Post by wayne on Jun 3, 2012 4:10:49 GMT -5
I was working on a hesitation free carby this afternoon and decided to check the AP setting as I had done it several years ago. While the angle gauge was on, I thought that I’d look at the limiter plate.
What I found is that the limiter plate freed the secondary throat at precisely where the shop manual states (page 61) which is 41 degrees of primary butterfly movement. And this was also the angle shown on the angle gauge.
The significance of this is the relationship between the opening of the port valve (PV) and the release by the limiter plate of the secondary throat opening.
There is a great and detailed post about carby settings made very early on in the board. But it errs in this one area and can lead you to misunderstand the relative timing of the PV and limiter plate.
The point is that the Primary butterfly when closed is actually at 8 degrees. However, this is completely irrelevant for all of the manual and bulletin 9 references to primary butterfly angles or angle settings. The carby setting post I’m referring to notes the 8 degree resting angle of the primary valve and therefore sees the PV angle meter setting of 35 degrees as actually being 35 + 8 = 43 degrees of primary butterfly movement. The shop manual states that the limiter plate starts to move at 41 degrees of primary butterfly movement. This leads you to understand that the PV should open slightly after the limiter plate first moves. This is not correct (but if this works for you, go for it !).
If you set the angle gauge at “0” when the primary butterfly is fully closed (which is as instructed), then the limiter plate moves at 41 on the gauge. The limiter plate is factory set and not user adjustable. It is therefore very clear that the factory takes the primary butterfly closed position as “0” even though it is resting at 8 degrees.
So when the manual says to set the port valve actuation at 35 degrees on the angle gauge and that the limiter plate opens at 41 degrees movement of the primary butterfly, both these angles are referenced to the same thing.
Therefore, the PV is supposed to open 6 degrees before the limiter plate starts to move.
I think it may still be worthwhile setting the PV visually to the limiter plate, perhaps timing them to open together. Then test the bike. From this point, wind the PV cable adjuster OUT a tiny bit at a time (which opens the valve earlier). At some, point, in theory, you’ll be at the right setting and hopefully the bike will be both hesitation and lag free (assuming your carby is clean and all other things being equal).
When I recently solved my A model hesitation, I initially matched the PV and limiter visually. The bike had a real lag in acceleration, but no hesitation. I wound the cable in to delay the PV after the limiter plate movement but this didn’t help. I ended up winding it out a little bit from the initial matched position (1/2 a turn) and it worked but this indicated that the PV was opening earlier. In light of my previous readings, this seemed confusing but this recent finding explains everything (to me at least).
The only time the 8 degree resting angle of the primary butterfly is relevant is when you look at full throttle (primary butterfly fully horizontal in its throat) and wonder why bulletin 9 says 82 degrees. Because 82 + 8 = 90.
I'll post a little video demonstrating this. It may be of interest to the insomniacs among us who can't find anything better to do at 3 am.
EDIT: just flicking through the "Suzuki New Model Technical Bulletin". It refers to the difference between "old" and "new" PV timing. The old being 41 and the new being 35. So basically, regardless of model, you shouldn't go wrong timing PV to limiter plate and, if necessary, using the method above.
What I found is that the limiter plate freed the secondary throat at precisely where the shop manual states (page 61) which is 41 degrees of primary butterfly movement. And this was also the angle shown on the angle gauge.
The significance of this is the relationship between the opening of the port valve (PV) and the release by the limiter plate of the secondary throat opening.
There is a great and detailed post about carby settings made very early on in the board. But it errs in this one area and can lead you to misunderstand the relative timing of the PV and limiter plate.
The point is that the Primary butterfly when closed is actually at 8 degrees. However, this is completely irrelevant for all of the manual and bulletin 9 references to primary butterfly angles or angle settings. The carby setting post I’m referring to notes the 8 degree resting angle of the primary valve and therefore sees the PV angle meter setting of 35 degrees as actually being 35 + 8 = 43 degrees of primary butterfly movement. The shop manual states that the limiter plate starts to move at 41 degrees of primary butterfly movement. This leads you to understand that the PV should open slightly after the limiter plate first moves. This is not correct (but if this works for you, go for it !).
If you set the angle gauge at “0” when the primary butterfly is fully closed (which is as instructed), then the limiter plate moves at 41 on the gauge. The limiter plate is factory set and not user adjustable. It is therefore very clear that the factory takes the primary butterfly closed position as “0” even though it is resting at 8 degrees.
So when the manual says to set the port valve actuation at 35 degrees on the angle gauge and that the limiter plate opens at 41 degrees movement of the primary butterfly, both these angles are referenced to the same thing.
Therefore, the PV is supposed to open 6 degrees before the limiter plate starts to move.
I think it may still be worthwhile setting the PV visually to the limiter plate, perhaps timing them to open together. Then test the bike. From this point, wind the PV cable adjuster OUT a tiny bit at a time (which opens the valve earlier). At some, point, in theory, you’ll be at the right setting and hopefully the bike will be both hesitation and lag free (assuming your carby is clean and all other things being equal).
When I recently solved my A model hesitation, I initially matched the PV and limiter visually. The bike had a real lag in acceleration, but no hesitation. I wound the cable in to delay the PV after the limiter plate movement but this didn’t help. I ended up winding it out a little bit from the initial matched position (1/2 a turn) and it worked but this indicated that the PV was opening earlier. In light of my previous readings, this seemed confusing but this recent finding explains everything (to me at least).
The only time the 8 degree resting angle of the primary butterfly is relevant is when you look at full throttle (primary butterfly fully horizontal in its throat) and wonder why bulletin 9 says 82 degrees. Because 82 + 8 = 90.
I'll post a little video demonstrating this. It may be of interest to the insomniacs among us who can't find anything better to do at 3 am.
EDIT: just flicking through the "Suzuki New Model Technical Bulletin". It refers to the difference between "old" and "new" PV timing. The old being 41 and the new being 35. So basically, regardless of model, you shouldn't go wrong timing PV to limiter plate and, if necessary, using the method above.
