends up as a bad ignition module. The first one I did would swear was a fuel issue. I have warranteed a few.

Yup, same here, and it wasn't until we put an old fashioned neon strobe timing light on them and watched the erratic and inconsistent timing that we figured it out.

That said, we have also seen a couple where a leaking v/c gasket caused improper mixtures. For the price of the v/c gasket, not changing it when the cover is off is crazy.

cheers eh?

PS : have seen then same module trouble in the FS55 and 38's.
 
A few years ago the module had a diode that was dissipating too much heat and causing premature failure.

Two things to watch -

Coil gap - it's smaller then the typcial saw, and needs to be correct. Two sheets of paper is about 6 thou.. close enough.

Insulator - little black insulators the coil mounts on are requried to keep the cylinder heat from the coil.
 
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I had to get my feet wet on one of these hybrid engines sooner or later and yeaterday was the day and most of the night.

My problem is exactly like the the first post in the thread. The coil issue makes sense because after I was finally able to get my 101 to at least start and idle. I could hear or detect a slight spark misfire if I could get the engine up to high speed. It is running but is erratic and all over the place. High speed performance is poor.

Questions I have about these engines are.

Approximately how much gap is needed between the rocker and the valve stem?? Can an average person get one of those feeler gauges from Sthil to set these valves correctly. I don't have a feeler gauge small enough to go into that little gap in the rocker arm to check valve stem clearance.

Are these engines prone to same problems with the valves that you encounter with a regular four stroke. Excessive carbon build up??? How about burnt valves??? Poor seating of the valves???

I knew I would find some kind of answer to my problem on this one by doing a search.

Any other little tidbits of info on these engines would be helpful. They are good engines but I still favor a regular 2-stroke for a HT type saw. The 4 stroke lacks the speed to make good pruning cuts on a tree. For doing work that doesn't require a cosmetic asthetic look like when your doing clearing work the 4 stroke is great because the torque these engines have makes the bull work on the ground easier.

Larry
 
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The 0.1mm feeler gauge part number is is 4180 893 6400 - have your dealer order a couple.. The'll cost lest then 50 cents each.


Carbon? not particularly on the trimmers. Thermal cycling takes care of it. The blowers can build up unless you use a semi or full synthetic mix. I'll never run my 4-mix on dino oil,and with synthetics keep the mix ratio at 50:1, or even more if using Stihl Ultra. BTW, it's not carbon that builds on on the 4-mixes - it's calcium deposits from the mix additives. Stihl has a EDTA "decarbonizer") - not for carbon though - to clean up the valves if they do get deposits from poor mix ratios or quality. Ther EDTA was intended for dealer only service, so don't try it at home without taking to someone as to the required techniques (and the instructions on the bottle are wrong!). I took a blower from zero compression to 90% of new power with a single application of EDTA.

The valve clearance is 0.004 inch when set. Up to 0.010 is fine. Make sure you really are TDC when setting. If you do suspect any buildup on the seats (use a leak-down tester..) you need to deal with it before setting the gaps. And excessively large rocker gap is an indicator of a problem.

Did your erratic running start suddenly or happen gradually over time?

You should get a copy of the 4-mix engine service manual. I'm sure someone on AS can send you one. Also, spend $29 at harbor freight and get a leak-down tester. A compression tester is of no use as the engine has an integral decomp...



Also.. I'm curoius as to what you mean about "speed" for clean cuts. Are you taking chain speed or engine speed?
 
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I took lakesides advice and picked up the feeler gauges and it was a huge help for checking the clearance.so definetly get a couple. I work for a large county forest preserve district and almost all our conventional stihl 2 stroke trimmers have been phased out and the 4 mixers phased in. they have been extremely reliable and have had 0 concerns with carbon and valves. I would definetely use genuine stihl oil as we do see a diffence in carbon buildup ( not bad, just more) when the operators use the other label mix from the bulk dispenser. I have run across one more faulty coil since my first one in this post, both units were older ones. Maybe the coil would still be under warranty because they did have problems with the earlier units.
 
I took lakesides advice and picked up the feeler gauges and it was a huge help for checking the clearance.so definetly get a couple. I work for a large county forest preserve district and almost all our conventional stihl 2 stroke trimmers have been phased out and the 4 mixers phased in. they have been extremely reliable and have had 0 concerns with carbon and valves. I would definetely use genuine stihl oil as we do see a diffence in carbon buildup ( not bad, just more) when the operators use the other label mix from the bulk dispenser. I have run across one more faulty coil since my first one in this post, both units were older ones. Maybe the coil would still be under warranty because they did have problems with the earlier units.

Those ignition modules have a 2 year parts and labor warranty and a 5 year part only meaning the module is under warranty for 5 years but labor to put it on is only 2 years. However I've found that any of those modules that go bad that were the original part on the unit Stihl will cover regardless of age. Those original modules had some issues, failing under heat and the biggest issue I dealt with was them getting stuck in the advance mode. The unit would act like it was getting no fuel, would fire but not start for hell or high water. After doing a few of these units a couple of pulls on the pull cord will tell you right off whether the module is faulty or not. Fire but no start, fire but no start, chances are high the module is bad.

Other than the module issue that has been addressed those 4-mix engines have been extremely reliable. The blower 4-mix had alot more issues than the trimmer type 4-mix. Cracking engine pans, burning exhaust valves and sometimes valve guides would come loose. I've also heard of some rocker arms cracking but have never seen one do that myself. The blowers had some fanwheel issues as well when they first came out that delayed delivery of those new units.

