Stihl hl 100 cutting out when hot

[bertsmobile1]

I you want to diagnose it there are two fairly simple things to do
1) fill the tank right up to the top of the filler neck then go trim
Problem goes away till the tank is say 1/2 empty then you have a fuel line problem

2) buy a red inline spark tester fit it , tie it out of the way then go trim
Watch it when the engines starts to play up
If it keeps on flashing the same while the engine is missing then the coil is working fine .
Note this does not confirm the spark is timed properly, just that it is happening .

Most times bad seals on a 2 stroke manifest themselves by the engine being near impossible to start if it has been sitting unused for a couple of weeks but once started it will start & run fine but be low in power and reving at the wrong speeds (usually to fast ) for the throttle position .
A classic sign is continually having to wind the throttle stop open to maintain an idle because it is sucking air through the seals & not the carb.

You can only confirm this by doing a crankcase pressure / vacuum test
To do this you need both a 2 way pump , blanking plates , an input spiggot ( usually through the spark plug hole ) plus a fair bit of time & skill.
I charge 1 hour to do these test for customers and many times that would be a loss as some are really difficult to access .

However when presented with a machine like yours I follow the proceedures shown in the Joe Pace videos and start with the tank & cap, fixing each & every problem as I come across them .
Not uncommon to find a bad fuel cap, bad tank vent, leaking fuel line , leaking fuel grommet & partially blocked fuel filter , before you get to a varnished up cab with a blocked internal filter .

People seadfastly refuse to maintain hand held 2 stroke tools .
This is not helped by most of the owners manuals having wrong or no long term storage information even if the owner is one of the 2% who actually read it before they start using the tool.

 

[robmar0se]

Not necessarily my old Husqvarna 36 would not act up until I was actually cutting up a fallen tree.

First on these 4 mix engine (hybrid 4 cycle engine) the crankcase is part of the intake system. With seals on the crankshaft they wear one sided in the most used position and harden so as the ball bearing develop play it allow the crankshaft move off center. As the engine is rotated around it allows the crankshaft to open up the seal, creating both a vacuum and pressure air leakage. The engine will lean out causing problems from a surging as the area opens and closes to an engine dying from fuel starvation. The crankshaft seals should be done by a confident 2 cycle tech as the engine must nearly fully disassembled.

This type seal wear happens even larger mower engines. I have inspected seals that I removed leaking oil that are worn one sided and harden. Just replacing the seals most times fixes the oil leaks.

Similar thing happen with the valves out adjustment as the engine can no longer properly breathe. And this adjustment requires a 1/8 wide .004" feeler gauge. The adjustment itself is quite simple though you should replace the cork rocker cover gasket at the time of the adjustment.

Thank you for the explanation, makes a lot more sense.

Lets hope its not the crankshaft!

I will write a separate report on my misadventure with changing the fuel filter - below!!

 

[robmar0se]

Likely a fuel line issue.

Well Ihope you're right.............

Today I replaced the spark plug and fuel filter - now it wont start at all (unless I inject fuel direct into the cylinder).

What I did first was the turn upside down and drain the fuel.. I hooked the fuel filter out and carefully removed the old one and push fit the new one. Refuel the tank.

There was still fuel in the primer cone, however on pressing a number of times the fuel left the cone (which I guess is right), but wouldn't refresh, all I get was a squeaking noise, irresepctive of whether the fuel cap was on or off.. Having watched Craig Kirkman's excellent video, I guess there must be a blockage/fuel line issue!! ie vacuum is imperfect?

Not being an expert here, other than replacing the carb, anything simple to suggest?

Its been relly helpful on this forum - many thanks for yr advice,

 

[Fish]

Well Ihope you're right.............

Today I replaced the spark plug and fuel filter - now it wont start at all (unless I inject fuel direct into the cylinder).

What I did first was the turn upside down and drain the fuel.. I hooked the fuel filter out and carefully removed the old one and push fit the new one. Refuel the tank.

There was still fuel in the primer cone, however on pressing a number of times the fuel left the cone (which I guess is right), but wouldn't refresh, all I get was a squeaking noise, irresepctive of whether the fuel cap was on or off.. Having watched Craig Kirkman's excellent video, I guess there must be a blockage/fuel line issue!! ie vacuum is imperfect?

