my MS290 rebuild, help with port timing please

[mcb]

that sounds pretty reasonable. i think in this saw just smoothing the ports out and doing the muffler + retune is a pretty major improvement and like timberwolf outlined above, theres not a lot of modding to be done to a clamshell saw in terms of port alteration beyond a touch of extra width.

be sure you are measuring port dimensions at the bore side, not the inlet or outlet flange, two different things. you will either have to rub the port shape onto paper inside the cylinder or use inside calipers. dont forget to keep a safe distance from those ring gaps, and bevel/chamfer/smooth the edges where the port intersects the bore liner. ballbrush last.

 

[mcb]

oh yeah, honda-bond is a honda brand gasket rtv available at honda auto dealers that every mechanic should have. its not as fickle about grease, oil or coolant as most others and seals exceptionally well when applied in very thin, even amounts to a clean surface.

 

[mcb]

i set up my camera and stopwatch to get some video and see how this saw is performing, but hit a 25 year old nail buried in the log first cut, toasted the chain and my last Pferd square file has about had it. some other day i guess.

 

[kodiakyardboy]

Those ports look good!

Nice looking ports on the 290, I am doing another 290-390 build and will be smoothing out the ports as well. Looks like your head building experience is paying off.. rep sent for good referance pics.

 

[terry2tmd]

Being that's a clam shell motor, you don't want to raise the exhaust or you can kiss compression bye bye. Given you are not raising exhaust, you don't want to raise transfers as you would then be hurting top end with insufficient blowdown. And as you are not raising the other two ports and increasing RPM, you likely don't want to increase the intake durration any signifficant amount either or you will loose base compression.

Just widen out the exhaust, maybe aim the transfers a little more back and try to improve the top corner at the outside of the transfer duct a little. then widen out the intake, match everything up and with a good muffler mod, that about all that can be had from a 290 as a work saw. Might get away advancing the timing a couple degs to make up for not being able to increase compression.

But myself, I would get it running stock with a new piston an make sure there are no problems before getting into porting, The idea of doing some porting as the saw is disassembled sounds good, but it can bite you in the a$$ if there are pre-existing problems with car, air leasks or whatever. Might only take an hour to put the saw together test it out and then pull it down to mess with porting.

This caught my eye I recently bought a MS 391 and I think it is also a clamshell design, I like the idea of advanceing the timing how is the best way to go about this?

 

[mcb]

either youve got to move the coil pickup or move the flywheel, right? i would guess an offset timing key is easiest but dont have experience with it.

 

[mcb]

update on my ancient clamshell thread.

i tried pulling a 20" bar with square ground full chisel using 2 different sprockets for a while(think it was a 7 and an 8 tooth) and the saw just didnt have the nut to be much more than a backup saw like that. so i recently went back to the 16" bar with square ground full chisel and a 7tooth sprocket. it pulls that very well with a lot of torque now. you can lean on it pretty hard in the cut, fully buried in red oak and still keep it humming along. it tears through 8-10" rounds now on the push or pull side without dropping much RPM from a free rev. im happy with the results and it was worth the time. much heartier saw than when i got it.

hoping to get the carb dialed in a little better this week, seems to be running rich at idle. i dont quite have the ear for tuning in the cut yet.

 

[CJ8Ted]

Thanks for the up date, I have a ?
As for the increase gas useage after the MM, can you cut as much wood per tank? or does it seem to always be empty.

Ted

 

[mcb]

i use the saw so sporadically, and its been so long since it was stock, that i couldnt answer that with any degree of accuracy. it goes through fuel twice as fast as bar oil when it used to be near 1:1 ratio. i do think i have it set up quite rich though.

 

[CJ8Ted]

My 021 uses gas and oil close to the same "tank size" when the gas is low so is the oil. As for my 290 (with the oil turned up the whole way) the gas would still run out before the oil does. I'm reading the info and waiting untill the saw is a year old. The few downsides to the MM I have been reading is the noise and the fuel use. Just trying to decide if a MM on my 290 will be worth it for my skill level and use.

Ted

 

[mcb]

my stock jonsered 50cc is louder than my opened up 290. probably more compression. jonsered has a raspy pop pop pop and the 290 is a lower, burbly braaaap tone. its not obnoxious in any way.

 

[CJ8Ted]

Thanks, I do wear ear plugs when bucking firewood with the 290 now, so that is not as much of an issue. I just don't want to be filling the tank every five minutes.

Ted

 

[Stumpys Customs]

Just in case you want to do some reading. Here's what I have done with a MS290. This thing turned out to be a a real nice runner.
http://www.arboristsite.com/chainsaw/176046.htm
Those mufflers need to really be slit apart & gutted, then welded back together to get the max out of them.

 

[CJ8Ted]

So after watching the vids it is more about "smiles per gallon" than "miles per gallon". I don't think I will port it, just do a MM and re-tune after the warrantee is up.

