Stihl MS290 F/B upgrade??

[HusqyStihl]

A friend of mine wants me to mod his MS290 and figure id go with a 390 top. A local i found on craigslist (also a member on here) mentioned he had a great condition 026S top i might be able to grab off him. What route would an experienced 290 builder go? Ive been through many husqies and im not intimidated by this project at all and have already begun the MM, removed the limiters and hope to finish up by the end of this week once i pick up a dremel since mine crapped out. Will the 026S slide right in like the 390 top? He's looking for power so which would yeild better results? If its even possible and which way would most go?

Ive heard the 390 conversion is quick and simple on the same platform. Any other parts need to be changed or modded if i went that way?

If i went with the 026S top, same question, anything else needed? Special tools? Different sprockets? Etc?

 

[splitpost]

026 top end will not fit

 

[HusqyStihl]

I apologize, i meant to type 029S top end not 026S, my bad

 

[Roll Tide]

I'd go with the 390 for sure.

 

[fearofpavement]

The 029S is such a small increase in power it wouldn't be worth disassembling it for that. Go with the 039/MS390 cylinder kit. The 029 is 45mm, the 029S is 46mm, the 039 is 49mm. Or in other terms, 54cc, 56cc and 64+cc. Do a muffler mod while you have it apart, pull and trim the limiters if it has any and retune as required.

 

[Mud man]

I have a ms 290 that I'm going through now. I got a complete ms 390 engine off of eBay for 111.00 delivered to my door plus all the rubber hardware for 80.00 with dirko. I burnt up my 290 by not mixing the gas properly.

 

[Roll Tide]

I'd go ahead and throw on a new fuel line, fuel filter, impulse line, and a carb kit in it just for ***** and giggles. I always do with any rebuild.

 

[Roll Tide]

I have a ms 290 that I'm going through now. I got a complete ms 390 engine off of eBay for 111.00 delivered to my door plus all the rubber hardware for 80.00 with dirko. I burnt up my 290 by not mixing the gas properly.

Looks like straight gassed to me.

 

[Mud man]

I'd go ahead and throw on a new fuel line, fuel filter, impulse line, and a carb kit in it just for ***** and giggles. I always do with any rebuild.

I changed all of that plus the intake boot. I used dirko stihl approved sealer also. I'll have it back running in a few days.

 

[HusqyStihl]

Ive actuall pulled the limiter caps in advanced of the MM. Should i wait for the mod before i throw a390 top on it? I dont see how it could make a difference besides a retune. Looking for a decent but cheaper tach and i think ive acquired one temporarily from a friend. Fuel lines, filters, impulse line and plug has been changed already, intake boot is good, its a brand new machine. I should be ok with the stock carb right?

 

[HusqyStihl]

And of course i know to re-tune again after a 390 top

 

[Roll Tide]

You get great gains with a mm on these models.

 

[HusqyStihl]

Ive read that more than once on here. Dying to try it. Case splitter needed? Im eager to take it on! Id love to do a before and after vid, maybe 1) stock 290 MM mod then 2) 390 with MM mod. See what gains i can pull

 

[Roll Tide]

No need to split the muffler just look it up on the search bar. They are really straight forward. Just remove the two 8mm nuts and remove your muffler. The threads have pics on them are easy to see how you cut them out.

 

[deereguy]

Moose, I'm sure you already know this as you've done a number of rebuilds. But, suggest "Pressure testing the cylinder/piston assembly prior to final installation". Clam shell setups have a higher rate of failure (pressure) for me anyway. deereguy

 

[HusqyStihl]

No need to split the muffler just look it up on the search bar. They are really straight forward. Just remove the two 8mm nuts and remove your muffler. The threads have pics on them are easy to see how you cut them out.

Yeah ive already pulled the muffler, came in half no problem. Seems like an easy mod (on the 290 anyway) unless youre suggesting i need a new 390 muffler

Moose, I'm sure you already know this as you've done a number of rebuilds. But, suggest "Pressure testing the cylinder/piston assembly prior to final installation". Clam shell setups have a higher rate of failure (pressure) for me anyway. deereguy

Your talkin about pressure testing prior to the 390 final install? Ive worked on many husqs, do these Stihl setups have a 2 piece jug?? Or do you mean something else?

Again thanks to everyone, all great advice and very helpful!!

 

[Roll Tide]

390 muffler is the exact same !

 

[Roll Tide]

Doing some grinding to the exit of the muffler is where you find your gains. After removing the front with the screen there are just two small slits for the exhaust to exit. Opening them up there is where you get your gains. Many good threads on it.

 

[HusqyStihl]

Thats what i thought, like i said i pulled the muff on the 290, didnt wanna modify it until i decided which way to go top end wise. I did find 3 or 4 markups on the MM on AB and dyin to dremel and drill into it but figured id wait till i went one way or the other on the jug and piston. Or is it possible to still modify the muffler prior to a 390 top conversion? All i did so far was pull the muffler, pulled the limiter caps to tune once i either leave as a 290 or upgrade to 390. Kinda where it sits now. Wanted to see the internals of the 290 muffler and take it slow. Wanted to make sure i didnt go to crazy with a MM on the 290, then switch top ends just to find out that i went too far with a muffler on a 390 and have to buy another

 

[Roll Tide]

No reason to mess with the internals of the muffler. If you dremel the exit slots open that's all you need to do. I open up the entire
square that's stamped under the cover. Onceyou open that up your good to go. Make sure to flush out the muffler real good to get all the shavings out. I'd do it now and you may find you ddon't need the 390 motor. If you want to still put the 390 motor on it that modded muffler will work just fine.