APT SmartCarb

[Corey]

Originally Posted by Jakobi

I was also wondering how much of the inconsistancy I am getting is due to the spring binding and hooking sometimes. I noticed last ride it would sometimes be notchty at the lower settings, and other times pull smoothly.

Well it seems KTMTalk has shut us off for some reason. There were several questions over there that I was hoping to answer. Please ask those questions here and I will try to reply. Corey

[drehwurm]

Originally Posted by Corey

Well it seems KTMTalk has shut us off for some reason. There were several questions over there that I was hoping to answer. Please ask those questions here and I will try to reply. Corey

Well, I seriously hope I'm welcome here both by the GG guys and Corey. Anyways, here is what my last q's were:

@Corey: Which area is influence the most by changing the float level ? For example if I lower the float level a bit would it lean out more at idle or near half throttle?

@Liz: I sent an e-mail with a request for some spare parts last week - haven't gotten a response yet. What would be the best way to order those parts?

Michael

[Jakobi]

Michael, welcome to the forum. You'll find most of us here also own bikes of other colours and quite easily discuss pro's and con's of everything including our own bikes. Not much of the coolaid power tripping here, and your APT reports will be welcomed.

Corey, thanks for picking up where we left off. Now to try and remember what I actually asked over there again.

[Jakobi]

Also from drehwurm - @those who would like a correction circuit (air or fuel) at the idle area for their SC: KTM part# "81241060000 STARTER VALVE COMP" and a M12x1 fine thread pitch metric tap could be your solution. The starter valve is the adjustable hot start/idle air bypass of the older SXF throttle bodies which fits the SC perfectly except for the mounting thread. Depending if you disable the choke fuel jet or leave it enabled you could create an additional air (like an air screw on the PWK) or fuel (like the 4-stroke carb fuel screw) bypass to change the mixture of the SC at the idle area. It works on the EFI throttle bodies so why shouldn't it on the SC (at least the air side). Worst case, it doesn't work you just use it as a choke like the stock setup on the SC.

We had contemplated trying this with the Lectron and after some research actually found a kit available which even indicated the correct size and placement of the hole. Never got around to trying it. Really as you add more circuits to them you are just increasing the complexity of the carb again, and I think its the simplicity that appeals to a lot of the market more than "perfect" jetting. When you also consider how easy they are to get in the ballpark, and how much smoother and consistent they are over a stock jetted PWK they really sound good.

I'm also curious to hear about the float height adjustment. I haven't had my carb back out to confirm the float height since installation, but at the time it was set at 20mm from the top. I haven't appeared to experience any flooding that I can tell.

[(F5)]

Originally Posted by drehwurm

Well, I seriously hope I'm welcome here both by the GG guys and Corey. Anyways, here is what my last q's were:



Michael

Quite right, you're always welcome here no matter what you ride. . .

Unless its a stinkn 4 stroke in which case you will be Smited by the ghost of Soichiro Honda (who had a pathological dislike of 2 strokes, so I'm not sure why he will be smitting you rather than, say Walter Kaaden, but Honda thought water cooling was a waste of time so he's probably confused).

[drehwurm]

Originally Posted by (F5)

Quite right, you're always welcome here no matter what you ride. . .

I have to admit I have been lurking here since the introduction of the new generation GG, but have been scared away by the almost mandatory (seemed like it) bashing of other brands before even getting to post GG infos.

Anyways, I haven't played with the float level on the SC yet since mine also seemed to be at 20mm every time I checked, but infos posted on that topic seem contradictory. MikeS and his testing with the Grose Jet indicated that float level is important as did some other posts with levels ranging from 17-19mm to fix a lean mid. A statement from APT was that float level would be less important. So I guess I have to see myself.

When testing the float level I noticed that you have to be careful when filling up an empty float bowl. Open the fuel valve too quick and the sudden raise in pressure within the float bowl will close the tip-over valves causing an air pocket inside. This air pocket will keep the floats from closing the float valve, the fuel will continue to flow and exit through the needle jet (metering tube or however you want to call it). This could be misunderstood as sticking floats/float valve which it is not. Just sayin.

Last but not least - did anyone notice the SC going crazy (rich) with a high vacuum just after idle. For example if you are coasting on a road in a high gear with almost no load on it and cracking open the throttle just the tiniest bit to keep the speed it will run extremely rich - impossible to ride with a constant speed there and pretty annoying on transfer sections on the pavement (= 80km/h 6th gear on a KTM 300). As soon as there is a little slope or head wind this effect is gone.

Michael

[Corey]

Originally Posted by drehwurm

Well, I seriously hope I'm welcome here both by the GG guys and Corey. Anyways, here is what my last q's were:



Michael

Like any carburetor the float level setting affects the entire fuel curve to a very slight degree. Unless it is too low and runs out of fuel on the very top end.

