APT 40mm Billet Smart Carb mounted on a 431 Puma. With important mounting notes.

[Pumashine]

Started running the 40mm billet smart carb back in February 2014. The loaner carb had float bowl issues. After resetting the float heights it was not refilling the bowl quick enough. It would like just die at full throttle. Low and behold the tech at APT says it is very touchy setting the float height while still maintaining refill flow rate. The carb was real lean compared to a normal carb on the bottom end. Seemed to breath fresh air into riding in first and second gear. This prompted me into getting a 40mm billet for myself. Put her on and got her started. Seemed to be just a tad to lean so I proceeded to richen the clicker every couple hours fearing I was going to seize her up at WOT. From 1/2 to full throttle there was a stumbling spot. I contacted APT and requested a richer Fuel Metering Rod or FMR.

Received a new 76 FMR a couple weeks later and put it in to replace the leaner 78 FMR. I did not write down how many clicks I had the clicker set at. I was instructed to get the bike started going about 50 to 60 clicks from full rich. Then keep going leaner until the idle started to get angry. Like when your bike is running out of gas. It will rev up for awhile and then come back down a little and repeat. Once the idle gets a little angry you then set it 2-3 clicks richer until you have a perfect idle. Once you get a perfect idle you can then drop the idle speed down to where you like it at.

I was really excited now the FMR was richer and I hope to get the stumbling out of the 1/2 throttle area. Went out for the usual dune ride at Winchester bay. Was great 0 to 1/2 throttle. Was stumbling still at 1/2 throttle. When full throttle was achieved she ran great. I was still not sure what was causing her to stumble. Rode the rest of the day and figured I would ask questions on Monday. Kyle Burns put it this way summarizing where the clicker works.

My understanding is this is alot like a Lecton. But there is no jet.  You slide the FMR up or down to control idle to 1/2 throttle.  1/2 to full throttle I determined by the FMR itself.

So I went 3 clicks richer the next weekend. I get to the dunes and go to start her up and she just won't start. I notice gas dripping out of the header pipe. Had someone pull start me. Had to get pulled around the parking lot but would not start until I let off the throttle completely and just barely fired. It gets going and I go for another dune ride. After coming back and having a beer and refueling I go to start up again. Won't start. So I do the pull start thing again. Same results, like it was flooded. Went for another ride and same scenario. Was making chirping noises under full throttle. Like metal on metal as the train goes by. Would not start again after cooling down in the parking lot. Seemed strange if you stopped out on the dunes for a minute she would start right back up when hot. Loaded her back up and went home.

The next week I took the seat off and double checked the boot was sealing around the intake manifold. It seemed a little loose when I checked it out riding the weekend before and tightened the clamp. My thoughts were maybe it was loose and moved on me. After loosening and trying to move the carb forward I tightened it back up and turned 3 clicks richer, it actually started. Thought maybe it would not start due to extreme lean condition as stated in the manual.

Tried again the next weekend. Again the bike won't start so I got a pull start. Each time coming back for more fuel I just let her idle instead of hitting the kill switch. Just turned the idle up a bit. I had noticed after setting my idle at home I had to turn it up after getting to the dunes the last couple weekends. I went and gave her 3 clicks richer and was going to go do a plug check. As I got to 1/2 throttle just to about 3/4 open the piston froze up. SOB, did I go 3 clicks the wrong way? I got off the bike and started pushing her back to the parking lot. A guy rides up and asks me if I am out of gas. I look at him and say "I Wish" As I was sitting there waiting I kicked and the piston broke loose. Zero compression.

I'm like :wtf?:

APT says if the carb is hitting the frame it vibrates the carb not allowing it to atomize the fuel correctly. This week Kyle or Ryan was saying this creates a lean condition. So I went and took pics to show no frame touching.





Measuring from the carb to the intake is 3/4" in this pic
I then removed the boot and set it back to 3/4"



Now you can see the carb is touching the intake on the far side. This indicates to me that the carb touching the motor may do the same thing as the carb touching the frame. Even though no one mentioned this as a possibility. Heres a better pic so you can see how hard it is touching. The black sharpie line is where the boot was on the intake. It was up tight against the carb.



