Dr. Blair on Dyno Hill- Place your bets!

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Fast Eddie said:
If it were a race, time would be THE important factor, NOTHING else would matter. Many things influence time, tyre grip, suspension, rider skill etc, etc.

But it’s not a race, it’s a power test. And SPEED needs POWER.

Yes, aerodynamics would have a big effect and would have to be taken into consideration if comparing a JPN to a Hi Rider for example. But so long as we’re talking about the same rider, on a ‘normal‘ naked bike, we can pretty much rule this out for our purposes.

So, Glen is measuring pure speed up a fixed gradient. I believe that within the confines of our interest (ie practical, real world relevance) this is pretty bloody good test.

My main criticism is that he clearly needs a better stocked jet collection !
Click to expand...
Yawn.......oh sorry.
 
I used this method to tune my near standard 47 Rapide prior to shipping it to the IOM in 2007. 180 Vincents were permitted to lap the course, closed roads.
It went by every bike I pointed it at including 5 twins a row on Sulby Straight. All the riders were flat on the tank and doing well over 100 mph.
I came around the corner full bore and there they were. First thought was " I might catch a couple of these guys"
That happened quickly and then I realized I could get all five. The front runner was a beautiful Godet restored Black Shadow owned by a youngish French fellow. I had admired the bike prior to the Lap and again when he flashed by me on a corner.
Got by him right at the end of Sulby Straight, my bike showing between115 and 120mph ( the Sulby Straight is very rough at that speed!)


Glen
 
I love your test method, I just want to know a little bit more about it. Next time you do a run could you please try to get a rough estimate of either distance or time - preferably both, to improve our appreciation of the test. I'm just trying to get a sense for the duration of the full throttle pull - 3 sec, 5 sec, 10 sec, 15 sec? 15 seconds would likely seem to last an eternity, as that would be one long pull.
 
I can get an approximate et tomorrow. I suspect it's about a 15 second pull.

Just rec'd some 280s Special Delivery, will try those tomorrow, weather permitting.

Glen
 
What air filter system are you using if any..
 
Did a plug read right after cresting the hill tell you more main jet was required? 280 is a chubby jet. Looking forward to the results.
 
Yes it is and me too. It’s been discussed the Black Box is restrictive. I’m not so sure. Would be interesting to know if pulling the element changes anything. I think Pulling the whole box would have a negative effect.
I will say these real world tests are interesting.
 
Correct me if I'm wrong but I think Glenn is doing all of this to assess the pipe alone.... For possible use on the light weight custom he is gathering parts for. I think he is using his stock Mklll as a test mule in this and not trying to get this bike set up with the pipe..... Either way it's a great thread.
 
Chubby rider, chubby jets.
It seemed to make sense.
We had a little bit of end-of-day sunshine so I ran it again, first with no changes from last time. Since it is much colder today I thought there might be some difference there. The result was the same 109kms/hr.
Changed the Jets to the 280s and thought it felt stronger.
The hill says no, it's weaker.
Three runs at 106!
So I lost 3 kms by going from 260 to 280, no other changes.

I now know 280 MJs are too rich for this setup on this bike.
Will try going the other way a little.... carefully.
Also found another 270 in an old carb, so I can try those first.

The full bore climb takes 12 seconds +-


Glen
 
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I suspect that the black box airfilter might be restrictive to a Kenny Cummings race bike at 7000 rpm trying to go to 7500 but not to my common old MK3 pulling a hill at 3900-4200 rpm.
It's a big airfilter and box, looks like it would let plenty of air through for the midrange.
 
"
Changed the Jets to the 280s and thought it felt stronger.
The hill says no, it's weaker."

Ah, the classic "butt dyno" result: feels faster but is actually slower! :rolleyes:

FWIW, contrary to the common assumption, leaner-than-stock jetting will often produce more power. IOW, I would try a set of 250 main jets just to see what happens. Nice thing about Concentrics is that mains are easy to change...unless they are too tight in the jet holder.
 
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Yes, for the 260-280 change, the jet holder came with the jets, so the bowls had to be removed.
Now the jet holders are cinched up it should easy peasy on the next jetting change.

Glen
 
Move the clip up on the needles with the 260's and see what happens.

2:1 on my Norton motor was richer everywhere. I would imagine that is the same with the 2:1:2 pipe you have. Mine was particularly richer through the upper midrange and losing power transitioning to the main until I moved the clip up. Oh yeah, also gutted it and and lengthened the pipe 9 inches in the middle. Yours is probably the right length already, and just needs a little tuning. It took me a long time to dial mine in. Bolt on HP is usually more work than anything else.
 
The bolt on horsepower does seem pretty elusive at the moment!
I've never found any change in wot performance with needle clip position change. The chart shows the range for effectiveness of clip position and other factors .
I will try various mainjets.
 
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Although mine is a 750- i did not findit necessary to increase main jet size though have always run without airfilter .so it wouldnhave started at default of 250.
 
Fortunately the hill will sort the jetting out pretty quickly once I lay my hands on the appropriate jets. In my mind I had a good selection of Amal mj sizes but in reality there are some big gaps in the collection. Amal carbs and parts aren't available in any motorcycle shops here.

Glen
 
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