DynoJet theories.

[Varastorm]

Thought I'd start this thread off & try and get a bit of hard data together.

Many have tried to get to the bottom of the DynoJet main jet riddle. Looking up many of the cross referencing graphs that frequently pop up on many forums prove it.

So, here is my little tin foil hat theory. Recently, I've been for a run on my local dyno, but this time I used Dynojet mains rather than the usual Keihin.

What I/we noticed was a 5 BHP loss right across the power graph due to the air fuel ratio being so rich, around 10/1 to 11.5/1 AFR.

The only mod I did was fit the DJ mains, 185:Front 190:Rear.

So it got me wondering, how come it's across the graph? Not just the top end fueling? Where the mains control.

So today, I pulled the carbs again for a look at what could cause the issue.

What I've noticed & have noticed for a while is the significant difference in height of the main jets.

When measured (not the threaded section), the DynoJet main is 4.3mm long & the Keihin jet is 3.0mm long.

This got me reading about what happens to your AFR when you change the float bowl fuel heights, here's my take.

To me, it looks as if Dynojet are cheating the carbs into thinking the float bowl fuel height has been increased by 1.3mm. This has been accomplished by lengthening the main jet by the said amount. This then lowers the main jet into the bowl, tricking the carbs into thinking the fuel bowl has a higher level of fuel than it actually has.

It's no wonder the cross referencing graphs don't work. It's not the venturi design lots think it is.

Its the length of the Main Jets This then richens up the AFR across the board.

I am sure you could simulate a Dynojet main by using a small "1.3mm" copper washer under a Keihin main jet if you wanted too.

Carburettor Float Height Tuning

I am sure you already know that fuel level or float height can be used to tune your carburettors jetting, so how is this done? Well to put is simply any change in the fuel level in your carburettors fuel chamber will change the static head of fuel on all of your carburettors fuel jetting circuits and therefore the higher the fuel level, then the richer will be your overall jetting and conversely the lower your fuel level, then the weaker will be your overall jetting.

What do you recon??

[Varastorm]

Another thought,

Initially, I was going to increase the mains from Std Keihin 175 Front & 178 Rear, to Keihin 178 Front & 180 Rear.

I didn't have a Keihin 180 rear so I used DynoJet mains instead. but they interfered with the AFR across the whole range.

Knowing what I know now, Perhaps I could of got away with using very thin 5mm washers

My thinking is, if you've got a linear AFR across the board. But say your too rich everywhere you could richen the whole AFR just by adding a washer under the main jet.

If you need to lean it off, but a jet size is too much, just drop a jet size & use some washers to get the AFR up to what you want.

Ideal for fine tweaking. Obviously common sense comes to play. But it's food for thought in my book

Comments & tin foil hat theories welcomed

[fabiostar]

well i havent had any D\j stuff near the storm but before it i had a zx7r with a dyno kit in it and i must have spent 6 months pulling my hair out to get it to run sweet across the range . in the end i ditched it and just used standard kawa stuff and about a week later all was well.. i know 7Rs are a bitch to get right but it put me of DJ kits

[8541Hawk]

Just a couple quick points:

Both DynoJet and Factory Pro have stated that the difference between jets is the shape of the venturi.

As DynoJet mains are universal, if the slight difference in length was a major player I'm pretty sure it would be well know and a internet wide thing after being found on some bike somewhere.
As they haven't changed the design in as long as I can remember.

Even then that small a change in float height isn't going to create much of a change.

Changing main jet design will, as it shows that even though the "charts" show the mains only working at certain throttle settings, this isn't true

Just like the pilots, the mains don't have a "shut off" and while it is a small amount, they flow all the time.

Another example of why you have to balance all the circuits when you tune a CV.

[fabiostar]

some bikes can be very touchy on float heights. my ZX7R ran like a tractor with 12mm float heights then really well with 14mm? pickled my head lol

[Varastorm]

Hawk, all I am doing is posting my findings & facts.

I will post up the dyno graph when I pop & visit the Dyno. Hopefully the printer will be working.

I'll have my camera too

Perhaps I might of found out something no one else has thought of, even yourself

Try swapping the jets yourself, it's fact not fiction.

I ain't reading this stuff from any book or website. Its costing me.

[Stephan]

The only mod I did was fit the DJ mains, 185:Front 190:Rear.

So it got me wondering, how come it's across the graph? Not just the top end fueling? Where the mains control.

not sure what you are hunting for. Main jets comes into play from 4k (but with small effect from the beginning) where needles which restrict mains are lifted up. For sure top end is affected more by this change. But top end is as well affected by lenght of needles, there is difference in AFR between FactoryPro and stock.

Problem was, that instead of small change in size of 2 on keihin main jets, you just went up too much. 185 and 190 DJ is overkill.

edit: need to slightly restate my comment regarding main jet effect. As main jet is not fully shut off by needle, it has effect from the lowest rpm.

[bigtwinthing]

i think you need to get a bike with fuel injection and just ride it. Possibly a power commander if you get a 2006 FZ1. apart from that just have fun on it. I have a very slight issue with surging at low throttle openings but once past 2000rpm its so sweet all the way through.

I admire your commitment etc but there seems to be a lot of modding constantly to get 3-5bhp. i could not be arsed tbh.

[Varastorm]

not sure what you are hunting for.