The plug is tan at piston freeze. I took this pic as I was taking the cylinder off.



So the whole time starting February until now (November) the carb has been experiencing the lean condition intermittently? (every 5 minutes)  I am guessing. Seems the aluminum has been eaten away on the exhaust side of the piston.

[Jerry Hall]

Make sure you do a plug chop with the smart carb. Burns had to make the change to the metering rod. Mine just fried the piston. You don't want to be too lean breaking in the 363

What type of riding were you doing the last 15 seconds or so before the piston failure?  Show us the top and all sides of the piston.

[Pumashine]

What type of riding were you doing the last 15 seconds or so before the piston failure?  Show us the top and all sides of the piston.

Straight line from the parking lot to the flats for a plug chop. What does it look like happened or is happening?

[rsss396]

Take it or leave it but this comes from someone that knows a little about vibration owning a cr500 in a quad chassis haha. try running a drop or 2 of silicone per gallon in your gas/oil mix
The oil industry uses silicone to stop foaming so this is not just some crazy idea you read on the internet. still not convinced? take a clear pickle jar and put your oil/gas mix in it and shake it very hard, then add some silicone from armor all or a tire dressing that uses silicone. now shake it just like you did the first time, in my testing i had less bubbles with silicone than without.
yeah yeah you will have someone tell you the silicone is going to foul your plugs blah blah blah, listen to someone that runs it in every tank full if you want to help with foaming.

[Pumashine]

Take it or leave it but this comes from someone that knows a little about vibration owning a cr500 in a quad chassis haha. try running a drop or 2 of silicone per gallon in your gas/oil mix
The oil industry uses silicone to stop foaming so this is not just some crazy idea you read on the internet.  listen to someone that runs it in every tank full if you want to help with foaming.

I did not know there was a term for it. I was gonna take a pie shape piece out of the cr500 intake manifold so the carb was not touching. Will this help to stop foaming or is it the nature of the beast?

[Jerry Hall]

The piston shows severe detonation.  An engine that experiencing that much detonation was announcing very loudly that it was experiencing detonation and it was going to make you walk home if you do not do something to stop the detonation.  If you do not know what detonation sounds like, try to remember the noise the engine made especially the last 15 seconds or so of its life.  Detonation usually sounds like large rocks hitting the engine cases or skid plate.  I have never heard detonation create a chirping noise.  Many times an engine will emit a chirping noise from the muffler when the ignition timing is severely retarded or the air fuel ratio is so lean it is causing a lean miss-fire.

When the onset of detonation begins or has lite detonation, it may make the knocking noise every second or so and will increase it's frequency to occurring almost every engine revolution if the conditions causing the detonation is not eliminated.  Most detonation on a problematic engine is predictable in the sense it can be initiated by letting the engine reach a particular engine temp. a particular RPM and or throttle position to re-create the detonation so the source can be determined.  

If the engine experiences detonation at the same RPM regardless of the throttle position it may be a foaming the fuel due to vibration like Dave mentioned.  If the engine experiences detonation at a particular RPM and throttle position it is probably carburetor mixture related.  On conventional carburetors the correct circuit can be enriched or leaned once you know the throttle position the problem occurs.  I do not know how many different needles Smart Carb makes and if their needles can change the mixture in one throttle position without affecting the mixture on either side of that particular throttle position.  When I worked with the Edmonds on the Lectron in the Late 1970s we could not make these throttle position specific adjustments to get precise fuel metering at one throttle position without affecting it on either side of that throttle position even with all of the custom needs they made for our works bikes.  

The carburetor touching the engine or chassis will often cause the fuel in the float bowl to turn to foam at a particular RPM and the mixture will go very lean when this condition exists.  I also noticed you have a Boysen Rad Valve.  I have had a lot of problems on the Dyno with the fuel foaming on engines that have the Rad Valve.  Most of the time it foams the fuel over a very narrow RPM range and does not cause a problem in the real world unless you stay in problematic RPM range for more than a second or two.  The Rad Valves typically flow air real well and make good power but their design eliminated the necessary vibration isolation that the stock rubber manifolds provide.  Many old rubber manifolds when they get hardened will also cause carburetor vibration issues.
 
