Update from Power Apt on cast smart carbs

[Pumashine]

Thay things a beauty Clark!

We got 2 more members to try it out this weekend. OJ and Pat want to know what a smart carb does!!! Ride report coming Sunday

[christph]

Wow, looks sweet.  Is there a reason you went with the billet version?  I just called APT and the guy on the phone tried to sell me on the billet version.  He said the tolerances are tighter (which means better performance?) and it is more serviceable.  I was thinking about getting the cast version because $700 bucks is a little steep for a carb, but if it works better I might be able to convince myself to pony up the extra money.  I certainly think the billet looks better than the gray cast version.

It looks like a tight fit.  Any fitment problems?

[Fire1]

Glad you got it fired up Puma mine is still performing great couldn't be more pleased !

[Pumashine]

It looks like a tight fit.  Any fitment problems?

The manual shows it is 3/4" longer than the stock carb. Yes, it is tight. The flanges between carb and intake about touch. Its hard to make the corner. This is a 431cc motor. You need at least a 38mm just to make it run. The 40mm has not been cast yet. So you have to pay if you need the bigger carb. The 38 cast should work fine for motors up to 363cc

[rablack21]

The funny thing is they said that the cast versions would also be 3/4" longer from flange to flange than a keihin carb, but mine measured the exact same as my keihin 38 A/S did.

[rk88r]

Cool Ryan Apt's spec sheet says the cast ones are the same length as pwk.

[Pumashine]

Cool Ryan Apt's spec sheet says the cast ones are the same length as pwk.

The lil ribbed intake manifold boot does not want to be sqaure to each flange. Kinda has to make the corner. Next time I will use the smooth radiator hose type boot.

[Pumashine]

Tried running the smart carb yesterday. It needed the mid-range richened up. Very snappy off throttle but would act like its running out of gas. I went to take off and go for a plug check and the motor about died until I let of the throttle. This happened a few times while testing. Went back to the parking lot and richen it up. Did like 4 clicks to rich. Tried again and only seemed a little bit better. Went back to do a few more clicks and the retainer clip came off. I had forgot where the Allen wrenches were and decided to pack it up. There was alot of snappy bottom end which the Kiehien just never had. Today I pull it apart and put it back together wrong and the adjuster would not click. I am not sure I got the adjuster to work yesterday. So I decided the use a screwdriver to see where this was set. I read here they set them at 50 clicks from rich. I turned the adjustment 94 clicks until it got real hard to turn. So were talking it was set 44 clicks to the lean side. No wonder it was not working correctly. I think I will set it 60 clicks from rich and start, there. I think I saw where Jasons cr500 was supposed to be set 72 clicks from rich. Since this is a 431 I am thinking this is a little safer than the 94 clicks it was at. Any idea's?

[christph]

Do they offer different needles or metering rods for different applications, or do they all use the same rod and it is just a matter of adjusting the knob on top?

[Pumashine]

Do they offer different needles or metering rods for different applications, or do they all use the same rod and it is just a matter of adjusting the knob on top?

They give you a top end metering rod for your application. The mid-range is worked by a thumb screw adjuster on the top of the carb and the idle circuit is a thumb screw on the side. There are only 3 adjustments overall. A different metering rod has to be ordered separate for a different application.

[rablack21]

Tony,

Just a little background info for you. I believe that most of the carbs they set up to be 50-58 clicks from full rich, atleast I know for sure they do on the 250-350cc engines. I think the problem that you are running into is that you are running that carb on a 431cc and it was set up for a 363cc. The needle affects just above midrange through full throttle. The click adjuster only affects off idle up to mid throttle with some bleed over. I bet that APT recommends a different needle for your size engine that would work alot better. I bet this is where your problem lies.

[Hawaiiysr]

where you guys at with this? i just picked up a 38mm cast.

[Jerry Hall]

                                          Survey


I would also like an update on those that bought smart carbs back in 2015 or earlier. 

Were you able to tune them to your satisfaction?

Were you able to tune them to run more reliable, better fuel mileage, fewer seized  or holed pistons than a Keihin or Mikuni carb?

Are you still running them?

If you had it to do over, would you buy another Smart Carb? ...............and why.

[jcs003]

Smart carb is junk!

[rk88r]

I have  been pleased with my 40mm billet.  It's  definitely less temperature and altitude sensitive than pwk.