APT Smart Carb

[eskimojoe77]

I know that the snow has melted in most places, but I'm trying to get a jump on next season with a new bike. I'm doing my own Cr500 engine into a 2007 CRF250R chassis. Anyhow I am wanting to run a APT smart carb and am trying to balance price and performance when it comes to either a billet 40mm ($775) or a cast 38mm ($375). Has anyone run the 38mm on a CR500? Does flow well enough on the top end? I don't want to be a tight wad, but I don't want to choke off the bike either. It's currently a stock engine, but will someday get mild mods: porting, reeds, rekluse, etc. Thanks for any help.

 

[summitboy]

You won't need the 40mm for a stock motor or a ported motor. I have Adam Millars TWIRP porting and Corey at APT told me to stick with the 38mm. I just heard they are out of 38mm for now and are substituting 40mm. You prob will lose a little bottom end with the 40mm. Best to talk to Corey and tell him what you are after.

 

[mtn-doo]

Yes. Corey will be your best advise. He will set you up. The 38 will be great for low and mid range benefits. You need to consider your altitude as well. If you are riding high elevations, the 40 will give you more overall HP, and top end.

 

[thejean]

Well that sucks. I was about to order a cast unit. Looks like I'll be waiting till fall.

 

[summitboy]

Yup. They are way oversold as well. I heard they may stop the cast pre orders until they catch up. Sweet carb though

 

[CATSLEDMAN1]

going with the flow

different carbs on two strokes rarely mean more hp, just better throttle response if they work well, doubt you will be giving anything away with a flat slide 38 on a mildly wooped 500 single.

 

[CATSLEDMAN1]

going with the flow

different carbs on two strokes rarely mean more hp, just better throttle response if they work well, doubt you will be giving anything away with a flat slide 38 on a mildly wooped 500 single.

 

[Ausm7499]

different carbs on two strokes rarely mean more hp, just better throttle response if they work well, doubt you will be giving anything away with a flat slide 38 on a mildly wooped 500 single.

The major appeal of the smart carb is it's ability to maintain an optimal jetting regardless of altitude or air density without making any changes to the carb. I don't know about anybody else but I use the same jetting in my CR500 all season whether I am at 4k or 8k in elevation or the temp is 0 to 50 so I know I am leaving a lot of performance on the table under most of my riding conditions. The smart carb also doesn't have any vent hoses to spill fuel out of or freeze up and it provides better atomization of the fuel so yes they make more power. Everything stated is only what I have read but there are a lot of reviews confirming those statements and hopefully they get their casting figured out so I will be running one this coming season.

 

[summitboy]

Depending on the bike of course, better fuel mileage, better bottom and top end, alt and temp compensation, for snowbikes intake/filter ice doesnt change the way the bike runs unlike fuel injection and stock carb. All great bonuses for APT.

Plus it looks cool LOL ! APT also has some of the greatest customer service/technical help i have ever seen for a product.

 

[summitboy]

Well I finally changed out my stock 80 needle for a 76 (richer needle)on my CR 500. I initially started at 76 clicks. I was at 20C, 55% humidity, 3600 feet. It was way too rich. I ended up at 101 clicks out (max lean is 125) and it runs sweet ! No burbles, instant throttle response and idles better than my KTM 300 LOL. This carb will be the best snowbike carb going bar none. I will be purchasing a cast 36mm for my 300 once they are on the market.

Corey from ATP has been awesome knowledge wise and is a true asset to ATP !

 

[mtn-doo]

Well I finally changed out my stock 80 needle for a 76 (richer needle)on my CR 500. I initially started at 76 clicks. I was at 20C, 55% humidity, 3600 feet. It was way too rich. I ended up at 101 clicks out (max lean is 125) and it runs sweet ! No burbles, instant throttle response and idles better than my KTM 300 LOL. This carb will be the best snowbike carb going bar none. I will be purchasing a cast 36mm for my 300 once they are on the market.

Corey from ATP has been awesome knowledge wise and is a true asset to ATP !

Yes, Isn't Corey awesome! Super sharp guy and will get you dialed in. They are a #1 operation. Their technology is amazing. 5 stars to APT. Thanks guys

 

[thejean]

I will be purchasing a cast 36mm for my 300 once they are on the market.

I pre-ordered one for my 300.

 

[summitboy]

Been on the sand for 2 weeks. Bike runs flawless. Had a few other issues with engine mount bolts etc. Plug is brown and burning perfect. Its a monster on Choke Cherry and Devils !

Picked up the minty LT kit while i was here. Looks good.

Smarty carb is the bomb ! Im at 95 clicks here at 4900ft. Once the cast versions are prefected i will own a couple more im sure.

My only complaint is the adjuster is a pile of junk. I think i have nerve damage in my thimb from adjusting it LOL. They have a redesign in the works so Corey has told me. I hope it works.

 

[carbondaddy]

Summiyboy, I would like some info on the smartcarb. Are they available now? What size should I get for my ported, 520cc Honda? Any set up details you can pass along? Do you have any contact info? Thanx in advance, bud.
CD

 

[summitboy]

Hey CD,

APT is about to release the cast versions this month. You have to get on a list to get one i think. They are 375US. The billet versions which may still be available are like 650ish i think. Adam just got another billet for pulse testing.

They are the same more or less. I believe the cast will make a little more power. The cast also has no vent lines on the outside of the carb. It doesnt matter what mods you have, the carb has a good signal and supplies the engine with the right fuel.

You could use either a 38mm or a 40mm. The 38mm will have more bottom with a nice over rev the 40 a little more top but both will be similar. I think they call for the 38 for the 500. My motor is TWIRP ported and makes some great power. It runs flawless, better than my KTM 300.

I have the specs to drill for the heater or you can get them to do it before it leaves the factory. You may have to mod the top adjuster for the stock CR throttle cable though. No biggy.

I did run a richer needle than the stock which is a 80. I went to a 76 as per Adam Miller. It had a little lean spot at the 3/4 range which this solved. I believe MtnDoo ran a 80 in his 40mm and noticed the same thing.

I use choke to start. Some do some don't. Not sure if its a elevation thing or not. My carb ran superb in the sand down in Idaho. I was impressed. I had a few other issues with the bike but have since fixed. Damn aftermarket subframe LOL

You can tell when its not in the zone when initially adjusted. It almost seems like 5 clicks either side of optimum is good or you get a little bog. Once its set thats it. I do know the new carbs have the newer updated adjuster. Mine does not. Thats my only complaint. The old adjuster sucks ! Hard to feel the clicks and hard to turn. Better to use a screwdriver. Like i said the new carbs will be better so they say.

If you need anything let me know !

C