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Old 07-08-2013, 08:11 AM   #9046
alonzo
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Quote:
Originally Posted by motolab View Post
Put some tape on the throttle housing and the edge of the grip. Mark zero throttle with a sharpie. This is best done with the engine idling, so you can tell when the slack in the cable has just been taken up. Turn off the engine and mark wide open. Now take a tape measure (metric works best in my opinion) and measure the length of the arc. Put a mark at the mid point. Duplicate this procedure to mark the mid-point between here and zero throttle opening to get 1/4 open. Repeat for 1/8 and 1/16 openings. With the help of the marks, determine precisely during what throttle opening(s) it misbehaves. Don't have an accident trying to look at the marks while riding. If you do, I'm not responsible! Report back with results. This will help us determine what circuit(s) are responsible.

Regards,

Derek
OK. The results are highly subjective but:
Altitude: ~1600'. Temperature: upper 70's. Humidity: yes.

I begin to get stumble at 1/2 throttle but only at higher engine rpm.
At an indicated 65 mph in 5th gear and 3/4 throttle: stumble.
At an indicated 65 mph in 6th gear and 3/4 throttle: no stumble.
At anything above 3/4 throttle in 4th, 5th land 6th it's pretty much going to stumble.
Interestingly, at high enough rpm (like a slight downhill at ~65 mph) it will stumble a bit at as little as 3/8 throttle.

With the hills around here it's hard to have steady enough conditions to determine just what is going on. Load on engine and engine speed are changing all the time.

But, maybe there will be some clues in the above data.

EDIT: I think I'm beginning to see where this is going. Just because it was so easy to do I pulled the airbox cover off and went back out on the freeway.

WOT at an indicated 80 mph -- no stumble. And, no stumble at all (well, maybe a rare 'hick' but nothing I can't live with.)
So, looks like a smaller main jet and/or more holes in the top of the airbox.

-- alonzo

alonzo screwed with this post 07-08-2013 at 08:45 AM
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Old 07-08-2013, 09:25 AM   #9047
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Quote:
Originally Posted by alonzo View Post
OK. The results are highly subjective but:
Altitude: ~1600'. Temperature: upper 70's. Humidity: yes.

I begin to get stumble at 1/2 throttle but only at higher engine rpm.
At an indicated 65 mph in 5th gear and 3/4 throttle: stumble.
At an indicated 65 mph in 6th gear and 3/4 throttle: no stumble.
At anything above 3/4 throttle in 4th, 5th land 6th it's pretty much going to stumble.
Interestingly, at high enough rpm (like a slight downhill at ~65 mph) it will stumble a bit at as little as 3/8 throttle.

With the hills around here it's hard to have steady enough conditions to determine just what is going on. Load on engine and engine speed are changing all the time.

But, maybe there will be some clues in the above data.

EDIT: I think I'm beginning to see where this is going. Just because it was so easy to do I pulled the airbox cover off and went back out on the freeway.

WOT at an indicated 80 mph -- no stumble. And, no stumble at all (well, maybe a rare 'hick' but nothing I can't live with.)
So, looks like a smaller main jet and/or more holes in the top of the airbox.

-- alonzo
i wish i had just gone back down 2.5 on the main jet instead of drilling holes in the side of the airbox. Now when i go thru water I have to really watch to make sure get any inside the airbox. I might just go ahead and buy some waterproof mat'l we used on jetski's to keep water out of the intake and put that in there.
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Old 07-08-2013, 10:39 AM   #9048
alonzo
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Originally Posted by dav_dman View Post
i wish i had just gone back down 2.5 on the main jet instead of drilling holes in the side of the airbox. Now when i go thru water I have to really watch to make sure get any inside the airbox. I might just go ahead and buy some waterproof mat'l we used on jetski's to keep water out of the intake and put that in there.
I looked at the airbox this morning and since there's no room on top for extra holes (unless you enlarge the snorkel hole) I've decided that I won't be drilling it. Like you, I don't want holes in the side cover.

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Old 07-08-2013, 12:37 PM   #9049
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Quote:
Originally Posted by alonzo View Post
So, looks like a smaller main jet and/or more holes in the top of the airbox.
Your assessment is correct.

Be aware that in order to produce symptoms on the rich side, the mixture must be quite far from optimal. In other words, if you simply reduce the main jet size to a point where the symptoms disappear, the main jet size will still be too large.

Regards,

Derek
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Old 07-08-2013, 01:15 PM   #9050
alonzo
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Originally Posted by motolab View Post
Your assessment is correct.

Be aware that in order to produce symptoms on the rich side, the mixture must be quite far from optimal. In other words, if you simply reduce the main jet size to a point where the symptoms disappear, the main jet size will still be too large.

Regards,

Derek
Hmmm. OK. I'll see if I can pick up a 127.5 main jet when the shop opens tomorrow and I have the original 125.

There were so many recommendations to go to the 130 when doing the Z1 mod and snorkel removal but best I can tell now is that older XT's used a 127.5 stock while the later ones used a 125 stock (therefore, the reason why the 130 is too rich on my bike.)

Thank you very much for your input on this.