Ted

 

[mcb]

tuning help. hows this sound to you?

this saw has been back together a while and its fussy to tune. theres a very small margin between where itll bog when snapped open from idle to wot, so you have to kinda feather the throttle up... or itll stall when hot on the other end.

ive got one vid of the saw running happy right in between the two, where it doesnt stall after a while in the cut and doesnt bog when snapped open. dont go by the cut speed, its a dull semi-chisel from cutting in the dirt all day and was actually cutting crooked by the time i got the carb dialed. just tell me what you think of the sound, if this is rich, lean or right on. i still dont have the ear for it. do you hear any "4stroking" ? if so, at what time?

dont mind the asscrack.
http://youtu.be/r2e-GY0UYIg

 

[mcb]

got her runnin pretty decent. light porting, muffler mod and tune with a 20" square filed full chisel on a 7 pin in red oak. dont mind me leaning on it a bit too hard toward the end of the first cut. im happy. would love to see how it stacks up against a stock 361.

Picture 801 - YouTube

 

[Andrew Wellman]

Back from the past

this saw has been back together a while and its fussy to tune. theres a very small margin between where itll bog when snapped open from idle to wot, so you have to kinda feather the throttle up... or itll stall when hot on the other end.

ive got one vid of the saw running happy right in between the two, where it doesnt stall after a while in the cut and doesnt bog when snapped open. dont go by the cut speed, its a dull semi-chisel from cutting in the dirt all day and was actually cutting crooked by the time i got the carb dialed. just tell me what you think of the sound, if this is rich, lean or right on. i still dont have the ear for it. do you hear any "4stroking" ? if so, at what time?

dont mind the asscrack.
Picture 489 - YouTube

The narrow tune range is normal from my experience with ported saws. This is Andy the one who started the thread 3 years ago. Since then I have learned a great deal about saws and have have ported a half dozen. I not and expert but I think your low idle mixture is too lean given that you need to nurse it to keep running at low rpms. I am sure you have removed the limiter caps, but if not do so and open up the L and turn the idle up to balance the decrease in rpms so it idles 25-2600 rpm.

 

[Andrew Wellman]

Fourstroking

this saw has been back together a while and its fussy to tune. theres a very small margin between where itll bog when snapped open from idle to wot, so you have to kinda feather the throttle up... or itll stall when hot on the other end.

ive got one vid of the saw running happy right in between the two, where it doesnt stall after a while in the cut and doesnt bog when snapped open. dont go by the cut speed, its a dull semi-chisel from cutting in the dirt all day and was actually cutting crooked by the time i got the carb dialed. just tell me what you think of the sound, if this is rich, lean or right on. i still dont have the ear for it. do you hear any "4stroking" ? if so, at what time?

dont mind the asscrack.
Picture 489 - YouTube

I just viewed your video and it looks good an may sound a bit lean. Don't be afraid of running the saw rich and you should first after a rebuild. Even using synthetic mix oil in warm weather you should see unburned fuel in the form of smoke coming from the exhaust until you have warmed up the saw. Four stroking/burbling/etc sounds like you hit a rev limiter on a motorcycle and has a distinct sound difference. It makes the saw should likes its underperforming or being slightly choked of at hi rpm. I tune my saws with a tachometer, by ear, and feel in cut, but the best way just by ear if you learn to listen. Just as a test, turn your H open to 2 full turns, then hold the saw at full rev for a 5 sec count and listen. It should run poorly and smoke. Then close it 1/4 turn at a time and peg the throttle for 5 sec again. Do this until you get to about 1/2 a turn from closed (no more!!!). Note what the sound of the rpm changes are and the sound of the exhaust. There will be a point in the tuning were the saw will go from a stifled rev to screaming. At this point turn the H open counter clock wise 1/4 turn to add fuel. The saw will be rich and be burbling at full throttle. Then go to some wood, Peg the throttle and start to cut with a medium amount of down pressure and listen to the motor tone. You are looking a change in tone that makes the saw sound get cleaner or distinctly different than an out of wood free rev. This is something that I did not hear in your video. What the saw sounds like and the rpm outside of the cut does not matter, since you are not interested un cutting air but rather the cutting performance in wood. When the saw is warm the saw tone would change when entering and exiting the cut. The saw will run rich with no load and burble, and when cutting and the saw is loaded, the demand for fuel is raised the the saw no longer runs rich but the correct fuel mixture for power and engine cooling. The key is engine tone difference in cut. Another sign that you have done it correctly is that when the saw is completely cold it will take a couple of minutes of cutting to heat the combustion chamber enough burn the the fuel with little to no smoke and hi rpm. If your saw is too lean, then at cold start your saw will stop smoking quickly and rev high immediately. Remember fuel is coolant, and heat is the enemy of saws, it is better to error on the rich side. I hope this helps and does not sound like a know-it-all.

Andy

 

[mcb]

you took the thread over for a little while on page 1 but it was actually about my saw, im the OP.

thanks for all the great tuning info, ill try your technique and see how
it goes.

 

[Andrew Wellman]

woops

you took the thread over for a little while on page 1 but it was actually about my saw, im the OP.

thanks for all the great tuning info, ill try your technique and see how
it goes.

Sorry, my mistake. Im in vt, and my email is [email protected], so if you need help or want to swap parts let me know.