# Big Bore kit worth it?



## nate379 (Apr 27, 2012)

I modified the muffler today on my 290 along with a good tuneup and it woke it up pretty good.

I found on eBay they are selling 47mm bore jugs/pistons for around $100.  Stock is a 46mm.  I think it works out to me the same jug as a 390 saw, though I dunno if the stroke is the same on the 2 saws?


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## thinkxingu (Apr 28, 2012)

The problem I always have with upgrading average gear is that for the money invested I could buy better.  For example, if you sold your 290 and added the $100 to what you get for it, you'd probably be able to pick up a nice used pro saw.  I've seen nice 361s around here for $350-400.  My $.02.

S


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## TreePointer (Apr 28, 2012)

I thought I read that Baileys will be selling a new 390 kit for the 290/310/390 platform this year. Searching for link....

EDIT:  This link has the kit's status as of April 18, 2012.  http://www.arboristsite.com/baileys/151020.htm

There was another link somewhere talking about likely price.


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## Cowboy Billy (Apr 28, 2012)

I heard on some of the big bore kits the intake port is too flat across the top and it can break the rings under some conditions. While you can put more of a radius on you are also changing the port timing. The BB kit for the 2171 is one and my brother is going to radius his before he puts it together.

Billy


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## ScotO (Apr 28, 2012)

for a 290 used as a general woodcutting saw, I would say no to the big bore kit. Now if you have a 440 or bigger saw and you are looking for more power, then a big bore kit may be worth it. The muffler mod works wonders on these newer saws ( we have to remember that the saws made nowadays are under very strict EPA rules and regs, and the manufacturers are forced to constrict the airflow on modern saws). Just don't make the muffler outlet TOO big, or it can make the saw run like chit!!


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## nate379 (Apr 28, 2012)

Muffler outlet I made as big as possible without cutting the baffle.  Also took out the screen.  Runs fine after I turned the high mixture out about 2 turns and dialed in teh low and idle speed.  Would barely run after I threw the muffler on and fired it up to adjust.


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## ScotO (Apr 28, 2012)

Ideally you want the muffler outlet just slightly smaller than the exhaust outlet on the jug.  Two cycles like a little bit of backpressure.  But if it is running fine for ya, run it....


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## MasterMech (Apr 30, 2012)

Bailey's sells a complete aftermarket engine ($150.00) for the 290/310/390 and it's the 390 spec. Making a 290 into a 390 is a big upgrade and the aftermarket kit is the way to go IMO if you already have a 3/8" B&C on it.

http://baileysonline.com/itemdetail.asp?item=SBN 390&catID=



BTW: 47mm is not worth the $$ IMO. Go big (49mm) or go home!


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## nate379 (Apr 30, 2012)

There's still plenty of backpressure with the baffle still in the muffler. I used to have a weedeater I ran for several years with no muffler at all, never was able to kill it.  Tossed it after got ran over (yeah great place to put yard equipment is in the weeds right behind a D8 dozer. 

Dunno what he's cutting there, but if my 290 took that long to get threw a log I would have tossed it deep into the woods by now! I'd still be trying to cut the firewood I burned last year hahaha.

Yeah 3/8" chain, is there anything else?


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## kettensÃ¤ge (Apr 30, 2012)

nate379 said:


> There's still plenty of backpressure with the baffle still in the muffler. I used to have a weedeater I ran for several years with no muffler at all, never was able to kill it. Tossed it after got ran over (yeah great place to put yard equipment is in the weeds right behind a D8 dozer.
> 
> Dunno what he's cutting there, but if my 290 took that long to get threw a log I would have tossed it deep into the woods by now! I'd still be trying to cut the firewood I burned last year hahaha.
> 
> Yeah 3/8" chain, is there anything else?


 

Gotta agree it is kinda slow, the chain looks dull. Hard to tell from the video but it doesn't look like the usual jet of confetti sized chips pouring out of the saw, more like clods of dust. Sounds decent though.


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## HittinSteel (Apr 30, 2012)

nate379 said:


> There's still plenty of backpressure with the baffle still in the muffler. I used to have a weedeater I ran for several years with no muffler at all, never was able to kill it. Tossed it after got ran over (yeah great place to put yard equipment is in the weeds right behind a D8 dozer.
> 
> Dunno what he's cutting there, but if my 290 took that long to get threw a log I would have tossed it deep into the woods by now! I'd still be trying to cut the firewood I burned last year hahaha.
> 
> Yeah 3/8" chain, is there anything else?


 
That's Brad Snelling in the video....one thing is for sure, the chain is sharp and it's dumping chips. Imagine that was an initial run so the rings need time to seat. I've seen the video before and though if someone gave me a blown up 290 it would probably be worth putting that big bore kit in for $150.


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## lukem (Apr 30, 2012)

kettensÃ¤ge said:


> Gotta agree it is kinda slow, the chain looks dull. Hard to tell from the video but it doesn't look like the usual jet of confetti sized chips pouring out of the saw, more like clods of dust. Sounds decent though.


