APT SmartCarb

I still can't gel with this carb. There is something about it that I can't put my finger on, but its inconsistant. IE I'll start it, run it, dial it in well, have it so it idles on and on and on and doesn't hang after putting a big load on it, and then put it away. Go and ride it half an hour later and it'll have a hanging idle, or run rich, blow smoke and spooge. Maybe its the floats hooking up or the needle not seating? I don't know but I've had a gutful of it.

Add to that that I did a bit more tinkering today to get it dialled in and now its gone from running clean to a bit more smokey and spoogey. The power is grunty though. I'm a bit lost with it all. My experience with this has been anything but plug and play perfection.
 
I've gota big 2 day ride coming up, and currently stuck and not sure where to go from here. The bike feels like its running strong top to bottom, however is now showing signs of both being rich and lean together. Rich as in I have a small dribble of spooge at the tailpipe, which may just be a result of some testing I'd been doing and loading the packing up with some excess oil (heres hoping). Lean symptom is a hanging idle after giving it a good buzz along. Torque spread is very good across the rev range, and I think the lean hang is mostly caused when riding high in the revs, with under 1/4 throttle. If it was a Keihin I'd go up 1 needle diameter and it would be great.

I also found the slide height has very little influence on the idle speed. IE it takes considerable adjustments to make a change in idle, however it has a massive effect in off idle torque and cleanliness. It also adds to the hanging idle effect if having the slide up too high. The issue I face is that going a click richer on the MR means lifting the slide some more to maintain the idle, which kind of defeats the purpose of richening it up, as the adjustment then leans off the lower openings again.

I'm hoping the latest round of mods to the MR haven't negatively impacted fuel economy as I need to stretch a 90km section.. I'll have 1L in the back pack. Last week doing a similar loop of 70kms I used 6.4L, but the spooge is scaring me. Every other time I've seen it I've seen fuel economy suffer.
 
Want me to send your keihin back up mate?
That sucks you're still struggling with it.
Do you think it's possible it is simply a 'bad' carb. If so what are the chances of swapping the whole thing for a new one to see??
 
I guess I could put that to Corey. Maybe I'll see if he'll let me sample a Cast when they hit production for comparisons sake.

You can hold onto my Keihin a bit more yet Nath. I've still got TSPs Lectron here if things get really bad. After this weekend I'll pull the whole Smart Carb and double check the floats, inspect for wear and damage, fix the MR to stop it rotating, and maybe lightly sand it a little more where I think the straight section would typically be. I don't have much of anywhere to go with the R080 rod anymore as I'm at 90 clicks out to compensate for my orginal lapping. At the moment I think I'm a bit rich back towards WOT too, but I'm still getting around 9100rpm on the taco and not breaking up so it can't be too rich. I've got to pull the shock for a revalve so might as well treat the carb at the same time. I was hoping I'd be using this time to send the SC to TSP for Dyno time. Might yet depending on how the weekend progresses.
 
Jakobi said:
I also found the slide height has very little influence on the idle speed. IE it takes considerable adjustments to make a change in idle, however it has a massive effect in off idle torque and cleanliness. It also adds to the hanging idle effect if having the slide up too high. The issue I face is that going a click richer on the MR means lifting the slide some more to maintain the idle, which kind of defeats the purpose of richening it up, as the adjustment then leans off the lower openings again.
Click to expand...

I have seen the exact same symptoms before I got my rod/nozzle sorted. One thing you can try is to go in really far with the slide stop till there comes a point where the RPMs finally react to the slide height and work from there.

Michael
 
A leaky float valve can deffinately give you those symptoms. If you set the idle high enough so it will idle consistently for a period of time well then it is too high after you run it at higher rpm's. This will give the bike a lean feeling when coming down from higher rpm's. You might try shutting the gas off while it is idling and see what kind of feed back you get. I know this is stuff you already know, but sometimes a guy gets so rapped up in a problem that we forget to try some of the simple things.
 
Jakobi said:
I also found the slide height has very little influence on the idle speed. IE it takes considerable adjustments to make a change in idle, however it has a massive effect in off idle torque and cleanliness.
Click to expand...