I'm not hunting for anything Stephan, all I am trying to do is highlight my take "theory" on what the Dynojet mains do to the mixture everywhere. Not just from 4000rpm'ish up. Like normal Keihin jets would & have done, for me anyway.

My theory is, this is the reason you cant just swap like for like.

I appreciate that I did go too large on the Dynojet mains with 185/190, but this was only a stab in the dark guess.

But for them to alter the whole fueling/power graph. Honestly, it looks as if the same graph has been over laid 5BHP lower on top of the original.

When I post the graph, you'll see what I mean

I admire your commitment etc but there seems to be a lot of modding constantly to get 3-5bhp. i could not be arsed tbh.

It's not 3-5bhp BTT, it's 23BHP over all

Also, I've got it up from 30 MPG to 45 MPG Better than buying a new bike

[Stephan]

some info, just for curiosity

We are often asked for a "cross reference" sheet that compares our main jets to Mikuni or Keihin. The fact is you cannot directly interchange the jets for a given size. Many things affect fuel flow through a jet of the same orifice size. The entry and exit tapers of our main jets differ from those of other companies. Due to this, the fuel flow changes as a function of velocity through the carburetor venture. This means that two jets of equal orifice size will have a different fuel flow curve relative to intake air speed. At a certain speed the two may flow equally, but a change in velocity changes the flow characteristics. The Dynojet main jet hole size is measured in millimeters. For example, a DJ142 has a 1.42mm hole.

Michael Cory
Research & Development
Phone: 800-992-4993 EXT. xxx
Michael@Dynojet.com

http://www.trx450r.org/forum/index.php? ... =32469&hl=

[Varastorm]

I appreciate what they & you say Stephan, I have read it many many times.

But the fact that they don't mention that they alter the length of the jets, only venturi's is food for thought.

Also the impact in doing so has such a massive effect on the overall fueling of a carburettor.

[bigtwinthing]

not sure what you are hunting for.

I'm not hunting for anything Stephan, all I am trying to do is highlight my take "theory" on what the Dynojet mains do to the mixture everywhere. Not just from 4000rpm'ish up. Like normal Keihin jets would & have done, for me anyway.

My theory is, this is the reason you cant just swap like for like.

I appreciate that I did go too large on the Dynojet mains with 185/190, but this was only a stab in the dark guess.

But for them to alter the whole fueling/power graph. Honestly, it looks as if the same graph has been over laid 5BHP lower on top of the original.

When I post the graph, you'll see what I mean

I admire your commitment etc but there seems to be a lot of modding constantly to get 3-5bhp. i could not be arsed tbh.

It's not 3-5bhp BTT, it's 23BHP over all

Also, I've got it up from 30 MPG to 45 MPG Better than buying a new bike

t's not 3-5bhp BTT, it's 23BHP over all really 23 bhp by carb mods and the cams. Thats a tad hard to believe,

[Varastorm]

really 23 bhp by carb mods and the cams. Thats a tad hard to believe,

Here's a link to a guy who had a bit of work bone on his Varadero BBT.

http://www.honda-varadero-uk.org/forum/ ... pic=7293.0

....thrrottle response now is instant .....crisp and immiadiate brilliant job ....back to full range now but what a difference ..... response
these are both with the akros fitted its around 5 bhp up on stock pipes accross the range
a pretty healthy 93 bhp at the rear wheel [highest reading gained ]

His was a fuel injection model & they were known for giving a bit more power than the carbed model.

This is where I am at.

[bigtwinthing]

That is impressive, my only issue is if i wanted more BHP and a twin and an upright riding position wouldn't i buy a KTM ride it and not mess with it.

[8541Hawk]

Hawk, all I am doing is posting my findings & facts.

And all I have done was post my findings and fact.
Though then in lies one of the main issues, at least from my point.

It might just be your writing style but at times it does really appear that if someone disagrees with one of your theories, they are dismissed.

You might get a lot farther if you actually discuss stuff with folks, not just tell them they are wrong staight out when you are learning something new.
Kind of like the "Is it too lean thread" Saw a few posts from guys who have been tuning for a while and it was the same thing..... no asking why they might have the opinion that they do....nope they are just wrong.

I will post up the dyno graph when I pop & visit the Dyno. Hopefully the printer will be working.

I'll have my camera too

Not sure the point here but have fun

Perhaps I might of found out something no one else has thought of, even yourself

Try swapping the jets yourself, it's fact not fiction.

Swapping jets doesn't prove any of what you are trying to say as the venturi design is different. Not to be a kill joy but DynoJet has be around since 1972 so finding "new" stuff about their jets is pretty rare.

I ain't reading this stuff from any book or website. Its costing me.

Well believe it or not folks have been trying to save you some cash but it is hard when it's like talking to a wall at times.

So one last tid bit in your latest quest. As you have become obsessed with the over all length of the main jet.

IMHO the critical measurement would be where the venturi starts inside the jet, that is where the flow starts. The overall length of the main jet really isn't much of an issue unless you change things drastically

Add to that, again +\- 1mm of float height isn't going to change much...... let look at what is actually going on, What are the manufacturing tolerances of not only the carb body but also the plastic float and the valve body that shuts off the fuel..... think you have more than +\- 1mm in that assembly?

Carry on and have fun.