The Varastorm Dyno run (VTR cams)

[NZSpokes]

2 things, stock and DJ springs are not much different. You would need to pre-load the spring.

The slide would need to go down to one hole that is smaller than stock. More holes mean faster lift.

[mik_str]

2 things, stock and DJ springs are not much different. You would need to pre-load the spring.

The slide would need to go down to one hole that is smaller than stock. More holes mean faster lift.

Unless folks downunder get very different DJ slide springs from those of us in the northern hemisphere, there is a significant difference between stock and DJ springs (the OEMs are at least twice as long).....

[NZSpokes]

2 things, stock and DJ springs are not much different. You would need to pre-load the spring.

The slide would need to go down to one hole that is smaller than stock. More holes mean faster lift.

Unless folks downunder get very different DJ slide springs from those of us in the northern hemisphere, there is a significant difference between stock and DJ springs (the OEMs are at least twice as long).....

I was meaning in pressure put on the slide by the spring. But My guess is the longer spring has a lower spring rate.

[8541Hawk]

This is the start/finish fuelling zones on the VTR carbs. Pilot circuit = 0rpm to 2500rpm---Needle 2500rpm to 7000rpm---Mains 7000rpm to max rpm.

Well I have tried to help but it does appear that you don't want to listen to anything I have to say so I will refrain from commenting on this anymore except to say I strongly disagree with the numbers you posted.
In my experience those numbers are off by quite a bit on where the carbs on the VTRs I have tuned hit the different circuits.

Also IMHO running 3 lift holes is the root of your issues.

[NZSpokes]

This is the start/finish fuelling zones on the VTR carbs. Pilot circuit = 0rpm to 2500rpm---Needle 2500rpm to 7000rpm---Mains 7000rpm to max rpm.

Well I have tried to help but it does appear that you don't want to listen to anything I have to say so I will refrain from commenting on this anymore except to say I strongly disagree with the numbers you posted.
In my experience those numbers are off by quite a bit on where the carbs on the VTRs I have tuned hit the different circuits.

Also IMHO running 3 lift holes is the root of your issues.

What would your thoughts be on the DJ springs having a higher rate? Being shorter?

Im not sure on this and are happy to be proven wrong. Could that be why they run the extra hole in the slide?

[Stephan]

NZSpokes: I think there is US and non US version of dynojet kit. US comes with different springs, nonUS without. Both with recommended 3 slide holes. I hope somebody can confirm it.

[VTRDark]

Yep I confer. No springs are supplied in the UK Dynojet kits. Don't know about the rest of Europe or world (outside US) for that matter but I suspect the kits vary from country to country. It's either weird or a big con and my guess is, it's a con according to the conditions of the market UK kits also come with only a pair of 170, 180 and 190 mains. The US kits come with 170, 175,180, 185, 190 and 195 mains. Go figure.

(:-})

[Furrybiker]

^^^ Could the greater number of jets be for the larger range in altitude that a bike in the US might find itself in rather than the UK?

[VTRDark]

It certainly gives more to play with and it could very well be the reason. But they already supply a range to deal with altitude in their kits here and in the US. This is what the other jets are for in the first place as it says in their installation instructions. What I find strange is that the UK kits suggest a 180 in each carb yet as standard these bikes rear main jet is slightly richer. Why not supply the 185's as well. 185s seem popular over the pond. And yet again it's strange that in the dynojet US installation instruction they say to install a 180F and 185R with the US kits plus they get springs IMO these are only baseline figures that they give in the installation instructions anyhow. Needle profile could also differ from country to country as barometric pressure differs all over the world. Yeh we have 1atm of pressure on us all over the world at Sea Level.

(:-})

[NZSpokes]

It certainly gives more to play with and it could very well be the reason. But they already supply a range to deal with altitude in their kits here and in the US. This is what the other jets are for in the first place as it says in their installation instructions. What I find strange is that the UK kits suggest a 180 in each carb yet as standard these bikes rear main jet is slightly richer. Why not supply the 185's as well. 185s seem popular over the pond. And yet again it's strange that in the dynojet US installation instruction they say to install a 180F and 185R with the US kits plus they get springs IMO these are only baseline figures that they give in the installation instructions anyhow. Needle profile could also differ from country to country as barometric pressure differs all over the world. Yeh we have 1atm of pressure on us all over the world at Sea Level.

(:-})

Well here we run 15 points leaner than the US.

[VTRDark]

Is that the low open planes of the USA or the Rocky mountain highs in Colorado. You see what I'm getting at though.