PM me here and I will put in your order request for the small parts with Liz, don't know if she has jumped over here yet. Jeb at KTMTalk administrator informed me that he did not lock the KTM thread. Said he would check it but I see it is still locked.Corey

[Corey]

Originally Posted by drehwurm

I have to admit I have been lurking here since the introduction of the new generation GG, but have been scared away by the almost mandatory (seemed like it) bashing of other brands before even getting to post GG infos.

Anyways, I haven't played with the float level on the SC yet since mine also seemed to be at 20mm every time I checked, but infos posted on that topic seem contradictory. MikeS and his testing with the Grose Jet indicated that float level is important as did some other posts with levels ranging from 17-19mm to fix a lean mid. A statement from APT was that float level would be less important. So I guess I have to see myself.

When testing the float level I noticed that you have to be careful when filling up an empty float bowl. Open the fuel valve too quick and the sudden raise in pressure within the float bowl will close the tip-over valves causing an air pocket inside. This air pocket will keep the floats from closing the float valve, the fuel will continue to flow and exit through the needle jet (metering tube or however you want to call it). This could be misunderstood as sticking floats/float valve which it is not. Just sayin.

Last but not least - did anyone notice the SC going crazy (rich) with a high vacuum just after idle. For example if you are coasting on a road in a high gear with almost no load on it and cracking open the throttle just the tiniest bit to keep the speed it will run extremely rich - impossible to ride with a constant speed there and pretty annoying on transfer sections on the pavement (= 80km/h 6th gear on a KTM 300). As soon as there is a little slope or head wind this effect is gone.

Michael

Like most of the manufacturing we have been trying to source in the USA we have been challenged by the vendors we have chosen to manufacture our metering rods. This is just until we can equip our facilities with enough equipment to keep the manufacturing in house on this critical part. With little exception the majority of inconsistent running has to do with the critical dimensions on the metering rod, specifically in or near the idle area. We have changed vendors and are working with the machinists on a new process that so far has net great results and much more consistency across the board. This should be very close to not only providing optimum results but will allow us to arrive at much more consistent clicker settings carb to carb. These will be available as a trade out to anyone who is struggling getting the low speed setting right, based on a flawed metering rod.

[Corey]

Originally Posted by Jakobi

Also from drehwurm - @those who would like a correction circuit (air or fuel) at the idle area for their SC: KTM part# "81241060000 STARTER VALVE COMP" and a M12x1 fine thread pitch metric tap could be your solution. The starter valve is the adjustable hot start/idle air bypass of the older SXF throttle bodies which fits the SC perfectly except for the mounting thread. Depending if you disable the choke fuel jet or leave it enabled you could create an additional air (like an air screw on the PWK) or fuel (like the 4-stroke carb fuel screw) bypass to change the mixture of the SC at the idle area. It works on the EFI throttle bodies so why shouldn't it on the SC (at least the air side). Worst case, it doesn't work you just use it as a choke like the stock setup on the SC.

We had contemplated trying this with the Lectron and after some research actually found a kit available which even indicated the correct size and placement of the hole. Never got around to trying it. Really as you add more circuits to them you are just increasing the complexity of the carb again, and I think its the simplicity that appeals to a lot of the market more than "perfect" jetting. When you also consider how easy they are to get in the ballpark, and how much smoother and consistent they are over a stock jetted PWK they really sound good.

I'm also curious to hear about the float height adjustment. I haven't had my carb back out to confirm the float height since installation, but at the time it was set at 20mm from the top. I haven't appeared to experience any flooding that I can tell.

20mm is just about right. The idea is to carry enough bowl capacity to feed the engine at wide open, but low enough to keep a strong force against the tang arms to provide a nice tight float needle sealing. There is no need for an idle correction circuit (or any other circuit) if the metering rod is accurate (and perfect jetting) and is a step in the wrong direction. In fact you are then just weakening the signal at the metering rod. Which will require you to raise the needle to make up fuel flow due to the diminished signal. Affecting both economy and emissions.

[drehwurm]

Originally Posted by Corey

These will be available as a trade out to anyone who is struggling getting the low speed setting right, based on a flawed metering rod.

I'll be at the Romaniacs with the SC next week so do you have any experience setting up these "flawed" rods to work acceptable?

Originally Posted by Corey

There is no need for an idle correction circuit (or any other circuit) if the metering rod is accurate (and perfect jetting) and is a step in the wrong direction. In fact you are then just weakening the signal at the metering rod. Which will require you to raise the needle to make up fuel flow due to the diminished signal. Affecting both economy and emissions.

I see your argumentation, but after my experience so far I'd really like to have a way to adjust the idle area independently from the rod setting (be it a flawed rod or not). Less signal would be leaner, wouldn't it?

Anyway after next week I'll know a lot more about the SC and I hope to be able to contribute a bit more positive information then.

Thanks for answering the questions.

Michael