How exactly do you tune a 4mix?

[SawAddictedFarmer]

Normal usage, they go out of spec, and cause running issues, and harder starting.

What oil are you running? Our fs110 has had 10 years of abuse and they were only just out of spec. Almost it's entire life it's been 40:1 or 32:1.

 

[hacskaroly]

What was the reason you had to adjust the valves?

They are easy to check and quick to adjust as part of (at least) annual maintenance. I have had my FS 91 for four years and it is getting hard to start but runs great when it finally does...I have not done anything to it yet besides add fuel and string...so its about time to check the filters, spark plug and valve lash.

 

[lilspenny]

From my experience with my fs131r, br800x, and fs100rx the valves have needed very little adjustment. It's not as big of a deal as some naysayers think. Once every year or two and it takes 10 minutes at most. Twenty years on my fs100rx and even then they didn't really need it. I love the 4-mix low end torque for string trimmers. Not a big deal with blowers.

 

[lilspenny]

What oil are you running? Our fs110 has had 10 years of abuse and they were only just out of spec. Almost it's entire life it's been 40:1 or 32:1.

I have found a few oils that I really like. These are for 4-mix engines.... Saber at 64:1, Motul 710 2t at 50:1, and Motorex Cross Power 2t at 50:1. I like Maxima K2 at 50:1 but think 60:1 would be better. One oil, one ratio for all types including chainsaws? Saber at 50:1 with good quality 93 octane ethanol free. I've been testing 10 oils and those are top quality insofar as lubrication, cleanliness, and runability.

 

[bogieboy]

What oil are you running? Our fs110 has had 10 years of abuse and they were only just out of spec. Almost it's entire life it's been 40:1 or 32:1.

I use stihl hp ultra at 40:1... also, i am a certified stihl tech, so out of spec to me is different than most peoples idea of out of spec.....

 

[EFSM]

I see 4 mix’s every year that barely crank due to extremely excessive valve lash. I don’t know how someone can run them till they have .020” lash

 

[bogieboy]

I see 4 mix’s every year that barely crank due to extremely excessive valve lash. I don’t know how someone can run them till they have .020” lash

Same.... as soon as that feeler slips freely in, it gets adjusted on mine, same goes with any that i work on... if i touch it, its getting valves adjusted.... period...

 

[lilspenny]

Same.... as soon as that feeler slips freely in, it gets adjusted on mine, same goes with any that i work on... if i touch it, its getting valves adjusted.... period...

Are you finding more tight or loose valves. Another question... Are you seeing any evidence of ash buildup from using "low ash" oils such as Saber instead of Stihl Ultra?

 

[EFSM]

Are you finding more tight or loose valves. Another question... Are you seeing any evidence of ash buildup from using "low ash" oils such as Saber instead of Stihl Ultra?

5-10 years ago, I saw more tight valves, almost like they had a batch of engines that pounded the valve seats into the head or had higher wear valves/seats. Nowadays they’re mostly loose.

 

[bogieboy]

Are you finding more tight or loose valves. Another question... Are you seeing any evidence of ash buildup from using "low ash" oils such as Saber instead of Stihl Ultra?

5-10 years ago, I saw more tight valves, almost like they had a batch of engines that pounded the valve seats into the head or had higher wear valves/seats. Nowadays they’re mostly loose.

Like EFSM said, there was a run of tight ones, but now they are usually loose, to the point of not allowing the compression release to do its job.

As for ash/carbon buildup only time i see significant amounts of buildup are from opti2, and trufuel 50:1use.

 

[lilspenny]

Wow... So now the next questions... Where is the issue that is causing the loose valves? What might cause a pushrod to drop out of sight?

 

[bogieboy]

Wow... So now the next questions... Where is the issue that is causing the loose valves? What might cause a pushrod to drop out of sight?

Wear, typically on the cam lobe in my experience. As for dropping pushrod out the bottom, thats from excess valve lash.... like .030"+ lash, it allows the ball end to come out of the cup and drop down into the crankcase

Edit: a piece of carbon stuck in a valve can also drop the push rods, if it breaks free and gets sandwiched inbetween the valve seat and face.

 

[16TAF]

How would you go about tuning something like a fs110?

I look up the rpm spec and set to that. I can’t do a 4 mix by ear.

 

[lilspenny]

Wear, typically on the cam lobe in my experience. As for dropping pushrod out the bottom, thats from excess valve lash.... like .030"+ lash, it allows the ball end to come out of the cup and drop down into the crankcase

Edit: a piece of carbon stuck in a valve can also drop the push rods, if it breaks free and gets sandwiched inbetween the valve seat and face.

Thanks

 

[lilspenny]

Thanks

I have other questions now... Sorry!

Carbon... Do you see carbon in 4-mix engines from particular brand(s) of oil?

Also .. have you noticed ash buildup from use of oils besides Stihl Ultra?

As a general rule how often should 4-mix valves be checked for proper clearance?

Any particular 4-mix engine more troublesome than the other 4-mix engines?

 

[Vintage Engine Repairs]

From my experience with my fs131r, br800x, and fs100rx the valves have needed very little adjustment. It's not as big of a deal as some naysayers think. Once every year or two and it takes 10 minutes at most. Twenty years on my fs100rx and even then they didn't really need it. I love the 4-mix low end torque for string trimmers. Not a big deal with blowers.

Just depends on use. Around every 100 hours check valves. I do it every 6 weeks for comercial customers.

Re tuning, the low side is just like a 2 stroke - just slightly rich of peak. Though they all run accelerator pumps so if you like, you can set it at peak and they still accelerate well.

The high side - find the point it runs the fastest, then open the h until you hear it just start to drop a little in rpm and leave it there. They'll be just off the limiter and run well. You can push them a bit further but there is no benefit. They are less sensitive to adjustments compared to 2 strokes, so you may find you need to open it a full turn in some cases.

I normally finish up with checking the max rpm specs with a tach before returning it to the customer.