(:-})

[tony.mon]

Question re slide holes....
If I'm not mistaken the slides are lifted by the vacuum above the diaphragm. The number or size of lide holes doesn't change the vacuum heading to the diaphragm side. The slide holes are there for a reason, let's see if we can work out how they affect the carburation.
If the slide was sealed (no holes) then the diaphragm would have the vacuum above it, and atmospheric below it, lifting the slide. But the area below the slide (carb throat) also has the same vacuum, except that air can also flow into this area from the airbox, past the slide.
This extra air "lessens" the effect of the vacuum on the pre-slide part of the carb throat, meaning that there's more vacuum above the diaphragm, lifting it.

I suppose what I'm saying is that the vacuum effect is really the difference in pressure between the gas after the slide compared to that before the slide.

The pressure differential above and below the diaphragm is what causes the diaphragm to lift and therefore lift the slide.
Slde holes lessen the vacuum under the slide, and effectively increase the vacuum above it- I'm not talking about vacuum and pressure here, merely the difference in pressure.
More or bigger slide holes allow more air to leak into the underside of the diaphragm, meaning that for a given vacuum above the diaphragm there will be a greater difference between the pressure above the diaphragm and the pressure below it.
That means bigger or more holes will give more slide lift- but this is only useful if the vacuum is constant.

Because the vacuum increases with engine revs, there can't be a direct correlation between the slide's number and size of holes and slide lift.
What might work ok at 3000 may be "wrong" at 5000.

Non CV carbs are so much easier...

Your thoughts?

[VTRDark]

Because the vacuum increases with engine revs, there can't be a direct correlation between the slide's number and size of holes and slide lift.
What might work ok at 3000 may be "wrong" at 5000.

Now that has me thinking. Surly the given percentage would be the same throughout and only an increase or decrease in volume. To put this another way. At 1atm (sea level) we have about 14.7 pounds of pressure resting on us so atoms and molecules are squashed by so much. We all have the weight of a small car resting on our heads As atmospheric pressure changes these atoms and modules will either increase or decrease in size to allow more or less according to how squashed they are within a given space.

[youtube][/youtube]
https://www.youtube.com/watch?v=gUfhvbnBWs0

(:-})

[Varastorm]

So many reply's, but no emails to notify me so I didn't know

You lot have lost me on the chemistry side, so I'll stay well out of that area

I know a few of you think it's the slide speed, but I don't tbh.

If I have the Dj needle in slot 4, there is no issue with coughing & spluttering at the 3000rpm zone but does not pull as hard after 5000rpm. = no power wheelies, but it behaves low down.

If I have the Dj needle in slot 2, there is an issue with coughing & spluttering at the 3000rpm zone but pulls very hard after 5000rpm. = Wants to summersault wheelie on the throttle alone & I have to cover the rear brake, but popping & coughing low down.

Nothing has changed apart from the needle height.

Surely if there was an issue with the slide opening too fast as a few mention, a few mm in needle lift wouldn't interfere with lift speed.
Or would it ?

Update,

So, I still have an issue with the 3000rpm zone & am very aware when it starts & clears.
I have gone back down to #48's & 1 1/4 out.(Bet you Carls Laughing )
DJ needles at second groove down, 3 holes (again) & DJ springs.
Mains 178f & 178r.

So, knowing exactly what revs it starts to play up, I started to experiment with & modify the throttle cutaway Just so I can learn & know when & how it controls the mixture & at what revs.

I know that I couldn't richen the mixture with the slides, but I thought I would have a play anyway. I have a spare set of slides, so if it goes wrong I have a safety net.

Firstly, I started to radius the leading edge slightly Then I flatted the bottom until there was practically no radius

All I can say it, what a waste of slides

But now I know that it changed the mixture to an even leaner setting from 3200rpm to 5000rpm & also, not to mess with the slides

Since tossing the slides in the bin, I have started to file a flat 2.72mm on the needles, from 2.80mm diameter on the straight section so far. It doesn't sound a lot, but it sure looks it

I feel that when running the filed needles that there is no change at all from my ass dyno, but am sure the Rolling road would highlight a slight difference. But I feel not enough to run her up again on the rolling road.

Will update again soon with modified needle's

[Varastorm]

Just thought of a question for all the carb tuners out there

If you wanted to richen the 3000rpm fuelling zone, how would you go about it?

It doesn't have to be accurate at all, too rich would be okay

BTW, Happy Fathers day to all you lucky pop's out there