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

[udontknowme]

nice to see you joined up  :redbull:

ill bet its a difficult business to be in. surely your aware that alot, maybe most, of your carbs are going to customers with near zero mechanical ability, or so it seems. this leaves the door open for a ton of backlash from customers that cant tune a simple lawnmower let alone a high performance 2stroke. i certainly dont have the patience you do to deal with that stuff. so my hats off to you for having nerves of titanium  :congratulatory:

perhaps the squeeky wheel stories stand out in my mind more than the sucess stories for some reason. like you say though, maybe very few of the good experiences get told on the forums . but when i think of smart carb i just remember the not so good experiences ive heard about. like the guy whos tipover balls ( i think that was the problem if i recall) got stuck and floaded his crank case, and i believe blew his reeds out. then some how the engine caught fire. not to find humor in someone elses misfortune but the story was kinda funny

 maybe someday ill get the chance to ride a bike with a welll tuned smartcarb and i can get a first hand glimpse what its all about

[SmartCarb]

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.


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.

pumashine, I have replied to this twice but doesn't come up on the main forum and others are asking about it. Perhaps it was all the pictures, so I've removed them in this reply. I'm not sure how you were able to see it and others were not so I'll post again.

 It's clear from your pictures, especially the color/condition of the spark plug that the mixtures were pretty close to optimum, (light tan, mocha) and did not cause the localized overheating and ultimate seizure of your piston. I believe the evidence suggests that the front spigot of the carburetor touching the intake manifold was enough to shake the snot out of the carburetor and aerate the fuel to cause a critical lean condition in the mid to top. As I suggested in the two earlier posts and in your PM last night that after you rebuild your engine and clearance the intake manifold I would suggest you inspect the fuel inlet needle and seat for damage and replace if necessary. I further suggest that this was also the cause of the intermittant flooding and hard starting issues you had prior to the seizure and the float needle/seat wasn't doing well with all the shaking. I apologize to everyone here if you were not able to see this reply as it was my first post and the idea was to come on here to offer suggestions and advice. I thought this post was under review by moderators before other posts otherwise I would have waited to address other questions/concerns. Chris thank you for letting me know you were not able to see the post. Corey

[SmartCarb]

ll

Testing, testing, testing, testing and using the process of elimination can only answer this question.  A fully instrumented bike with data loggers while testing riding in the real world, is the only way I have been able to solve these types of problems when doing consulting for engine manufactures.

 Sometimes all that needs to be done is change the riding style (the throttle position and RPM) to that for which the engine was designed. Two stroke engines that have been developed to medium to high levels of power output should not be used for just cruising around because of detonation related issues due to poor scavenging.  This is the main reason manufactures pulled the plug on large two stroke street bikes.  It was not because of emissions like most of the world believes.

I believe you mean light load misfiring and not detonation. The typical "four stroking" you hear with a high performance two stroke at light loads is caused by the engines inability to adequately clean (scavenge) the cylinder of the previous exhaust residuals and the engine has to pump the cylinder clean until a charge of adequate density is able to fire off. And this is most definitely a major contributor to high hydrocarbon emissions released from modern two strokes. What is interesting is that the very fine atomization of the SC dramatically dimiinshes this light load misfiring as the extra surface area of the finely atomized fuel will light off more easily.  This also correlates to large reductions in emissions and big gains in fuel economy.

[rablack21]

Corey, aka SmartCarb, thanks for taking the time to come on the forum and offer help and explanations. This forum is all about helping one another and the sharing of helpful information, especially when it comes to something that we all love and enjoy so much, 250R's. I know that you are really busy with dyno testing and other activities right now, but if you get the chance, I would love for you to start a new thread where you could speak about the differences between the SmartCarb design and the older Lectron design just from a perspective of why they are different and not necessarily mentioning why one is better than the other. For example, when we spoke on the phone, you mentioned how the Lectron relies heavily on various compound tapers of the needle to change the supply of the fuel where as the SmartCarb is designed with a different shape throat to rely more heavily on the signal of the engine and not on various compound tapers of needles. This being the reason that 90% of the SmartCarbs on the market have the same taper needle. We also talked about how the pressurized fuel bowl acts like a powerjet already. And how a richer fuel metering rod (FMR) is really used more for diminished signal at WOT. Could you elaborate on these things?

