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

[SmartCarb]

Bruce did spin out back then. Went through a divorce, then a group remade Scorpion brand snowmobiles and ordered ALL the production motors from Bruce and didn't pay or went belly up. Sad deal. Last I knew he out in Utah playing with mountain sled heads.

Odd thing about patents, they don't stop anyone from using it. It just gives you the right to take them to court and fight

It's all true unfortunately and a shame.

Scorpion never had a chance though. Can you say Cannondale? Too much too soon, the Genesis engines were a work of art though and I had an 890 that is still racing today. PSI is in a small building near Ogden Utah. I didn't want to fight with Bruce, as I highly respect the man and knew of him when he worked for Aaen, we were hoping they would just play ball and we all sell better carburetors. Understandably I think he is pretty embittered by his loss, you may recall they had just built a huge facility in Wild Rose Wisconsin before it all went down.

[Jerry Hall]

................Odd thing about patents, they don't stop anyone from using it. It just gives you the right to take them to court and fight

Some other things most people do not understand about patents and the patent process is:

A patent is not a guarantee that the idea or device that is patented functions as the unique features claims in the abstract.  The patent office does not test the ideas or device during the patent search or during the patenting process.  If a patent is granted it gives the patent holder the legal right to stop someone else that may reproduce the idea or device for financial gain.  

Sometimes an original patent holder has a device that works really well but does not know how or why (scientific process involved or the appropriate way to use the device) the device worked. Due to the claims made in the abstract (why it works or how to use it) some one else can be granted a patent on an identical device if the new patent holder can prove that it can be used in a 15% different way or prove the claims made in the original patent were not accurate.

[Pumashine]

Furthermore this was also the cause of the intermittent flooding issues that you were dealing with prior to the seizure. After your rebuild and necessary clearancing of the manifold I would also inspect your SC to see if any damage has occured the the fuel inlet needle/seat.

The flange of the SC was touching the RAD valve from 6 to 10 o'clock as marked in black sharpie in the picture. There is a sharp burr there where the aluminum was push back into the SC bore.


Are you saying I should pull the Allen bolt that holds the needle/seat in there to look at it or just check for flooding before hooking the carb the the motor?

[Tbone07]

The flange of the SC was touching the RAD valve from 6 to 10 o'clock as marked in black sharpie in the picture. There is a sharp burr there where the aluminum was push back into the SC bore.


Are you saying I should pull the Allen bolt that holds the needle/seat in there to look at it or just check for flooding before hooking the carb the the motor?

Who taught you those incredible sharpie skills, Tony? :excitement:

[SmartCarb]

The flange of the SC was touching the RAD valve from 6 to 10 o'clock as marked in black sharpie in the picture. There is a sharp burr there where the aluminum was push back into the SC bore.

Are you saying I should pull the Allen bolt that holds the needle/seat in there to look at it or just check for flooding before hooking the carb the the motor?

Easier to just gently pull the wire bail from around the needle and slip the needle out. Look carefully with a magnifying glass at the tapered end of the needle for a heavy ring where the needle has been seating/impacting the seat, then check the spring plunger on the top of the needle for return tension. If all good, take a pen light and look down into the brass seat, the edge leading into the inlet where the needle rests should be reasonably sharp without a large chamfer, look for rotational type impacting or hard wearing. There should be little to no ring on the needle, brass smearing or galling down in the seat. If there is I would recommend replacing it. The frequency being transfered into the little parts and pieces at 8-9000 rpm is severe.

And of course cut and file the burr out of the venturi, then I would flat sand the end of the venturi, even at the angle it is worn, won't hurt it. You can do this on a piece of plate glass and a sheet of 220 grit sandpaper.

[Pumashine]

The needle/seat was damaged so I put the new 40mm SC in and rode for an hour to break in new piston and rings. After refueling I was going to try some small hills. Got stuck 3/4 of the way up and had to go back to the bottom. Tried again but when I got to the same spot/soft sand the rings were siezed. I am guesiing this piston needed a little more break in time. Plug was fine and seemed rich enough. Whats it look like?





Smartcarb suggested going with a slightly richer metering rod.

