Intake/Exhaust advise

[Brassneck]

Hey All,

I posted the below summary in my build thread, but don't think it will be seen as much as if I repost in a more appropriate spot, like here.

Note: This is a new build...and I'm new to these bikes...So thanks in advance for any suggestions!

(Repost from my last post on my build thread: http://motorbicycling.com/showthread.php?t=60258) This is a 66/80cc kit.

Been playing with the bike for a few days now...starts up great, idles great...but tuning it is still on the list as it's not perfect.

After about 40 miles on the bike (Still breaking it in), I wanted to check the spark plug. As I suspected, it's is oily/black. I know the mixture is heavy but also likely rich (16:1...moving to a higher rate for next tank). Before I messed with the carb any more (Needle clip at the leanest position) I wanted to play with a few things to see if/what will impact a leaner condition--Specifically with regard to exhaust and air intake.

With regard to air intake, I've run the bike without the stock filter to see how it breathed and it seemed to be a little better in terms of smoother idle and overall running. So I think the breathing of the carb could be better than the stock air filter...Not sure on what works best (More reading to do), but I see them advertised all over...so there seems to be some options there.

Anyone have a recommendation for a better air filter to fit the NT stock carb? I think SBP's has one that looks decent: http://www.sickbikeparts.com/catalo...ducts_id=99&osCsid=kva4ht4srbe2eh30u5lf6l9d87

As to exhaust, I am guessing this has the most impact for leaning out the bike. With the 16:1 ratio, it's pretty much dripping oil from the exhaust cap...so I took it off to clean...and for kicks ran it with the cap off... WAY louder! But also very very peppy! Lots of torque and ZERO 4 stroking! I'm sure this would impact top end speed, but I liked the power.

I think 2 strokes need back pressure, but how much? I think the baffles in there provided enough without the cap and still allow the motor to breath better (my only other 2 stroke was back in college and I didn't know anything about it other than mixing fuel/oil and riding it like an crazed idiot...so I never really played with tuning on one until now). I'd be happy to run it without the cap, but the noise level isn't really appropriate for anyone...so I recapped it and it fell back into it's mild sound and loss of torque , it's not ideal, but I'mm still breaking in the engine...so nothing is of HUGE importance right now. However, I want to figure out a way to open up the exhaust and minimize the sound down the road.

I've read up on a few ideas to drill out the baffles, but for some reason, all the posts on this are a few years older at least and I don't see anyone with the same type of exhaust (internals) as mine. When I unscrew the cap, all that comes out is the little exhaust pipe that's attached to the cap. Everything else (baffles, etc) are welded (I think) inside.

Is there a picture or two of the modern style exhaust internals anywhere?

Some ideas I had:
1) I could drill a hole or two in the little pipe (The one attached to the end cap that comes out when I unscrew the cap) I believe this pipe goes up into the baffles and pulls exhaust from within the baffle chambers.

2) I could cut the little tube off just inside the end cap...so that it no longer requires the gasses to be pulled from within the baffles

3) I could drill a hole in the baffle end-cap...this is the part of the internal baffle that's closest to the ground (Away from engine)...and is visible when the cap is removed and you look down into the exhaust pipe. This cap has a tube welded to it with lots of holes. (Not sure if drilling this cap will do all that much?)

4) I could drill the inner baffle end cap (I imagine this is closest to the engine side and isn't visible without removing the entire baffle assembly.) Maybe a combo of option #2 & 3 might work?

5) I could simply add another hole in the end cap?

Anyone have experience with any or all of these? Which would be the better route to go? (The good thing is these pipes are cheap and messing one up isn't the end of the world...but I'd like to do what's been proven to work as the first steps).

Thanks for the help/advise!

 

[Springfieldscooter]

I would continue with the break-in process.
Put some more miles on it with a heavy mixture like 16 to 1, or 20 to 1.
Don't worry about oil leaks out the exhaust.
Then get a speedometer, and I think youll find, that LOUD does not necessarily equate to FAST.

 

[Brassneck]

I would continue with the break-in process.
Put some more miles on it with a heavy mixture like 16 to 1, or 20 to 1.
Don't worry about oil leaks out the exhaust.
Then get a speedometer, and I think youll find, that LOUD does not necessarily equate to FAST.

Yep...Not doing much to it until it's broken in. Nope...not worried about the oil drippping from exhaust, that's expected.

That being said, It's running rich...and I'm looking for ways to lean it out more. Hence the intake/exhaust questions (for things to do later on). I'm not focused on speed... I simply liked the torque and responsiveness when the exhaust cap was off...and it ran a lot leaner. Coming up with a compromise on sound/responsiveness/torque/leaner condition would be ideal.