There are two different types of foaming of liquids that I am aware of.  One type, the foam builds on the surface and liquid is still under the layer of foam.  The other type is when the fuel in the float bowl is foam from the top to the bottom of the float bowl and is usually caused from cavitation.  I am not sure if changing the surface tension of the liquid by adding silicone will prevent foaming due to cavitation.  

My experience with foaming due to cavitation on the dyno, causes the floats to sink to the bottom of the float bowl and opens float valve and causes fuel to run out of the vent lines while the engine goes severely lean because the main jet is sucking foam.  It is not possible to observe if this phenomena is occurring with the Smart Carb because of its lack of vent lines.

I will continue with the evaluation when I have more time.

[rsss396]

Tony have you tried the rubber UPP cr500 boot? If you don't like Vforce reed try a stock cr500'cage with the UPP boot

calvin told me the a Kart guy with a liger running the short mikuni 2 bolt rubber intake was losing 2 horsepower from vibrations transferring to the carb. I believe he fiquired that out by holding the carb with his hand To dampen the vibes. I believe calvin was working with UPP to build them a straight boot like the caracal but less downward angle I believe.

[Pumashine]

Tony have you tried the rubber UPP cr500 boot?

I am a rad valve guy from the beginning. I am not opposed to the other systems but have never had a need to. I am switching to V-force on the mini-tooth. This is all new to me and have not considered anything other than dealing with the current problem. I am thankful for all the advice. We are building an intake for the mini-tooth as the UPP boot is way extremely to large for the 40mm. For now I was just going to alter the carb to intake contact and use the armor all as you suggested.

[udontknowme]

if you were using a unmodified boyesen intake boot, theres no way the carb can touch the reed block because theres rubber spacer inside the boot that wont allow it to happen

[Jerry Hall]

if you were using a unmodified boyesen intake boot, theres no way the carb can touch the reed block because theres rubber spacer inside the boot that wont allow it to happen

Even with a an unmodified Boysen rubber connector, there are sometimes problems with the vibrations reaching the carburetor.  I believe that the 5mm or so of rubber spacer used between the reed and carb on the majority of the Boysen boots are too short and not flexible enough to keep the vibrations of the engine from getting to the carb.  Oem rubber manifolds often have over an inch of rubber between the carb and reed to help damp the vibrations.

[rsss396]

Tony here is a couple options for the mini tooth, the first one uses a cr500 manifold, the second is a cr250 manifold using the plates you made for me.
The first picture using the cr500 manifold does not show your plate but it was setup to use it also for a better seal to the reed cage.
this setup is using the arctic cat m1000 reed cage along with a removable reed stuffer only found in the 500's.  Everything gets port matched from the carb outlet to the stuffer.






Cr500 cleaned up to look good




Cr250 manifold

[Pumashine]

I believe that the 5mm or so of rubber spacer used between the reed and carb on the majority of the Boysen boots are too short and not flexible enough to keep the vibrations of the engine from getting to the carb.  Oem rubber manifolds often have over an inch of rubber between the carb and reed to help damp the vibrations.

OK I get. Thank you Jerry for your insights. Even if there is a gap it really needs to be an inch or so long or foaming will occur. Thanks Dave for the pics. I will have to do some homework and find out which Cr 500 intake will work with the 40mm SC. I recall having a heck of a time fitting the 39mm carb into the stock pilot boot.

[rsss396]

The cr500 only uses a 38 carb so any of them will work, the later years are the only ones available

[rsss396]

both those intake were setup for a 44 lectron carb ( with the outlet turned down some )

[udontknowme]

Even with a an unmodified Boysen rubber connector, there are sometimes problems with the vibrations reaching the carburetor.  I believe that the 5mm or so of rubber spacer used between the reed and carb on the majority of the Boysen boots are too short and not flexible enough to keep the vibrations of the engine from getting to the carb.  Oem rubber manifolds often have over an inch of rubber between the carb and reed to help damp the vibrations.

definatly the oem inlet boot isolates the carb in more rubber than the boyesen boot.  but why is the smartcarb not doing well with vibration, if indeed vibration is the culprit to the seizure ?  ive used radvalves in the past with keihins and dont ever recall any tuning problems from vibration transfering from the engine to carb