 
Looks plenty sharp to me.  That log is dry as a bone...which means it will throw some dust in addition to the chips and it is probably much harder than your average green tree.


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## MasterMech (Apr 30, 2012)

kettensÃ¤ge said:


> Gotta agree it is kinda slow, the chain looks dull. Hard to tell from the video but it doesn't look like the usual jet of confetti sized chips pouring out of the saw, more like clods of dust. Sounds decent though.


  He's also not really leaning on it.  Remember those are initial break in runs and not race passes.  I would agree that the saw probably has some breaking in to do.


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## smokinj (Apr 30, 2012)

Sleeper 290 is just about as cool as you can get! 100.00 be at-least a couple 100's worth of fun....


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## nate379 (Apr 30, 2012)

Yeah, I think I'm going to wait till I kill the motor and go from there, $150 is a bunch of money to put into a $400 saw.


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## smokinj (Apr 30, 2012)

nate379 said:


> Yeah, I think I'm going to wait till I kill the motor and go from there, $150 is a bunch of money to put into a $400 saw.


 
This is why most do not do it to a 290. Now keep an eye open for a 390 parts saw.


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## nate379 (Apr 30, 2012)

A sleeper saw would be fun to have though. I'd love to be able to cut near as fast as my brother with a 460 hahaha!

Hmm... Tim, what's up your your saw?  Yeah I dunno man, better trade trade pile of junk in! hehe


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## kettensÃ¤ge (Apr 30, 2012)

MasterMech said:


> He's also not really leaning on it. Remember those are initial break in runs and not race passes. I would agree that the saw probably has some breaking in to do.


 

Most video's like that showcase a saws potential, so why do a video if you are going to baby it or before it's ready to run? I guess only the video producer can answer that.
It doesn't take that much to seat rings and be ready to cut full bore for a video.

If that is meant to sell the kit I think a lot of people will be confused, heck my 180C is faster than that.

It is probably worth it to take a 290 out to a 390 so yea, I would do it.


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## smokinj (Apr 30, 2012)

nate379 said:


> A sleeper saw would be fun to have though. I'd love to be able to cut near as fast as my brother with a 460 hahaha!
> 
> Hmm... Tim, what's up your your saw? Yeah I dunno man, better trade trade pile of junk in! hehe


 
Only one way to beat a 460..........Its going to take More cc's!


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## nate379 (Apr 30, 2012)

So fit an 880 motor on a 290 your saying? 





smokinj said:


> Only one way to beat a 460..........Its going to take More cc's!


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## smokinj (Apr 30, 2012)

nate379 said:


> So fit an 880 motor on a 290 your saying?




No just more cc's than a 390 has...70+ would be a good starting point. ( Oh and I hope no one brings up a pipe for play 361)  With a sticker saying 460 killer!


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## Thistle (Apr 30, 2012)

nate379 said:


> So fit an 880 motor on a 290 your saying?




 Havent seen that in 20 yrs.


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## wkpoor (May 1, 2012)

I can't vouch for whats going on in that vid but I know Brad personally. He knows his stuff. The BB kits on various saws have been discussed many times. One reason I have never done it is because of just what you saw. Eric Copsey talked about the kits at one of my GTGs and said they rarely improve a saws performance. I would much rather spend the money on a professional port job.


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## MasterMech (May 1, 2012)

I am curious as to what the power output of that aftermarket engine is compared to a genuine MS390.


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## wkpoor (May 1, 2012)

MasterMech said:


> I am curious as to what the power output of that aftermarket engine is compared to a genuine MS390.


Not sure how the mfgs check pto hp on their saws but in the field we just do timed cuts. If the saws cuts slower than it obviously has less power. For this to be relevant  you need to use wood sized for the saw to take advantage of the torque bigger saws have.


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## kettensÃ¤ge (May 1, 2012)

wkpoor said:


> I can't vouch for whats going on in that vid but I know Brad personally. He knows his stuff. The BB kits on various saws have been discussed many times. One reason I have never done it is because of just what you saw. Eric Copsey talked about the kits at one of my GTGs and said they rarely improve a saws performance. I would much rather spend the money on a professional port job.


 


 Not familiar with these "kits" but, if you are increasing displacement isn't a larger carb also required?


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## wkpoor (May 1, 2012)

kettensÃ¤ge said:


> Not familiar with these "kits" but, if you are increasing displacement isn't a larger carb also required?


Maybe, maybe not. Mfgs use same carb on different models and sizes. Just did work on a 5100s and same carb used on it and the one size below.


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## nate379 (May 1, 2012)

I was guessing the kit came with a jet kit for the carb?  I don't imagine there is enough adjustment with just the screws anyhow.


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## zzr7ky (May 1, 2012)

most of the time there is enough adjustment once the anti-tamper cap is defeated.


