Stihl MS 290 NIGHTMARE!

[94 wrangler]

Okay, I have a Stihl MS 290. It would seem that I am not getting any fuel or at least not enough fuel to get the engine to fire. I rebuilt the carburetor and cleaned it in my ultra sonic cleaner with "Mechanic in a bottle" as my cleaning solution. Installed a new Stihl impulse line. I have also replaced two fuel lines and two new fuel filters. I have very good spark. The engine is a new after market big bore that was already together when I got it. I used orange Durko as a gasket / sealer between the lower pan and the cylinder. Has very good compression too. Now with that all said, I am wondering if the fuel line is getting a 90 degree bend in it when I have the carburetor in place and since it's in place, I can not see it. Has anyone ever encountered that problem on these 290's? Thanks in advance for any suggestions. I am at my wits end!!!

 

[lone wolf]

@dmb2613

 

[PV Hiker]

You can try priming a little mix down the carb and see if it pops.

 

[Wood Doctor]

Usually something like this is a mistake made during the carb rebuild process. I suggest trying a new aftermarket carb and see if it does the same thing. Doesn't cost much and is better than throwing the saw in the boneyard. If it works, you can then safely buy a OEM carb with little penalty.

 

[cscltd]

Could be massive air leak if won’t pop, bad seal or airboot not on properly
flywheel key broke and not timed right.
like mentioned Before, try little mix down throat. If won’t pop then pressure vac check

 

[HarleyT]

Aftermarket fuel lines can bend and pinch. But if you cannot even get it to pop on a squirt of fuel, then something else is wrong.

 

[94 wrangler]

I found the problem! As cscltd mentioned. I gave her a shot of fuel into the carburetor and no pop. I removed the starter and the fly wheel. BINGO....broken flywheel key. So, since the key is part of the flywheel itself, I am going to have to get another flywheel. Question, what could have made it break?

 

[lone wolf]

I found the problem! As cscltd mentioned. I gave her a shot of fuel into the carburetor and no pop. I removed the starter and the fly wheel. BINGO....broken flywheel key. So, since the key is part of the flywheel itself, I am going to have to get another flywheel. Question, what could have made it break?

Too loose the nut wasn't tight enough for one .

 

[dmb2613]

You dont need a new flywheel, the key only lines up the crank to flywheel for timing. Clean the crank and inside of the flywheel very clean make sure there is no grease or oil on either one. Line up the flywheel to the crank mark it and in stall the nut and tighten it up look at your marks to make sure it did not slip.
You should be good

 

[PV Hiker]

I found the problem! As cscltd mentioned. I gave her a shot of fuel into the carburetor and no pop. I removed the starter and the fly wheel. BINGO....broken flywheel key. So, since the key is part of the flywheel itself, I am going to have to get another flywheel. Question, what could have made it break?

As said too loose for the nut. Also the mating parts need to be super clean to seat fully down the tapered shaft.

If it was my saw and I have one that had a sheared key on the aluminum flywheel given to me, Clean up all the transfer from the key smeared. Clean the flywheel side. Mark where the key edges is. After this and the mating surfaces are good, put the flywheel back on and torque to specifications.

The flywheel will stay put with clamping force in the proper placement as long as the two mating surfaces match and super clean.

 

[PV Hiker]

HaHa I type too slow.....

 

[stihltech]

The flywheel nut came loose. Unless someone had it off, not likely. Stihl recommended roughening the crank taper with a fine valve grinding compound when I went to one of the schools, clean, line up the key and tighten. Do not be surprised that the end of the crank breaks off when tightening. Have had a few different models do this. The will be a crack you cannot see, but it will be evident when it comes off.

And if I am wrong on this saw, good for you!

 

[94 wrangler]

This was new crankshaft. I guess I screwed up by putting a little light oil on the crankshaft taper and I didn't clean up the inside taper of the flywheel. Live and learn.
I want to thank all that replied. I appreciated everyone's comments and advice.

 

[Patrick1903]

You dont need a new flywheel, the key only lines up the crank to flywheel for timing. Clean the crank and inside of the flywheel very clean make sure there is no grease or oil on either one. Line up the flywheel to the crank mark it and in stall the nut and tighten it up look at your marks to make sure it did not slip.
You should be good

I thought the key also provided a means for the shaft and flywheel to “connect” and essentially help transfer the rotational force of the crank to the flywheel. Based on what you said it’s just an alignment tool.

I’m thinking of a riding mower rear wheels. Is that key in a mower axle different because the flywheel shaft is tapered on a saw? Obviously the wheel on a mower is not tightened down onto the axle and axle would spin without the key in the axle shaft.

Learned something new today…thanks.

 

[Patrick1903]

The flywheel nut came loose. Unless someone had it off, not likely. Stihl recommended roughening the crank taper with a fine valve grinding compound when I went to one of the schools, clean, line up the key and tighten. Do not be surprised that the end of the crank breaks off when tightening. Have had a few different models do this. The will be a crack you cannot see, but it will be evident when it comes off.

And if I am wrong on this saw, good for you!

For reference - flywheel torque. I’m looking at a 290 service manual. (Granted op said he has a 390 crank I think?). But this manual also covers 390. Torque value for flywheel nut shows 28Nm which equals 20.6 ft/lb.