Smart carb questions?

[Wheel House Motorsports]

So I got to talking with a buddy about the smart carb and I was curious about a few things. He has a yz250 smoker, and that carb has the TPS and an electronic acel pump built into it.

The smart carb doesn't look like they have any provisions for hooking up either of them? The accel pump may be built in mechanically, i don't know. But without the TPS, would the motor not just go into a "safe" timing map since it has no idea whats going on? I know most motors revert to the lowest timing value in such a situation and that seems like it would make the bike kinda lazy?

Thoughts?

I like the idea of the smart carb, just curious about the application!

 

[dirtrebel]

smarty

after recieving my 38mm billet I did some more research on the yamaha 2 stroke and have not installed it yet, I might make it a snow only accessory. When you unplug the tps the cdi reverts back to 2d ignition mapping, noone is really sure what that looks like or how tame that is, but guys running them claim little difference. It is not a safe mode, just an old school 2d style curve. As far as the electronic power jet the consensus is the smart carb does not need it to work correctly so it makes no difference if you eliminate it. The electronic power jet on the keihen pwk works actually differently than you might think. It is normally open enriching the mixture at all times, when you reach near full throttle it closes leaning the mixture for more "over rev." There is a long thread about it on thumpertalk. Unfortunately it sounds like the carb is not as effective on the yamaha as other bikes. It seems to not fit as well (as a bike the intake boot rubs the spring) and they claim the engine has weak "signal." Maybe that's because it is a piston port engine vs. case reed? I've got my avid carb heat kit coming so I will for sure try it. If not I will make my own pwk heat collar and stick with the stock carb. So I have alot of the same questions as wheelhouse.

 

[mtn-doo]

As dirtrebel explained, the TPS and accel pump are mute. No safe or limp mode. The S.C. is ultra sensitive to signal. You will get what is demanded. They are also a good taddle tale, they are so sensitive, any other "small issue" is revealed in the S.C., Case gaskets leaking, reeds that have never been flipped, etc etc,. The "soft" feel when new is lean. They are super lean and clean for the first few hours. The Rod needs "lapped" by stroking to settle in. Some tech's have accomplished this by rubbing the rod with leather and polishing. That initial polish is accomplished by a couple good hard rides as well. You will then click back lean a few clicks. They are super tight, new. Once settled, you will never touch it.

As far as boot fitting goes, the S.C. is 1/2" longer than the PWK. You simply need to trim 1/2" from the boot to not "Bunch it up", which causes a bulge that will rub against your shock. Just trim 1/2" off your boot and all fits stock.

 

[jskattum606]

Just got mine and tried it last week. Feels like it needs an accel pump. Feels lean when you hit it. Then seems good when you hold it. Smokes more than the stock carb but still feels lean. Has noticeable less power everywhere. Put the stock carb back on and it is much better. Not happy with the smarty for now. Gonna call apt and see what's up. Maybe I'm doing something wrong

Bike is a yz 250 smoker

 

[mtn-doo]

Just got mine and tried it last week. Feels like it needs an accel pump. Feels lean when you hit it. Then seems good when you hold it. Smokes more than the stock carb but still feels lean. Has noticeable less power everywhere. Put the stock carb back on and it is much better. Not happy with the smarty for now. Gonna call apt and see what's up. Maybe I'm doing something wrong

Bike is a yz 250 smoker

What carb are you running? What size and Cast or Billet? Also, how much time do you have on it? Was it just the install and test, or do you have several days of hard use? There is a brake in cycle. They are not a "controlled leak with holes everywhere" like a conventional Carb. They are air tight and need some "lapping" the first few rides for brake in. Then they get rich and you make your final adjustments. I will p.m. you.

 

[Wheel House Motorsports]

the TPS and accel pump are mute. No safe or limp mode. The S.C. is ultra sensitive to signal. You will get what is demanded.

The fueling i figured the carb can handle it, different method to supply demand, not so much concerned about that.

Mainly the ignition mapping. They basically use, TPS, RPM and gear position for timing maps. Well, if you suddenly remove one of those inputs, it cant utilize its full map, and if I know anything about the japs its they love making things bulletproof. So given that I would assume in this case the timing map would revert to the lower range of RPM and gear position so the bike doesn't detonate. Not that its the end of the world, but we all know that a lazy timing curve makes a lazy bike.

 

[jskattum606]

What carb are you running? What size and Cast or Billet? Also, how much time do you have on it? Was it just the install and test, or do you have several days of hard use? There is a brake in cycle. They are not a "controlled leak with holes everywhere" like a conventional Carb. They are air tight and need some "lapping" the first few rides for brake in. Then they get rich and you make your final adjustments. I will p.m. you.

Cast carb. 38MM i believe. Ordered it in january and just got it. Put two very hard tanks of fuel through it. Lots of throttle movement.
We also set out bikes on there side to go check out certain terrain some times and it spews fuel out of the choke punger. Maybe this leak is causing an air leak that needs to be addressed.
Never had a stock carb leak out of this location

 

[dirtrebel]

Cast carb. 38MM i believe. Ordered it in january and just got it. Put two very hard tanks of fuel through it. Lots of throttle movement.
We also set out bikes on there side to go check out certain terrain some times and it spews fuel out of the choke punger. Maybe this leak is causing an air leak that needs to be addressed.
Never had a stock carb leak out of this location

can u take it for a quick rip with the stock carb on and then unplug the tps and ride it again and see if there is a noticeable difference due to ignition mapping? I can try the same thing this afternoon.