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## mecreature (May 1, 2012)

from what I have gathered the 290 has plenty of adjustment to put in the BB.


is this the way to go with the 029, sounds like fun.

NWP 49mm Short Block


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## smokinj (May 1, 2012)

mecreature said:


> from what I have gathered the 290 has plenty of adjustment to put in the BB.
> 
> 
> is this the way to go with the 029, sounds like fun.
> ...


 
If you can get done cheap enough. Most back off once there into 290 for 5-6 hundred.


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## mecreature (May 1, 2012)

smokinj said:


> If you can get done cheap enough. Most back off once there into 290 for 5-6 hundred.


 
LOL.. probably so. It would have to be a good used deal or a pretty decent saw to start with.


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## jeff_t (May 1, 2012)

wkpoor said:


> Maybe, maybe not. Mfgs use same carb on different models and sizes. Just did work on a 5100s and same carb used on it and the one size below.



My Dolmar required absolutely no adjustment going from 64 to 79 cc. Guess it was a bit rich from the start, but ran perfectly after the install. I did have to tune it a bit when I put the HD air filter on, but I know a little more now than I did then.


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## MasterMech (May 1, 2012)

nate379 said:


> I was guessing the kit came with a jet kit for the carb? I don't imagine there is enough adjustment with just the screws anyhow.


 
If there wasn't enough carb adjustment the saw wouldn't run for chit.  I'd more interested in power gains from a larger throttle bore (more air).  Usually a carb has the ability to mix more than enough fuel for it's given airflow capacity.

A "jet kit" would only be required if the jet sizes were fixed in the first place, which any carb that has non-adjustable fuel jets is the first thing to get chit-canned on a saw undergoing modifications.


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## nate379 (May 2, 2012)

I have not pulled this carb apart but most small engines have replacable jets.  Sometimes you can't buy different sizes though, all depending.



MasterMech said:


> If there wasn't enough carb adjustment the saw wouldn't run for chit. I'd more interested in power gains from a larger throttle bore (more air). Usually a carb has the ability to mix more than enough fuel for it's given airflow capacity.
> 
> A "jet kit" would only be required if the jet sizes were fixed in the first place, which any carb that has non-adjustable fuel jets is the first thing to get chit-canned on a saw undergoing modifications.


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## MasterMech (May 2, 2012)

nate379 said:


> I have not pulled this carb apart but most small engines have replacable jets. Sometimes you can't buy different sizes though, all depending.


 

I've yet to see that on any chainsaw carbs from the last 30 years.  You'd be correct tho if we were talking about the carbs you find on most mowers/tractors.


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## wkpoor (May 2, 2012)

MasterMech said:


> If there wasn't enough carb adjustment the saw wouldn't run for chit. I'd more interested in power gains from a larger throttle bore (more air). Usually a carb has the ability to mix more than enough fuel for it's given airflow capacity.
> 
> A "jet kit" would only be required if the jet sizes were fixed in the first place, which any carb that has non-adjustable fuel jets is the first thing to get chit-canned on a saw undergoing modifications.


Right on MM. My PP346 has a 357 carb on it. The Zama and most likely the Walbro does have a pressed in main jet but never hear tell of anyone actually changing one. Those carbs are so small and precise not many do anything custom to them. I know of one guy that says the carb gets some work after a port job but he doesn't say exactly what so could be snake oil.


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## MasterMech (May 2, 2012)

wkpoor said:


> Right on MM. My PP346 has a 357 carb on it. The Zama and most likely the Walbro does have a pressed in main jet but never hear tell of anyone actually changing one. Those carbs are so small and precise not many do anything custom to them. I know of one guy that says the carb gets some work after a port job but he doesn't say exactly what so could be snake oil.


 Perhaps the "carb work" is a simple diaphram kit.  Always a good idea if the carb has not had recent attention.


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## greythorn3 (May 2, 2012)

nate379 said:


> I modified the muffler today on my 290 along with a good tuneup and it woke it up pretty good.
> 
> I found on eBay they are selling 47mm bore jugs/pistons for around $100. Stock is a 46mm. I think it works out to me the same jug as a 390 saw, though I dunno if the stroke is the same on the 2 saws?


 
just stop being cheap and buy a real saw.


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## MasterMech (May 3, 2012)

greythorn3 said:


> just stop being cheap and buy a real saw.


 
There, I fixed that for you.


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## oilstinks (May 5, 2012)

i put the NWP big bore on my 460 after burning the piston by the exhaust port (another story ive got a thread somewhere on it). It runs good. Id say more like stock. the exhaust port is pitiful lots of casting marks and imperfections. With 2 strokes thats where power is determined per givin cc all other things being good. I needed the saw so i put it together without cleanin it up. Id like to take it apart now and send it to a respectable port tuner now that i have plenty of saws. For the money as opposed to stock you cant beat it.


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