[Tbone07]

This is a great thread. Very informative

[Pumashine]

pumashine, I have replied to this twice but doesn't come up on the main forum and others are asking about it.  Corey

I apologize Corey as I did not see the post was moderated last night. I just now approved the first post but will leave the second out. I am a moderator on this forum so I see what others do not. Thank you for coming to the forum to answer the question of what my problem is and explain how the carb functions.  I have spoke to Tom and he helps out as you are busy. I ran Doug Patterson's 40mm billet for a few rides on the dunes. The carb was flooding when I got it and set the float height. But I guess it also effected the refill rate at the same time as it was running out of fuel in about 5 seconds at full throttle. Back then I was experiencing a lean misfire at about 1/2 throttle or more. I have run the carb from lean to rich a good 20 clicks either side of the factory setting. After putting in the richer FMR I was still experiencing the lean misfire right before full throttle. It would then clear up just as it did with the factory FMR at 3/4 to full throttle. As I learned Kyle Burns was having a hard time getting rich on the top end then he mentioned the carb was hitting the frame. By this time it was too late. I had been running a good 20 hours of time with the carb hitting the motor. Got a new piston coming Friday and my new Intake manifold will be in next week. I will take the carb apart and inspect it. Proly just put the second new one in to make sure as it has the factory FMR I believe.

[SmartCarb]

Corey, aka SmartCarb, thanks for taking the time to come on the forum and offer help and explanations. This forum is all about helping one another and the sharing of helpful information, especially when it comes to something that we all love and enjoy so much, 250R's. I know that you are really busy with dyno testing and other activities right now, but if you get the chance, I would love for you to start a new thread where you could speak about the differences between the SmartCarb design and the older Lectron design just from a perspective of why they are different and not necessarily mentioning why one is better than the other. For example, when we spoke on the phone, you mentioned how the Lectron relies heavily on various compound tapers of the needle to change the supply of the fuel where as the SmartCarb is designed with a different shape throat to rely more heavily on the signal of the engine and not on various compound tapers of needles. This being the reason that 90% of the SmartCarbs on the market have the same taper needle. We also talked about how the pressurized fuel bowl acts like a powerjet already. And how a richer fuel metering rod (FMR) is really used more for diminished signal at WOT. Could you elaborate on these things?

The Lectron and the SmartCarb are each a very fine example stemming from the original Edmonston designed single circuit flat slide carburetor. The distinctions however between the Lectron and the SmartCarb span nearly 45 years of development with no less than five other varieties in between. These less known iterations include the EI Blue Magnum, the Daytona Quicksilver I and Quicksilver II's, Edelbrock Quicksilver, AFT and finally theSmartCarb.

William H. "Red" Edmonston and I were partners at the time of his passing and most of the development work for the SmartCarb took place at the University of Wyoming in our 2 stroke research and development laboratories. Red clearly understood the limitations of a single circuit system and the fundamental flaw imposed by a more or less round throat venturi. The trough or valley at the bottom of an Edmonston designed venturi was quite well understood by this time and it can be found on a Lectron. It is this feature that led to what was really the beginning of our understanding the importance of concentrating and accelerating as much of the actual airflow through the venturi, right at the base of the metering rod and nozzle interface as possible, at all throttle positions. In a more or less round venturi, the rate of throttle opening from idle to half open is exponentially divergent, meaning it’s getting much larger, faster, the farther you open it. From half to wide open, however, the lines of the circle are converging and the rate of opening is slowing even though you are now almost wide open. This causes the pressures through the venturi to swing wildly as you move the throttle slide bottom to top and vice versa, which in turn causes the signal to the metering rod to fluctuate, and unless corrections are made by altering the angle of the metering rod crisp throttling and consistent fueling suffers.

(Signal referred to here is the negative value created by the piston displacing air as the engine cycles, creating a pressure drop within the venturi as air rushes in, thus allowing atmosphere to push fuel up through the nozzle, past the surface of the metering rod and into the intake airstream. In the case of a metering rod carburetor this signal is also read by the flat of the metering rod which creates another secondary low pressure zone.)

The difficulty of putting very accurate changes in angle along a 1/8” surface of a metering rod is maddening and is Lectron’s biggest challenge. This is one reason Lectrons are most noted as a drag racing carburetor and was a place they were found to work really well. Today I do believe they have made tremendous progress in metering rod development and the addition of a power-jet has made their job a little easier. IF all the angles are correct, for the right engine, and the PJ is set correctly they work really well through the whole range much better than a conventional carburetor.

