Stihl 4-Mix tuning

[tcartwri]

Hey,

So last year I bought a new FS90R trimmer with the 4-Mix motor. I have to say it has not been a great experience, and this coming from someone who has always owned and used Stihl powerheads.

From the factory, it had no mid range. It would idle fine, but you could not ease into the throttle. It would go full pin with just a touch of throttle, which is useless for trimming. So I bought the special tool from stihl to adjust the carb, which I have done with some success. However, it is nearly impossible to tune the high end by ear like a traditional 2-stroke. It just doesn't change tone and I'm concerned about the actual mixture being off. There are no baseline tuning settings from the factory, as it has been "pre-set for optimal performance". Well 'optimal' in my mind is obviously different from Mr.Stihl's idea. The machine only has about 30 hours on it, and I'm ready to sell it....

I only use Premium fuel with Stihl oil fwiw. I guess I could start reading the plug to get a better idea of what's going on, but that's not something you want to have to do routinely.

Anyone have any tips on how to go about this.

 

[PapaPerk]

Hey,

So last year I bought a new FS90R trimmer with the 4-Mix motor. I have to say it has not been a great experience, and this coming from someone who has always owned and used Stihl powerheads.

From the factory, it had no mid range. It would idle fine, but you could not ease into the throttle. It would go full pin with just a touch of throttle, which is useless for trimming. So I bought the special tool from stihl to adjust the carb, which I have done with some success. However, it is nearly impossible to tune the high end by ear like a traditional 2-stroke. It just doesn't change tone and I'm concerned about the actual mixture being off. There are no baseline tuning settings from the factory, as it has been "pre-set for optimal performance". Well 'optimal' in my mind is obviously different from Mr.Stihl's idea. The machine only has about 30 hours on it, and I'm ready to sell it....

I only use Premium fuel with Stihl oil fwiw. I guess I could start reading the plug to get a better idea of what's going on, but that's not something you want to have to do routinely.

Anyone have any tips on how to go about this.

I have a FS90 and it has full throttle range. Sounds like yours has issues. Have you watch throttle butterfly to see if it is snapping from idle to full throttle? If butterfly barely moves and engine goes to full power there's something very odd going on.

Did you take back to dealer? It should have a 4 year warranty if you use the prem oil.

 

[Kiotikarl]

What brand of carb is on your FS90? The ZAMA carbs are made in china, we have our share of problems with them.

 

[Scooby074]

SOmething sounds weird for sure. On my 4mix 130kombi I have a very featherable throttle. Have you taken it back to the dealer before its out of warranty?

 

[Baby Grand]

My FS130 has very good throttle response - sounds like a carb problem or fuel tank vent/filter.

 

[tcartwri]

Have not been back to the dealer yet. I guess it was hard for me to accept that a brand new unit would perform like this, and not being familiar with these hybrid motors I thought it might be normal.

I'm not sure what carb is on it.

I will drop it off and see what they have to say.

 

[PapaPerk]

Have not been back to the dealer yet. I guess it was hard for me to accept that a brand new unit would perform like this, and not being familiar with these hybrid motors I thought it might be normal.

I'm not sure what carb is on it.

I will drop it off and see what they have to say.

New stuff can have problems too... Yeah it's messed up and not your fault. Take it back and have them make it right for u. Good luck

 

[94BULLITT]

Your trimmer is a 4 stroke so you will not be a able to tune it like you do a 2 stroke. I tune my 4 mix with a tach.

I would check the throttle like Papaperk suggested.

 

[mikehaugen]

Your trimmer is a 4 stroke so you will not be a able to tune it like you do a 2 stroke. I tune my 4 mix with a tach.

I would check the throttle like Papaperk suggested.

what kind of tach do you use? Ignition or optical?

 

[94BULLITT]

what kind of tach do you use? Ignition or optical?

Ignition

Design Technology, Inc., Home of the Tiny-Tach - More Tachometers

 

[mikehaugen]

Ignition

Design Technology, Inc., Home of the Tiny-Tach - More Tachometers

Thanks... after posting that I started wondering how it would be possible to use an optical tach.

 

[tcartwri]

Your trimmer is a 4 stroke so you will not be a able to tune it like you do a 2 stroke. I tune my 4 mix with a tach.

I would check the throttle like Papaperk suggested.

Yup I understand that, however it should still respond to leaning out the high side which it does not. My ear >> my tach....

 

[94BULLITT]

Thanks... after posting that I started wondering how it would be possible to use an optical tach.

It would be more hassle than what it was worth to use an optical tach.

Yup I understand that, however it should still respond to leaning out the high side which it does not. My ear >> my tach....

It would probably be best if you took it to the dealer before you tear into too deep. They may not want to warranty it if they can tell someone has been messing with it.

 

[PapaPerk]

It would be more hassle than what it was worth to use an optical tach.

It would probably be best if you took it to the dealer before you tear into too deep. They may not want to warranty it if they can tell someone has been messing with it.

Yes... No point messing with the thing if it's new. Take it back to dealer and have them correct or get another trimmer from them. It's new and that's the whole point of buying new... To not work on stuff! (0:

I just returned a FS 94 because I didn't like how it ran. Dealer took it back and I got a FS 100rx which is very nice!