I bring up all these issues as a testiment to Stihl and their eagerness to correct problems. All these issues were addressed by none other than Peter Stihl himself at a visit to the Va Beach factory. He made it known Stihl would indeed correct these problems by backing the dealers 100%, payimg the costs for these issues whether in warranty or not, and promising all these issues would be corrected ASAP. He also made it known company wide the 4-mix engine was here to stay. That vist took place a few years ago and today you rarely see a 4-mix unit, be blower type or trimmer type with any issues at all. At the shop I work in 2-cycle repairs out number the 4-mix repairs by a huge number. Seems any 4-mix unit produced in the last 2-3 years has been fault free. Quite obivious Peter Stihl kept his word..
 
Thanks Lake for the info.

This 101 has been going downhill gradually over time. The 101 was getting harder to start and the high speed performance was starting to fall off. It basically quit last year.It would start but not run and then die. When this HT started acting up I had just finished overhauling my other HT which is a 75. The 75 got us by nicely all of last year and is still going strong. I finally have gotten around to this 101. This will be the first time anything has been done to it other than a bar and chain since I bought back in 03. I was suppose to take it back to the dealer to get the valves reset for free but that didn't happen as it wasn't causing me any trouble. It is not a tool that gets used everyday either.

I had it going good for a short time last night after getting the fuel filter cleaned, checking for air leaks in fuel line and made sure the venting system was working. Tested carb for air leaks and took it apart enough to know their was nothing in the inlet screen. Carb was clean as a whistle actually. Plug was fuel fouled, bad, it has been running rich. Cleaned it and put everthing back together, it ran good for a short time then started falling off running erratic. I could hear a slight ignition misfire it didn't want to run as smooth as it could. High speed accelaeration was up and down also. You would swear this was a fuel delivery problem, all that is good though unless the carb is junk it is one of those Zama(?) C1Q S88. My 75 had kind of the same problem but not as bad till I replaced the whole carb instead of just going the kit route.

I played with the valves a little setting them basically the way I do on regular engine. The rocker to valve stem clearance was a bit much to me. They are set about what appears to be close to that .004 you mentioned Lake. That was why I asked about getting a feeler gauge. Yes. I am at true TDC. Exhaust valve closed, piston at top of stoke before intake opens.

I do have a leakdown testor, homemade. There was a thread here on AS on how to make one. I really haven't found it to of much use on a chainsaw though. But like all things that I think I have wasted some time and money on, it looks like it will have a purpose now. Thanks again Lake.

To answer the last question I would say chain speed. The HT 75 turns a little faster in the cut to me which makes a cleaner neater cut. This is an arborist thing basically. Even with a properly applied 1,2,3 basic limb removal type cut the 101 doesn't move fast enough at the end of the cut to finish it clean. Leaves a slight tear at the bottom of the branch collar, never had this problem with the HT 75.

Personally, my opinion only, I have never really truly cared for the 101 as pruning tool where a finished look means everything. To me it is a heavy tool to operate when you have to do some reaching with it. The 101 is great for doing roadside pruning for height clearance, cutting clumpy ugly trees when doing clearing work or eliminating lower large limbs for a tree removal.

FXST, Sthil products are the only products we use, expensive as they are especially with the rise in oil prices they are still a bargain. Not to mention peace of mind.

Like I said earlier my 101 was bought back in 03. I don't think a warranty would fly. I could hope though but I don't think it will happen.

Loooong winded post. I do have a pic of my valves if anyone wants to see what the top of one of those 4-mixes look like. They look like a mini vesion of what you see on a regular car or truck engine.

Larry
 
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Thall,

You got your post in probaly while I was editting and reedditting.

Could I get a free module??? I have my original registration form from the dealer I bought it from.

I would feel a little awkward going in after five years saying I want a new module because the guys on AS said I could get one.

I don't need anyone to install it but it would be nice to get a freebie if it is a manufactures problem.

I am not real crazy about the two Sthil dealers I have been dealing with as of late. Been thinking hard about changing and giving the new guy in town a try. I don't think my registration would be any good at the new guys dealership.

Would this so called warranty apply to my paticular case for commercial use.

Larry
 
Thall,

You got your post in probaly while I was editting and reedditting.

Could I get a free module??? I have my original registration form from the dealer I bought it from.

I would feel a little awkward going in after five years saying I want a new module because the guys on AS said I could get one.

I don't need anyone to install it but it would be nice to get a freebie if it is a manufactures problem.

I am not real crazy about the two Sthil dealers I have been dealing with as of late. Been thinking hard about changing and giving the new guy in town a try. I don't think my registration would be any good at the new guys dealership.

Would this so called warranty apply to my paticular case for commercial use.

Larry

Yes you can get a free module providing the module on it is the one that came on it. Stihl has no problem what so ever taking care of things way out of warranty especially when they know there was a problem with the module to begin with.

If your dealers won't step up to the plate for you because they don't want to do the file claim just give Stihl Inc a call and explain the deal with them. If you were in my area I'd getcha a module and put on for you free of charge. Your dealers should do the same, its only a 10 minute job. You will find Stihl the company will reach far more to take care of you the customer than its dealers will, sadly thats the way it is. Keep me posted on your module issue...
 
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