If you have advice on the questions I posed, that would be great. Thanks.

 

[maniac57]

Only comment I have is you're using far too much oil.
I break all my chinadolls in at 40:1 from the start. Too much oil leads to poor performance, poor ring seal and overall snotty engine.
Ignore the Chinese "instruction" book. the MOST you should ever run with ANY modern two stroke oil is 32:1
Most call for 40:1 or even 50:1

 

[Brassneck]

Thanks Maniac57,

Yep, I am definitely going to a higher ratio on my next tank.

 

[Kioshk]

Use HALF that oil, set your needle to it's middle-position, and don't ride around without your muffler (it's inconsiderate, and will negatively impact your fuel-economy).

Since you're new to these builds, take some time to understand the basics of the standard kit. I know how tempting it can be to try to search for "performance upgrades", when you're better off learning how to properly tune what you already have. You have an NT-carb? It's PERFECT for these engines, trust me. And leave that filter on; it's there for your engine's protection...you won't gain nearly enough performance benefit as to justify its removal.

So, be patient and break 'er in. There are many degrees of freedom to tuning these kits, and you'll only learn by moderate adjustment. Since you're near sea-level, I'll repeat my recommendation that you return the needle to its middl-setting, reducing the oil by 1/2, and do some plug-chops to check for richness. You may need a different jet-size. I'm on Long Island, and we have a similar atmospheric environment to Seattle. The best performance improvement I've found has been to reduce the jet-size of the off-the-shelf NT. I have a set of pin-drills and some solder to adjust that.

 

[Brassneck]

Thanks Kioshk... much appreciated! My thinking and reason of writing this thread was that before I change out the jet (which is sounds like the best thing to do really) if I could get it to breath better/exhaust a bit more open, that that would potentially help it lean out...hence my questions.

Since by going with a higher oil/fuel ratio, it's actually going to make the bike even more rich... and while that may be ok for where I'm at in the break-in process... I'd like to see if this route would work as well... If nothing else, it's an experiment. Regardless, nothing is going to be changed until I've broken in the motor...

and don't ride around without your muffler (it's inconsiderate, and will negatively impact your fuel-economy).

No worries on that...it was just a test run to see how it responded. The stock muffler is on, and doing it's job.

Since you're new to these builds, take some time to understand the basics of the standard kit. I know how tempting it can be to try to search for "performance upgrades", when you're better off learning how to properly tune what you already have. You have an NT-carb? It's PERFECT for these engines, trust me. And leave that filter on; it's there for your engine's protection...you won't gain nearly enough performance benefit as to justify its removal.

Yep, NT Carb. Note: I only ran with it off to see how it ran down the street and back...I've got a new air filter from SBP...it's on, works great.

Regarding "performance upgrades" I'm actually only looking to lean out the motor...performance upgrade is a relative term and for me, that means simply: running great. Not looking for top speed, etc (I have plenty of other vehicles for that--and I actually don't trust the integrity of the bike to go much faster than 30mph...lol)...I'm more interested in getting it to not 4-stroke and to pull throughout the rev range once it's broken in. From what I've read about 4 stroking (And from what I've seen on the plug), it's running rich despite the 16:1 ratio. I think that a smaller jet would be the next step...since I've got the needle at the leanest setting already.

So, be patient and break 'er in. There are many degrees of freedom to tuning these kits, and you'll only learn by moderate adjustment. Since you're near sea-level, I'll repeat my recommendation that you return the needle to its middl-setting, reducing the oil by 1/2, and do some plug-chops to check for richness. You may need a different jet-size. I'm on Long Island, and we have a similar atmospheric environment to Seattle. The best performance improvement I've found has been to reduce the jet-size of the off-the-shelf NT. I have a set of pin-drills and some solder to adjust that.

Yep, I think you're right on the jet size....and I'll drop the needle to the middle spot when I get the new jets...but I'm thinking of getting a set of various jet sizes vs. drilling, as I don't trust my soldering skills and would hate for it to come loose while running (Soldering electrical connections is one thing, but those joints aren't potentially breaking loose and getting into the piston LOL).

I appreciate your advise!

 

[leo]

i would recommend getting your engine running the way you want it, then gear for your local terrain.
i am in southern wv, lots of hills everywhere. so i went with a 56 tooth rear sprocket, and literally haven't looked back.
my top speed is only around 20-25, but it climbs hills like a freakin' goat. i take it out on the hatfield mccoy trail system all the time.
it still wont climb the super steep black diamond trails. but then again, i don't ride those anyway.
as for police, i took mine down to the police station to ask. it was a huge hit, all the officers were going on about it. they said to ride wherever i wanted (completely legal). and now they all know my bike on sight... being totally up front with it payed off.