Stihl 090 tuning

[macstrange]

I have a stihl 070 that's been giving me issues. I'll try to keep this short. I picked up a carburetor rebuild kit and installed it. Swapped out the inlet needle only to find out that it was a little too long and the inlet control lever would not act on it. But the old inlet needle back in, still couldn't get it started. After examining the piston and cylinder, I decided to put the 66 mm head and cylinder on. I was able to get it started, but I have a problem getting it to idle smoothly and can't get any top end out of it. I've been running 50 to 1 in it but I'm thinking of going to 30 to 1. Any one have any ideas? Your input is greatly appreciated.

 

[Vintage Engine Repairs]

Start us from the beginning,

Where did you get this saw from and why was it sold?

Did it have any issues when you got it originally?

What has been replaced on it and why?

What aftermarket parts have been added?

Why did you replace the carb kit

Why did you replace the top end?

Is it oem?

Have you pressure and vacuum tested it?

What is the condition of the fuel filter and fuel line?

 

[macstrange]

Start us from the beginning,

Where did you get this saw from and why was it sold?

Did it have any issues when you got it originally?

What has been replaced on it and why?

What aftermarket parts have been added?

Why did you replace the carb kit

Why did you replace the top end?

Is it oem?

Have you pressure and vacuum tested it?

What is the condition of the fuel filter and fuel line?

I bought the saw off Facebook marketplace for $500. It was missing the muffler. After installing a new muffler, it didn't take much to get it running. After some use, though, I have replaced the fuel pickup line, filter, and fuel line. At one point I was having issues with air in the fuel line. I tried several different fuel elbows, figuring the air was coming from the seal at the elbow. I was told the modern fuel lines were no bueno and I needed to use nitrile lines. They are much smaller tubing and fit tighter on the fittings. After swapping the fuel lines, I still haven't been able to get it running properly even though the compression testing was around 140. I figured the problem was in the carburetor so I put a new carb kit in. That didn't seem to work so, for the hell of it, I bought the bigger jug and piston and mounted that. I must say though, I thought I saw some discoloration in the original cylinder and thought maybe it was wore out. I also swapped the three shoe clutch for the six shoe clutch so I could run a 60-in bar. I've also had to replace the pull start cup because it disintegrated when I was running it.
I've been running the farmetec 070 for a few years previously without too many issues, though it is interesting to note, both saws started having air in fuel line problem at about the same. time.
A friend of mine, who was a stihl tech at one time, told me I would need to change the Jets on the carburetor to provide more fuel to a larger volume cylinder. As far as I can tell though there is no difference between the '070 carburetor and the 090 carburetor except for the placement of the adjustment screws. As a side note, the farmatec 070 has the adjustment screws on the side of the carburetor and the stihl 070 has the adjustment screws on the back of the carburetor.
I've also replaced the oil pump, oil tank gasket, and fuel tank gasket.

 

[Vintage Engine Repairs]

You can try to tune the carburetor first, here is a video on that, but if you don’t have any luck, your very first port of call is a pressure and vacuum test.



Once you’ve ruled out any leaks you can move onto the fuel system. You don’t need a mityvac - if your budget doesn’t stretch grab this one, it’s one of the most useful tools for any engine repairs that you’ll have In your tool box.

A budget friendly option - https://amzn.to/3Q6C1ix
Mityvac - https://amzn.to/3vysI3V

 

[macstrange]

You can try to tune the carburetor first, here is a video on that, but if you don’t have any luck, your very first port of call is a pressure and vacuum test.



Once you’ve ruled out any leaks you can move onto the fuel system. You don’t need a mityvac - if your budget doesn’t stretch grab this one, it’s one of the most useful tools for any engine repairs that you’ll have In your tool box.

A budget friendly option - https://amzn.to/3Q6C1ix
Mityvac - https://amzn.to/3vysI3V

Thanks allot for the info. I'll have to figure out what I need to do the pressure/vac test. I have a vac pump, I'm not sure if it does press. I spent allot of time trying to tune it yesterday with no luck. Hopefully the pressure vac test will reveal something.