Big Bore kit worth it?

[kettensäge]

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?

 

[wkpoor]

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.

 

[nate379]

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.

 

[zzr7ky]

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

 

[mecreature]

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

 

[smokinj]

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

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

 

[mecreature]

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.

 

[jeff_t]

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.

 

[MasterMech]

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.

 

[nate379]

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

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.

 

[MasterMech]

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.

 

[wkpoor]

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.

 

[MasterMech]

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.

 

[greythorn3]

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.

 

[MasterMech]

just stop being cheap and buy a real saw.

There, I fixed that for you.

 

[oilstinks]

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.