 

[Wheel House Motorsports]

can u take it for a quick rip with the stock carb on and then unplug the tps and ride it again and see if there is a noticeable difference due to ignition mapping? I can try the same thing this afternoon.

^^ science. ^^ thats what we need to find out is how much the timing plays into it. and maybe do the same thing with the accel pump.

 

[jskattum606]

can u take it for a quick rip with the stock carb on and then unplug the tps and ride it again and see if there is a noticeable difference due to ignition mapping? I can try the same thing this afternoon.

That's a good idea. I did call apt and they recommend pulling the choke out of the carb and cleaning it. I'll try that too

 

[mtn-doo]

Cast carb. 38MM i believe. Ordered it in january and just got it. Put two very hard tanks of fuel through it. Lots of throttle movement.
We also set out bikes on there side to go check out certain terrain some times and it spews fuel out of the choke punger. Maybe this leak is causing an air leak that needs to be addressed.
Never had a stock carb leak out of this location

No. That should be sealed when the choke is down. If you're leaking there, then you're pulling fuel there as well. There is an O-ring on the bottom of the plunger. Clean the brass plunger and seat. You might also polish the plunger with some fine emery as well. Something held the plunger up and you got a leak. They are air tight and there should be no leaks. The reason I asked Billet or Cast is these minute casting issues. There is a change in the Cast models going to a true "Di-Cast". The tolerances will be the same as the Billet models. Your choke plunger is not sealing. Polish the brass plunger and clean the o-ring on the bottom.

 

[wwillf01]

Just got mine and tried it last week. Feels like it needs an accel pump. Feels lean when you hit it. Then seems good when you hold it. Smokes more than the stock carb but still feels lean. Has noticeable less power everywhere. Put the stock carb back on and it is much better. Not happy with the smarty for now. Gonna call apt and see what's up. Maybe I'm doing something wrong

Bike is a yz 250 smoker

I will second the break in period... On my Lectron I started messing with the rod right off the bat... But after about 7 engine hours everything settle in and I had to readjust the rod back to the original setting.. I would give the engine some time.... On another note I find when my exhaust starts to leak through the gasket and it looses seal that it starts really richening the fuel automatically... So you need to make sure o rings are good ect... Which I am sure you have but sometimes we miss the simple things... This causes my 300 to loose low end and the only time I start dripping oil out of the silencer..


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[mtn-doo]

I will second the break in period... On my Lectron I started messing with the rod right off the bat... But after about 7 engine hours everything settle in and I had to readjust the rod back to the original setting.. I would give the engine some time.... On another note I find when my exhaust starts to leak through the gasket and it looses seal that it starts really richening the fuel automatically... So you need to make sure o rings are good ect... Which I am sure you have but sometimes we miss the simple things... This causes my 300 to loose low end and the only time I start dripping oil out of the silencer..


Excellent point. It is natural and automatic to "blame a carb", we all do it. I have found with this ultra precise, sealed fuel system, ANY little item elsewhere in your bike will show up. It is a great assessment tool. We have had bleep, bleep carb guy's frustrated and find a variety of little issues elsewhere. Once the entire bike system is correct, magically they have perfect tuning. It's interesting to realize we have tuned and jetted our simple carbs over the years compensating for "other factors" and didn't realize it. A simple carb can be tuned and jetted to make a troubled bike "seem" to run good. We were actually masking symptoms of other issues. Really opened my eyes to be meticulous about ALL pieces of the system.

 

[jskattum606]

Went for a long ride this weekend with the stock carb. Rode for the first half of the day with everything stock. Then un pluged the tps wires. HMMMM felt just like the smart carb did. soft on the bottom and about the same on top, just like the SC did. Best way to describe it is it feels like turbo lag.

 

[Wheel House Motorsports]

Went for a long ride this weekend with the stock carb. Rode for the first half of the day with everything stock. Then un pluged the tps wires. HMMMM felt just like the smart carb did. soft on the bottom and about the same on top, just like the SC did. Best way to describe it is it feels like turbo lag.

maybe like it has a flat timing curve since there is no TPS input?? thats strange... lol

doesnt matter how good the SC meters fuel if the timing is in lazy mode because of no TPS.

 

[J&L Snowhawk]

good

this is good info If DR;s yz300 works good im prolly gonna look that direction. Just get older 250 without that type of ecu setup for TPS.
there were some good deals on 250s at haydays!!!

 

[dirtrebel]

ignition without tps

how can we get 3d mapping without the tps?, or forget the 3d and just mhave a better 2d, if ktm can do it so can yamaha. Can u buy a programable cdi or a different cdi that would keep ignition and fueling seperate? I dont think a bunch of old yz's is the answer buddy (jnl haha)!

 

[wwillf01]

Couldn't you just get a vortex cdi?

 

[dirtrebel]

sweet!

Couldn't you just get a vortex cdi?

could be an option, thanks! 535 au dollars! 496.43 usd, and it says it uses stock wiring, so it could still rely on the tps bs, hopefully not.

http://www.vortexcdi.com/model_product.php?product=1&model=47&mp_id=1362

 

[wwillf01]

Yes they are very proud of it... but you are able to set custom maps.. ...