Red felt the better solution was to shape the venturi as such that we could maintain an even pressure against the metering rod through the whole range of throttling. The question was how to do that without giving up a lot of flow and limit the carb’s full potential size for size. He understood laminar flow very well and we did a lot of experimenting with lead in curves to control airflow and get the carburetor to gulp a lot of air, even though the neck of the venturi was unconventionally restrictive. We also added a nose to the slide to further direct and compress airflow leading into the metering rod. What really tipped the scales technology wise though is the ambient air density correction circuit and how it interrelates to the venturi. Most people understand this to be the altitude correction circuit, which it is, but it is really much more. It provides an instantaneous dynamic balance between the pressures the throat of the carburetor is actually seeing and the ambient air pressure against the top of the fuel in the float bowl in all conditions. Perhaps a more familiar term people recognize for this effect is Manifold Absolute Pressure and is something that all modern closed loop EFI systems rely on for correcting air/fuel ratios with changes in ambient air density. Apart from the venturi shape this feature alone is what allows the SmartCarb to only need a single angle grind metering rod, and in most cases a common grind across a very large variety of products and applications.   This circuit also acts much like a power jet at the very top end when the static pressure being applied to the fuel in the float bowl also becomes dynamic and liquid flow lift ensues, hammering fuel up the nozzle directly proportional to total flow through the venturi. This is actually much superior to a power jet in that it remains finely atomized, because it is after all still using the main (and only) circuit, whereas a power-jet is literally throwing fuel on the fire and is emitted as almost pure liquid when it enters high into the air stream. This isn’t the worst thing, however it does dramatically affect Lectron’s full potential for fuel economy gains, altitude compensation and emissions reductions and it effectively makes it yet another multi circuit carburetor.

The drawback to the SmartCarb air density correction circuit is lack of a float bowl overflow and the necessity of tip over valves, along with the additional problems they create. The performance benefits the system offers are more than worth the effort though and the tip over valves, along with additional functionality to further protect our patents for the scoop and venting system, offer a very desirable side benefit in that now the carburetori s completely sealed. Certification testing shows the SC to be the lowest evaporative emissions carburetors ever test. Plus there is no raw fuel spillage on the ground and it fits very conveniently into the new epa tip over ruling for motorcycles. Who’d of known they were about to implement that? We are continuing to improve the system and are implementing changes to eliminate sticking issues.

With all of that said, I have just one more thing. Make no mistake, Lectron is not our competition. Our competition is all modern fuel systems worldwide, electronic or mechanical. Here’s why; any emissions reduction strategy requires a fuel system that is able to two things very well. Finely atomize fuel and maintain extremely accurate air/fuel ratios. TheSmartCarb simply does those two things better than anything else we currently know of period, and it does it without electronics. For instance we are in the second leg of EPA Tier II and ARB on road emissions certification for Zaeta’s TM powered 530 DT motorcycle (google it). This is TM’s open enduro race 4t engine they have attempted to prior certify in North America themselves. They have tried twice , both times using two precious metal catalysts and a race TMXX Mikuni downdraft, both times unsuccessful. APT is actually touching on Euro III numbers with this bike and is passing EPA and ARB easily with just our new 40mm side pull FCR replacement carburetor and no cats. In fact we are under Tier II CO emissions by nearly 90% and HC and Nox 38% and 16% respectively all this with a 28% gain in fuel economy. This is no joke and these aren’t the types of things you are hearing about in the forums and possibly in a lot of people’s minds on a performance related forum  this may not seem like a big deal at all. But actually it is everything.

