In search of snap… Is this stuff useful?

This was still on my computer from when I had put it up on TT some time ago, with the new discussions about the 2010 TC250s happening I thought it would be good to have the same information here.
Link to thread in tech ref section - LINK
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Ok think I found “snap” 5000 rpms in 1st & 2nd gear – whack the throttle and good response. This is what I found. Could not find this information anywhere so made the measurements myself and it took a whole bunch of time – and everything was repeated a few times.

Basically by adjusting the AP screw, adding and not adding o-rings the squirt can be altered (somewhat) without changing the leak jet, which was a big help to me on my bike - 2006 TE250 with a Keihin 37mm FCR-MX carb.

Here is a short video showing the AP in action most of you have already seen it but here it is again:
http://www.youtube.com/watch?v=1uYJmpOXKGI

Here is the AP as it comes from the factory - with cap over AP screw:



Here is the AP without the cap:



Here is the AP without cap over AP screw and with “O-Ring” that is referred to often:



Here is how to measure the “distance” of the “AP screw”:



Here is a graph of at what throttle position the AP squirt starts at:

Keihin recommends the distance set to 2.75mm, which results in the AP starting to squirt ¼ WOT. The AP cap disables the squirt by setting the distance very high – 5mm?


Here are the numbers:
2 mm - 6%
2.25mm – 12%
2.5mm – 18%
2.75mm – 25% <- Keihin recommended setting
3mm – 33%

Here is a graph of amount of squirt vs AP screw setting, the “mLs for 50 WOTs” means the throttle was whacked open and collected into a jar 50 times then measured…with 1 O-ring and 3 different leak jets:




The amount of squirt is determined by leak jet and the AP screw setting when going from fully closed to WOT.

Here is the same graph with just the 65 and 70 leak jets:



Here is a graph of a 65 leak jet with no O-Ring, 1 O-Ring, and 2 O-Rings:



That is just plain weird, but the experiments were repeated many – far too many – times and it is real. Where maximum squirt occurs changes depending on if there is an O-Ring on the AP arm……

Here is squirt duration time vs. AP screw setting with a 70 leak jet:


The squirt duration is mainly determined by strength of O-Ring – if there is an O-Ring installed especially, between 2mm and 3mm. Video camera captured the squirt then single stepped through frame by frame to determine time.

Here is the same information but with a 35 leak jet – Series 1 is no O-Ring, Series 2 is 1 O-Ring, Series 3 is 2 O-Rings:


What does this mean? Squirt duration, amount of squirt, where the squirt starts to occur can all be set (sort of) independently by adjusting the AP screw, O-Ring, and leak jet. It also means changing the AP screw and O-Ring can have a similar effect as changing the leak jet to some extent.

If AP screw = 2.25mm, then squirt starts at 12% of WOT and:
Adding an O-Ring = shorter duration and more squirt
Larger leak jet = longer duration and more squirt

If AP screw = 2.75mm, then squirt starts at 25% of WOT and:
Adding an O-Ring = shorter duration and same amount of squirt
Larger leak jet = longer duration and more squirt

Everything else stays the same and AP screw changes then:
Where the AP starts changes (see graph), duration stays (roughly) the same, and the amount of squirt changes – see graphs.

Useful? Could use a little feedback on this... seriously could use some feed back...

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Info added as of Feb 21 2007:

Here is a summary of all the AP videos:
70 vs 35 vs blank leak jets (new as of Feb 21 2007) - 1:44 in length:
http://www.youtube.com/watch?v=CDrttBUCFos

AP cap vs 35 leak vs 70 leak - 50 seconds in length:
http://www.youtube.com/watch?v=1uYJmpOXKGI

slow motion 35 vs 70 leak jet both with no O-Ring 2.75mm - 1:20 in length:
http://www.youtube.com/watch?v=LD7EvRgMQm4

Squirt vs screw setting no ORing 70 leak - 1:33 in length:
http://www.youtube.com/watch?v=ool_jiy4kxQ


blank leak jet data:



This graph (below) continues to show the shift in peak squirt from (about) 2.75mm to 2.25mm when an O-Ring is added. This phenomenon continues to be useful when experimenting. Set the screw for 2.25mm with O-Ring then to make a smaller squirt flip the O-Ring off for instance. Or flip the O-Ring off, and turn the screw to take it up to 3mm and it will squirt later in the rotation of the throttle, be less fuel, but a slower squirt. Then put the O-Ring on and have the same quantity but a faster squirt - that was very handy.

Of course the simplest way to experiment is to double blip the throttle very fast and get a double squirt to make it rich that way...



Results:
Put the blank leak jet in and it worked surprisingly well - thought it would stumble & bog - it didn't - it did act jerky & on/off... as if unstable. If a small amount of throttle were being applied at least for a few seconds and the throttle was whacked open it had good power and lifted the front way easy. For any normal on / off / on / off throttle operation normally used off road it would load up a bit. It seems it all comes down to riding style - at least that is my take - and have seen that posted by excellent TTrs before. Seems the faster the rider (and the more on/off/on/off throttle they use) the higher number leak jets works better.

At this point 35 or 45 is in the bike - they both work well for my riding style - like it a bunch.

I am glad you mentioned the Yamaha.

Bikes in recent years have a variety of AP setups that changed (relatively) frequently - at least that is my impression. I do not have access to all those bikes so I cannot test. Although I believe the information is applicable to those bikes it may not apply exactly.

Specifically: The AP screw distance setting graph could easily have an offset either because the AP linkage rod is different or more likely the diaphragm stud (metal rod attached to the AP diaphragm) is a different length.

If in doubt, measure the AP screw setting, pull off the carb, and twist the throttle to observe. It works just like any squirt gun from Toys R Us and is nothing magical.

Honestly I do not have my 'thinking cap' on at the moment. I did take a look at some leak jets and the bigger the number, the bigger the hole. It is called a 'leak' jet because it is parallel with the AP (think of that as a simple squirt gun from a toy store).

The bigger the hole, the less goes through the squirt gun (AP). So it appears the words in bold are backwards. It should say the smaller the leak jet number, the smaller the hole, and the larger the squirt.

Input?



Yes.... very very very tedious. After I had done all those experiments I had found pictures of JD doing something similar on his pbase picture site. The reason the experiments were done is because I could not figure out from reading various forums how it worked. There seemed to many conflicting pieces of information, which looking back on it I would attribute to carelessness. Something I myself appear to have done.