-- alonzo

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Old 07-08-2013, 02:11 PM   #9051
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In 100 miles I had it miss a total of 4 distinct times. I only drilled 7 1/4 inch holes in the exhaust. Should I drill a couple of more holes in the exhaust before I drill a one inch hole in the air box?
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Old 07-08-2013, 06:05 PM   #9052
alonzo
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Originally Posted by jspringator View Post
In 100 miles I had it miss a total of 4 distinct times. I only drilled 7 1/4 inch holes in the exhaust. Should I drill a couple of more holes in the exhaust before I drill a one inch hole in the air box?
Don't know but, if I did the math right (and I often don't) a 1" dia hole = 0.7854 sq. in.
A 1/4" hole = 0.0491 sq. in. Which times 7 = 0.3436 sq. in. or, a bit less than half of what a 1" dia hole would give you.
I'm pretty sure that I drilled mine 1" (at least.)

Have you removed the snorkel? I would definitely do that before I drilled the airbox cover.
EDIT: going back and reading one of your previous posts I see that you did remove the snorkel. So, I'm guessing that opening the exhaust a bit more might be helpful. Since your bike is an `06 (as is mine) and the stock main jet is a 125 I'm going to guess that the 130 (like in my bike) it too rich.
I'm going to try to find a 127.5 tomorrow and if I do will report back here with the results.

I am curious as to why the earlier (at least to 1999) XT's used a 127.5 Main while the later (at least an `06) uses a 125 main jet stock. I'm betting that it has something to do with EPA stuff and, most likely other things changed besides the jet.

-- alonzo

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Old 07-09-2013, 09:18 AM   #9053
jspringator
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Four 1/4's equal 1. I've got 1 3/4's inches of area open, but as I understand it inasmuch as it is in 7 different holes, it performs differently than one large hole. My original plan was eight 1/4 inch holes, but I had trouble getting the drill to bite on the last hole! My intent was to approximate the performance of one 1 inch hole.

As I learned in my Quantitative Business Management class (the hard way), converting fractions to decimals causes more problems than it solves.
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Old 07-09-2013, 09:50 AM   #9054
motolab
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Quote:
Originally Posted by jspringator View Post
Four 1/4's equal 1.
If we are comparing area of holes, then no. In that case four 1/4" holes are equal to one 1/2" hole.
Quote:
As I learned in my Quantitative Business Management class (the hard way), converting fractions to decimals causes more problems than it solves.
In this case we're converting diameter to area.

Regards,

Derek
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Old 07-09-2013, 10:27 AM   #9055
Tom S
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Quote:
Originally Posted by alonzo View Post
Don't know but, if I did the math right (and I often don't) a 1" dia hole = 0.7854 sq. in.
A 1/4" hole = 0.0491 sq. in. Which times 7 = 0.3436 sq. in. or, a bit less than half of what a 1" dia hole would give you.
Your math is 100% correct.
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Old 07-09-2013, 10:59 AM   #9056
alonzo
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...
As I learned in my Quantitative Business Management class (the hard way), converting fractions to decimals causes more problems than it solves.
As I learned at the School of Hard Knocks, converting fractions to decimal is often the only sensible way to deal with them.

I can do a lot of fractional calculations in my head (from my cabnetmaking/boatbuilding days ... and, decimal can be a nuisance here) but in the mechanical world decimal is king.

There is a place for everything. Would I want to say "Hand me that 0.5625" (9/16") wrench?"
... No Way! (Works pretty good in Metric Land though..)

-- alonzo
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Old 07-09-2013, 11:30 AM   #9057
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Damn! I guess I'll have to drill more holes. That is probably the problem.

I had this professor that could stand at the board and do fractional calculations in his head for 50 minutes. It was amazing to watch. He hated decimals. Of course, this was in 1980.
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Old 07-09-2013, 11:44 AM   #9058
Tom S
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As I learned at the School of Hard Knocks, converting fractions to decimal is often the only sensible way to deal with them.
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Old 07-09-2013, 11:46 AM   #9059
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Originally Posted by alonzo View Post

There is a place for everything. Would I want to say "Hand me that 0.5625" (9/16") wrench?"
... No Way! (Works pretty good in Metric Land though..)

-- alonzo
If it weren't for fractions they would have never made a 9/16 or .5675 wrench. It would probably be a .6 wrench or something like that.

I love the metric system. It is so much easier on my brain. I just wish the US would adopt it.
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Old 07-09-2013, 06:35 PM   #9060
alonzo
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Originally Posted by duanew1 View Post
If it weren't for fractions they would have never made a 9/16 or .5675 wrench. It would probably be a .6 wrench or something like that.

I love the metric system. It is so much easier on my brain. I just wish the US would adopt it.
Having been born into the imperial system of miles/yards/feet/inches/etc. (in fractions and decimals) I deal with it pretty good. Feet and inches work good for most woodworking applications. But, yes. Metric is much more logical and many measurements/calculations are just a lot easier in metric. Dividing something like 9 feet ,3 5/16 inches into seven equal spaces can be a real pain in the ass with the imperial system but, a cake-walk with metric. So, I just use whatever works best for the job at hand. Most of my woodworking tools and measuring devices are calibrated in inches and fractions thereof but my metal lathe and mill are calibrated in inches and decimals thereof. However, my Bosch router was built to metric standards and sometimes it's easier to use metric measurements with it.

I'm currently restoring a 1970 Triumph Bonneville and half the fasteners are British (BSF) and half of them are SAE. That means two of everything.... sigh...

-- alonzo
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