This to me based on my Lectron experience is caused from to rich rod at the initial setting. If the slide opening is about typical for a good idle yet you cant change the idle much it is rich. If the idle if erratic and sensitive it is lean. This is a slide to rod position thing. Lectron tells me it is this critical area, at idle and just off idle, that is the most important part of the rod profile. The super small slide opening, high velocity, and super small opening at the base of the rod is very sensitive to this setting. The issue if you don't have the rod profile super dialed you can get the bike to idle nice but might have a huge bog as it is lean all of a sudden when you open the slide. If the rod profile is not spot on you have inconsistencies and cant get both a good idle and good bottom end. As you have found from sanding the rod, taking .0001 off can make a difference. This shows the rod profiles on these are very critical. They like lean at idle but need to ramp up to rich pretty quick right after that so no bog or soft bottom end. Sounds like your rod does not have the profile to support the needed lean idle AND ramp up so you have good bottom. You have dialed it so it runs good and has good torque (rich) but this is making it run erratic at idle.

How does it start hot? Do you need your choke when cold or no?
 
drehwurm said:
I have seen the exact same symptoms before I got my rod/nozzle sorted. One thing you can try is to go in really far with the slide stop till there comes a point where the RPMs finally react to the slide height and work from there.

Michael
Click to expand...

Basically what I have done Michael. I backed the adjuster right off to nothing. Rode the bike until it came up to temp and then started dialling it until the bike just ticks over. At this point one click richer on the MR is enough to flame it out and take the idle away.

rosco said:
A leaky float valve can deffinately give you those symptoms. If you set the idle high enough so it will idle consistently for a period of time well then it is too high after you run it at higher rpm's. This will give the bike a lean feeling when coming down from higher rpm's. You might try shutting the gas off while it is idling and see what kind of feed back you get. I know this is stuff you already know, but sometimes a guy gets so rapped up in a problem that we forget to try some of the simple things.
Click to expand...

Thanks rosco. Appreciate the thoughts. The inconsistancy is what makes me think it might be float related. I've always set my bikes up for the lowest slide height possible. It makes for good signal when starting, punchy response off idle, reduces the chance of hanging idle, and more so I found you don't get the pipe bang with a nice low slide.

Motosportz said:
This to me based on my Lectron experience is caused from to rich rod at the initial setting. If the slide opening is about typical for a good idle yet you cant change the idle much it is rich. If the idle if erratic and sensitive it is lean. This is a slide to rod position thing. Lectron tells me it is this critical area, at idle and just off idle, that is the most important part of the rod profile. The super small slide opening, high velocity, and super small opening at the base of the rod is very sensitive to this setting. The issue if you don't have the rod profile super dialed you can get the bike to idle nice but might have a huge bog as it is lean all of a sudden when you open the slide. If the rod profile is not spot on you have inconsistencies and cant get both a good idle and good bottom end. As you have found from sanding the rod, taking .0001 off can make a difference. This shows the rod profiles on these are very critical. They like lean at idle but need to ramp up to rich pretty quick right after that so no bog or soft bottom end. Sounds like your rod does not have the profile to support the needed lean idle AND ramp up so you have good bottom. You have dialed it so it runs good and has good torque (rich) but this is making it run erratic at idle.

How does it start hot? Do you need your choke when cold or no?
Click to expand...

Starts on the choke when cold. Starts easy when hot. Like in gear easy. No issues with the starting or the idle mix. The bike won't idle well off choke when cold for the first 30 secs, and loads up and won't take revs on choke when hot. Everything is as it should be.

I know I have a very small lean spot just off idle. Very small think 1/8th turn Air Screw small. And then the bike runs very well through the revs and if anything is probably a touch rich towards WOT.

I had got some hanging idle issues on run down from high rpms, but I'm also getting some spooge at the tip of the silencer which I hadn't experienced before, so I may have taken a bit too much off towards the end of the MR.

I guess what I was trying to highlight is that the slide height has a substantial effect on the lower openings. Lifting it 2 turns say, will most definitely lean the bottom end out and cause a hanging idle. You can then tune it back into the range again moving the MR richer which adds fuel right across the range. Having the slide up so high though then conflicts with the inital ramp up, and as you say leavs it hanging lean too long and torque off idle is lost. Lower slide and a leaner MR position gives the great response but hanging idle on decel.