Not being an expert here, other than replacing the carb, anything simple to suggest?

Its been relly helpful on this forum - many thanks for yr advice,

Make sure that you have the fuel lines hooked back up correctly.

 

[robmar0se]

Thanks guys.

Weather & work got in the way, today I picked it up and hey presto primer was magically full, and started on 2nd pull.

However, still stuttering & cutting out after 5 mins.

Is it worth replacing the carb with an after market item available on the usual market places? Maybe also adjusting valves?

 

[robmar0se]

Update:

Valves adjusted, made sure it was TDC on right rev, not realy an issue there.

So having checked the least costly alternative, will now move on to replacing the carb, as it is still cutting out when it gets hot.

Thanks to advice from these guys, also some very helpful tips on Youtube on the methodology to fixing these things - the guy on the Stihl Saloon was particularly helpful on adjusting valves.

 

[robmar0se]

I you want to diagnose it there are two fairly simple things to do
1) fill the tank right up to the top of the filler neck then go trim
Problem goes away till the tank is say 1/2 empty then you have a fuel line problem

2) buy a red inline spark tester fit it , tie it out of the way then go trim
Watch it when the engines starts to play up
If it keeps on flashing the same while the engine is missing then the coil is working fine .
Note this does not confirm the spark is timed properly, just that it is happening .

Most times bad seals on a 2 stroke manifest themselves by the engine being near impossible to start if it has been sitting unused for a couple of weeks but once started it will start & run fine but be low in power and reving at the wrong speeds (usually to fast ) for the throttle position .
A classic sign is continually having to wind the throttle stop open to maintain an idle because it is sucking air through the seals & not the carb.

You can only confirm this by doing a crankcase pressure / vacuum test
To do this you need both a 2 way pump , blanking plates , an input spiggot ( usually through the spark plug hole ) plus a fair bit of time & skill.
I charge 1 hour to do these test for customers and many times that would be a loss as some are really difficult to access .

However when presented with a machine like yours I follow the proceedures shown in the Joe Pace videos and start with the tank & cap, fixing each & every problem as I come across them .
Not uncommon to find a bad fuel cap, bad tank vent, leaking fuel line , leaking fuel grommet & partially blocked fuel filter , before you get to a varnished up cab with a blocked internal filter .

People seadfastly refuse to maintain hand held 2 stroke tools .
This is not helped by most of the owners manuals having wrong or no long term storage information even if the owner is one of the 2% who actually read it before they start using the tool.

Sorry mate, I've only just seen your post.....but thank you for your input.

I think I've done most of this, replaced the coil, plug and filter, no leaks, and adjusted valves. starts fine, but just starts to stutter and then cut-out after 5 mins - the fuel cap was replaced a while ago, and as far as poss, I have tried to run it with the cap off - I will try the cap trick when it starts to stutter. Other than that, as after market carbs are cheap compared to labor costs, thats my next item to deal with.

Thanks again for your ideas - couldn't find a Pace video that you referred to, got the gospel singuing tho'.

Cheers

 

[bertsmobile1]

Not sure if it was mentioned before but check the exhaust port in the cylinder
If you have been using too much oil or labouring the engine carbon builds up around the edges and blocks off the port.
A very small amount of build up can make a very big difference as the saw literally chokes on it's own exhaust

 

[robmar0se]

Thank you bertsmobile1, upto now mixture appeared okay, not smoking once choke off (always off quickly).

I have now fitted an aftermarket carb and is running but is now perhaps running too rich.

My problem is that unlike the original Stihl carb which had philips type heads to adjust, the after maket item, my best guess needs a nut spinner/driver, what size I have no idea.

Can anyone with experience of these aftermaket carbs know what size spinner is needed - assuming it can be adjusted!

Many thanks.

UPDATE: item is Hexagon 4mm Screwdriver - Stihl OEM No. 5910 890 2307

 

[robmar0se]

Final solution!

Problem was discovered to be the fuel intake pipe/lead. It had sufferred deterioration in that it had gone "soft", and was closing/flatening causing fuel starvation.