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jrutkows

AP tuning for altitude

14 posts in this topic

Has anybody tried the honda AP diaphram in their WR at altitude? I ride 07-450, mostly 7000-9000ft. If so, what leak jet are you running?

Seems like the tailpipe is always black like it's running way to rich but I'm pretty sure I've got everything else jetted well, 155main, 42pilot, NFLR needle on second clip. The only thing left is the AP?

I know this mod is popular with the KTM boys for altitude, and while it wouldn't be as big of a difference from the yamaha diaphram, I'm going to give it a go.

Pulling the carb is a pain, so if anyone has any experiences to share I'd love to hear as it may save me some iterations.

j-

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You have the right main for altitude. Your pilot is actually a little lean, but if it runs fine, that's all that matters.

The 3 '08's that I've been around all used a 48 at altitude, and the local dealer suggests a 50 based on their dyno tuning.

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I'm no expert but I don't see what the pilot circuit has to do with dyno tuning? If it's way out, then I suppose it could effect off-idle performance but once you open the throttle the pilot circuit is not really active anymore. Bike starts right up and idles nice so seems like it's fine. With a 45, the bike would still run with the fuel screw all the way in.

On a separate note, it seems like a 70 leak jet causes a nasty bog and a 60 works well. The button on the AP diaphram seems pretty tall and the squirt seems close 1 second, perhaps I should leave well enough alone?

The stream is really close to the bore of the carb and even with the timing srcew all the way out it would not hit the slide?

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Check your jetting by riding at altitude, up a grade, steady throttle. If it is flawless, leave it alone.

Tweaking the AP has two key components that have overlaping abilities. A Longer rivet reduces total volume and duration. Leak jet does the same and it reduces sensitivity.

Sotty pipe can just be the result of constantly on and them off the gas.

Edited by William1
I am a moron - Had it backards! DooH!

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The dyno measure the A/F mixture all across the RPM range, so you can check pilot, needle, and main. It takes away guessing.

As William sez, if your settings work, go with them. There is quite a difference between good and great, though.

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A shorter rivet reduces total volume and duration. Leak jet does the same and it reduces sensitivity.
I could be wrong, and it wouldn't be the first time, but wouldn't a shorter rivet increase volume and duration by allowing the diaphragm to travel further before bottoming? :thumbsup:

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I could be wrong, and it wouldn't be the first time, but wouldn't a shorter rivet increase volume and duration by allowing the diaphragm to travel further before bottoming? :thumbsup:

You are correct.... sometime I think I am dyslexic. I fixed my original post. Thanks for questioning me! :bonk:

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Thanks for the input, I'll be a bit more specific:

The physics of AP operation are pretty straightforward. Leak jet lowers/controlls the pressure in the squirt, the diaphragm button limits the stroke. They both effect the volume and duration but my intuition tells me the button is more effective for duration and leak jet for volume/pressure. I realize Yamaha has probably put a lot of thought into the correct combination, but then again they were not doing there testing on top of mt Fuji, so I have to believe some tweaking for 9000ft would help. Nothing has been done to my bike. I'm either on the gas at WOT or on the brakes, so while I think I've got all my other jetting dialed in (riding at constant throttle), the AP is going to make a big difference for how I ride, I'd like to get that dialed as well.

Seems like a 60 leak jet is good, with a 70 the squirt looks bad and the bike bogs something terrible.

All that said, here are the options from yamaha (part 31 on the fishce) for diaphram options, how to find out what the difference is, (button size)?

5JG-14940-18-00

5JG-14940-17-00

5JG-14940-16-00

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Any updates to this? I'm wondering if I need to tweak my accelerator pump as well. My buddies also ride WRs and we noticed that my bike is not as responsive as theirs. It starts & idles fine, so I'm thiking it's the AP.

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The 'Honda' AP diaphragm is preferred on KTMs cause they come with the old version diaphragm with the long rivet.

You can order a Apump upgrade kit from R&D or Merge racing:

New softer diaphragm

New stiffer diaphragm spring

New o-rings to seal cover

New Apump detent spring <<<< this is the 'must have' improvement

Leak jet should be 60-70 (mostly stock motor) to 45-60 (pipe, yz timing, etc)

You could do a Q&D upgrade with a stiff o-ring around the apump linkage, but I don't like the 'feel' of it, and the o-ring doesn't last.

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Has anybody tried the honda AP diaphram in their WR at altitude? I ride 07-450, mostly 7000-9000ft. If so, what leak jet are you running?

Seems like the tailpipe is always black like it's running way to rich but I'm pretty sure I've got everything else jetted well, 155main, 42pilot, NFLR needle on second clip. The only thing left is the AP?

I know this mod is popular with the KTM boys for altitude, and while it wouldn't be as big of a difference from the yamaha diaphram, I'm going to give it a go.

Pulling the carb is a pain, so if anyone has any experiences to share I'd love to hear as it may save me some iterations.

j-

I normally ride at 6-9K feet in the mountains. I run the JD Kit and have a 45 pilot with a 165 main and it runs great. I have an adjustable leak jet now, but before that, I replaced the stock 50 leak jet with a 40 and it cleared up my problems with the bog.

Are you really looking at the black stuff from the exhaust to tell you if you are running rich? How does the bike run?

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Bike runs good, but excessive black on the tailpipe means it's running rich at some point, somewhere. This may not mean that the jetting is wrong, or that it can even be fixed given the constraints of carburation, but it's valid information. My truck is fuel injected and does not exhibit this issue. Under hard acceleration, it seems that it would be difficult or impossible without some very special tools to know if you are slightly rich or lean. You could be both during the time the AP is in play depending on the initial intensity and duration of the squirt. I have to believe that the AP comes dialed for sea level, so it only stands to reason that it needs tweaking for high altitude, leaning out.

Now I have a 60 leak jet and have tweaked the timing, no bog, pulls hard. So the initial intensity of the squirt is probably right but what if the duration is still too long? I realize that at some point you go with good enough, but at the time of my original post I hadn't yet spent any time tweaking anything so was looking for any experience that people had. I'm happy with it now, runs fine, could always be better though.

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Bike runs good, but excessive black on the tailpipe means it's running rich at some point, somewhere. This may not mean that the jetting is wrong, or that it can even be fixed given the constraints of carburation, but it's valid information. My truck is fuel injected and does not exhibit this issue. Under hard acceleration, it seems that it would be difficult or impossible without some very special tools to know if you are slightly rich or lean. You could be both during the time the AP is in play depending on the initial intensity and duration of the squirt. I have to believe that the AP comes dialed for sea level, so it only stands to reason that it needs tweaking for high altitude, leaning out.

Now I have a 60 leak jet and have tweaked the timing, no bog, pulls hard. So the initial intensity of the squirt is probably right but what if the duration is still too long? I realize that at some point you go with good enough, but at the time of my original post I hadn't yet spent any time tweaking anything so was looking for any experience that people had. I'm happy with it now, runs fine, could always be better though.

Deposits on your tailpipe are pretty normal. You don't have a cat convertor, or a pre-muffler like your truck does, and your truck is probably very lean, from the factory, to make EPA and mileage numbers.

The only way to tell is with a AF mixture gauge.

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Also, it depends on your riding style and type of riding you do. If you do a lot of technical single track, on and off the gas a lot, you will get a soottier pipe than a guy that cruises fire roads.

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