[rablack21]

Tony, the 2nd smartcarb came with too lean of a needle for that engine setup due to an error by Tom not recording information about this engine being heavily modified from stock, right? It normally would have come with a richer needle if he had recorded the correct information, right?

[Pumashine]

Tony, the 2nd smartcarb came with too lean of a needle for that engine setup due to an error by Tom not recording information about this engine being heavily modified from stock, right? It normally would have come with a richer needle if he had recorded the correct information, right?

Yes, Corey went back to the build sheet and could see no reason why I would need a richer metering rod. Apparently Tom does not consider a 431cc 2 stroke a modded motor.  The build sheet has a place for mods to consider when building a carb for it. I would guess the whole big bore thing is overlooked. After reading the thread Corey said the carb would have shipped with a richer metering rod if he had known what motor I was running. All he sees is 250r on the build sheet.

[rablack21]

LOL. Yes, I do believe a 431 big bore would be count as a "mod" for a 250r. I think that qualifies.

[udontknowme]

rode for an hour  I am guesiing this piston needed a little more break in time. .

thats about 55min more than you needed. most likely your a/f ratio still isnt right. never assume your piston clearance is correct either. regardless who assembles it. always double check for yourself.

[Pumashine]

thats about 55min more than you needed. most likely your a/f ratio still isnt right.

That's the general consensus. I have lots of clearance now that the molten aluminum has been sanded off the rings. :lol:

[udontknowme]

you might have to take the bike to someone with equipment that can check a/f ratios through the full throttle range. i dont really see any other way to get it sorted out.

[SmartCarb]

Tony, the 2nd smartcarb came with too lean of a needle for that engine setup due to an error by Tom not recording information about this engine being heavily modified from stock, right? It normally would have come with a richer needle if he had recorded the correct information, right?

OK let's do a little review so we can all understand what is happening here and avoid any more costly mistakes. Tony was given a loaner carb to try, after installing it had a sticky float issue. He started calling our tech service line, where he was advised how to handle the float issue and some basic tuning tips. From there a persistent mid range stumble showed up and we started chasing things around to determine the cause. My guess is our service technician was guiding him through proper float bowl settings thinking we had a capacity or fill rate issue. None of that worked so we likely went on to metering rod selection and started stepping up richer. All this by the way working with a non alpha customer using a borrowed SC and supplying parts to help Tony get his modified engine dialed. We love you guys. Anyway it was finally discovered that the carburetor was indeed hard rubbing (inside the intake boot) and likely the issue all along. Some pictures were posted and the plug showed a nice light tan and apparently at or near a perfect burn which we are all used to seeing with an SC. The piston on the other hand is not happy at all and shows localized over-heating, yielding of the exhaust edge and chunking off.

It's clear the carb touching the intake caused the fuel to turn to a highly aerated froth along some frequency (mid range) causing the carburetor to deliver pre-aerated mixture to the engine at those points and burned the piston. Alright, in the meantime another carburetor is ordered but nothing I have is specifying this is going onto this same engine we spent a couple months trying to dial in and had a reasonable expectation of what metering rod it should come with. This is clearly our fault for not requesting enough information. Notwithstanding on the other end, had I the earlier carburetor and several metering rod variants in my hand, a brand new bored, ported custom engine needing broken in and several months of plug readings. Intuition would have led me to the richest rod I had already been running.  I am reasonably certain from looking at your plug the .074 MR is very close to what you will need with this engine. The .080 MR, which is our standard issue for 300 class stock to lightly modified dirt bikes will not work and your piston has brought that to your attention.  When we receive your original carb back  we can validate these things and make sure we are correct. The new 40 SC you have will require the richer rod for best performance and to protect your engine. Sand of course is the hardest loads there are and any engine will want more fuel under these conditions.

[Pumashine]

OK let's do a little review so we can all understand what is happening here and avoid any more costly mistakes.

Yep, that is a good summarization. Thanks Corey for your help. I was beginning to have fears of ever getting this thing going correctly when I had to pull start the bike.  Got the .074 MR in and idle set last night. Hope to head to the dunes today to break the piston in. Ha ha, even started 2nd kick after getting the rings unstuck! That was surprising.

[Fire1]

Cory when will the next round of cast carbs be available ?