Its almost got me beat. Few more tricks to try yet; nozzles and orientation of the MR. Double checking the floats and needle for any signs of hanging or binding. Corey states they have encountered issues with sticking check valves, generally in humid conditions (I live in rainforest - Right now 8am 76%RH and 21C). I also suspect that the inconsistancy (inc hanging idle) may be the result of an air leak. Now what could cause an intermittent air leak? A bad seal somewhere? Like... the seal on the clicer mechanism? Thats what I'm thinking and going to focus on today. I'm not sure how it seals but I assume it will be an o-ring. I've noticed after pressing the clicker adjuster in, and making an adjustment it doesn't spring right back to the top and I guess its possible that in some instances I haven't pulled it back up and air has been able to sneak back past the o-ring.
 
Jakobi said:
the seal on the clicer mechanism? Thats what I'm thinking and going to focus on today. I'm not sure how it seals but I assume it will be an o-ring.
Click to expand...

Don't get me started on that :D Yes, it's a single o-ring which acts as seal and guide at once (made an extra guide ring to stabilize the clicker :rolleyes:). Nevertheless to answer your question: remove the screws from the slide cover, start the bike, lift the cover without raising the slide and see what it does! It wouldn't make a difference in idle quality on my bike so I assume the slide is sealing well enough at idle/low throttle.

Parts are on the way!

Michael
 
Thanks Michael.

Took the bike out for a 30km test run today. She used just under 3L which is on par for normal consumption. Fuelling is still not ideal, but I have a setting where I only have a little break up at smaller throttle openings. Not quite at idle, but just off it. Its most noticable in the lower gears where there isn't as much load on the engine. Very strong mid and seems to pull well towards WOT. No smoke or spooge when running the bike well, but I feel it will start to load up and spooge a bit if I granny it around off idle for too long. Its still very much a compromise between jetting for max grunt under load, or clean throttle application. Likely more noticable being a 250 too. It always seems if you try and get the hit away then the bike becomes a bit flat. Still some room for improvement, but I think I'm ahead of where I was.

Do you notice your carb is very sensitive to engine temp?

I still have my A100 MR here. Not sure if I'll have a go at modding that or keeping it as a stock example.
 
Motosportz said:
The super small slide opening, high velocity, and super small opening at the base of the rod is very sensitive to this setting. The issue if you don't have the rod profile super dialed you can get the bike to idle nice but might have a huge bog as it is lean all of a sudden when you open the slide.
Click to expand...

This is spot on IMO and 100% applicable to the SC as well. Unfortunately APT doesn't offer a solution/option yet. As I wrote you, the new nozzle with tighter tolerances than the APT one hopefully works as well for you as it did for me in clearing up all the idle inconsistencies. The modified rod should take care of the lean bog after that. Not much more else we could do so lets keep the fingers crossed.

Michael
 
Still refining the process and testing the product. IMO this is a good if not great thing. While I bit the bullet and upgraded my cast order to the billet, the last 50 engine hours using it has been nothing but trouble. Mostly I was just unhappy with the fuelling stock, where it was always a compromise between an overly rich bottom end and strong mid, or a clean bottom and flat lean mid. Tried a few things along the way to address it, made some gains and then undid my good work too. Identified a few more issues along the way, but ultimately it seems the carb is very sensitive to internal tolerances and the slightest changes result in significant changes to the fuelling.

Nozzle position, break-in of the nozzle, float heights, hanging floats, sticking check valves, inconsistent metering rod grinds (inc the early ones which had the threads brazed on), the poor feel/enagagement/faults associated with the clicker assembly, the binding of the throttle spring during break-in.

Let APT take as long as they need to ensure the product meets tolerances, and will stay in tolerance. Its in everyones best interest.. including their own. When the carb runs well, its beaut! But when you spend more time dicking around with it than you did with your PWK... let's just say my SC is sitting on the bench now - until some updates are rolled out.
 
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