[SmartCarb]

I apologize Corey as I did not see the post was moderated last night. I just now approved the first post but will leave the second out. I am a moderator on this forum so I see what others do not. Thank you for coming to the forum to answer the question of what my problem is and explain how the carb functions.  I have spoke to Tom and he helps out as you are busy. I ran Doug Patterson's 40mm billet for a few rides on the dunes. The carb was flooding when I got it and set the float height. But I guess it also effected the refill rate at the same time as it was running out of fuel in about 5 seconds at full throttle. Back then I was experiencing a lean misfire at about 1/2 throttle or more. I have run the carb from lean to rich a good 20 clicks either side of the factory setting. After putting in the richer FMR I was still experiencing the lean misfire right before full throttle. It would then clear up just as it did with the factory FMR at 3/4 to full throttle. As I learned Kyle Burns was having a hard time getting rich on the top end then he mentioned the carb was hitting the frame. By this time it was too late. I had been running a good 20 hours of time with the carb hitting the motor. Got a new piston coming Friday and my new Intake manifold will be in next week. I will take the carb apart and inspect it. Proly just put the second new one in to make sure as it has the factory FMR I believe.

Your problem could have easily been overlooked by anybody. Glad we have things beginning to narrow down and once you get things back up and running I'm certain you will be very pleased with the results. I do believe the factory metering rod should be correct for the application, however the richer MR would offer an additional buffer for when you break it in or if you get wild with the rebuild and change some things in the mean time.

[Hawaiiysr]

Longest technical post ever. Thank you. Welcome to 250R.Org
We are a passionate two stroke enthusiast group here to exchange knowledge. I hope you will make your presences known often.

[SmartCarb]

Longest technical post ever. Thank you. Welcome to 250R.Org
We are a passionate two stroke enthusiast group here to exchange knowledge. I hope you will make your presences known often.

:redbull:

[Jerry Hall]

I believe you mean light load misfiring and not detonation. The typical "four stroking" you hear with a high performance two stroke at light loads is caused by the engines inability to adequately clean (scavenge) the cylinder of the previous exhaust residuals and the engine has to pump the cylinder clean until a charge of adequate density is able to fire off. And this is most definitely a major contributor to high hydrocarbon emissions released from modern two strokes. What is interesting is that the very fine atomization of the SC dramatically dimiinshes this light load misfiring as the extra surface area of the finely atomized fuel will light off more easily.  This also correlates to large reductions in emissions and big gains in fuel economy.

I was not referring to four stroking (miss-fire) at light loads (small throttle openings) when the RPM is low and the engine is off the pipe    I was referring to the detonation that is inherent with highly developed two-strokes when the RPMs are high and the engine is on the pipe, the throttle opening is low, and the resulting crankcase filling is minimal.  When these three conditions occur simultaneously, short-circuiting of the fresh charge occurs, the cylinder is not scavenged sufficiently, and too much residual exhaust is mixed with the fresh charge.  When enough fresh charge is trapped with the exhaust residuals, the residual exhaust often raises the temperature of the remaining fresh charge to the point that it is prone to detonate during the combustion event.
 
When short-circuiting occurs, HCs are increased even when a combustion event occurs at the end of the current cycle.  HCs are increased even more when a misfire occurs regardless of what caused the misfire.

[atvcrazy]

Tony I hate to see you spend more money but if I were you before Arlen sends that piston to you get him to send you one of his air filter set ups and ditch that stock 250r air boot and air box. I noticed a difference in performance when I installed his setup I think the stock stuff is restrictive on your large motor.  The filter size is 1.5 times larger with his these big motors need air

[Jerry Hall]

Tony I hate to see you spend more money but if I were you before Arlen sends that piston to you get him to send you one of his air filter set ups and ditch that stock 250r air boot and air box. I noticed a difference in performance when I installed his setup I think the stock stuff is restrictive on your large motor.  The filter size is 1.5 times larger with his these big motors need air

There is 2 hp on a national level 250 when you get the tuned length right and an air filter that has adequate surface area over that of a stock airbox with a K&N with the lid off.  I would expect even larger gains with an engine that is over 150 cc larger.

[Pumashine]

There is 2 hp on a national level 250 when you get the tuned length right and an air filter that has adequate surface area over that of a stock airbox with a K&N with the lid off.  I would expect even larger gains with an engine that is over 150 cc larger.

Does the tuned length differ from a 250cc to a 430cc motor?

[Jerry Hall]

Does the tuned length differ from a 250cc to a 430cc motor?

I have not tested different intake system lengths on the Dyno for the 430.  If the power peak and torque peaks occur at about the same RPM on the 430 as the 250, I would expect the tuned length of the intake system to be similar.  The exhaust pipe has the major influence on the RPM of where the peaks occur.

If you are using a "250" pipe with a larger stinger and larger silencer core, a 250 intake would probably be an improvement.